Hydrostatic equilibrium

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Hydrostatic_equilibrium

Diagram of a newly formed planet in a state of hydrostatic equilibrium.

In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planetary physics of Earth, the pressure-gradient force prevents gravity from collapsing the planetary atmosphere into a thin, dense shell, whereas gravity prevents the pressure-gradient force from diffusing the atmosphere into outer space.

Hydrostatic equilibrium is the distinguishing criterion between dwarf planets and small solar system bodies, and features in astrophysics and planetary geology. Said qualification of equilibrium indicates that the shape of the object is symmetrically rounded, mostly due to rotation, into an ellipsoid, where any irregular surface features are consequent to a relatively thin solid crust. In addition to the Sun, there are a dozen or so equilibrium objects confirmed to exist in the Solar System.

Mathematical consideration

If the highlighted volume of fluid is not accelerating, the forces on it upwards must equal the forces downwards.

For a hydrostatic fluid on Earth:

${\displaystyle dP=-\rho (P)\cdot g(h)\cdot dh}$

Derivation from force summation

Further information: Mechanical equilibrium

Newton's laws of motion state that a volume of a fluid that is not in motion or that is in a state of constant velocity must have zero net force on it. This means the sum of the forces in a given direction must be opposed by an equal sum of forces in the opposite direction. This force balance is called a hydrostatic equilibrium.

The fluid can be split into a large number of cuboid volume elements; by considering a single element, the action of the fluid can be derived.

There are three forces: the force downwards onto the top of the cuboid from the pressure, P, of the fluid above it is, from the definition of pressure,

${\displaystyle F_{\text{top}}=-P_{\text{top}}\cdot A}$

Similarly, the force on the volume element from the pressure of the fluid below pushing upwards is

${\displaystyle F_{\text{bottom}}=P_{\text{bottom}}\cdot A}$

Finally, the weight of the volume element causes a force downwards. If the density is ρ, the volume is V and g the standard gravity, then:

${\displaystyle F_{\text{weight}}=-\rho \cdot g\cdot V}$

The volume of this cuboid is equal to the area of the top or bottom, times the height — the formula for finding the volume of a cube.

${\displaystyle F_{\text{weight}}=-\rho \cdot g\cdot A\cdot h}$

By balancing these forces, the total force on the fluid is

${\displaystyle \sum F=F_{\text{bottom}}+F_{\text{top}}+F_{\text{weight}}=P_{\text{bottom}}\cdot A-P_{\text{top}}\cdot A-\rho \cdot g\cdot A\cdot h}$

This sum equals zero if the fluid's velocity is constant. Dividing by A,

${\displaystyle 0=P_{\text{bottom}}-P_{\text{top}}-\rho \cdot g\cdot h}$

Or,

${\displaystyle P_{\text{top}}-P_{\text{bottom}}=-\rho \cdot g\cdot h}$

P_top − P_bottom is a change in pressure, and h is the height of the volume element—a change in the distance above the ground. By saying these changes are infinitesimally small, the equation can be written in differential form.

${\displaystyle dP=-\rho \cdot g\cdot dh}$

Density changes with pressure, and gravity changes with height, so the equation would be:

${\displaystyle dP=-\rho (P)\cdot g(h)\cdot dh}$

Derivation from Navier–Stokes equations

Note finally that this last equation can be derived by solving the three-dimensional Navier–Stokes equations for the equilibrium situation where

${\displaystyle u=v=\frac{\mathrm{\partial }p}{\mathrm{\partial }x}=\frac{\mathrm{\partial }p}{\mathrm{\partial }y}=0}$

Then the only non-trivial equation is the ${\displaystyle z}$-equation, which now reads

${\displaystyle \frac{\mathrm{\partial }p}{\mathrm{\partial }z}+\rho g=0}$

Thus, hydrostatic balance can be regarded as a particularly simple equilibrium solution of the Navier–Stokes equations.

Derivation from general relativity

By plugging the energy–momentum tensor for a perfect fluid

${\displaystyle T^{\mu \nu }=(\rho c^{-2}+P)u^{\mu }{u}^{\nu }+P{g}^{\mu \nu }}$

into the Einstein field equations

${\displaystyle R_{\mu \nu }=\frac{8\pi G}{c^4}\left(T_{\mu \nu }-\frac{1}{2}{g}_{\mu \nu }T\right)}$

and using the conservation condition

${\displaystyle {\mathrm{\nabla }}_{\mu }{T}^{\mu \nu }=0}$

one can derive the Tolman–Oppenheimer–Volkoff equation for the structure of a static, spherically symmetric relativistic star in isotropic coordinates:

${\displaystyle \frac{dP}{dr}=-\frac{GM(r)\rho (r)}{r^2}\left(1+\frac{P(r)}{\rho (r)c^2}\right)\left(1+\frac{4\pi r^{3}P(r)}{M(r)c^2}\right){\left(1-\frac{2GM(r)}{r{c}^2}\right)}^{-1}}$

In practice, Ρ and ρ are related by an equation of state of the form f(Ρ,ρ) = 0, with f specific to makeup of the star. M(r) is a foliation of spheres weighted by the mass density ρ(r), with the largest sphere having radius r:

${\displaystyle M(r)=4\pi {\int }_0^{r}d{r}^{\prime }{r}^{\prime 2}\rho (r^{\prime }).}$

Per standard procedure in taking the nonrelativistic limit, we let c→∞, so that the factor

${\displaystyle \left(1+\frac{P(r)}{\rho (r)c^2}\right)\left(1+\frac{4\pi r^{3}P(r)}{M(r)c^2}\right){\left(1-\frac{2GM(r)}{r{c}^2}\right)}^{-1}\to 1}$

Therefore, in the nonrelativistic limit the Tolman–Oppenheimer–Volkoff equation reduces to Newton's hydrostatic equilibrium:

${\displaystyle \frac{dP}{dr}=-\frac{GM(r)\rho (r)}{r^2}=-g(r)\rho (r)⟶dP=-\rho (h)g(h)dh}$

(we have made the trivial notation change h = r and have used f(Ρ,ρ) = 0 to express ρ in terms of P). A similar equation can be computed for rotating, axially symmetric stars, which in its gauge independent form reads:

${\displaystyle \frac{{\mathrm{\partial }}_{i}P}{P+\rho }-{\mathrm{\partial }}_i\ln u^t+u_t{u}^{\phi }{\mathrm{\partial }}_i\frac{u_{\phi }}{u_t}=0}$

Unlike the TOV equilibrium equation, these are two equations (for instance, if as usual when treating stars, one chooses spherical coordinates as basis coordinates ${\displaystyle (t,r,\theta ,\phi )}$, the index i runs for the coordinates r and ${\displaystyle \theta }$).

Applications

Fluids

The hydrostatic equilibrium pertains to hydrostatics and the principles of equilibrium of fluids. A hydrostatic balance is a particular balance for weighing substances in water. Hydrostatic balance allows the discovery of their specific gravities. This equilibrium is strictly applicable when an ideal fluid is in steady horizontal laminar flow, and when any fluid is at rest or in vertical motion at constant speed. It can also be a satisfactory approximation when flow speeds are low enough that acceleration is negligible.

Astrophysics

In any given layer of a star, there is a hydrostatic equilibrium between the outward thermal pressure from below and the weight of the material above pressing inward. The isotropic gravitational field compresses the star into the most compact shape possible. A rotating star in hydrostatic equilibrium is an oblate spheroid up to a certain (critical) angular velocity. An extreme example of this phenomenon is the star Vega, which has a rotation period of 12.5 hours. Consequently, Vega is about 20% larger at the equator than at the poles. A star with an angular velocity above the critical angular velocity becomes a Jacobi (scalene) ellipsoid, and at still faster rotation it is no longer ellipsoidal but piriform or oviform, with yet other shapes beyond that, though shapes beyond scalene are not stable.

