Sympatric speciation
In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organisms whose ranges overlap so that they occur together at least in some places.
[4] In bacteria, however, the analogous process (defined as "the origin of new bacterial species that occupy definable ecological niches") might be more common because bacteria are less constrained by the homogenizing effects of sexual reproduction and are prone to comparatively dramatic and rapid genetic change through horizontal gene transfer.
[5] Sympatric speciation events are quite common in plants, which are prone to acquiring multiple homologous sets of chromosomes, resulting in polyploidy.
[6] Maynard Smith suggested that homozygous individuals may, under particular environmental conditions, have a greater fitness than those with alleles heterozygous for a certain trait.
The medium ground finch (Geospiza fortis) is showing gene pool divergence in a population on Santa Cruz Island.
Some characteristics (termed magic traits) such as beak morphology may drive speciation because they also affect mating signals.
In these bats, the constant frequency component of the call not only determines prey size but may also function in aspects of social communication.
Work from one species, the large-eared horseshoe bat (Rhinolophus philippinensis), shows that abrupt changes in call frequency among sympatric morphs is correlated with reproductive isolation.
(Drès and Mallet, 2002)[10] Rhagoletis pomonella, the apple maggot, may be currently undergoing sympatric or, more precisely, heteropatric (see heteropatry) speciation.
[14] Isolated and relatively homogeneous habitats such as crater lakes and islands are among the best geographical settings in which to demonstrate sympatric speciation.
[15][16] Monostroma latissimum, a marine green algae, also shows sympatric speciation in southwest Japanese islands.
Female choice for good genes and sensory bias is one of the deciding factors in this case, selecting for calls that are within her species and that give the best fitness advantage to increase the survivability of the offspring.
Allochrony offers some empirical evidence that sympatric speciation has taken place, as many examples exist of recently diverged (sister taxa) allochronic species.
A case of ongoing sympatric divergence due to allochrony might be found in the marine insect Clunio marinus.
[25] A rare example of sympatric speciation in animals is the divergence of "resident" and "transient" orca forms in the northeast Pacific.
[3] It was believed by many, and championed by Ernst Mayr, that the theory of evolution by natural selection could not explain how two species could emerge from one if the subspecies were able to interbreed.
The German evolutionary biologist Ernst Mayr argued in the 1940s that speciation cannot occur without geographic, and thus reproductive, isolation.
[35] By adapting to have the highest possible fitness in the distinct niches, two species may emerge from one even if they remain in the same area, and even if they are mating randomly.
[3] Mallet et al. (2002) claims that the new non-spatial definition is lacking in an ability to settle the debate about whether sympatric speciation regularly occurs in nature.
They suggest using a spatial definition, but one that includes the role of dispersal, also known as cruising range, so as to represent more accurately the possibility for gene flow.
[31] Because they are palms they send pollen through the air they could freely interbreed, except that speciation has already occurred, so that they do not produce viable hybrids.
[36] In 2015 Cichlid fish from a tiny volcanic crater lake in Africa were observed in the act of sympatric speciation using DNA sequencing methods.
It is thus is a refinement of sympatric speciation, with a behavioral, rather than geographical barrier to the flow of genes among diverging groups within a population.
[39] In recognition of the importance of this behavioral versus geographic distinction, Wayne Getz and Veijo Kaitala introduced the term heteropatry in their extension of Maynard Smiths' analysis[40] of conditions that facilitate sympatric speciation.
Although some evolutionary biologists still regard sympatric speciation as highly contentious, both theoretical[41] and empirical[42] studies support it as a likely explanation of the diversity of life in particular ecosystems.
