Low vagility species may hold strong genetic signatures of past biogeographic processes but are also vulnerable to habitat loss. Flightless grasshoppers of the morabine group were once widespread in south-eastern 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 characterise SNP 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 south-western Victoria. Mainland populations showed isolation by distance. These patterns are consistent with expectations from past biogeographic 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 biogeographic patterns within a species, which in turn can inform decisions on potential source populations for translocations.

Conservation research is dominated by vertebrate examples but the shorter generation times and high local population sizes of invertebrates may lead to different management strategies. Here we investigate the genetic structure of an endangered flightless grasshopper, Keyacris scurra, used in classical evolutionary studies in the 60s. It had a wide distribution across New South Wales (NSW) and Victoria in pre-European times but has now become threatened because of land clearing for agriculture. We revisited remnant sites of K. scurra, with populations now restricted to only one area in Victoria and a few small patches in NSW and the Australian Capital Territory (ACT). Using DArTseq to generate SNP markers as well as mtDNA sequence data, we show that the remaining Victorian populations in an isolated valley are genetically distinct from the NSW populations and that all populations are genetically unique, with large FST values up to 0.8. We also find that, with one exception, the NSW/ACT populations separate genetically into chromosomal races (2n = 15 vs. 2n = 17). Isolation by distance was detected across both the SNP and mtDNA data sets, and there was substantial differentiation within chromosomal races. Genetic diversity as measured by heterozygosity was not correlated with the size of remaining habitat patches, with high variation present in some remnant cemetery sites. However, inbreeding correlated negatively with estimated habitat size at 25-500 m patch radius. These findings emphasize the importance of small fragments in conserving genetic variation across the species, and they highlight populations suitable for future translocations.