Sympatric speciation
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Sympatry is one of three theoretical models for the phenomenon of speciation. In complete contrast to allopatry, species undergoing sympatric speciation are not geographically isolated by, for example, a mountain or a river. The speciating populations generally share the same territory.
A debate 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 required conditions which scientists expect. 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.
A number of models have been proposed to account for this mode of speciation. The most popular, disruptive speciation, was first put forward by John Maynard Smith in 1962. 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.
Rhagoletis pomonella (Apple maggot) may be currently undergoing sympatric 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 does not now normally feed on [[hawthorn]s, and the hawthorn feeding race does not now normally feed on apples. This may be an early step towards the emergence of a new species. Template:Ref
Sympatric speciation events are most common in plants when they double or triple the number of chromosomes, resulting in a condition called polyploidy.
See also
Reference
- Template:Note Reference for emergence of new race of apple maggot flies [1]
Template:Speciationes:Especiación simpátrica nl:Sympatrische soortvorming sv:Sympatrisk utbredning