Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

Ecological speciationis a form of speciation that has come into and fallen out of favor (Via 2001). Ecological speciation is generally termed sympatric speciation in discussions related to this subject. As sympatric speciation also includes a number of types of instant speciation which, understandably, have completely different mechanisms, this established terminology is not really appropriate. Ecological speciation very frequently has the character of parapatric speciation. A great many species of organisms have a rather broad ecological valence, while the environment in which they occur has a heterogeneous and discontinuous character from the viewpoint of the prevailing conditions. Thus, it is advantageous for the population to specialize on various local environmental conditions by evolving various ecological forms, each of which is adapted to a certain type of environment or certain strategy for utilization of these conditions. The numbers of the individual ecological forms can fluctuate in the population in dependence on the character of the environment in which they occur. If the individual types of environment are also separated spatially and the organisms are not very mobile, there is a greater chance that the members of a single ecological form will preferentially reproduce together and will only occasionally cross with members of the opposite form.

 The existence of large phenotype differences between the members of the two forms, as a result of which they need not recognize one another as members of the same species, can have similar consequences. In some cases, such a situation can even lead to differentiation of the parent species into two daughter species, which divide up the original ecological niche and then each of them will have lower ecological valence than the original species. The effect of disruptive natural selection, caused by the original differentiation into two ecological forms, is frequently further reinforced by the fact that the crosses of the two forms have a transition phenotype, which is suboptimal in both types of environment. This creates a selection pressure on the creation of further, this time prezygotic (for example ethological) mechanisms that could reduce the probability of crossing between the members of the two ecological forms. The main problem in functioning of ecological speciation is the necessity of preventing recombination, which would break the connection between the genes responsible for the ecological differentiation between the two forms and the genes responsible for their prezygotic reproductive isolation. Mathematical models have shown that the formation of a new species is favored by a situation in which only a small number of genes is responsible for prezygotic isolation and a medium number of genes is responsible for ecological differentiation (Kondrashov & Kondrashov 1999; Via 2001).

 To the present day, only a few systems have been described in which the mechanism of ecological speciation is assumed to play a role. Primarily, this applies to the historically documented case of speciation of the apple maggot fly Rhagoletis pomonella in America, which moved from the hawthorn to apple trees in the middle of the nineteenth century (Bush 1969). Other probable candidates for ecological speciation include cichlids in one of the African crater lakes {12524}, palms in Lord Howe Island {12340} and possibly also American freshwater sticklebacks.