Misplaced Pages

#513486

84-615: The San Marcos salamander ( Eurycea nana ) is a small species of aquatic, lungless salamander native to the United States, endemic to Spring Lake and a small region of the headwaters of the San Marcos River near Aquarena Springs , in Hays County, Texas . It is one to two inches long, with a slender body and external gills , and is reddish-brown in color. E. nana is an aquatic salamander. It does not leave

168-424: A diploid cell (the zygote ) is formed, which rapidly grows into a new organism. While the non-mammalian animal egg was obvious, the doctrine ex ovo omne vivum ("every living [animal comes from] an egg"), associated with William Harvey (1578–1657), was a rejection of spontaneous generation and preformationism as well as a bold assumption that mammals also reproduced via eggs. Karl Ernst von Baer discovered

252-423: A mutation–selection balance . It is predicted that a viral quasispecies at a low but evolutionarily neutral and highly connected (that is, flat) region in the fitness landscape will outcompete a quasispecies located at a higher but narrower fitness peak in which the surrounding mutants are unfit, "the quasispecies effect" or the "survival of the flattest". There is no suggestion that a viral quasispecies resembles

336-715: A threatened species since 1980. Due to its extremely limited geographic range, it is threatened primarily by the contamination of groundwater sources and heavy dependence of central Texas cities upon the Edwards Aquifer for water. Other threats include drying of the spring and introduced species. As migration cannot introduce genetic variation due to limited geographic range, the loss of genetic diversity cannot recover naturally when lost. Availability of food and sufficient prey also remain of concern for these salamanders, but less so than habitat loss or change. The San Marcos salamander and four other listed species are covered by

420-400: A "classical" method of determining species, such as with Linnaeus, early in evolutionary theory. However, different phenotypes are not necessarily different species (e.g. a four-winged Drosophila born to a two-winged mother is not a different species). Species named in this manner are called morphospecies . In the 1970s, Robert R. Sokal , Theodore J. Crovello and Peter Sneath proposed

504-424: A 'smallest clade' idea" (a phylogenetic species concept). Mishler and Wilkins and others concur with this approach, even though this would raise difficulties in biological nomenclature. Wilkins cited the ichthyologist Charles Tate Regan 's early 20th century remark that "a species is whatever a suitably qualified biologist chooses to call a species". Wilkins noted that the philosopher Philip Kitcher called this

588-428: A connected series of neighbouring populations, each of which can sexually interbreed with adjacent related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" population. Such non-breeding, though genetically connected, "end" populations may co-exist in the same region thus closing

672-432: A different species from its ancestors. Viruses have enormous populations, are doubtfully living since they consist of little more than a string of DNA or RNA in a protein coat, and mutate rapidly. All of these factors make conventional species concepts largely inapplicable. A viral quasispecies is a group of genotypes related by similar mutations, competing within a highly mutagenic environment, and hence governed by

756-508: A genetic boundary suitable for defining a species concept is present. DNA barcoding has been proposed as a way to distinguish species suitable even for non-specialists to use. One of the barcodes is a region of mitochondrial DNA within the gene for cytochrome c oxidase . A database, Barcode of Life Data System , contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomy and DNA barcoding, which they consider

840-465: A lineage should be divided into multiple chronospecies , or when populations have diverged to have enough distinct character states to be described as cladistic species. Species and higher taxa were seen from the time of Aristotle until the 18th century as categories that could be arranged in a hierarchy, the great chain of being . In the 19th century, biologists grasped that species could evolve given sufficient time. Charles Darwin 's 1859 book On

924-427: A long neck with a wider base containing the egg cell. Upon maturation, the neck opens to allow sperm cells to swim into the archegonium and fertilize the egg. The resulting zygote then gives rise to an embryo, which will grow into a new diploid individual, known as a sporophyte . In seed plants , a structure called the ovule contains the female gametophyte. The gametophyte produces an egg cell. After fertilization ,

SECTION 10

#1732798327514

1008-492: A misnomer, need to be reconciled, as they delimit species differently. Genetic introgression mediated by endosymbionts and other vectors can further make barcodes ineffective in the identification of species. A phylogenetic or cladistic species is "the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts)". The empirical basis – observed character states – provides

