Apomixis

From Wikipedia, the free encyclopedia

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

Vegetative apomixis in Poa bulbosa; bulbils form instead of flowers

In botany, apomixis was defined by Hans Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttings or leaves, has never been considered to be apomixis, but replacement of the seed by a plantlet or replacement of the flower by bulbils were categorized as types of apomixis. Apomictically produced offspring are genetically identical to the parent plant.

Some authors included all forms of asexual reproduction within apomixis, but that generalization of the term has since died out.

In flowering plants, the term "apomixis" is commonly used in a restricted sense to mean agamospermy, i.e., clonal reproduction through seeds. Although agamospermy could theoretically occur in gymnosperms, it appears to be absent in that group.

Apogamy is a related term that has had various meanings over time. In plants with independent gametophytes (notably ferns), the term is still used interchangeably with "apomixis", and both refer to the formation of sporophytes by parthenogenesis of gametophyte cells.

Male apomixis (paternal apomixis) involves replacement of the genetic material of an egg by the 

genetic material of the pollen.

Evolution

Because apomictic plants are genetically identical from one generation to the next, each lineage has some of the characters of a true species, maintaining distinctions from other apomictic lineages within the same genus, while having much smaller differences than is normal between species of most genera. They are therefore often called microspecies. In some genera, it is possible to identify and name hundreds or even thousands of microspecies, which may be grouped together as species aggregates, typically listed in floras with the convention "Genus species agg." (such as the bramble, Rubus fruticosus agg.). In some plant families, genera with apomixis are quite common, for example in Asteraceae, Poaceae, and Rosaceae. Examples of apomixis can be found in the genera Crataegus (hawthorns), Amelanchier (shadbush), Sorbus (rowans and whitebeams), Rubus (brambles or blackberries), Poa (meadow grasses), Nardus stricta (Matgrass), Hieracium (hawkweeds) and Taraxacum (dandelions). Apomixis is reported to occur in about 10% of globally extant ferns. Among polystichoid ferns, apomixis evolved several times independently in three different clades.

Although the evolutionary advantages of sexual reproduction are lost, apomixis can pass along traits fortuitous for evolutionary fitness. As Jens Clausen put it

The apomicts actually have discovered the effectiveness of mass production long before Mr Henry Ford applied it to the production of the automobile. ... Facultative apomixis ... does not prevent variation; rather, it multiplies certain varietal products.

Facultative apomixis means that apomixis does not always occur, i.e. sexual reproduction can also happen. It appears likely that all apomixis in plants is facultative; in other words, that "obligate apomixis" is an artifact of insufficient observation (missing uncommon sexual reproduction).

Apogamy and apospory in non-flowering plants

The gametophytes of bryophytes, and less commonly ferns and lycopods can develop a group of cells that grow to look like a sporophyte of the species but with the ploidy level of the gametophyte, a phenomenon known as apogamy. The sporophytes of plants of these groups may also have the ability to form a plant that looks like a gametophyte but with the ploidy level of the sporophyte, a phenomenon known as apospory.

See also androgenesis and androclinesis described below, a type of male apomixis that occurs in a conifer, Cupressus dupreziana.

In flowering plants (angiosperms)

Agamospermy, asexual reproduction through seeds, occurs in flowering plants through many different mechanisms and a simple hierarchical classification of the different types is not possible. Consequently, there are almost as many different usages of terminology for apomixis in angiosperms as there are authors on the subject. For English speakers, Maheshwari 1950 is very influential. German speakers might prefer to consult Rutishauser 1967. Some older text books on the basis of misinformation (that the egg cell in a meiotically unreduced gametophyte can never be fertilized) attempted to reform the terminology to match the term parthenogenesis as it is used in zoology, and this continues to cause much confusion. 

Agamospermy occurs mainly in two forms: In gametophytic apomixis, the embryo arises from an unfertilized egg cell (i.e. by parthenogenesis) in a gametophyte that was produced from a cell that did not complete meiosis. In adventitious embryony (sporophytic apomixis), an embryo is formed directly (not from a gametophyte) from nucellus or integument tissue (see nucellar embryony).

Types in flowering plants

Caribbean agave producing plantlets on the old flower stem.

Maheshwari used the following simple classification of types of apomixis in flowering plants:

• Nonrecurrent apomixis: In this type "the megaspore mother cell undergoes the usual meiotic divisions and a haploid embryo sac [megagametophyte] is formed. The new embryo may then arise either from the egg (haploid parthenogenesis) or from some other cell of the gametophyte (haploid apogamy)." The haploid plants have half as many chromosomes as the mother plant, and "the process is not repeated from one generation to another" (which is why it is called nonrecurrent). See also parthenogenesis and apogamy below.
• Recurrent apomixis, is now more often called gametophytic apomixis: In this type, the megagametophyte has the same number of chromosomes as the mother plant because meiosis was not completed. It generally arises either from an archesporial cell or from some other part of the nucellus.
• Adventive embryony, also called sporophytic apomixis, sporophytic budding, or nucellar embryony: Here there may be a megagametophyte in the ovule, but the embryos do not arise from the cells of the gametophyte; they arise from cells of nucellus or the integument. Adventive embryony is important in several species of Citrus, in Garcinia, Euphorbia dulcis, Mangifera indica etc.
• Vegetative apomixis: In this type "the flowers are replaced by bulbils or other vegetative propagules which frequently germinate while still on the plant". Vegetative apomixis is important in Allium, Fragaria, Agave, and some grasses, among others.

