Partitioning genetic structure of a subterranean rodent at multiple spatial scales: accounting for isolation by barriers, distance, and environment

Context

Understanding genetic structure at multiple spatial scales and identifying drivers of genetic isolation are important for developing comprehensive conservation plans including for grassland conservation efforts. However, few studies account for multiple genetic isolation processes nor partition genetic variance among these processes.

Objectives

We assess key processes that can create spatial genetic patterns including isolation by barrier (IBB), isolation by distance (IBD), and isolation by environment (IBE) for a widespread pocket gopher species (Geomys bursarius) and a spatially restricted subspecies (Geomys bursarius illinoensis). We further partition genetic variation to each isolating effect and identify genetic variation that was shared between processes.

Methods

We used seven microsatellites to determine spatial genetic clustering and identify environmental factors impacting genetic similarities. Then, we used redundancy analysis to partition variance explained by IBB, IBD, and IBE.

Results

Major rivers including the Mississippi River acted as barriers and explained the most genetic variation across the species. In contrast, IBD explained the most genetic variation for G. b. illinoensis. Gophers had genetic associations to soil sand percent and soil color, but IBE uniquely explained a small amount of genetic structure for G. bursarius, with additional variation shared with other isolating processes.

Conclusions

Gopher genetic structure resulted from barriers, distance, and environmental factors at the species range as well as for a subspecies’ region, but the relative amount of genetic variance assigned to unique isolating processes differed between scales. Delineation of conservation units should consider major rivers as natural boundaries, and finer-scale management should identify and protect areas close to source populations with similar soil friability. Our study exemplifies how analyzing gene flow at rangewide and regional scales can aid managers in developing localized strategies that fit within broader conservation units.