If the star has a massive nearby companion object then tidal forces come into play as well, distorting the star into a scalene shape when rotation alone would make it a spheroid. An example of this is Beta Lyrae.

Hydrostatic equilibrium is also important for the intracluster medium, where it restricts the amount of fluid that can be present in the core of a cluster of galaxies.

We can also use the principle of hydrostatic equilibrium to estimate the velocity dispersion of dark matter in clusters of galaxies. Only baryonic matter (or, rather, the collisions thereof) emits X-ray radiation. The absolute X-ray luminosity per unit volume takes the form ${\displaystyle {\mathcal{L}}_X=\mathrm{\Lambda }(T_B){\rho }_B^2}$ where ${\displaystyle T_B}$ and ${\displaystyle {\rho }_B}$ are the temperature and density of the baryonic matter, and ${\displaystyle \mathrm{\Lambda }(T)}$ is some function of temperature and fundamental constants. The baryonic density satisfies the above equation ${\displaystyle dP=-\rho gdr}$:

${\displaystyle p_B(r+dr)-p_B(r)=-dr\frac{{\rho }_B(r)G}{r^2}{\int }_0^{r}4\pi r^2{\rho }_M(r)dr.}$

The integral is a measure of the total mass of the cluster, with ${\displaystyle r}$ being the proper distance to the center of the cluster. Using the ideal gas law ${\displaystyle p_B=k{T}_B{\rho }_B/m_B}$ (${\displaystyle k}$ is Boltzmann's constant and ${\displaystyle m_B}$ is a characteristic mass of the baryonic gas particles) and rearranging, we arrive at

${\displaystyle \frac{d}{dr}\left(\frac{k{T}_B(r){\rho }_B(r)}{m_B}\right)=-\frac{{\rho }_B(r)G}{r^2}{\int }_0^{r}4\pi r^2{\rho }_M(r)dr.}$

Multiplying by ${\displaystyle r^2/{\rho }_B(r)}$ and differentiating with respect to ${\displaystyle r}$ yields

${\displaystyle \frac{d}{dr}\left[\frac{r^2}{{\rho }_B(r)}\frac{d}{dr}\left(\frac{k{T}_B(r){\rho }_B(r)}{m_B}\right)\right]=-4\pi G{r}^2{\rho }_M(r).}$

If we make the assumption that cold dark matter particles have an isotropic velocity distribution, then the same derivation applies to these particles, and their density ${\displaystyle {\rho }_D={\rho }_M-{\rho }_B}$ satisfies the non-linear differential equation

${\displaystyle \frac{d}{dr}\left[\frac{r^2}{{\rho }_D(r)}\frac{d}{dr}\left(\frac{k{T}_D(r){\rho }_D(r)}{m_D}\right)\right]=-4\pi G{r}^2{\rho }_M(r).}$

With perfect X-ray and distance data, we could calculate the baryon density at each point in the cluster and thus the dark matter density. We could then calculate the velocity dispersion ${\displaystyle {\sigma }_D^2}$ of the dark matter, which is given by

${\displaystyle {\sigma }_D^2=\frac{k{T}_D}{m_D}.}$

The central density ratio ${\displaystyle {\rho }_B(0)/{\rho }_M(0)}$ is dependent on the redshift ${\displaystyle z}$ of the cluster and is given by

${\displaystyle {\rho }_B(0)/{\rho }_M(0)\propto (1+z{)}^2{\left(\frac{\theta }{s}\right)}^{3/2}}$

where ${\displaystyle \theta }$ is the angular width of the cluster and ${\displaystyle s}$ the proper distance to the cluster. Values for the ratio range from .11 to .14 for various surveys.

Planetary geology

See also: List of gravitationally rounded objects of the Solar System

Further information: Clairaut's theorem (gravity)

The concept of hydrostatic equilibrium has also become important in determining whether an astronomical object is a planet, dwarf planet, or small Solar System body. According to the definition of planet adopted by the International Astronomical Union in 2006, one defining characteristic of planets and dwarf planets is that they are objects that have sufficient gravity to overcome their own rigidity and assume hydrostatic equilibrium. Such a body will often have the differentiated interior and geology of a world (a planemo), though near-hydrostatic or formerly hydrostatic bodies such as the proto-planet 4 Vesta may also be differentiated and some hydrostatic bodies (notably Callisto) have not thoroughly differentiated since their formation. Often the equilibrium shape is an oblate spheroid, as is the case with Earth. However, in the cases of moons in synchronous orbit, nearly unidirectional tidal forces create a scalene ellipsoid. Also, the purported dwarf planet Haumea is scalene due to its rapid rotation, though it may not currently be in equilibrium.

Icy objects were previously believed to need less mass to attain hydrostatic equilibrium than rocky objects. The smallest object that appears to have an equilibrium shape is the icy moon Mimas at 396 km, whereas the largest icy object known to have an obviously non-equilibrium shape is the icy moon Proteus at 420 km, and the largest rocky bodies in an obviously non-equilibrium shape are the asteroids Pallas and Vesta at about 520 km. However, Mimas is not actually in hydrostatic equilibrium for its current rotation. The smallest body confirmed to be in hydrostatic equilibrium is the dwarf planet Ceres, which is icy, at 945 km, whereas the largest known body to have a noticeable deviation from hydrostatic equilibrium is Iapetus being made of mostly permeable ice and almost no rock. At 1,469 km Iapetus is neither spherical nor ellipsoid. Instead, it is rather in a strange walnut-like shape due to its unique equatorial ridge. Some icy bodies may be in equilibrium at least partly due to a subsurface ocean, which is not the definition of equilibrium used by the IAU (gravity overcoming internal rigid-body forces). Even larger bodies deviate from hydrostatic equilibrium, although they are ellipsoidal: examples are Earth's Moon at 3,474 km (mostly rock), and the planet Mercury at 4,880 km (mostly metal).

Solid bodies have irregular surfaces, but local irregularities may be consistent with global equilibrium. For example, the massive base of the tallest mountain on Earth, Mauna Kea, has deformed and depressed the level of the surrounding crust, so that the overall distribution of mass approaches equilibrium.

Atmospheric modeling

Further information: Atmospheric model

In the atmosphere, the pressure of the air decreases with increasing altitude. This pressure difference causes an upward force called the pressure-gradient force. The force of gravity balances this out, keeping the atmosphere bound to Earth and maintaining pressure differences with altitude.

Gemology

Gemologists use hydrostatic balances to determine the specific gravity of gemstones. A gemologist may compare the specific gravity they observe with a hydrostatic balance with a standardized catalogue of information for gemstones, helping them to narrow down the identity or type of gemstone under examination.

Cannibalism

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Cannibalism

A slug, Arion vulgaris, eating a dead individual of the same species

Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, both in ancient and in recent times.

The rate of cannibalism increases in nutritionally poor environments as individuals turn to members of their own species as an additional food source. Cannibalism regulates population numbers, whereby resources such as food, shelter and territory become more readily available with the decrease of potential competition. Although it may benefit the individual, it has been shown that the presence of cannibalism decreases the expected survival rate of the whole population and increases the risk of consuming a relative. Other negative effects may include the increased risk of pathogen transmission as the encounter rate of hosts increases. Cannibalism, however, does not—as once believed—occur only as a result of extreme food shortage or of artificial/unnatural conditions, but may also occur under natural conditions in a variety of species.

