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Selection at Electrophoretic Loci for Reproductive Parameters in Island and Mainland Voles

Peter H. Kohn and Robert H. Tamarin
Evolution
Vol. 32, No. 1 (Mar., 1978), pp. 15-28
DOI: 10.2307/2407407
Stable URL: http://www.jstor.org/stable/2407407
Page Count: 14
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Selection at Electrophoretic Loci for Reproductive Parameters in Island and Mainland Voles
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Abstract

A 3-yr live-trapping study was conducted on two species of voles, Microtus breweri, endemic to Muskeget Island, Massachusetts and Microtus pennsylvanicus, its mainland counterpart. Monthly rotation of trap lines on four areas on both the island and the mainland was carried out. Fifteen genetic loci were examined by horizontal starch gel electrophoresis of blood samples. Microtus pennsylvanicus was found to be polymorphic for both transferrin (Tf) and leucine aminopeptidase (Lap), while M. breweri was polymorphic only for Tf. The four M. breweri trapping areas were genetically homogeneous, while the four M. pennsylvanicus areas were not. Both the Tf and Lap polymorphisms were balanced in both species. There were no deviations from Hardy-Weinberg equilibrium and no significant differences between male and female gene frequencies at either locus. A negative relationship for TfE frequency and density was found in both species. Voles were autopsied and reproductive data taken. In M. pennsylvanicus males the LapS/LapS homozygote had the highest index of breeding activity and the LapF/LapF homozygote the lowest. In M. pennsylvanicus females the LapS/LapF heterozygote possessed the highest index of breeding activity, and the LapF/LapF homozygote the lowest. None of the environmental, reproductive, or demographic variables examined in M. breweri showed any statistically significant relation to the genetic data except for differences in day caught in males. Microtus breweri appears to be non-cyclic and to have undergone numerous genetic bottlenecks in the past. From 15 loci analyzed electrophoretically, an estimate of genetic distance between M. breweri and M. pennsylvanicus was calculated. The estimate categorized the two populations as probably conspecific.

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