Types of gametophytic apomixis

Gametophytic apomixis in flowering plants develops in several different ways. A megagametophyte develops with an egg cell within it that develops into an embryo through parthenogenesis. The central cell of the megagametophyte may require fertilization to form the endosperm, pseudogamous gametophytic apomixis, or in autonomous gametophytic apomixis endosperm fertilization is not required.

• In diplospory (also called generative apospory), the megagametophyte arises from a cell of the archesporium.
• In apospory (also called somatic apospory), the megagametophyte arises from some other (somatic) cell of the nucellus.

Considerable confusion has resulted because diplospory is often defined to involve the megaspore mother cell only, but a number of plant families have a multicellular archesporium and the megagametophyte could originate from another archesporium cell.

Diplospory is further subdivided according to how the megagametophyte forms:

• Allium odorum–A. nutans type. The chromosomes double (endomitosis) and then meiosis proceeds in an unusual way, with the chromosome copies pairing up (rather than the original maternal and paternal copies pairing up).
• Taraxacum type: Meiosis I fails to complete, meiosis II creates two cells, one of which degenerates; three mitotic divisions form the megagametophyte.
• Ixeris type: Meiosis I fails to complete; three rounds of nuclear division occur without cell-wall formation; wall formation then occurs.
• Blumea–Elymus types: A mitotic division is followed by degeneration of one cell; three mitotic divisions form the megagametophyte.
• Antennaria–Hieracium types: three mitotic divisions form the megagametophyte.
• Eragrostis–Panicum types: Two mitotic division give a 4-nucleate megagametophyte, with cell walls to form either three or four cells.

Incidence in flowering plants

Apomixis occurs in at least 33 families of flowering plants, and has evolved multiple times from sexual relatives. Apomictic species or individual plants often have a hybrid origin, and are usually polyploid.

In plants with both apomictic and meiotic embryology, the proportion of the different types can differ at different times of year, and photoperiod can also change the proportion. It appears unlikely that there are any truly completely apomictic plants, as low rates of sexual reproduction have been found in several species that were previously thought to be entirely apomictic.

The genetic control of apomixis can involve a single genetic change that affects all the major developmental components, formation of the megagametophyte, parthenogenesis of the egg cell, and endosperm development. However, the timing of the various developmental processes is critical to successful development of an apomictic seed, and the timing can be affected by multiple genetic factors.

Some related terms

• Apomeiosis: "Without meiosis"; usually meaning the production of a meiotically unreduced gametophyte.
• Parthenogenesis: Development of an embryo directly from an egg cell without fertilization is called parthenogenesis. It is of two types:
  • Haploid parthenogenesis: Parthenogenesis of a normal haploid egg (a meiotically reduced egg) into an embryo is termed haploid parthenogenesis. If the mother plant was diploid, then the haploid embryo that results is monoploid, and the plant that grows from the embryo is sterile. If they are not sterile, they are sometimes useful to plant breeders (especially in potato breeding, see dihaploidy). This type of apomixis has been recorded in Solanum nigrum, Lilium spp., Orchis maculata, Nicotiana tabacum, etc.
  • Diploid parthenogenesis: When the megagametophyte develops without completing meiosis, so that the megagametophyte and all cells within it are meiotically unreduced (a.k.a. diploid, but diploid is an ambiguous term), this is called diploid parthenogenesis, and the plant that develops from the embryo will have the same number of chromosomes as the mother plant. Diploid parthenogenesis is a component process of gametophytic apomixis (see above).
• Androgenesis and androclinesis are synonyms. These terms are used for two different processes that both have the effect of producing an embryo that has "male inheritance".

The first process is a natural one. It may also be referred to as male apomixis or paternal apomixis. It involves fusion of the male and female gametes and replacement of the female nucleus by the male nucleus. This has been noted as a rare phenomenon in many plants (e.g. Nicotiana and Crepis), and occurs as the regular reproductive method in the Saharan Cypress, Cupressus dupreziana.

The second process that is referred to as androgenesis or androclinesis involves (artificial) culture of haploid plants from anther tissue or microspores.