Cannibalism is prevalent in aquatic ecosystems, in which up to approximately 90% of the organisms engage in cannibalistic activity at some point in their life-cycle. Cannibalism is not restricted to carnivorous species: it also occurs in herbivores and in detritivores. Sexual cannibalism normally involves the consumption of the male by the female individual before, during or after copulation. Other forms of cannibalism include size-structured cannibalism and intrauterine cannibalism.

Behavioral, physiological and morphological adaptations have evolved to decrease the rate of cannibalism in individual species.

Benefits

In environments where food availability is constrained, individuals can receive extra nutrition and energy if they use members of their own species, also known as conspecifics, as an additional food source. This would, in turn, increase the survival rate of the cannibal and thus provide an evolutionary advantage in environments where food is scarce. For example, female Fletcher's frogs lay their eggs in ephemeral pools that lack food resources. Therefore, in order to survive, tadpoles within the same clutch are forced to consume each other and exploit their conspecifics as the only available source of nutrition. A study conducted on another amphibian, the wood frog, tadpoles showed that those that exhibited cannibalistic tendencies had faster growth rates and higher fitness levels than non-cannibals. An increase of size and growth would give them the added benefit of protection from potential predators such as other cannibals and give them an advantage when competing for resources.

The nutritional benefits of cannibalism may allow for the more efficient conversion of a conspecific diet into reusable resources than a fully herbaceous diet; as herbaceous diets may consist of excess elements which the animal has to expend energy to get rid of. This facilitates for faster development; however, a trade-off may occur as there may be less time to ingest these acquired resources. Studies have shown that there is a noticeable size difference between animals fed on a high conspecific diet which were smaller compared to those fed on a low conspecific diet. Hence, individual fitness could only be increased if the balance between developmental rate and size is balanced out, with studies showing that this is achieved in low conspecific diets.

Cannibalism regulates population numbers and benefits the cannibalistic individual and its kin as resources such as extra shelter, territory and food are freed, thereby increasing the fitness of the cannibal by lowering crowding effects. However, this is only the case if the cannibal recognizes its own kin as this won't hinder any future chances of perpetuating its genes in future generations. The elimination of competition can also increase mating opportunities, allowing further spread of an individual's genes.

Costs

Animals which have diets consisting of predominantly conspecific prey expose themselves to a greater risk of injury and expend more energy foraging for suitable prey as compared to non-cannibalistic species.

Predators often target younger or more vulnerable prey. However, the time necessitated by such selective predation could result in a failure to meet the predator's self-set nutritional requirements. In addition, the consumption of conspecific prey may also involve the ingestion of defense compounds and hormones, which have the capacity to impact the developmental growth of the cannibal's offspring. Hence, predators normally partake in a cannibalistic diet in conditions where alternative food sources are absent or not as readily available.

Failure to recognize kin prey is also a disadvantage, provided cannibals target and consume younger individuals. For example, a male stickleback fish may often mistake their own "eggs" for their competitor's eggs, and hence would inadvertently eliminate some of its own genes from the available gene pool. Kin recognition has been observed in tadpoles of the spadefoot toad, whereby cannibalistic tadpoles of the same clutch tended to avoid consuming and harming siblings, while eating other non-siblings.

The act of cannibalism may also facilitate trophic disease transmission within a population, though cannibalistically spread pathogens and parasites generally employ alternative modes of infection.

Diseases transmitted through cannibalism

Cannibalism can potentially reduce the prevalence of parasites in the population by decreasing the number of susceptible hosts and indirectly killing the parasite in the host. It has been shown in some studies that the risk of encountering an infected victim increases when there is a higher cannibalism rate, though this risk drops as the number of available hosts decreases. However, this is only the case if the risk of disease transmission is low. Cannibalism is an ineffective method of disease spread as cannibalism in the animal kingdom is normally a one-on-one interaction, and the spread of disease requires group cannibalism; thereby it is rare for a disease to have evolved to rely solely on cannibalism to spread. Usually there are different means of transmission, such as with direct contact, maternal transmission, coprophagy, and necrophagy with different species. Infected individuals are more likely to be consumed than non-infected individuals, thus some research has suggested that the spread of disease may be a limiting factor to the prevalence of cannibalism in the population.

Some examples of diseases transmitted by cannibalism in mammals include Kuru which is a prion disease that degenerates the brain. This disease was prevalent in Papua New Guinea where tribes practiced endocannibalism in cannibalistic funeral rituals and consume the brains infected by these prions. It is a cerebellar dysfunctional disease which has symptoms including a broad-based gait and decreased motor activity control; however, the disease has a long incubation period and symptoms may not appear until years later.

Bovine spongiform encephalopathy, or mad cow disease is another prion disease which is usually caused by feeding contaminated bovine tissue to other cattle. It is a neurodegenerative disease and could be spread to humans if the individual were to consume contaminated beef. The spread of parasites such as nematodes may also be facilitated by cannibalism as eggs from these parasites are transferred more easily from one host to another.

Other forms of diseases include sarcocystis and iridovirus in reptiles and amphibians; granulosus virus, chagas disease, and microsporidia in insects; stained prawn disease, white pot syndrome, helminthes and tapeworms in crustaceans and fish.

Foraging dynamics

Cannibalism may become apparent when direct competition for limited resources forces individuals to use other conspecific individuals as an additional resource to maintain their metabolic rates. Hunger drives individuals to increase their foraging rates, which in turn decreases their attack threshold and tolerance to other conspecific individuals. As resources dwindle, individuals are forced to change their behaviour which may lead to animal migration, confrontation, or cannibalism.

Cannibalism rates increase with increasing population density as it becomes more advantageous to prey on conspecific organisms than to forage in the environment. This is because the encounter rate between predator and prey increases, making cannibalism more convenient and beneficial than foraging within the environment. Over time, the dynamics within the population change as those with cannibalistic tendencies may receive additional nutritional benefits and increase the size ratio of predator to prey. The presence of smaller prey, or prey which are at a vulnerable stage of their life cycle, increases the chances of cannibalism occurring due to the reduced risk of injury. A feedback loop occurs when increasing rates of cannibalism decreases population densities, leading to an increased abundance of alternative food sources; making it more beneficial to forage within the environment than for cannibalism to occur. When population numbers and foraging rates increase, the carrying capacity for that resource in the area may be reached, thus forcing individuals to look for other resources such as conspecific prey.

Sexual cannibalism

Main article: Sexual cannibalism

Sexual cannibalism is present largely in spiders and other invertebrates, including gastropods. This refers to the killing and consumption of conspecific sexual partners during courtship, and during or after copulation. Normally, it is the female which consumes the conspecific male organism, though there have been some reported cases of the male consuming the adult female, however, this has only been recorded under laboratory conditions. Sexual cannibalism has been recorded in the female redback spider, black widow spider, praying mantis, and scorpion, among others.

In most species of spiders, the consumption of the male individual occurs before copulation and the male fails to transfer his sperm into the female. This may be due to mistaken identity such as in the case of the orb weaving spider which holds little tolerance to any spider which is present in its web and may mistake the vibrations for those of a prey item. Other reasons for male consumption before mating may include female choice and the nutritional advantages of cannibalism. The size of the male spider may play a part in determining its reproductive success as smaller males are less likely to be consumed during pre-copulation; however, larger males may be able to prevent the smaller ones from gaining access to the female. There exists a conflict of interest between males and females, as females may be more inclined to turn to cannibalism as a source of nutritional intake while the male's interest is mostly focused on ensuring paternity of the future generations. It was found that cannibalistic females produced offspring with greater survival rates than non-cannibalistic females, as cannibals produced greater clutches and larger egg sizes. Hence, species such as the male dark fishing spider of the family Dolomedes self-sacrifice and spontaneously die during copulation to facilitate their own consumption by the female, thereby increasing the chance of survivorship of future offspring.

