Long-term biogeographic 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
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.