• Apogamy: Although this term was (before 1908) used for other types of apomixis, and then discarded as too confusing, it is still sometimes used when an embryo develops from a cell of the megagametophyte other than the egg cell. In flowering plants, the cells involved in apogamy would be synergids or antipodal cells.
• Addition hybrids, called B_III hybrids by Rutishauser: An embryo is formed after a meiotically unreduced egg cell is fertilized. The ploidy level of the embryo is therefore higher than that of the mother plant. This process occurs in some plants that are otherwise apomictic, and may play a significant role in producing tetraploid plants from triploid apomictic mother plants (if they receive pollen from diploids). Because fertilization is involved, this process does not fit the definition of apomixis.
• Pseudogamy refers to any reproductive process that requires pollination but does not involve male inheritance. It is sometimes used in a restrictive sense to refer to types of apomixis in which the endosperm is fertilized but the embryo is not. A better term for the restrictive sense is centrogamy.
• Agamospecies, the concept introduced by Göte Turesson: "an apomict population the constituents of which, for morphological, cytological or other reasons, are to be considered as having a common origin," i.e., basically synonymous with "microspecies.

Biological life cycle

From Wikipedia, the free encyclopedia

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

 

Life cycle of a mosquito. An adult (imago) lays eggs which develop through several stages to adulthood. Reproduction completes and perpetuates the cycle.

 

Life cycle of the single-celled parasite Babesia.

 

In biology, a biological life cycle (or just life cycle or lifecycle when the biological context is clear) is a series of changes in form that an organism undergoes, returning to the starting state. "The concept is closely related to those of the life history, development and ontogeny, but differs from them in stressing renewal." Transitions of form may involve growth, asexual reproduction, or sexual reproduction. 

In some organisms, different "generations" of the species succeed each other during the life cycle. For plants and many algae, there are two multicellular stages, and the life cycle is referred to as alternation of generations. The term life history is often used, particularly for organisms such as the red algae which have three multicellular stages (or more), rather than two.

Life cycles that include sexual reproduction involve alternating haploid (n) and diploid (2n) stages, i.e., a change of ploidy is involved. To return from a diploid stage to a haploid stage, meiosis must occur. In regard to changes of ploidy, there are 3 types of cycles:

• haplontic life cycle — the haploid stage is multicellular and the diploid stage is a single cell, meiosis is "zygotic".
• diplontic life cycle — the diploid stage is multicellular and haploid gametes are formed, meiosis is "gametic".
• haplodiplontic life cycle (also referred to as diplohaplontic, diplobiontic, or dibiontic life cycle) — multicellular diploid and haploid stages occur, meiosis is "sporic".

The cycles differ in when mitosis (growth) occurs. Zygotic meiosis and gametic meiosis have one mitotic stage: mitosis occurs during the n phase in zygotic meiosis and during the 2n phase in gametic meiosis. Therefore, zygotic and gametic meiosis are collectively termed "haplobiontic" (single mitotic phase, not to be confused with haplontic). Sporic meiosis, on the other hand, has mitosis in two stages, both the diploid and haploid stages, termed "diplobiontic" (not to be confused with diplontic).

Discovery

The study of reproduction and development in organisms was carried out by many botanists and zoologists. 

Wilhelm Hofmeister demonstrated that alternation of generations is a feature that unites plants, and published this result in 1851.

Some terms (haplobiont and diplobiont) used for the description of life cycles were proposed initially for algae by Nils Svedelius, and then became used for other organisms. Other terms (autogamy and gamontogamy) used in protist life cycles were introduced by Karl Gottlieb Grell. The description of the complex life cycles of various organisms contributed to the disproof of the ideas of spontaneous generation in the 1840s and 1850s.

Haplontic life cycle

Zygotic meiosis

 

A zygotic meiosis is a meiosis of a zygote immediately after karyogamy, which is the fusion of two cell nuclei. This way, the organism ends its diploid phase and produces several haploid cells. These cells divide mitotically to form either larger, multicellular individuals, or more haploid cells. Two opposite types of gametes (e.g., male and female) from these individuals or cells fuse to become a zygote. 

In the whole cycle, zygotes are the only diploid cell; mitosis occurs only in the haploid phase. 

The individuals or cells as a result of mitosis are haplonts, hence this life cycle is also called haplontic life cycle. Haplonts are:

• In archaeplastidans: some green algae (e.g., Chlamydomonas, Zygnema, Chara)
• In stramenopiles: some golden algae
• In alveolates: many dinoflagellates, e.g., Ceratium, Gymnodinium, some apicomplexans (e.g., Plasmodium)
• In rhizarians: some euglyphids, ascetosporeans
• In excavates: some parabasalids
• In amoebozoans: Dictyostelium
• In opisthokonts: most fungi (some chytrids, zygomycetes, some ascomycetes, basidiomycetes)

Diplontic life cycle

Gametic meiosis

 

In gametic meiosis, instead of immediately dividing meiotically to produce haploid cells, the zygote divides mitotically to produce a multicellular diploid individual or a group of more unicellular diploid cells. Cells from the diploid individuals then undergo meiosis to produce haploid cells or gametes. Haploid cells may divide again (by mitosis) to form more haploid cells, as in many yeasts, but the haploid phase is not the predominant life cycle phase. In most diplonts, mitosis occurs only in the diploid phase, i.e. gametes usually form quickly and fuse to produce diploid zygotes. 