Sexual dimorphism has been theorised to have arisen from sexual selection as smaller males were captured more easily than larger males; however, it is also possible that sexual cannibalism only occurs due to the difference in size between male and females. Data comparing female and male spider body length shows that there is little support for the prior theory as there is not much correlation between body size and the presence of sexual cannibalism. Not all species of spiders which partake in sexual cannibalism exhibit size dimorphism.

The avoidance of sexual cannibalism is present in males of certain species to increase their rate of survival, whereby the male uses cautionary methods to lower the risk of his consumption. Male orb weaving spiders would often wait for females to moult or to finish eating before attempting to initiate mating, as the females are less likely to attack. Males which are vulnerable to post-copulation consumption may gather mating thread to generate a mechanical tension which they could use to spring away after insemination, while other spiders such as the crab spider may tangle the female's legs in webs to reduce the risk of the female capturing him. Male choice is common in mantids whereby males were observed to choose fatter females due to the reduced risk of attack and were more hesitant to approach starved females.

Size-structured cannibalism

Nematode of the order Mononchida eating another Mononchid

Size-structured cannibalism is cannibalism in which older, larger, more mature individuals consume smaller, younger conspecifics. In size-structured populations, (where populations are made of individuals of various sizes, ages, and maturities), cannibalism can be responsible for 8% (Belding's ground squirrel) to 95% (dragonfly larvae) of the total mortality, making it a significant and important factor for population and community dynamics.

Size-structured cannibalism has commonly been observed in the wild for a variety of taxa. Vertebrate examples include chimpanzees, where groups of adult males have been observed to attack and consume infants.

Filial cannibalism

Main article: Filial cannibalism

Filial cannibalism is a specific type of size-structured cannibalism in which adults eat their own offspring. Although most often thought of as parents eating live young, filial cannibalism includes parental consumption of stillborn infants and miscarried fetuses as well as infertile and still-incubating eggs. Vertebrate examples include pigs, where savaging accounts for a sizable percentage of total piglet deaths, and cats.

Filial cannibalism is particularly common in teleost fishes, appearing in at least seventeen different families of teleosts. Within this diverse group of fish, there have been many, variable explanations of the possible adaptive value of filial cannibalism. One of these is the energy-based hypothesis, which suggests that fish eat their offspring when they are low on energy as an investment in future reproductive success. This has been supported by experimental evidence, showing that male three-spined sticklebacks, male tessellated darters, and male sphinx blenny fish all consume or absorb their own eggs to maintain their physical conditions. In other words, when males of a fish species are low on energy, it might sometimes be beneficial for them to feed on their own offspring to survive and invest in future reproductive success.

Another hypothesis as to the adaptive value of filial cannibalism in teleosts is that it increases density-dependent egg survivorship. In other words, filial cannibalism simply increases overall reproductive success by helping the other eggs make it to maturity by thinning out the numbers. Possible explanations as to why this is so include increasing oxygen availability to the remaining eggs, the negative effects of accumulating embryo waste, and predation.

In some species of eusocial wasps, such as Polistes chinensis, the reproducing female will kill and feed younger larvae to her older brood. This occurs under food stressed conditions in order to ensure that the first generation of workers emerges without delay. Further evidence also suggests that occasionally filial cannibalism might occur as a by-product of cuckoldry in fish. Males consume broods, which may include their own offspring, when they believe a certain percentage of the brood contains genetic material that is not theirs.

It is not always the parent that cannibalizes the offspring; in some spiders, mothers have been observed to feed themselves to their brood as the ultimate provision from mother to children, known as matriphagy.

The dinosaur Coelophysis was once suspected to practice this form of cannibalism but this turned out to be wrong, although Deinonychus may have done so. Skeletal remains from subadults with missing parts are suspected of having been eaten by other Deinonychus, mainly full-grown adults.

Infanticide

Main article: Infanticide (zoology)

Infanticide is the killing of a non-adult animal by an adult of the same species. Infanticide is often accompanied by cannibalism. It is often displayed in lions; a male lion encroaching on the territory of a rival pride will often kill any existing cubs fathered by other males; this brings the lionesses into heat more quickly, enabling the invading lion to sire his own young. This is an example of cannibalistic behaviour in a genetic context.

In many species of Lepidoptera, such as Cupido minimus and the Indian mealmoth, the first larvae to hatch will consume the other eggs or smaller larvae on the host plant, decreasing competition.

Intrauterine cannibalism

Further information: Oophagy

Intrauterine cannibalism is a behaviour in some carnivorous species, in which multiple embryos are created at impregnation, but only one or two are born. The larger or stronger ones consume their less-developed siblings as a source of nutrients.

In adelphophagy or embryophagy, the fetus eats sibling embryos, while in oophagy it feeds on eggs.

Adelphophagy occurs in some marine gastropods (calyptraeids, muricids, vermetids, and buccinids) and in some marine annelids (Boccardia proboscidia in Spionidae).

Intrauterine cannibalism is known to occur in lamnoid sharks such as the sand tiger shark, and in the fire salamander, as well as in some teleost fishes. The Carboniferous period chimaera, Delphyodontos dacriformes, is suspected of having practiced intrauterine cannibalism, also, due to the sharp teeth of the recently born (or possibly aborted) juveniles, and the presence of fecal matter in the juveniles' intestines.

Protection against cannibalism

Animals have evolved protection to prevent and deter potential predators such as those from their own kind. Many amphibian eggs are gelatinous and toxic to decrease edibility. Often, adults would lay their eggs in crevices, holes, or empty nesting sites to hide their eggs from potential conspecific predators which tend to ingest the eggs for an additional nutritional benefit or to get rid of genetic competition. In amphibians, the development of non-aquatic egg deposition has helped increase the survival rates of their young by the evolution of viviparity or direct development. In bees, worker policing occurs to prohibit worker reproduction, whereby workers cannibalize other worker laid eggs. Queen laid eggs have a different scent than worker laid eggs, allowing workers to differentiate between the two, allowing them to nurture and protect queen laid eggs rather than cannibalising them. Parental presence at nesting sites is also a common method of protection against infanticide committed by conspecific individuals, whereby the parent exhibits defensive displays to ward off potential predators. Parental investment in newborns are generally higher during their early stages of development whereby behaviours such as aggression, territorial behaviour, and pregnancy blocking become more apparent.

Morphological plasticity helps an individual account for different predation stresses, thereby increasing individual survival rates. Japanese brown frog tadpoles have been shown to exhibit morphological plasticity when they are in a high stress environment where cannibalism between tadpoles and more developed individuals were present. Shifting their morphology plays a key role in their survival, creating bulkier bodies when put into environments where more developed tadpoles were present, to make it difficult for the individuals to swallow them whole. Diet shifts between different stages of development have also evolved to decrease competition between each stage, thereby increasing the amount of food availability so that there is a decreased chance that the individuals will turn to cannibalism as an additional food source.

Cannibalism in the media

Cannibalism has been a subject for horror movies since the 1980s. This genre is called cannibal films. In Planet Dinosaur it shows two Majungasaurus fighting to eat each other.

