Genetic and morphological differences among relict marginal occurrences of Stenobothrus eurasius (Orthoptera)

Abstract

Steppes form large zonal habitats in Asia but only consist of localised outposts in Europe. An ideal subject for the study of differences within species between the main steppe zone and the localized more western outposts is the Orthopteran Stenobothrus eurasius, widespread across the Siberian and Central Asian steppes but present only in isolated relic populations at the western edge of its area. We used genetic and morphological analyses to detect possible differences among these relic populations. We carried out a study on morphological parameters of wings in parallel with the comparison of four DNA fragments (cytochrome c oxidase subunit I, 12S rRNA and the mtDNA control region, cytochrome B, nuclear internal transcribed spacers plus the 5.8S rRNA region) involving 15 extrazonal populations of the species. St. nigromaculatus was used as an outgroup taxon in the genetic analyses. Variability of the morphological characters of St. eurasius individuals was higher within the regions than amongst the regions. The two Stenobothrus species were not separated based on the CR gene. Samples of both Stenobothrus species were separated on the COI, cytB and ITS1-5.8S-ITS2 phylogenetic trees with high support (PP = 1) in Bayesian analyses but clear genetic lineages were not revealed, and populations of the focal species were not grouped according to their geographic locations. The similarity of this species in different steppe outposts supports the hypothesis that St. eurasius was widespread in the more extensive steppe areas that were once present, but the extension of agricultural landuse reduced the steppe habitats resulting in the current patchy distribution of St. eurasius limited to the remaining habitats.