1092-449: A particular species, including which genus (and higher taxa) it is placed in, is a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be corroborated or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as

1176-400: A perfect model of life, it is still a useful tool to scientists and conservationists for studying life on Earth, regardless of the theoretical difficulties. If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change. This obliges taxonomists to decide, for example, when enough change has occurred to declare that

1260-400: A short way of saying that something applies to many species within a genus, but not to all. If scientists mean that something applies to all species within a genus, they use the genus name without the specific name or epithet. The names of genera and species are usually printed in italics . However, abbreviations such as "sp." should not be italicised. When a species' identity is not clear,

1344-438: A single female producing potentially 176 eggs per year. Kyphosis due to microsporidia , intracellular protistan parasites, has been reported in captivated E. nana . Batrachochytrium dendrobatidis , a global threat to amphibians, has also been detected in E. nana . It causes chytridiomycosis and death in salamanders, and has led to multiple extinctions since its discovery. Species A species ( pl. : species)

1428-470: A snout-vent greater than 19 millimetres (0.75 in). Four classes of ova are present: small-clear ova, small-opaque ova, small-yellow ova, and large-yellow ova. Female E. nana with a snout-vent greater than 26 millimetres (1.0 in) carry large yellow ova, and are considered ready for oviposition. E. nana relies primarily on chemical cues rather than visual cues for association preference. Both males and females exhibit sexual discrimination, suggesting

1512-404: A specialist may use "cf." before the epithet to indicate that confirmation is required. The abbreviations "nr." (near) or "aff." (affine) may be used when the identity is unclear but when the species appears to be similar to the species mentioned after. With the rise of online databases, codes have been devised to provide identifiers for species that are already defined, including: The naming of

1596-523: A species as groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr's use of the adjective "potentially" has been a point of debate; some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in

1680-400: A species as determined by a taxonomist. A typological species is a group of organisms in which individuals conform to certain fixed properties (a type), so that even pre-literate people often recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens (such as longer or shorter tails) would differentiate the species. This method was used as

1764-491: A species. All species definitions assume that an organism acquires its genes from one or two parents very like the "daughter" organism, but that is not what happens in HGT. There is strong evidence of HGT between very dissimilar groups of prokaryotes , and at least occasionally between dissimilar groups of eukaryotes , including some crustaceans and echinoderms . The evolutionary biologist James Mallet concludes that there

SECTION 20

#1732798327514

1848-685: A species. Generally the term includes the unknown element of a distinct act of creation. Many authors have argued that a simple textbook definition, following Mayr's concept, works well for most multi-celled organisms , but breaks down in several situations: Species identification is made difficult by discordance between molecular and morphological investigations; these can be categorised as two types: (i) one morphology, multiple lineages (e.g. morphological convergence , cryptic species ) and (ii) one lineage, multiple morphologies (e.g. phenotypic plasticity , multiple life-cycle stages). In addition, horizontal gene transfer (HGT) makes it difficult to define

1932-528: A taxonomic decision at the discretion of cognizant specialists, is not governed by the Codes of Zoological or Botanical Nomenclature, in contrast to the PhyloCode , and contrary to what is done in several other fields, in which the definitions of technical terms, like geochronological units and geopolitical entities, are explicitly delimited. The nomenclatural codes that guide the naming of species, including

2016-504: A temporal diet, or a diet that varies with the availability of invertebrates present to them at a given time. It relies on the schedule of invertebrate behavior and locations, and generally consumes many aquatic invertebrates. The surrounding vegetation is a rich source of food. E. nana displays predator avoidance responses relying on chemical cues from its native predators, such as Micropterus salmoides . Antipredator responses include freezing behavior to its fish predators. Site tenacity,

2100-517: A traditional biological species. The International Committee on Taxonomy of Viruses has since 1962 developed a universal taxonomic scheme for viruses; this has stabilised viral taxonomy. Most modern textbooks make use of Ernst Mayr 's 1942 definition, known as the Biological Species Concept as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept. This defines