Cannibalism has also been a subject of video games. More recently, cannibalism has been featured in a positive light, with video games like Ark: Survival Evolved incentivizing players' virtual characters to eat each other.

Public health genomics

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Public_health_genomics

Public health genomics is the use of genomics information to benefit public health. This is visualized as more effective preventive care and disease treatments with better specificity, tailored to the genetic makeup of each patient. According to the Centers for Disease Control and Prevention (U.S.), Public Health genomics is an emerging field of study that assesses the impact of genes and their interaction with behavior, diet and the environment on the population's health.

This field of public health genomics is less than a decade old. A number of think tanks, universities, and governments (including the U.S., UK, and Australia) have started public health genomics projects. Research on the human genome is generating new knowledge that is changing public health programs and policies. Advances in genomic sciences are increasingly being used to improve health, prevent disease, educate and train the public health workforce, other healthcare providers, and citizens.

Public policy

Public policy has protected people against genetic discrimination, defined in Taber's Cyclopedic Medical Dictionary (2001) as unequal treatment of persons with either known genetic abnormalities or the inherited propensity for disease; genetic discrimination may have a negative effect on employability, insurability and other socio-economic variables. Public policy in the U.S. that protect individuals and groups of people against genetic discrimination include the Americans with Disabilities Act of 1990, Executive Order 13145 (2000) that prohibits genetic discrimination in the workplace for federal employees, and the Genetic Information Nondiscrimination Act of 2008.

Main public concerns regarding genomic information are that of confidentiality, misuse of information by health plans, employers, and medical practitioners, and the right of access to genetic information. Concerns also exist about the equitable deployment of public health genomics, and attention is needed to ensure that the implementation of genomic medicine does not further entrench social‐equity concerns.

Ethical concerns

One of the many facets involved in public health genomics is that of bioethics. This has been highlighted in a study in 2005 by Cogent Research, that found when American citizens were asked what they thought the strongest drawback was in using genetic information, they listed "misuse of information/invasion of privacy" as the single most important problem. In 2003, the Nuffield Council on Bioethics published a report, Pharmacogenetics: Ethical Issues. Authors of the document explore four broad categories of ethical and policy issues related to pharmacogenetics: information, resource, equity and control. In the introduction to the report, the authors clearly state that the development and application of pharmacogenetics depend on scientific research, but that policy and administration must provide incentives and restraints to ensure the most productive and just use of this technology. Involving the public in ethical oversight and other ways can improve public trust in public health genomics as well as acceptability of initiatives and ensuring that access to the benefits of genomics research is equitable.

Genetic susceptibility to disease

Single nucleotide polymorphisms (SNPs) are single bases within a gene sequence that differ from that gene's consensus sequence, and are present in a subset of the population. SNPs may have no effect on gene expression, or they can change the function of a gene completely. Resulting gene expression changes can, in some cases, result in disease, or in susceptibility to disease (e.g., viral or bacterial infection).

Some current tests for genetic diseases include: cystic fibrosis, Tay–Sachs disease, amyotrophic lateral sclerosis (ALS), Huntington's disease, high cholesterol, some rare cancers and an inherited susceptibility to cancer. A select few are explored below.

Herpesvirus and bacterial infections

Since the field of genomics takes into account the entire genome of an organism, and not simply its individual genes, the stud of latent viral infection falls into this realm. For example, the DNA of a latent herpesvirus integrates into the host's chromosome and propagates through cell replication, although it is not part of the organism's genome, and was not present at the birth of the individual.

An example of this is found in a study published in Nature, which showed that mice with a latent infection of a herpesvirus were less susceptible to bacterial infections. Murine mice were infected with murine gammaherpesvirus 68 and then challenged with the Listeria monocytogenes bacterium. Mice that had a latent infection of the virus had an increased resistance to the bacteria, but those with a non-latent strain of virus had no change in susceptibility to the bacteria. The study went on to test mice with murine cytomegalovirus, a member of the betaherpesvirinae subfamily, which provided similar results. However, infection with human herpes simplex virus type-1 (HSV-1), a member of the alphaherpesvirinae subfamily, did not provide increased resistance to bacterial infection. They also used Yersinia pestis (the causative agent of the Black Death) to challenge mice with a latent infection of gammaherpesvirus 68, and they found the mice did have an increased resistance to the bacteria. The suspected reason for this is that peritoneal macrophages in the mouse are activated after latent infection of the herpesvirus, and since macrophages play an important role in immunity, this provides the mouse with a stronger, active immune system at the time of bacterial exposure. It was found that the latent herpesvirus caused an increase in interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α), cytokines which both lead to activation of macrophages and resistance to bacterial infection.

Influenza and Mycobacterium tuberculosis

Variations within the human genome can be studied to determine susceptibility to infectious diseases. The study of variations within microbial genomes will also need to be evaluated to use genomics of infectious disease within public health. The ability to determine if a person has greater susceptibility to an infectious disease will be valuable to determine how to treat the disease if it is present or prevent the person from getting the disease. Several infectious diseases have shown a link between genetics and susceptibility in that families tend to have heritability traits of a disease.

During the course of the past influenza pandemics and the current influenza epizootic there has been evidence of family clusters of disease. Kandun, et al. found that family clusters in Indonesia in 2005 resulted in mild, severe and fatal cases among family members. The findings from this study raise questions about genetic or other predispositions and how they affect a person's susceptibility to and severity of disease. Continued research will be needed to determine the epidemiology of H5N1 infection and whether genetic, behavioral, immunologic, and environmental factors contribute to case clustering.

Host genetic factors play a major role in determining differential susceptibility to major infectious diseases of humans. Infectious diseases in humans appear highly polygenic with many loci implicated but only a minority of these convincingly replicated. Over the course of time, humans have been exposed to organisms like Mycobacterium tuberculosis. It is possible that the human genome has evolved in part from our exposure to M. tuberculosis. Animal model studies and whole genome screens can be used to identify potential regions on a gene that suggest evidence of tuberculosis susceptibility. In the case of M. tuberculosis, animal model studies were used to suggest evidence of a locus which was correlated with susceptibility, further studies were done to prove the link between the suggested locus and susceptibility. The genetic loci that have been identified as associated with susceptibility to tuberculosis are HLA-DR, INF-γ, SLC11A1, VDR, MAL/TIRAP, and CCL2. Further studies will be needed to determine genetic susceptibility to other infectious diseases and ways public health officials can prevent and test for these infections to enhance the concept of personalized medicine.

Type 1 Diabetes, immunomics, and public health

The term genomics, referring to the organism's whole genome, is also used to refer to gene informatics, or the collection and storage of genetic data, including the functional information associated with the genes, and the analysis of the data as combinations, patterns and networks by computer algorithms. Systems biology and genomics are natural partners, since the development of genomic information and systems naturally facilitates analysis of systems biology questions involving relationships between genes, their variants (SNPs) and biological function. Such questions include the investigation of signaling pathways, evolutionary trees, or biological networks, such as immune networks and pathways. For this reason, genomics and these approaches are particularly suited to studies in immunology. The study of immunology using genomics, as well as proteomics and transcriptomics (including gene profiles, either genomic or expressed gene mRNA profiles), has been termed immunomics.

Accurate and sensitive prediction of disease, or detection during early stages of disease, could allow the prevention or arrest of disease development as immunotherapy treatments become available. Type-1 diabetes markers associated with disease susceptibility have been identified, for example HLA class II gene variants, however possession of one or more of these genomic markers does not necessarily lead to disease. Lack of progression to disease is likely due to the absence of environmental triggers, absence of other susceptibility genes, presence of protective genes, or differences in the temporal expression or presence of these factors. Combinations of markers have also been associated with susceptibility to type-1 diabetes however again, their presence may not always predict disease development, and conversely, disease may be present without the marker group. Potential variant genes (SNPs) or markers that are linked to the disease include genes for cytokines, membrane-bound ligands, insulin and immune regulatory genes.