In the whole cycle, gametes are usually the only haploid cells, and mitosis usually occurs only in the diploid phase. 

The diploid multicellular individual is a diplont, hence a gametic meiosis is also called a diplontic life cycle. Diplonts are:

• In archaeplastidans: some green algae (e.g., Cladophora glomerata, Acetabularia)
• In stramenopiles: some brown algae (the Fucales, however, their life cycle can also be interpreted as strongly heteromorphic-diplohaplontic, with a highly reduced gametophyte phase, as in the flowering plants), some xanthophytes (e.g., Vaucheria), most diatoms, some oomycetes (e.g., Saprolegnia, Plasmopara viticola), opalines, some "heliozoans" (e.g., Actinophrys, Actinosphaerium)
• In alveolates: ciliates 
• In excavates: some parabasalids 
• In opisthokonts: animals, some fungi (e.g., some ascomycetes) Haplodiplontic life cycle

Sporic meiosis

In sporic meiosis (also commonly known as intermediary meiosis), the zygote divides mitotically to produce a multicellular diploid sporophyte. The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes. The gametophytes produce gametes via mitosis. In some plants the gametophyte is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the "dominant" stage of the life cycle.

Haplodiplonts are:

• In archaeplastidans: red algae (which have two sporophyte generations), some green algae (e.g., Ulva), land plants
• In stramenopiles: most brown algae
• In rhizarians: many foraminiferans, plasmodiophoromycetes
• In amoebozoa: myxogastrids
• In opisthokonts: some fungi (some chytrids, some ascomycetes like the brewer's yeast)
• Other eukaryotes: haptophytes

Some animals have a sex-determination system called haplodiploid, but this is not related to the haplodiplontic life cycle.

Vegetative meiosis

Some red algae (such as Bonnemaisonia and Lemanea) and green algae (such as Prasiola) have vegetative meiosis, also called somatic meiosis, which is a rare phenomenon. Vegetative meiosis can occur in haplodiplontic and also in diplontic life cycles. The gametophytes remain attached to and part of the sporophyte. Vegetative (non-reproductive) diploid cells undergo meiosis, generating vegetative haploid cells. These undergo many mitosis, and produces gametes. 

A different phenomenon, called vegetative diploidization, a type of apomixis, occurs in some brown algae (e.g., Elachista stellaris). Cells in a haploid part of the plant spontaneously duplicate their chromosomes to produce diploid tissue.

Parasitic life cycle

Parasites depend on the exploitation of one or more hosts. Those that must infect more than one host species to complete their life cycles are said to have complex or indirect life cycles, while those that infect a single species have direct life cycles.

If a parasite has to infect a given host in order to complete its life cycle, then it is said to be an obligate parasite of that host; sometimes, infection is facultative—the parasite can survive and complete its life cycle without infecting that particular host species. Parasites sometimes infect hosts in which they cannot complete their life cycles; these are accidental hosts.

A host in which parasites reproduce sexually is known as the definitive, final or primary host. In intermediate hosts, parasites either do not reproduce or do so asexually, but the parasite always develops to a new stage in this type of host. In some cases a parasite will infect a host, but not undergo any development, these hosts are known as paratenic or transport hosts. The paratenic host can be useful in raising the chance that the parasite will be transmitted to the definitive host. For example, the cat lungworm (Aelurostrongylus abstrusus) uses a slug or snail as an intermediate host; the first stage larva enters the mollusk and develops to the third stage larva, which is infectious to the definitive host—the cat. If a mouse eats the slug, the third stage larva will enter the mouse's tissues, but will not undergo any development. 

Life cycle of the apicomplexan, Babesia

Evolution

The primitive type of life cycle probably had haploid individuals with asexual reproduction. Bacteria and archaea exhibit a life cycle like this, and some eukaryotes apparently do too (e.g., Cryptophyta, Choanoflagellata, many Euglenozoa, many Amoebozoa, some red algae, some green algae, the imperfect fungi, some rotifers and many other groups, not necessarily haploid). However, these eukaryotes probably are not primitively asexual, but have lost their sexual reproduction, or it just was not observed yet. Many eukaryotes (including animals and plants) exhibit asexual reproduction, which may be facultative or obligate in the life cycle, with sexual reproduction occurring more or less frequently.

Phenology

From Wikipedia, the free encyclopedia

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

 

Phenological development of olive flowering, following BBCH standard scale. a-50, b-51, c-54, d-57, (<15 e-61="" flowers="" open="">50% open flowers); f-65, (>15% open flowers); g-67, (<15 2013="" al.="" div="" et="" flowers="" h-68="" open="" teros="">

 

Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation).

Examples include the date of emergence of leaves and flowers, the first flight of butterflies, the first appearance of migratory birds, the date of leaf colouring and fall in deciduous trees, the dates of egg-laying of birds and amphibia, or the timing of the developmental cycles of temperate-zone honey bee colonies. In the scientific literature on ecology, the term is used more generally to indicate the time frame for any seasonal biological phenomena, including the dates of last appearance (e.g., the seasonal phenology of a species may be from April through September). 