2184-447: A variation on the morphological species concept, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms. It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species

2268-515: A variety of reasons. Viruses are a special case, driven by a balance of mutation and selection , and can be treated as quasispecies . Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics . Early taxonomists such as Linnaeus had no option but to describe what they saw: this was later formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts,

2352-438: Is "an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies". This differs from the biological species concept in embodying persistence over time. Wiley and Mayden stated that they see the evolutionary species concept as "identical" to Willi Hennig 's species-as-lineages concept, and asserted that

2436-400: Is a group of sexually reproducing organisms that recognise one another as potential mates. Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms; no matter whether populations can hybridise successfully, they are still distinct cohesion species if

2520-452: Is a population of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring , typically by sexual reproduction . It is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity . Other ways of defining species include their karyotype , DNA sequence, morphology , behaviour, or ecological niche . In addition, paleontologists use

2604-458: Is a set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognise as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters. A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations. This

San Marcos salamander - Misplaced Pages Continue

2688-414: Is called speciation . Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species . Speciation depends on a measure of reproductive isolation , a reduced gene flow. This occurs most easily in allopatric speciation, where populations are separated geographically and can diverge gradually as mutations accumulate. Reproductive isolation

2772-412: Is called the specific name or the specific epithet (in botanical nomenclature , also sometimes in zoological nomenclature ). For example, Boa constrictor is one of the species of the genus Boa , with constrictor being the species' epithet. While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. For example,

2856-403: Is described formally, in a publication that assigns it a unique scientific name. The description typically provides means for identifying the new species, which may not be based solely on morphology (see cryptic species ), differentiating it from other previously described and related or confusable species and provides a validly published name (in botany) or an available name (in zoology) when

2940-415: Is flattened above with a dorsal furrow that extends from head to tail. The venter, the bottom of a salamander, is white in color, and males have larger vents than females do. There are 16–17 costal grooves present, with 6–7 occurring between limbs. It has four toes on its forefeet and five on its hind feet. The size of the species was measured to be 56 millimetres (2.2 in) total in length. The name nana

3024-544: Is from the Greek nanos, meaning dwarf, as these adult salamanders are small in size. It is a member of the family Plethodontidae (lungless salamanders). Genetic variation of the species has not yet been observed. E. nana may be confused with E. neotenes , the only other species thus found to be in its genus; however, E. nana is smaller in size with a more slender form. San Marcos River, located in Hays County, Texas,

3108-671: Is further weakened by the existence of microspecies , groups of organisms, including many plants, with very little genetic variability, usually forming species aggregates . For example, the dandelion Taraxacum officinale and the blackberry Rubus fruticosus are aggregates with many microspecies—perhaps 400 in the case of the blackberry and over 200 in the dandelion, complicated by hybridisation , apomixis and polyploidy , making gene flow between populations difficult to determine, and their taxonomy debatable. Species complexes occur in insects such as Heliconius butterflies, vertebrates such as Hypsiboas treefrogs, and fungi such as

3192-726: Is hard or even impossible to test. Later biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, and the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: (1) agamospecies for asexual organisms (2) biospecies for reproductively isolated sexual organisms (3) ecospecies based on ecological niches (4) evolutionary species based on lineage (5) genetic species based on gene pool (6) morphospecies based on form or phenotype and (7) taxonomic species,

3276-403: Is no easy way to tell whether related geographic or temporal forms belong to the same or different species. Species gaps can be verified only locally and at a point of time. One is forced to admit that Darwin's insight is correct: any local reality or integrity of species is greatly reduced over large geographic ranges and time periods. The botanist Brent Mishler argued that the species concept

3360-478: Is not valid, notably because gene flux decreases gradually rather than in discrete steps, which hampers objective delimitation of species. Indeed, complex and unstable patterns of gene flux have been observed in cichlid teleosts of the East African Great Lakes . Wilkins argued that "if we were being true to evolution and the consequent phylogenetic approach to taxa, we should replace it with