Meta-analyses have been able to identify additional associated genes, by pooling a number of large gene datasets. This successful study illustrates the importance of compiling and sharing large genome databases. The inclusion of phenotypic data in these databases will enhance discovery of candidate genes, while the addition of environmental and temporal data should be able to advance the disease progression pathways knowledge. HUGENet, which was initiated by the Centers for Disease Control and Prevention (U.S.), is accomplishing the integration of this type of information with the genome data, in a form available for analysis. This project could be thought of as an example of 'metagenomics', the analysis of a community's genome, but for a human rather than a microbial community. This project is intended to promote international data sharing and collaboration, in addition to creating a standard and framework for the collection of this data.

Nonsyndromic hearing loss

Variations within the human genome are being studied to determine susceptibility to chronic diseases, as well as infectious diseases. According to Aileen Kenneson and Coleen Boyle, about one sixth of the U.S. population has some degree of hearing loss. Recent research has linked variants in the gap junction beta 2 (GJB2) gene to nonsyndromic prelingual sensorineural hearing loss. GJB2 is a gene encoding for connexin, a protein found in the cochlea. Scientists have found over 90 variants in this gene and sequence variations may account for up to 50% of nonsyndromic hearing loss. Variants in GJB2 are being used to determine age of onset, as well as severity of hearing loss.

It is clear that there are also environmental factors to consider. Infections such as rubella and meningitis and low birth weight and artificial ventilation, are known risk factors for hearing loss, but perhaps knowing this, as well as genetic information, will help with early intervention.

Information gained from further research in the role of GJB2 variants in hearing loss may lead to newborn screening for them. As early intervention is crucial to prevent developmental delays in children with hearing loss, the ability to test for susceptibility in young children would be beneficial. Knowing genetic information may also help in the treatment of other diseases if a patient is already at risk.

Further testing is needed, especially in determining the role of GJB2 variants and environmental factors on a population level, however initial studies show promise when using genetic information along with newborn screening.

Genomics and health

Pharmacogenomics

Main article: Pharmacogenomics

The World Health Organization has defined pharmacogenomics as the study of DNA sequence variation as it relates to different drug responses in individuals, i.e., the use of genomics to determine an individual's response. Pharmacogenomics refers to the use of DNA-based genotyping in order to target pharmaceutical agents to specific patient populations in the design of drugs.

Current estimates state that 2 million hospital patients are affected by adverse drug reactions every year and adverse drug events are the fourth leading cause of death. These adverse drug reactions result in an estimated economic cost of $136 billion per year. Polymorphisms (genetic variations) in individuals affect drug metabolism and therefore an individual's response to a medication. Examples of ways in which genetics may affect an individual's response to drugs include: drug transporters, metabolism and drug interactions. Pharmacogenetics may be used in the near future by public health practitioners to determine the best candidates for certain drugs, thereby reducing much of the guesswork in prescribing drugs. Such actions have the potential to improve the effectiveness of treatments and reduce adverse drug events.

Nutrition and health

Nutrition is very important in determining various states of health. The field of nutrigenomics is based on the idea that everything ingested into a person's body affects the genome of the individual. This may be through either upregulating or downregulating the expression of certain genes or by a number of other methods. While the field is quite young there are a number of companies that market directly to the public and promote the issue under the guise of public health. Yet many of these companies claim to benefit the consumer, the tests performed are either not applicable or often result in common sense recommendations. Such companies promote public distrust towards future medical tests that may test more appropriate and applicable agents.

An example of the role of nutrition would be the methylation pathway involving methylene tetrahydrofolate reductase (MTHFR). An individual with the SNP may need increased supplementation of vitamin B12 and folate to override the effect of a variant SNP. Increased risk for neural tube defects and elevated homocysteine levels have been associated with the MTHFR C677T polymorphism.

In 2002, researchers from the Johns Hopkins Bloomberg School of Public Health identified the blueprint of genes and enzymes in the body that enable sulforaphane, a compound found in broccoli and other vegetables, to prevent cancer and remove toxins from cells. The discovery was made using a "gene chip," which allows researchers to monitor the complex interactions of thousands of proteins on a whole genome rather than one at time. This study was the first gene profiling analysis of a cancer-preventing agent using this approach. University of Minnesota researcher Sabrina Peterson, coauthored a study with Johanna Lampe of the Fred Hutchinson Cancer Research Center, Seattle, in October 2002 that investigated the chemoprotective effect of cruciferous vegetables (e.g., broccoli, brussels sprouts). Study results published in The Journal of Nutrition outline the metabolism and mechanisms of action of cruciferous vegetable constituents, discusses human studies testing effects of cruciferous vegetables on biotransformation systems and summarizes the epidemiologic and experimental evidence for an effect of genetic polymorphisms (genetic variations) in these enzymes in response to cruciferous vegetable intake.

Healthcare and genomics

Members of the public are continually asking how obtaining their genetic blueprint will benefit them, and why they find that they are more susceptible to diseases that have no cures.

Researchers have found that almost all disorders and diseases that affect humans reflect the interplay between the environment and their genes; however we are still in the initial stages of understanding the specific role genes play on common disorders and diseases. For example, while news reports may give a different impression, most cancer is not inherited. It is therefore likely that the recent rise in the rates of cancer worldwide can be at least partially attributed to the rise in the number of synthetic and otherwise toxic compounds found in our society today. Thus, in the near future, public health genomics, and more specifically environmental health, will become an important part of the future healthcare-related issues.

Potential benefits of uncovering the human genome will be focused more on identifying causes of disease and less on treating disease, through: improved diagnostic methods, earlier detection of a predisposing genetic variation, pharmacogenomics and gene therapy.

For each individual, the experience of discovering and knowing their genetic make-up will be different. For some individuals, they will be given the assurance of not obtaining a disease, as a result of familial genes, in which their family has a strong history and some will be able to seek out better medicines or therapies for a disease they already have. Others will find they are more susceptible to a disease that has no cure. Though this information maybe painful, it will give them the opportunity to prevent or delay the on-set of that disease through: increased education of the disease, making lifestyle changes, finding preventive therapies or identifying environmental triggers of the disease. As we continue to have advances in the study of human genetics, we hope to one day incorporate it into the day-to-day practice of healthcare. Understanding one's own genetic blueprint can empower oneself to take an active role in promoting their own health.

Genomics and understanding of disease susceptibility can help validate family history tool for use by practitioners and the public. IOM is validating the family history tool for six common chronic diseases (breast, ovarian, colorectal cancer, diabetes, heart disease, stroke) (IOM Initiative). Validating cost effective tools can help restore importance of basic medical practices (e.g. family history) in comparission to technology intensive investigations.

The genomic face of immune responses

A critical set of phenomena that ties together various aspects of health interventions, such as drug sensitivity screening, cancer or autoimmune susceptibility screening, infectious disease prevalence and application of pharmacologic or nutrition therapies, is the systems biology of the immune response. For example, the influenza epidemic of 1918, as well as the recent cases of human fatality due to H5N1 (avian flu), both illustrate the potentially dangerous sequence of immune responses to this virus. Also well documented is the only case of spontaneous "immunity" to HIV in humans, shown to be due to a mutation in a surface protein on CD4 T cells, the primary targets of HIV. The immune system is truly a sentinel system of the body, with the result that health and disease are carefully balanced by the modulated response of each of its various parts, which then also act in concert as a whole. Especially in industrialized and rapidly developing economies, the high rate of allergic and reactive respiratory disease, autoimmune conditions and cancers are also in part linked to aberrant immune responses that are elicited as the communities' genomes encounter swiftly changing environments. The causes of perturbed immune responses run the gamut of genome-environment interactions due to diet, supplements, sun exposure, workplace exposures, etc. Public health genomics as a whole will absolutely require a rigorous understanding of the changing face of immune responses.

