Ecology and evolution of sympatric sticklebacks (Gasterosteus): morphological and genetic evidence for a species pair in Enos Lake, British Columbia

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Abstract
Two morphological forms of three-spined stickleback (Gasterosteus) coexist in Enos Lake near Nanoose Bay, Vancouver Island. For convenience, the two forms are referred to as "benthics" and "limnetics." Morphological and biochemical characteristics of the two forms were examined and artificial hybrids (F1 and F2) reared in the laboratory. The two forms differ in male nuptial colour, body shape, and gill raker architecture. These differences are inherited and have remained stable for several generations. Benthics and limnetics also differ in allele frequencies at three loci (Mdh-3, Ck, and Pgm). At one of these loci (Mdh-3) the limnetic form is polymorphic and the benthic form is fixed. Since the two forms maintain themselves as discrete entities and there is no evidence of gene flow, they are considered separate biological species. It is not certain that either of these species is Gasterosteus aculeatus. Similar species pairs exist in other lakes in the Strait of Georgia region but, at present, their relationship to the species pair in Enos Lake is unknown.
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