Microspatial Genetic Heterogeneity in Pocket Gophers: Non-Random Breeding and Drift

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Abstract
T. bottae pocket gophers are characterized by high between population heterogeneity in allele frequencies yet may retain very high levels of within population variability (individual heterozygosity). The mechanisms which might be responsible for these 2 observations were explored by examining the extent of local population structuring and resulting variability levels in pocket gopher populations at Hastings Natural History Reservation in Carmel Valley, California [USA]. The specific components which can affect these parameters and which were examined in this study included: extent of inbreeding (consanguineous matings); the dispersion patterns of adults within fields in relation to breeding patterns; the sex ratio of adults in breeding units; the variance in male reproductive effort based on paternity determination of litters from pregnant females; and the effect of local experimental population extirpations on resulting structuring. Pocket gopher populations were composed of small numbers of individuals, usually significantly skewed in sex ratio in favor of females among breeding adults, and with high variance in male reproductive success. Inbreeding did not appear to be a significant component in the level of population structuring observed. These parameters combine to produce small genetically effective population units, with measured Ne ranging from 12-26, which can generate extensive between population genetic heterogeneity despite a moderate level of intergroup dispersal. The experimental population extinctions in some fields demonstrated that, while recolonization can produce some homogenizing effects across fields, extensive heterogeneity can be reinstated after a single generation of breeding when confined to the small numbers of individuals characterizing the breeding units at Hastings Reservation. Despite the momentary small Ne, empirical evidence shows that individual heterozygosity levels can remain high and within population variability thus appears to be a balance between small population size generating between population differentiation and effective dispersal maintaining individual heterozygosity.