Because many such phenomena are very sensitive to small variations in climate, especially to temperature, phenological records can be a useful proxy for temperature in historical climatology, especially in the study of climate change and global warming. For example, viticultural records of grape harvests in Europe have been used to reconstruct a record of summer growing season temperatures going back more than 500 years.  In addition to providing a longer historical baseline than instrumental measurements, phenological observations provide high temporal resolution of ongoing changes related to global warming.

Etymology

The word is derived from the Greek φαίνω (phainō), "to show, to bring to light, make to appear" + λόγος (logos), amongst others "study, discourse, reasoning" and indicates that phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle. 

The term was first used by Charles François Antoine Morren, a professor of Botany at the University of Liège (Belgium). Morren was a student of Adolphe Quetelet. Quetelet made plant phenological observations at the Royal Observatory of Belgium in Brussels. He is considered "one of 19th century trendsetters in these matters." In 1839 he started his first observations and created a network over Belgium and Europe that reached a total of about 80 stations in the period 1840-1870. 

Morren participated in 1842 and 1843 in Quetelets 'Observations of Periodical Phenomena' (Observations des Phénomènes périodiques), and at first suggested to mention the observations concerning botanical phenomena 'anthochronological observations'. That term had already been used in 1840 by Carl Joseph Kreutzer. 

But 16 December 1849 Morren used the term 'phenology' for the first time in a public lecture at the Royal Academy of Science, Letters and Fine Arts of Belgium in Brussels, to describe “the specific science which has the goal to know the ‘’manifestation of life ruled by the time’’.”

It would take four more years before Morren first published “phenological memories”. That the term was not really common in the decades to follow may be shown by an article in The Zoologist of 1899. The article describes an ornithological meeting in Sarajevo, where 'questions of Phaenology' were discussed. A footnote by the Editor, William Lucas Distant, says: “This word is seldom used, and we have been informed by a very high authority that it may be defined as "Observational Biology," and as applied to birds, as it is here, may be taken to mean the study or science of observations on the appearance of birds.”

Records

Historical

Historical day of year for first bloom index (FBI) for the Tallgrass Prairie National Preserve, Kansas (dots) fitted with a local polynomial regression model (loess in red) and a 2 standard error band (blue). Data from William Monahan.

 

Observations of phenological events have provided indications of the progress of the natural calendar since ancient agricultural times. Many cultures have traditional phenological proverbs and sayings which indicate a time for action: "When the sloe tree is white as a sheet, sow your barley whether it be dry or wet" or attempt to forecast future climate: "If oak's before ash, you're in for a splash. If ash before oak, you're in for a soak". But the indications can be pretty unreliable, as an alternative version of the rhyme shows: "If the oak is out before the ash, 'Twill be a summer of wet and splash; If the ash is out before the oak, 'Twill be a summer of fire and smoke." Theoretically, though, these are not mutually exclusive, as one forecasts immediate conditions and one forecasts future conditions. 

The North American Bird Phenology Program at USGS Patuxent Wildlife Research Center (PWRC) is in possession of a collection of millions of bird arrival and departure date records for over 870 species across North America, dating between 1880 and 1970. This program, originally started by Wells W. Cooke, involved over 3,000 observers including many notable naturalists of the time. The program ran for 90 years and came to a close in 1970 when other programs starting up at PWRC took precedence. The program was again started in 2009 to digitize the collection of records and now with the help of citizens worldwide, each record is being transcribed into a database which will be publicly accessible for use. 

The English naturalists Gilbert White and William Markwick reported the seasonal events of more than 400 plant and animal species, Gilbert White in Selborne, Hampshire and William Markwick in Battle, Sussex over a 25-year period between 1768 and 1793. The data, reported in White's Natural History and Antiquities of Selborne are reported as the earliest and latest dates for each event over 25 years; so annual changes cannot therefore be determined. 

In Japan and China the time of blossoming of cherry and peach trees is associated with ancient festivals and some of these dates can be traced back to the eighth century. Such historical records may, in principle, be capable of providing estimates of climate at dates before instrumental records became available. For example, records of the harvest dates of the pinot noir grape in Burgundy have been used in an attempt to reconstruct spring–summer temperatures from 1370 to 2003; the reconstructed values during 1787–2000 have a correlation with Paris instrumental data of about 0.75.

Modern

Great Britain

Robert Marsham, the founding father of modern phenological recording, was a wealthy landowner who kept systematic records of "Indications of spring" on his estate at Stratton Strawless, Norfolk, from 1736. These took the form of dates of the first occurrence of events such as flowering, bud burst, emergence or flight of an insect. Generations of Marsham's family maintained consistent records of the same events or "phenophases" over unprecedentedly long periods of time, eventually ending with the death of Mary Marsham in 1958, so that trends can be observed and related to long-term climate records. The data show significant variation in dates which broadly correspond with warm and cold years. Between 1850 and 1950 a long-term trend of gradual climate warming is observable, and during this same period the Marsham record of oak-leafing dates tended to become earlier.

