Zoogeography, Spacing Patterns, and Dispersal in Fishers

Abstract

We demonstrate how research questions generated from radiotelemetry studies of fishers (Martes pennanti) can be further elucidated by combining field and genetic data. We genotyped a sample of 20 fishers at 9 polymorphic microsatellite loci and used these data to calculate observed and expected heterozygosity, estimate coefficients of relatedness, and exclude potential parent-offspring combinations. Previous research indicated that the population of fishers occurring in the southern Cascade Range in Oregon is reintroduced. Due to the presence of potentially strong ecological and anthropogenic barriers between that population and fishers occurring in the northern Siskiyou Mountains of Oregon, we hypothesized that they are geographically isolated from each other. Analyses of microsatellite genotypes supported this hypothesis by providing empirical evidence that genetic introgression of fishers from the northern Siskiyou Mountains into the southern Cascade Range has not occurred. Results from our field study indicated that male fishers may exhibit either of 2 distinct behavioral strategies during the breeding season. For 3 successive breeding seasons, 2 adult males in our study area remained resident on their non-breeding home ranges, whereas 1 or 2 other males (one died after year 1) abandoned their non-breeding home ranges and encroached on the home ranges of resident males. To determine which strategy resulted in greater reproductive success, we used field and genetic data to exclude potential parent-offspring relationships between these 4 males and 7 juveniles. In contrast to resident males, encroaching males could not have fathered any of the juveniles. These results suggest that maintaining intrasexual territoriality during the breeding season may provide a reproductive advantage to male fishers. Our research also provides the first empirical evidence of male-biased juvenile dispersal and female philopatry in fishers. In accordance with predictions from genetic theory, our analyses showed that adult females had significantly higher relatedness values than adult males, and that there were many more potential first-order relationships among adult females than among adult males. As these examples demonstrate, including genetic information in data analysis can substantially improve the heuristic value of field studies and enable researchers to study additional aspects of population biology.