3444-586: Is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation. In the 21st century, a genetic species could be established by comparing DNA sequences. Earlier, other methods were available, such as comparing karyotypes (sets of chromosomes ) and allozymes ( enzyme variants). An evolutionarily significant unit (ESU) or "wildlife species" is a population of organisms considered distinct for purposes of conservation. In palaeontology , with only comparative anatomy (morphology) and histology from fossils as evidence,

San Marcos salamander - Misplaced Pages Continue

3528-419: Is sometimes an important source of genetic variation. Viruses can transfer genes between species. Bacteria can exchange plasmids with bacteria of other species, including some apparently distantly related ones in different phylogenetic domains , making analysis of their relationships difficult, and weakening the concept of a bacterial species. Egg cell When egg and sperm fuse during fertilisation ,

3612-469: Is the only known location of the San Marcos salamander. The population estimate in 1973 was about 20,880 salamanders living in the uppermost reaches of Spring Lake. An estimate in 1993 suggested about 30,451 salamanders across all ranges of Spring Lake and up to 150 metres (490 ft) downstream. The ratio of males to females was reported to be stable throughout the year. Clear, flowing spring water of

3696-594: Is threatened by hybridisation, but this can be selected against once a pair of populations have incompatible alleles of the same gene, as described in the Bateson–Dobzhansky–Muller model . A different mechanism, phyletic speciation, involves one lineage gradually changing over time into a new and distinct form (a chronospecies ), without increasing the number of resultant species. Horizontal gene transfer between organisms of different species, either through hybridisation , antigenic shift , or reassortment ,

3780-509: Is unknown and studies to answer this question are currently ongoing. The feeding behavior of the salamander is rather passive as it waits for prey to pass and will abruptly snap forward to catch its food. This suggests this response is likely generated from visual or vibrational cues from prey. The San Marcos salamander breeds and lays eggs in standing ponds in the middle of dense mats of aquatic vegetation. Eggs are jelly-covered and will hatch in about 24 days. Male E. nana reaches maturity with

3864-530: The ICZN for animals and the ICN for plants, do not make rules for defining the boundaries of the species. Research can change the boundaries, also known as circumscription, based on new evidence. Species may then need to be distinguished by the boundary definitions used, and in such cases the names may be qualified with sensu stricto ("in the narrow sense") to denote usage in the exact meaning given by an author such as

3948-399: The fly agaric . Natural hybridisation presents a challenge to the concept of a reproductively isolated species, as fertile hybrids permit gene flow between two populations. For example, the carrion crow Corvus corone and the hooded crow Corvus cornix appear and are classified as separate species, yet they can hybridise where their geographical ranges overlap. A ring species is

4032-418: The formative yolk ; and the nutritive yolk or deutoplasm , made of rounded granules of fatty and albuminoid substances imbedded in the cytoplasm. Mammalian ova contain only a tiny amount of the nutritive yolk, for nourishing the embryo in the early stages of its development only. In contrast, bird eggs contain enough to supply the chick with nutriment throughout the whole period of incubation. In

4116-507: The jaguar ( Panthera onca ) of Latin America or the leopard ( Panthera pardus ) of Africa and Asia. In contrast, the scientific names of species are chosen to be unique and universal (except for some inter-code homonyms ); they are in two parts used together : the genus as in Puma , and the specific epithet as in concolor . A species is given a taxonomic name when a type specimen

4200-406: The oviparous animals (all birds , most fish , amphibians and reptiles ), the ova develop protective layers and pass through the oviduct to the outside of the body. They are fertilized by male sperm either inside the female body (as in birds), or outside (as in many fish). After fertilization, an embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside

4284-406: The "cynical species concept", and arguing that far from being cynical, it usefully leads to an empirical taxonomy for any given group, based on taxonomists' experience. Other biologists have gone further and argued that we should abandon species entirely, and refer to the "Least Inclusive Taxonomic Units" (LITUs), a view that would be coherent with current evolutionary theory. The species concept

SECTION 50

#1732798327514

4368-409: The 1870s suggested that the production of oocytes (immature egg cells) stops at or shortly after birth. A review of reports from 1900 to 1950 by zoologist Solomon Zuckerman cemented the belief that females have a finite number of oocytes that are formed before they are born. This dogma has been challenged by a number of studies since 2004. Several studies suggest that ovarian stem cells exist within