Newborn screening

The experience of newborn screening serves as the introduction to public health genomics for many people. If they did not undergo prenatal genetic testing, having their new baby undergo a heel stick in order to collect a small amount of blood may be the first time an individual or couple encounters genetic testing. Newborn genetic screening is a promising area in public health genomics that appears poised to capitalize on the public health goal of disease prevention as a primary form of treatment.

Most of the diseases that are screened for are extremely rare, single-gene disorders that are often autosomal recessive conditions and are not readily identifiable in neonates without these types of tests. Therefore, often the treating physician has never seen a patient with the disease or condition and so an immediate referral to a specialty clinic is necessary for the family.

Most of the conditions identified in newborn screening are metabolic disorders that either involve i) lacking an enzyme or the ability to metabolize (or breakdown) a particular component of the diet, like phenylketonuria, ii) abnormality of some component of the blood, especially the hemoglobin protein, or iii) alteration of some component of the endocrine system, especially the thyroid gland. Many of these disorders, once identified, can be treated before more severe symptoms, such as mental retardation or stunted growth, set in.

Newborn genetic screening is an area of tremendous growth. In the early 1960s, the only test was for phenylketonuria. In 2000, roughly two-thirds of states in the US screened for 10 or fewer genetic diseases in newborns. Notably, in 2007, 95% of states in the US screen for more than 30 different genetic diseases in newborns. Especially as costs have come down, newborn genetic screening offers "an excellent return on the expenditure of public health dollars".

Because the risks and benefits of genomic sequencing for newborns are still not fully understood, the BabySeq Project, led by Robert C. Green of Brigham and Women's Hospital and Alan H. Beggs of Boston Children's Hospital (BCH) has been gathering critical research on newborn sequencing since 2015 as part of the Newborn Sequencing In Genomic medicine and public HealTh consortium (NSIGHT), which received a five-year grant of $25 million from the National Institute of Child Health and Human Development (NICHD) and the National Human Genome Research Institute (NHGRI).

Understanding traditional healing practices

Genomics will help develop an understanding of the practices that have evolved over centuries in old civilizations and which have been strengthened by observations (phenotype presentations) from generation to generation, but which lack documentation and scientific evidence. Traditional healers associated specific body types with resistance or susceptibility to particular diseases under specific conditions. Validation and standardization of this knowledge/ practices has not yet been done by modern science. Genomics, by associating genotypes with the phenotypes on which these practices were based, could provide key tools to advance the scientific understanding of some of these traditional healing practices.

Youth suicide

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Youth_suicide

Youth suicide is when a young person, generally categorized as someone below the legal age of majority, deliberately ends their own life. Rates of youth suicide and attempted youth suicide in Western societies and other countries are high. Youth suicide attempts are more common among girls, but adolescent males are the ones who usually carry out suicide. Suicide rates in youths have nearly tripled between the 1960s and 1980s. For example, in Australia suicide is second only to motor vehicle accidents as its leading cause of death for people aged 15 to 25.

In the U.S., according to the National Institute of Mental Health, the suicide rate is the 2nd leading cause of death for adolescents between the ages of 10 and 14, and the third leading cause of death for those between 15 and 19. In 2021, the American Academy of Pediatrics, the American Academy of ChiId and Adolescent Psychiatry, and the Children's Hospital Association released a joint statement announcing a mental health crisis among our youth. Emergency room visits for mental health issues have dramatically increased, especially after the COVID-19 pandemic.

Suicide contagion

According to research conducted by the Commission for Children and Young People and Child Guardian in 2007, 39% of all youth suicides are completed by young people who have lost someone of influence / significance to them to suicide. The Commission terms this suicide contagion and makes several recommendations as to the importance of safeguarding young people and communities from suicide contagion.

In 2011 the Australian Federal Parliament Standing Committee for Health and Ageing Inquiry into Youth Suicide met in a round table forum with young representatives from three organizations at the forefront of preventing youth suicide. These organizations included Sunnykids, Inspire, and Boys Town. The Standing Committee has since released a discussion paper highlighting the findings of their inquiry and will seek to make final recommendations on the most effective means for reducing youth suicide.

Teens at risk

One of the problems facing teenagers at risk of suicide is getting psychiatric counselling when it is needed. One research at the beginning of 2020 shows that compared with older adolescents, younger adolescents particularly agree that increased cyberbullying and despair are very important factors influencing suicide among adolescents. One study says, "In teenagers, depression is considered a major – if not the leading – cause of teen suicide." Factors and risks contributed to youth suicide are academic pressure, alcohol consumption, the loss of a valued relationship, frequent change of residency, and poor family patterns. Harassment is a leading cause of teen suicide, along with abuse. Gay teens or those unsure of their sexual identity are more likely to die by suicide, particularly if they have suffered bullying or harassment, as discussed next. The following campaigns have been started in hopes of giving teens hope and abolishing the feeling of isolation.

• It Gets Better
• Born This Way
• I Get Bullied Too
• Stop Youth Suicide

Lack of impulse control has been found to differentiate adolescent suicide attempters from a control group of adolescents with an acute illness (Slap, Vorters, Chaudhuri, & Centor, 1988). However, impulsivity does not characterize all suicide attempters, since group comparisons have found no differences between suicidal patients and psychiatric controls on a measure of cognitive impulsivity (Patsiokas, Clum, & Luscomb, 1979). Instead, impulsivity may be important in identifying high-risk subgroups.

Sexual minority youth and suicide

Youth that fall under the category of sexual minorities are at an elevated risk of depression and succumbing to self-harm. Among the population of sexual minority youth, on average, 28% explain having past experiences with suicidal actions and/or thoughts. Lesbian and gay youth are the group most likely to face negative experiences, leading to a higher likelihood of the development of suicidal thoughts according to mental care professionals. Bisexuality also carries a higher likelihood of suicidality with bisexuals being five times more likely to report suicidal thoughts and actions. Sexual minority youth also report a higher incidence of substance abuse when compared to heterosexuals. Overall, studies suggest that sexual minority youth carry a higher incidence of suicide and depression, and that reforms centered on alleviating minority stigma attenuate this disparity.

Previous exposure, attempts, and age impacting youth suicide

Exposure to suicide, previous attempts of suicide, and age are some of the most influential factors of young individuals and their probability of dying by suicide. Adolescent exposure to suicide through classmates has caused researchers to hypothesize suicide as a contagion. They note how a child's exposure to suicide predicts suicide ideation and attempts. Previous exposure to suicide through parental attempts have also been found to have a 3.5% increase in a youth's probability of having suicidal thoughts, with a 2.6% increased chance of them attempting suicide. Aggression in families and its transference can be one of the main causes of transmission of suicidal tendencies in families.

Previous attempts of suicide also play a major role in a youth attempting suicide again. On average, it has been recorded that the follow-up period for suicide-attempters was 3.88 years. Evidence shows those most at risk for suicide are those who previously attempted suicide, with research showing that they can have anywhere from a 40 to over a 100 times higher chance of dying by suicide compared to the general population.

