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Demographic consequences of artificial selection at the LAP locus in voles Microtus townsendi LeDuc, Janice Irene


A number of studies on small mammals have shewn that changes in the frequency of alleles at polymorphic loci are correlated with population fluctuations. To determine whether this association between demography and genetics is causal, I altered gene frequencies in two field populations of M. townsendi Using starch gel electrophoresis, I detected a leucine aminopeptidase (LAP) polymorphism in M. townsendi. The fast allele, LAP-F, was present in a control population at a frequency of about .35 from July 1971 to July 1973. By removing homozygous SS voles from one experimental population I maintained an LAP-F frequency of about .75. Removal of FF homozygotes from a second population resulted in an LAP-F frequency of about .25. I monitored demographic variables of the populations while the selection was being applied. The populations went through increasing and peak phases and then declined sharply during the spring of 1973. There were indications that different genotypes had an advantage in survival and reproduction during different phases of population density. The selection that maintained the polymorphism on the control area could be correlated with population density. However, the overall fitness of each experimental population was not affected by its genotypic composition at this locus.

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