After 1960 the rate of warming accelerated, and this is mirrored by increasing earliness of oak leafing, recorded in the data collected by Jean Combes in Surrey. Over the past 250 years, the first leafing date of oak appears to have advanced by about 8 days, corresponding to overall warming on the order of 1.5 °C in the same period. 

Towards the end of the 19th century the recording of the appearance and development of plants and animals became a national pastime, and between 1891 and 1948 the Royal Meteorological Society (RMS) organised a programme of phenological recording across the British Isles. Up to 600 observers submitted returns in some years, with numbers averaging a few hundred. During this period 11 main plant phenophases were consistently recorded over the 58 years from 1891–1948, and a further 14 phenophases were recorded for the 20 years between 1929 and 1948. The returns were summarised each year in the Quarterly Journal of the RMS as The Phenological Reports. Jeffree (1960) summarised the 58 years of data, which show that flowering dates could be as many as 21 days early and as many as 34 days late, with extreme earliness greatest in summer-flowering species, and extreme lateness in spring-flowering species. In all 25 species, the timings of all phenological events are significantly related to temperature, indicating that phenological events are likely to get earlier as climate warms.

The Phenological Reports ended suddenly in 1948 after 58 years, and Britain remained without a national recording scheme for almost 50 years, just at a time when climate change was becoming evident. During this period, individual dedicated observers made important contributions. The naturalist and author Richard Fitter recorded the First Flowering Date (FFD) of 557 species of British flowering plants in Oxfordshire between about 1954 and 1990. Writing in Science in 2002, Richard Fitter and his son Alistair Fitter found that "the average FFD of 385 British plant species has advanced by 4.5 days during the past decade compared with the previous four decades." They note that FFD is sensitive to temperature, as is generally agreed, that "150 to 200 species may be flowering on average 15 days earlier in Britain now than in the very recent past" and that these earlier FFDs will have "profound ecosystem and evolutionary consequences". In Scotland, David Grisenthwaite meticulously recorded the dates he mowed his lawn since 1984. His first cut of the year was 13 days earlier in 2004 than in 1984, and his last cut was 17 days later, providing evidence for an earlier onset of spring and a warmer climate in general.

National recording was resumed by Tim Sparks in 1998 and, from 2000, has been led by citizen science project Nature's Calendar, run by the Woodland Trust and the Centre for Ecology and Hydrology. Latest research shows that oak bud burst has advanced more than 11 days since the 19th century and that resident and migrant birds are unable to keep up with this change.

Continental Europe

In Europe, phenological networks are operated in several countries, e.g. Germany's national meteorological service operates a very dense network with approx. 1200 observers, the majority of them on a voluntary basis. The Pan European Phenology (PEP) project is a database that collects phenological data from European countries. Currently 32 European meteorological services and project partners from across Europe have joined and supplied data.

Other countries

There is a USA National Phenology Network in which both professional scientists and lay recorders participate. 

Many other countries such as Canada (Alberta Plantwatch and Saskatchewan PlantWatch), China and Australia also have phenological programs. 

In eastern North America, almanacs are traditionally used for information on action phenology (in agriculture), taking into account the astronomical positions at the time. William Felker has studied phenology in Ohio, US, since 1973 and now publishes "Poor Will's Almanack", a phenological almanac for farmers (not to be confused with a late 18th-century almanac by the same name). 

In the Amazon rainforests of South America, the timing of leaf production and abscission has been linked to rhythms in gross primary production at several sites. Early in their lifespan, leaves reach a peak in their capacity for photosynthesis, and in tropical evergreen forests of some regions of the Amazon basin (particularly regions with long dry seasons), many trees produce more young leaves in the dry season, seasonally increasing the photosynthetic capacity of the forest.

Airborne sensors

NDVI temporal profile for a typical patch of coniferous forest over a period of six years. This temporal profile depicts the growing season every year as well as changes in this profile from year to year due to climatic and other constraints. Data and graph are based on the MODIS sensor standard public vegetation index product. Data archived at the ORNL DAAC , courtesy of Dr. Robert Cook.

 

Recent technological advances in studying the earth from space have resulted in a new field of phenological research that is concerned with observing the phenology of whole ecosystems and stands of vegetation on a global scale using proxy approaches. These methods complement the traditional phenological methods which recorded the first occurrences of individual species and phenophases. 

