Long-term biogeographical processes dominate patterns of genetic diversity in a wingless grasshopper despite substantial recent habitat fragmentation.

Abstract

Low-vagility species may hold strong genetic signatures of past biogeographical processes but are also vulnerable to habitat loss. Flightless grasshoppers of the morabine group were once widespread in southeastern Australia, including Tasmania, but are becoming restricted to remnant patches of vegetation, with local ranges impacted by agriculture and development as well as management. Habitat fragmentation can generate genetically differentiated "island" populations with low genetic variation. However, following revegetation, populations could be re-established, and gene flow increased. Here we characterize single nucleotide polymorphism-based genetic variation in a widespread chromosomal race of the morabine Vandiemenella viatica (race 19) to investigate the genetic health of remnant populations and to provide guidelines for restoration efforts. We update the distribution of this race to new sites in Victoria and Tasmania, and show that V. viatica populations from northern Tasmania and eastern Victoria have reduced genetic variation compared to other mainland populations. In contrast, there was no effect of habitat fragment size on genetic variation. Tasmanian V. viatica populations fell into two groups, one connected genetically to eastern Victoria and the other connected to southwestern Victoria. Mainland populations showed isolation by distance. These patterns are consistent with expectations from past biogeographical processes rather than local recent population fragmentation and emphasize the importance of small local reserves in preserving genetic variation. The study highlights how genomic analyses can combine information on genetic variability and population structure to identify biogeographical patterns within a species, which in turn can inform decisions on potential source populations for translocations.