Spatial and temporal genetic dynamics of the grasshopper Oedaleus decorus revealed by museum genomics

Analysing genetic variation through time and space is important to identify key evolutionary and ecological processes in populations. However, using contemporary genetic data to infer the dynamics of genetic diversity may be at risk of a bias, as inferences are performed from a set of extant populations, setting aside unavailable, rare or now extinct lineages. Here, we took advantage of new developments in next-generation-sequencing to analyse the spatial and temporal genetic dynamics of the grasshopper Oedaleus decorus, a steppic Southwestern-Palearctic species. We applied a recently developed hybridisation capture (hyRAD) protocol that allows retrieving orthologous sequences even from degraded DNA characteristic of museum specimens. We identified single nuclear polymorphisms in 68 historical and 51 modern samples in order to (i) unravel the spatial genetic structure across part of the species distribution and (ii) assess the loss of genetic diversity over the past century in Swiss populations. Our results revealed (i) the presence of three potential glacial refugia spread across the European continent and converging spatially in the Alpine area. In addition, and despite a limited population sample size, (ii) our results indicate a loss of allelic richness in contemporary Swiss populations compared to historical populations, whereas levels of expected heterozygosities were not significantly different. This observation is compatible with an increase in the bottleneck magnitude experienced by central European populations of O. decorus following human-mediated land-use change impacting steppic habitats. Our results confirm that application of hyRAD to museum samples produces valuable information to study genetic processes over time and space.