SYMPATRIC SPECIATION IN ANIMALS - DISRUPTIVE SELECTION OR ECOLOGICAL SEGREGATION

Disruptive selection is usually considered as an exclusive mechanism of sympatric speciation. Analysis of empirical data on earlier stages of divergence in animals indicates that origination of biological races in many instances can not be explained on by disruptive selection action. A speciation model on the basis of ecological segregation is suggested for such cases. Unlike disruptive selection models, it does not imply disappearance of the initial ecological niche and respective morphotype as a result of modification of ecological situation or competition between derived and original morphs. New group, being first less adaptable than original species, then segregates from it and occupies a new ecological niche. Meanwhile, original species may remain unchangeable. Segregation speciation model requests several simple conditions which occur in the nature quite often, which are: occurrence of phenotypes with low adaptability or specialization possessing their own reproducibility and reaching high frequency, or possessing high frequency of origination in each generation. Likelihood of this model is exemplified by sympatric divergence in phytophags. Its application to origination of biological races in fishes and reticulate speciation is discussed.