Comparison of genetic variation between rare and common congeners of Dipodomys with estimates of contemporary and historical effective population size

Abstract

Organisms with low effective population sizes are at greater risk of extinction because of reduced genetic diversity. Dipodomys elator is a kangaroo rat that is classified as threatened in Texas and field surveys from the past 50 years indicate that the distribution of this species has decreased. This suggests geographic range reductions that could have caused population fluctuations, potentially impacting effective population size. Conversely, the more common and widespread D. ordii is thought to exhibit relative geographic and demographic stability. Genetic variation between D. elator and D. ordii samples was assessed using 3RAD, a modified restriction site associated sequencing approach. It was hypothesized that D. elator would show lower levels of nucleotide diversity, observed heterozygosity, and effective population size when compared to D. ordii. Also of interest was identifying population structure within contemporary samples of D. elator and detecting genetic variation between temporal samples that could indicate demographic dynamics. Up to 61,000 single nucleotide polymorphisms were analyzed. It was determined that genetic variability and effective population size in contemporary D. elator populations were lower than that of D. ordii, that there is only slight, if any, structure within contemporary D. elator populations, and there is little genetic differentiation between spatial or temporal historical samples suggesting little change in nuclear genetic diversity over 30 years. Results suggest that genetic diversity of D. elator has remained stable despite claims of reduced population size and/or abundance, which may indicate a metapopulation-like system, whose fluctuations might counteract any immediate decrease in fitness.