Everything about Sympatric totally explained
Sympatric speciation is the genetic divergence of various populations (from a single parent species) inhabiting the same geographic region, such that those populations become different species.
Etymologically, sympatry is derived from the roots sym- (meaning same, alike, similar, or fellow) and -patry (meaning homeland or fatherland).
Sympatry is one of four theoretical models for the phenomenon of
speciation. In contrast to
allopatry, populations undergoing sympatric speciation are not geographically isolated by, for example, a mountain or a river.
Debated almost since the beginning of popular evolutionary thought, sympatric speciation is still a highly contentious issue. By 1980 the theory was largely unfavourable given the void of empirical evidence available, and more critically the conditions scientists expect to be required.
Ernst Mayr, one of the foremost thinkers on evolution, completely rejected sympatry outright, ushering in a climate of hostility towards the theory. Since the 1980s, a more progressive ideology has been adopted. While still debatable, well documented empirical evidence now exists, and the development of sophisticated theories incorporating multilocus genetics have followed.
At least one recent study, though, provides evidence that sympatric speciation has occurred in Tennessee cave salamanders.
A number of models have been proposed to account for this mode of speciation. The most popular, which invokes the
disruptive selection model, was first put forward by
John Maynard Smith in 1962. Maynard Smith suggested that
homozygous individuals may, under particular environmental conditions, have a greater fitness than those with
alleles
heterozygous for a certain trait. Under the mechanism of
natural selection, therefore, homozygosity would be favoured over heterozygosity, eventually leading to speciation. Sympatric divergence could also result from the
sexual conflict.
Disruption may also occur in multiple-gene traits. The
Medium Ground Finch (
Geospiza fortis) is showing gene pool divergence in a population on
Santa Cruz Island. Beak morphology conforms to two different size ideals, while intermediate individuals are selected against. Some characteristics (termed
magic traits) such as beak morphology may drive speciation because they also affect mating signals. In this case, different beak
phenotypes may result in different
bird calls, providing a barrier to exchange between the gene pools.
Rhagoletis pomonella, the
apple maggot, may be currently undergoing sympatric or, more precisely, heteropatric (see
heteropatry) speciation. The apple feeding race of this species appears to have spontaneously emerged from the
hawthorn feeding race in the 1800 - 1850 AD time frame, after apples were first introduced into
North America. The apple feeding race doesn't now normally feed on
hawthorns, and the hawthorn feeding race doesn't now normally feed on apples. This may be an early step towards the emergence of a new species.
Allochrony offers some empirical evidence that sympatric speciation has taken place, as many examples exist of recently diverged (
sister taxa) allochronic species.
Sympatric
speciation events are vastly more common in plants, as they're prone to developing multiple
homologous sets of
chromosomes, resulting in a condition called
polyploidy. The polyploidal offspring occupy the same environment as the parent plants (hence sympatry), but are reproductively isolated.
A rare example of sympatric speciation in animals is the divergence of "resident" and "transient"
Orca forms in the northeast Pacific. Resident and transient orcas inhabit the same waters, but avoid each other and don't interbreed. The two forms hunt different prey species and have different diets, vocal behaviour, and social structures. Some divergences between species could also result from contrasts in microhabitats. The
polecat Mustela putorius exhibited a rare dark phenotype similar to the European
mink Mustela lutreola phenotype which is directely influenced by peculiarities of forest brooks.
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