4452-495: The 1996 San Marcos/Comal (Revised) Recovery Plan, which includes recovery goals such as preserving the integrity and function of the aquifer and developing strategies to address both local and broad regional issues related to recovery. Experiments at the Dallas Aquarium were initiated to develop captive breeding techniques in case the natural population was lost. E. nana in captivity showed a 30% hatching success rate, with

4536-626: The Origin of Species explained how species could arise by natural selection . That understanding was greatly extended in the 20th century through genetics and population ecology . Genetic variability arises from mutations and recombination , while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures . Genes can sometimes be exchanged between species by horizontal gene transfer ; new species can arise rapidly through hybridisation and polyploidy ; and species may become extinct for

4620-1246: The San Marcos River makes a well-delineated hydrologic system for the San Marcos Salamander. The springwater maintains a temperature of 21–22 °C (70–72 °F); the salamanders appeared to be stressed at waters over 30 °C (86 °F). Critical thermal maximum temperatures of the species show a lower threshold for juveniles than adults. E. nana are often found along the river substrates, such as rocks and vegetation. The uppermost shallow portion of Spring Lake features sand, gravel, and large limestone boulders that provide habitat. Further down, concrete banks and boulders provide space for aquatic moss such as L. riparium and blue-green algae. A variety of aquatic macrophytes , including S. platyphylla , M. brasiliense, L. repens , and V. americana are also present. Substrates without vegetation and muddy slit areas are unsuitable for E. nana, as those serve as protective covers against predation from larger fish, turtles, and aquatic birds. The diet of E. nana includes amphipods, fly larvae, and aquatic snails. San Marcos Salamanders typically follow

4704-405: The abbreviation "sp." in the singular or "spp." (standing for species pluralis , Latin for "multiple species") in the plural in place of the specific name or epithet (e.g. Canis sp.). This commonly occurs when authors are confident that some individuals belong to a particular genus but are not sure to which exact species they belong, as is common in paleontology . Authors may also use "spp." as

4788-445: The aid of a microscope or other magnification device. The human ovum measures approximately 120 μm (0.0047 in) in diameter. Ooplasm is like the yolk of the ovum, a cell substance at its center, which contains its nucleus , named the germinal vesicle , and the nucleolus , called the germinal disc . The ooplasm consists of the cytoplasm of the ordinary animal cell with its spongioplasm and hyaloplasm , often called

4872-570: The amount of hybridisation is insufficient to completely mix their respective gene pools . A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology , genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain. As a rule of thumb, microbiologists have assumed that members of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA–DNA hybridisation to decide if they belong to

4956-474: The biological species concept, "the several versions" of the phylogenetic species concept, and the idea that species are of the same kind as higher taxa are not suitable for biodiversity studies (with the intention of estimating the number of species accurately). They further suggested that the concept works for both asexual and sexually-reproducing species. A version of the concept is Kevin de Queiroz 's "General Lineage Concept of Species". An ecological species

5040-505: The biological species concept, a cladistic species does not rely on reproductive isolation – its criteria are independent of processes that are integral in other concepts. Therefore, it applies to asexual lineages. However, it does not always provide clear cut and intuitively satisfying boundaries between taxa, and may require multiple sources of evidence, such as more than one polymorphic locus, to give plausible results. An evolutionary species, suggested by George Gaylord Simpson in 1951,

5124-504: The blue colour after GUS staining reveals. Soon after fertilisation the FIE gene is inactivated (the blue colour is no longer visible, left) in the young embryo. In algae , the egg cell is often called oosphere. Drosophila oocytes develop in individual egg chambers that are supported by nurse cells and surrounded by somatic follicle cells. The nurse cells are large polyploid cells that synthesize and transfer RNA, proteins, and organelles to

