Hidden in plain sight: unveiling the distributions of green-winged grasshoppers (Aiolopus spp.) with citizen-science data

Understanding the geographical distribution of phenotypically highly similar species (i.e. cryptic species) represents a challenge to biogeographers, due to the obvious difficulties in identifying such taxa without specific expertise. Besides, citizen science is increasingly emerging as a key approach for supporting biodiversity data collection, but remains hard to apply in the case of cryptic species. Here we aim to test the combination of community records and photography-based quantitative methods, for assessing the distribution of cryptic taxa, by using two grasshopper species of the genus Aiolopus as models. To achieve these objectives, we first assess the reliability of photography-based diagnostic criteria to differentiate between A. thalassinus and A. puissanti without ambiguity from correctly identified records, and then apply such criteria to geographical regions of potential range overlap between the two species, in order to clarify their respective distributions. By applying a multivariate classification approach based on ratio measurements taken from photographs, we provide a quantitative tool to successfully identify the two species, and disclose that A. puissanti widely occurs outside of its currently known range, and outline potential research avenues on the biogeography of these poorly studied species. Our results also point at how some types of cryptic species may be effectively identified by adopting a quantitative photography-based approach, with applicability for clarifying species' distributions at wide scales by exploiting publicly available citizen-science records. Our study thus, besides shedding light onto the biogeography and distributions of Aiolopus grasshoppers across the Mediterranean, represents an effective and repeatable framework to disentangle the distributions of poorly studied cryptic species.