The most successful of these approaches is based on tracking the temporal change of a Vegetation Index (like Normalized Difference Vegetation Index(NDVI)). NDVI makes use of the vegetation's typical low reflection in the red (red energy is mostly absorbed by growing plants for Photosynthesis) and strong reflection in the Near Infrared (Infrared energy is mostly reflected by plants due to their cellular structure). Due to its robustness and simplicity, NDVI has become one of the most popular remote sensing based products. Typically, a vegetation index is constructed in such a way that the attenuated reflected sunlight energy (1% to 30% of incident sunlight) is amplified by ratio-ing red and NIR following this equation:

${\displaystyle \mathrm {NDVI} ={\mathrm {NIR} -\mathrm {red} \over \mathrm {NIR} +\mathrm {red} }}$

The evolution of the vegetation index through time, depicted by the graph above, exhibits a strong correlation with the typical green vegetation growth stages (emergence, vigor/growth, maturity, and harvest/senescence). These temporal curves are analyzed to extract useful parameters about the vegetation growing season (start of season, end of season, length of growing season, etc.). Other growing season parameters could potentially be extracted, and global maps of any of these growing season parameters could then be constructed and used in all sorts of climatic change studies. 

A noteworthy example of the use of remote sensing based phenology is the work of Ranga Myneni from Boston University. This work showed an apparent increase in vegetation productivity that most likely resulted from the increase in temperature and lengthening of the growing season in the boreal forest. Another example based on the MODIS enhanced vegetation index (EVI) reported by Alfredo Huete at the University of Arizona and colleagues showed that the Amazon Rainforest, as opposed to the long-held view of a monotonous growing season or growth only during the wet rainy season, does in fact exhibit growth spurts during the dry season.

However, these phenological parameters are only an approximation of the true biological growth stages. This is mainly due to the limitation of current space-based remote sensing, especially the spatial resolution, and the nature of vegetation index. A pixel in an image does not contain a pure target (like a tree, a shrub, etc.) but contains a mixture of whatever intersected the sensor's field of view.

Phenological mismatch

A picture depicting a hummingbird visiting and pollinating a flower. If the flower blooms too early in the season, or if the humming bird has a delay in migration, this interaction will be lost.

 

Most species, including both plants and animals, interact with one another within ecosystems and habitats, known as biological interactions. These interactions (whether it be plant-plant, animal-animal, predator-prey or plant-animal interactions) can be vital to the success and survival of populations and therefore species. 

Many species experience changes in life cycle development, migration or in some other process/behavior at different times in the season than previous patterns depict due to warming temperatures. Phenological mismatches, where interacting species change the timing of regularly repeated phases in their life cycles at different rates, creates a mismatch in interaction timing and therefore negatively harming the interaction. Mismatches can occur in many different biological interactions, including between species in one trophic level (intratrophic interactions) (ie. plant-plant), between different trophic levels (intertrophic interactions) (ie. plant-animal) or through creating competition (intraguild interactions). For example, if a plant species blooms its flowers earlier than previous years, but the pollinators that feed on and pollinate this flower does not arrive or grow earlier as well, then a phenological mismatch has occurred. This results in the plant population declining as there are no pollinators to aid in their reproductive success. Another example includes the interaction between plant species, where the presence of one specie aids in the pollination of another through attraction of pollinators. However, if these plant species develop at mismatched times, this interaction will be negatively affected and therefore the plant species that relies on the other will be harmed. 

Phenological mismatches means the loss of many biological interactions and therefore ecosystem functions are also at risk of being negatively effects or lost all together. Phenological mismatches his will effect species and ecosystems food webs, reproduction success, resource availability, population and community dynamics in future generations, and therefore evolutionary process and overall biodiversity.

Scholar

From Wikipedia, the free encyclopedia

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

 

Scholar and His Books by Gerbrand van den Eeckhout.

 

A scholar is a person who pursues academic and intellectual activities, particularly those that develop expertise in an area of study. A scholar may also be an academic, who works as a professor, teacher or researcher at a university or other higher education institution. An academic usually holds an advanced degree or terminal degree such as a PhD. Some independent scholars, such as philosophers and public intellectuals work outside of academia. They may still contribute to academic journals and participate in scholarly conferences even though they are unaffiliated with a university.

Definitions

The term scholar is sometimes used with equivalent meaning to that of academic and describes in general those who attain mastery in a research discipline. However, it has wider application, with it also being used to describe those whose occupation was researched prior to organized higher education. In 1847, minister Emanuel Vogel Gerhart delivered an extensive address on the role of the scholar in society, writing:

[A] scholar [is one] whose whole inward intellectual and moral being has been symmetrically unfolded, disciplined and strengthened under the influence of truth... No one faculty should be drawn out to the neglect of others. The whole inner man should be unfolded harmoniously.

Gerhart argued that a scholar can not be focused on a single discipline, contending that knowledge of multiple disciplines is necessary to put each into context and to inform the development of each:

[T]o be a scholar involves more than mere learning... A genuine scholar possesses something more: he penetrates and understands the principle and laws of the particular department of human knowledge with which he professes acquaintance. He imbibes the life of Science... [and] his mind is transfused and moulded by its energy and spirit.

A 2011 examination outlined the following attributes commonly accorded to scholars as "described by many writers, with some slight variations in the definition":

The common themes are that a scholar is a person who has a high intellectual ability, is an independent thinker and an independent actor, has ideas that stand apart from others, is persistent in her quest for developing knowledge, is systematic, has unconditional integrity, has intellectual honesty, has some convictions, and stands alone to support these convictions.