SECTION 60

#1732798327514

5208-428: The boundaries between closely related species become unclear with hybridisation , in a species complex of hundreds of similar microspecies , and in a ring species . Also, among organisms that reproduce only asexually , the concept of a reproductive species breaks down, and each clone is potentially a microspecies. Although none of these are entirely satisfactory definitions, and while the concept of species may not be

5292-433: The concept of a chronospecies can be applied. During anagenesis (evolution, not necessarily involving branching), some palaeontologists seek to identify a sequence of species, each one derived from the phyletically extinct one before through continuous, slow and more or less uniform change. In such a time sequence, some palaeontologists assess how much change is required for a morphologically distinct form to be considered

5376-416: The concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. About 14% of these had been described by 2011. All species (except viruses ) are given a two-part name , called a "binomial". The first part of a binomial is the genus to which the species belongs. The second part

5460-468: The egg nucleus. The resulting zygote develops into an embryo inside the ovule. The ovule, in turn, develops into a seed and in many cases, the plant ovary develops into a fruit to facilitate the dispersal of the seeds. Upon germination , the embryo grows into a seedling . In the moss Physcomitrella patens , the Polycomb protein FIE is expressed in the unfertilised egg cell (Figure, right) as

5544-435: The evidence to support hypotheses about evolutionarily divergent lineages that have maintained their hereditary integrity through time and space. Molecular markers may be used to determine diagnostic genetic differences in the nuclear or mitochondrial DNA of various species. For example, in a study done on fungi , studying the nucleotide characters using cladistic species produced the most accurate results in recognising

5628-406: The mammalian ovary. Whether or not mature mammals can actually create new egg cells remains uncertain and is an ongoing research question. In all mammals , the ovum is fertilized inside the female body. Human ova grow from primitive germ cells that are embedded in the substance of the ovaries . The ovum is one of the largest cells in the human body, typically visible to the naked eye without

5712-572: The mammalian ovum in 1827. The fusion of spermatozoa with ova (of a starfish) was observed by Oskar Hertwig in 1876. In animals, egg cells are also known as ova (singular ovum , from the Latin word ovum meaning ' egg '). The term ovule in animals is used for the young ovum of an animal. In vertebrates, ova are produced by female gonads (sex glands) called ovaries . A number of ova are present at birth in mammals and mature via oogenesis . Studies performed on humans, dogs, and cats in

5796-478: The mother's body shortly before birth, or just after the egg leaves the mother's body. Some fish, reptiles and many invertebrates use this technique. Nearly all land plants have alternating diploid and haploid generations. Gametes are produced by the haploid generation, which is known as the gametophyte . The female gametophyte produces structures called archegonia , and the egg cells form within them via mitosis . The typical bryophyte archegonium consists of

5880-400: The mother's body. See egg for a discussion of eggs of oviparous animals. The egg cell's cytoplasm and mitochondria are the sole means the egg can reproduce by mitosis and eventually form a blastocyst after fertilization. There is an intermediate form, the ovoviviparous animals: the embryo develops within and is nourished by an egg as in the oviparous case, but then it hatches inside

5964-483: The numerous fungi species of all the concepts studied. Versions of the phylogenetic species concept that emphasise monophyly or diagnosability may lead to splitting of existing species, for example in Bovidae , by recognising old subspecies as species, despite the fact that there are no reproductive barriers, and populations may intergrade morphologically. Others have called this approach taxonomic inflation , diluting

6048-403: The ovule develops into a seed containing the embryo. In flowering plants , the female gametophyte (sometimes referred to as the embryo sac) has been reduced to just eight cells inside the ovule . The gametophyte cell closest to the micropyle opening of the ovule develops into the egg cell. Upon pollination , a pollen tube delivers sperm into the gametophyte and one sperm nucleus fuses with

6132-593: The paper is accepted for publication. The type material is usually held in a permanent repository, often the research collection of a major museum or university, that allows independent verification and the means to compare specimens. Describers of new species are asked to choose names that, in the words of the International Code of Zoological Nomenclature , are "appropriate, compact, euphonious, memorable, and do not cause offence". Books and articles sometimes intentionally do not identify species fully, using