Age and experience also factor in suicide. It has been found that older, more experienced populations take more time to plan, choose deadlier methods, and have greater suicidal intent. This results in them eventually committing suicide at a higher rate than their younger counterparts.

Bereavement among young people

The primary goals of suicide postvention include assisting the survivors of suicide with the grief process, along with identifying and referring those survivors who may be at risk for negative outcomes such as depressive and anxiety disorders, and suicidal behaviour. With 42% of youth suicides being suicide bereavement (or contagion) related – further research and investment must be made into supporting this group of people. A few suggestions to make sure the support is effective include making the individuals feel connected and understood.

Epidemiology

Two possible determinants to suicide attempts are lifetime sexual abuse and adult physical violence. Among participants aged 18–25, the odds ratios for lifetime sexual abuse and adult physical violence are 4.27 and 3.85, respectively. In other words, those who died by suicide are 327% more likely to have experienced lifetime sexual assault. Similarly, a suicide victim is 285% more likely to have suffered physical violence as an adult. Based on a survey done on American high school students, 16% reported considering suicide and 8% reported attempting suicide sometime within the 12 months before taking the survey. Between 1980 and 1994, the suicide rates of young black males doubled. American Indians and Alaska Natives die by suicide at a higher rate than any other ethnic group in the United States. In India, one-third of suicides are young people 15–29. In 2002, 154,000 suicides were recorded in India. In the United States, about 60 percent of suicides are carried out with a gun. Some Aboriginal teens and gay or lesbian teens are at high risk, depending on their community and their own self-esteem. Several campaigns have been started to give them hope and help them to feel less isolated.

The 2019 Youth Risk Behavior Survey, which was conducted by the CDC, found that between 2009 and 2018, suicide rates among adolescents aged 14-18 years increased by 61.7%. Furthermore, the CDC reported that in 2019, among American adolescents in grades 9 to12:

• 18.8% of students reported seriously considering attempting suicide
• 15.7% of students made a suicide plan
• 8.9% of students attempted suicide

Intervention

One organization in Australia has found that young people who feel connected, supported, and understood are less likely to die by suicide. Reports on the attitudes of young people identified as at risk of suicide have been released. Such reports support the notion that connectedness, a sense of being supported and respected, is a protective factor for young people at risk of suicide. According to Pueblo Suicide Prevention Center (PSPC) for some reason kids today are experiencing more pressure.

For immediate help, contact SAMHSA's National Suicide Prevention Lifeline at 1-800-273-TALK (8255).

Issues for communities

Intervention issues for communities to address include suicide contagion, developmental understanding of suicide, development and suicide risk, and the influence of culture. Key matters in postvention responses for young people include: community context, life stage relevance of responses, identification, and referral (Postvention Co-ordination), developing a suite of services, and creating ongoing options.

Prevention

Crisis hotlines, such as the 988 Suicide & Crisis Lifeline, enable people to get immediate emergency telephone counselling.

One can help prevent adolescent suicide by discouraging isolation, addressing a child's depression which is correlated with suicide, getting rid of any objects that a child could use to attempt suicide, and simply paying attention to what the child does or feels.

Schools are a great place to provide more education and support for suicide prevention. Since students spend the majority of their time at school, the school can be either a haven from or a source of suicidal triggers, and students' peers can heavily influence their state of mind. The school setting is an ideal environment to educate students on suicide and have support readily available.

Suicide Prevention Resource Center provides professional information and resources on suicide prevention.

Prevention resources for parents, guardians, social workers, teachers, school staff, peers:

• Sibshops
• Youth Mental Health First Aid
• More can be found on U.S. Department of Health & Human Services website for Mental Health in Adolescent

National Suicide Prevention Lifeline for Youth provides resources and information for teens and adolescents such as:

• The Trevor Project
• You Matter
• StopBullying.gov
• Love is Respect
• Ditch the Label

Table of youth suicide rates (per 100,000)

Country	Year of Data	Rate of Males	Rate of Females	Total
Sri Lanka	1986	43.9	49.3	46.5
Lithuania	2002	38.4	8.8	23.9
Russian Federation	2002	38.5	8.3	23.6
Kazakhstan	2002	31.2	10.5	21.0
Luxembourg	2002	23.5	8.2	16.0
New Zealand	2000	22.3	8.2	15.3
El Salvador	1993	13.2	15.8	14.5
Belarus	2001	23.6	3.9	14.0
Estonia	2002	24.1	1.9	13.2
Turkmenistan	1998	16.6	8.8	12.8
Ukraine	2000	19.6	4.9	12.4
Ireland	2000	19.8	4.3	12.3
Mauritius	2000	10.1	12.5	11.3
Norway	2001	15.3	6.2	10.9
Canada	2000	16.3	5.2	10.8
Latvia	2002	16.9	4.4	10.8
Kyrgyzstan	2002	15.2	4.8	10.0
Austria	2002	15.1	3.8	9.6
Trinidad and Tobago	1994	8.9	10.5	9.6
Finland	2002	15.0	3.8	9.5
Uzbekistan	2000	12.5	6.4	9.5
Belgium	1997	14.5	3.9	9.3
Cuba	1996	6.1	12.5	9.2
Ecuador	1991	6.9	11.4	9.1
Australia	2001	13.8	3.8	8.9
Singapore	2001	9.2	7.8	8.5
Poland	2001	14.1	2.4	8.4
Switzerland	2000	12.6	4.0	8.4
Croatia	2002	14.0	2.1	8.2
USA	2000	13.0	2.7	8.0
Slovenia	1987	12.0	3.1	7.6
Hungary	2002	11.2	3.8	7.5
Japan	2000	8.8	3.8	6.4
Uruguay	1990	8.3	3.9	6.2
Bulgaria	2002	9.2	2.3	5.8
Czech Republic	2001	9.5	1.8	5.7
Argentina	1996	7.1	4.0	5.6
Costa Rica	1995	7.1	4.0	5.6
Germany	2001	8.7	2.4	5.6
Thailand	1994	6.1	5.1	5.6
Colombia	1994	6.7	4.2	5.5
Venezuela	1994	7.1	3.8	5.5
Republic of Korea	2001	5.9	4.9	5.4
Hong Kong	1999	5.1	5.3	5.2
France	1999	7.5	2.5	5.0
Denmark	1999	9.0	0.7	4.9
Israel	1999	8.7	0.0	4.9
Romania	2002	7.0	2.2	4.7
Netherlands	2000	7.4	1.8	4.6
Sweden	2001	5.7	2.8	4.3
Brazil*	1995	5.7	2.6	4.2
Puerto Rico	1992	8.3	0.0	4.2
United Kingdom	1999	6.5	1.8	4.2
Republic of Moldova	2002	7.1	1.1	4.1
China*	1999	3.2	4.8	4.0
Slovakia	2002	5.8	1.9	3.9
Chile	1994	6.2	1.3	3.8
Mexico	1995	5.1	2.3	3.7
Spain	2000	5.3	1.4	3.4
Panama	1987	4.6	1.6	3.1
Albania	2001	2.8	3.3	3.0
Dominican Republic	1985	2.7	3.2	2.9
Italy	2000	3.6	1.7	2.7
Macedonia	2000	1.2	3.7	2.4
Tajikistan	1999	3.3	0.9	2.1
Portugal	2000	2.6	0.9	1.8
Greece	1999	2.7	0.6	1.7
Peru	1983	1.3	0.7	1.0

Information taken from World Psychiatry, the official journal of the World Psychiatric Association. Numbers are per 100,000.