Scholars may rely on the scholarly method or scholarship, a body of principles and practices used by scholars to make their claims about the world as valid and trustworthy as possible, and to make them known to the scholarly public. It is the methods that systemically advance the teaching, research, and practice of a given scholarly or academic field of study through rigorous inquiry. Scholarship is creative, can be documented, can be replicated or elaborated, and can be and is peer-reviewed through various methods.

Role in society

Scholars have generally been upheld as creditable figures of high social standing, who are engaged in work important to society. In Imperial China, in the period from 206 BC until AD 1912, the intellectuals were the Scholar-officials ("Scholar-gentlemen"), who were civil servants appointed by the Emperor of China to perform the tasks of daily governance. Such civil servants earned academic degrees by means of Imperial examination, and also were skilled calligraphers, and knew Confucian philosophy. Historian Wing-Tsit Chan concludes that:

Generally speaking, the record of these scholar-gentlemen has been a worthy one. It was good enough to be praised and imitated in 18th century Europe. Nevertheless, it has given China a tremendous handicap in their transition from government by men to government by law, and personal considerations in Chinese government have been a curse.

In Joseon Korea (1392–1910), the intellectuals were the literati, who knew how to read and write, and had been designated, as the chungin (the "middle people"), in accordance with the Confucian system. Socially, they constituted the petite bourgeoisie, composed of scholar-bureaucrats (scholars, professionals, and technicians) who administered the dynastic rule of the Joseon dynasty.

In his 1847 address, Gerhart asserted that scholars have an obligation to constantly continue their studies so as to remain aware of new knowledge being generated, and to contribute their own insights to the body of knowledge available to all:

The progress of science involves momentous interests. It merits the attention of all sincere lovers of truth. Every ...scholar is under obligations to contribute towards the ever-progressive unfolding of its riches and power. [They]...should combine their energies to bring to view what has eluded the keen vision of those men of noble intellectual stature who have lived and died before them.  Many scholars are also professors engaged in the teaching of others. In a number of countries, the title "research professor" refers to a professor who is exclusively or mainly engaged in research, and who has few or no teaching obligations. For example, the title is used in this sense in the United Kingdom (where it is known as research professor at some universities and professorial research fellow at some other institutions) and in northern Europe. 

Research professor is usually the most senior rank of a research-focused career pathway in those countries, and regarded as equal to the ordinary full professor rank. Most often they are permanent employees, and the position is often held by particularly distinguished scholars; thus the position is often seen as more prestigious than an ordinary full professorship. The title is used in a somewhat similar sense in the United States, with the exception that research professors in the United States are often not permanent employees and often must fund their salary from external sources, which is usually not the case elsewhere.

Independent scholars

An independent scholar is anyone who conducts scholarly research outside universities and traditional academia. In 2010, twelve percent of US history scholars were independent. Independent scholars typically have a Master's degree or PhD. In history, independent scholars can be differentiated from popular history hosts for television shows and amateur historians "by the level to which their publications utilize the analytical rigour and academic writing style".

In previous centuries, some independent scholars achieved renown, such as Samuel Johnson and Edward Gibbon during the eighteenth century and Charles Darwin and Karl Marx in the nineteenth century, and Sigmund Freud in the twentieth century. As well, there was a tradition of the man of letters, such as Evelyn Waugh. The term "man of letters" derives from the French term belletrist or homme de lettres but is not synonymous with "an academic". In the 17th and 18th centuries, the term Belletrist(s) came to be applied to the literati: the French participants in—sometimes referred to as "citizens" of—the Republic of Letters, which evolved into the salon aimed at edification, education, and cultural refinement. 

In the United States, a professional association exists for independent scholars: this association is the National Coalition of Independent Scholars. In Canada, the equivalent professional association is the Canadian Academy of Independent Scholars (in association with Simon Fraser University). Similar organizations exist around the world. Membership in a professional association generally entails a degree of post-secondary education and established research. When independent scholars participate in academic conferences, they may be referred to as an unaffiliated scholar, since they do not hold a position in a university or other institution.

While independent scholars may earn an income from part-time teaching, speaking engagements, or consultant work, the University of British Columbia calls earning an income the biggest challenge of being an independent scholar. Due to challenges of making a living as a scholar without an academic position, "[m]any independent scholars depend on having a gainfully employed partner". To get access to libraries and other research facilities, independent scholars have to seek permission from universities.

Writer Megan Kate Nelson's article "Stop Calling Me Independent" says the term "marginalizes unaffiliated scholars" and is unfairly seen as an indicator of "professional failure". Rebecca Bodenheimer says that independent scholars like her attending conferences who do not have a university name on their official name badge feel like the "independent scholar" term is perceived as a "signal that a scholar is either unwanted by the academy or unwilling to commit to the sacrifices necessary to succeed as an academic."