The relationship between genetic variability and growth rate among populations of the pocket gopher, Thomomys bottae

Perhaps the oldest unresolved debate in conservation genetics is whether genetic variability matters - in other words, whether relatively low average genetic variation contributes to deficits in individual and population level vigor and fitness. Using a statistically powerful paired sampling design in which each of three pairs of populations consisted of one high genetic variability and one low genetic variability population from a particular subspecies of the pocket gopher, Thomomys bottae, we tested the hypothesis that individuals from populations with lower genetic variability have lower growth rates ( a commonly used surrogate for fitness) than those from populations with higher variability. We measured genetic variability using average allozyme heterozygosity and two measures of DNA fingerprint band sharing ( Jeffreys 33.15 and MS1 probes). The population rankings of the levels of genetic variability among the three measures were concordant. The least squares mean growth rate ( controlling for sex, subspecies and initial mass) of gophers from low variability populations ( 0.41 +/- 0.06 g/day, n = 48) was less than half that of gophers from high variability populations (1.04 +/- 0.07 g/ day, n = 45). This result lends credence to the premise that differences in population level genetic variability have significant fitness consequences and underscores the importance of maintaining genetic variability in managed populations.