6216-608: The pattern of returning to the same nest or breeding site dependent on the season, was observed in both males and females of E. nana. This suggests that there is a selection favoring aggregation and shelter use as a part of anti-predatory tactics . Lab results show that predator-naïve salamanders showed a greater reduction in activity compared to predator-experienced salamanders, suggesting behavioral plasticity in avoidance responses. E. nana are also known to show predator generalization in response to novel predators similar to native ones. The E. nana response to their crayfish predators

6300-674: The person who named the species, while the antonym sensu lato ("in the broad sense") denotes a wider usage, for instance including other subspecies. Other abbreviations such as "auct." ("author"), and qualifiers such as "non" ("not") may be used to further clarify the sense in which the specified authors delineated or described the species. Species are subject to change, whether by evolving into new species, exchanging genes with other species, merging with other species or by becoming extinct. The evolutionary process by which biological populations of sexually-reproducing organisms evolve to become distinct or reproductively isolated as species

6384-487: The result of misclassification leading to questions on whether there really are any ring species. The commonly used names for kinds of organisms are often ambiguous: "cat" could mean the domestic cat, Felis catus , or the cat family, Felidae . Another problem with common names is that they often vary from place to place, so that puma, cougar, catamount, panther, painter and mountain lion all mean Puma concolor in various parts of America, while "panther" may also mean

6468-586: The ring. Ring species thus present a difficulty for any species concept that relies on reproductive isolation. However, ring species are at best rare. Proposed examples include the herring gull – lesser black-backed gull complex around the North pole, the Ensatina eschscholtzii group of 19 populations of salamanders in America, and the greenish warbler in Asia, but many so-called ring species have turned out to be

6552-508: The same species. This concept was narrowed in 2006 to a similarity of 98.7%. The average nucleotide identity (ANI) method quantifies genetic distance between entire genomes , using regions of about 10,000 base pairs . With enough data from genomes of one genus, algorithms can be used to categorize species, as for Pseudomonas avellanae in 2013, and for all sequenced bacteria and archaea since 2020. Observed ANI values among sequences appear to have an "ANI gap" at 85–95%, suggesting that

6636-529: The same species. When two species names are discovered to apply to the same species, the older species name is given priority and usually retained, and the newer name considered as a junior synonym, a process called synonymy . Dividing a taxon into multiple, often new, taxa is called splitting . Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognising differences or commonalities between organisms. The circumscription of taxa, considered

6720-446: The seeking out of potential mates—a rare behavior among salamanders. In addition, female and intersexual pairs are found cohabiting more than male pairs, suggesting selective aggressive behavior. While natural courtship and egg deposition have not been observed and documented as of yet, eggs of similar species of salamanders are known to be deposited on single plants and stones about 24 hours after courtship. Depending on how light or dark

6804-506: The species concept and making taxonomy unstable. Yet others defend this approach, considering "taxonomic inflation" pejorative and labelling the opposing view as "taxonomic conservatism"; claiming it is politically expedient to split species and recognise smaller populations at the species level, because this means they can more easily be included as endangered in the IUCN red list and can attract conservation legislation and funding. Unlike

6888-425: The substrate is, E. nana can change its dorsal coloring from light tan to dark brown by migrating pigments in melanophores . The color of its gills also changes in response to the oxygen content of the surrounding water, where it appears bright red from increased blood flow in low-oxygenated waters to the point of resorption when kept at highly-oxygenated areas. The San Marcos salamander has been federally listed as

6972-480: The water to change into a terrestrial form, but rather matures in the water. As a neotenic form, E. nana retains its gills for its lifetime. The San Marcos salamander has a narrow head with a round snout , large eyes, and a dark iris. External gills are developed and pigmented. 2–6 palatopterygoid and 7–13 premaxillary teeth are present. The species is uniformly light brown in color, with a series of seven to nine irregular light spots present along its midline. The trunk

7056-540: The wild. It is difficult to define a species in a way that applies to all organisms. The debate about species concepts is called the species problem. The problem was recognised even in 1859, when Darwin wrote in On the Origin of Species : I was much struck how entirely vague and arbitrary is the distinction between species and varieties. He went on to write: No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of

#513486