The Genomics of Isolated Populations of Gampsocleis glabra (Orthoptera: Tettigoniidae) in Central and Western Europe

Simple Summary: Habitat destruction is one of the main reasons for the decline and extinction of species. Even if patches of habitat suitable for a certain species persist, the populations of this species may go extinct if the patches are too far apart for individuals to migrate. This is called habitat fragmentation and may also affect species with good migrating abilities if distances are too long. The heath bushcricket Gampsocleis glabra is such a species: it is a specialist of steppe-like habitats that are very rare and fragmented across Europe today. We used genetic data to investigate if the remnant populations in Germany are entirely isolated or if individuals are still able to migrate between locations. Our results indicate that all studied populations are isolated to some degree, but a certain degree of gene flow may persist or may have persisted until the recent past. Even today, gene flow appears to persist, possibly with human assistance. This indicates that, aside from the importance of protecting surviving populations in larger habitat fragments, the preservation and restoration of small and isolated patches of steppe-like habitats may be helpful for the conservation of this rare and threatened species. Habitat destruction and fragmentation are among the major current threats to global biodiversity. Fragmentation may also affect species with good dispersal abilities. We study the heath bushcricket Gampsocleis glabra, a specialist of steppe-like habitats across Europe that are highly fragmented, investigating if these isolated populations can be distinguished using population genomics and if there are any traces of admixture or dispersal among them. We try to answer these questions using genome-wide SNP data generated with ddRAD sequencing. We calculated F-statistics and visualized differentiation using STRUCTURE plots. While limited by the difficulty of sampling this threatened species, our results show that all populations except one that was represented by a singleton were clearly distinct, with pairwise FST values between 0.010 and 0.181. STRUCTURE indicated limited but visible admixture across most populations and probably also an exchange of individuals between populations of Germany and The Netherlands. We conclude that in G. glabra, a certain amount of gene flow has persisted, at least in the past, also among populations that are isolated today. We also detect a possibly more recent dispersal event between a population in The Netherlands and one in Germany, which may be human aided. We suggest that the conservation of larger populations should be maintained, that efforts should be taken to restore abandoned habitat, that the preservation even of small habitat fragments may be beneficial for the conservation of this species, and that these habitats should be regularly monitored for possible (re-)colonization.