DNA-barcoding and ecological niche analysis of Wart Biters (Decticus spp.) from an endemism hotspot (Tettigoniidae: Tettigoniinae)

Understanding biogeographical patterns is a challenging task, particularly in the case of poorly studied organisms, whose phylogenetic affinities and ecological needs are not yet understood. Such a case is common among invertebrates and particularly among insects, whose extensive diversity may hamper full and deep comprehension of their ecological and evolutionary patterns. Within insects, orthopterans also represent a relatively poorly studied group. Building knowledge upon biogeography and evolution of orthopterans may provide key insights to their conservation, especially in the case of range-restricted taxa that are inherently more vulnerable, and prone to extinction. In this study we thus applied an integrated approach, combining DNA-barcoding and ecological niche modelling, for investigating the diversity of wart biters (Orthoptera Tettigoniidae, genus Decticus). We particularly aimed at providing a first screening of the molecular identity of species within the genus, and an assessment of their macro-ecological needs. We analysed mitochondrial DNA (cytochrome oxidase I COI) and bioclimatic niche data for the four Decticus species that occur in the Italian Peninsula (D. verrucivorus, D. albifrons, D. loudoni, and D. aprutianus), reconstructing their phylogenetic relationships based on molecular approaches, and comparing their ecological preferences. We provide COI sequences for all the species found in Italy, including the first one available for two endemic ones. We found a clear molecular differentiation among the four species, with D. albifrons being the most distinct and basal taxon, as based on the COI sequence adopted. Our results also bring evidence of significant ecological niche differentiation, with each species occupying a distinct portion of the climatic space available within Italy. Notably, the two range-restricted and short-winged species, D. loudoni and D. aprutianus, result as sister taxa according to COI, and exhibit greater ecological specialisation compared to the more widespread species. Besides, we also highlight significant intra-taxon diversity for both D. verrucivorus sensu stricto and D. albifrons, suggesting that further research on potential intraspecific variability may be needed to clarify the taxonomic position of Italian populations. The observed genetic divergence and ecological niche differentiation found among wart biters suggest that adaptation to different ecological conditions may have played a role in the diversification of these range-restricted species. Our results confirmed the importance of the Italian Peninsula as a biodiversity hotspot for Orthoptera and provide a solid baseline for more in-depth molecular studies, besides providing novel sequences that may be used for e.g., DNA metabarcoding or eDNA campaigns. Further research is in fact needed to explore the specific ecological factors driving niche differentiation in this and other taxa, and to investigate the evolutionary pathways that led to the genus’ current diversity and distribution.