High cryptic diversity in aquatic insects: an integrative approach to study the enigmatic Leuctra inermis species group (Plecoptera)

Within the genus Leuctra (Plecoptera: Leuctridae) the L. inermis species group comprises 17 – 18 species in which males lack the characteristic tergal abdominal ornamentation of many Leuctra species, and females have an accessory receptacle in the dorsal portion of the vagina. Taxonomically the group is challenging, and congruence of existing morphological species concepts and phylogenetic relationships of taxa is hitherto not assessed. Here, we estimate phylogenetic relations of morphologically defined species by concatenated maximum likelihood (ML) and Bayesian combined species tree and species delimitation analysis. We aim to clarify the status of 15 European species of the L. inermis group and 2 potential new species. To this end, we infer relationships on a 2580 bp, 4 loci (mtCOI, mt12S, nuH3, nu28S) molecular sequence dataset. We further depict abdominal terminalia with their morphological characteristics for 15 L. inermis group species, and describe 2 micro-endemic species from the Southern Alps and the Apennine Mountains corroborated by distinct morphological and molecular characteristics. Our analyses support close relationships of the L. inermis group species and corroborate the a priori morphological definition of all included species. However, relationships among species are largely unresolved, indicative of a putatively recent diversification of the group. Phylogenetic inference suggests sister taxon relationships between morphologically similar species. Morphological variation within single species is linked to geographical location of populations. Our results thus suggest that further study on the differentiation of geographically isolated populations as distinct lineages or species is warranted. Based on the high number of regional endemic lineages and species we highlight the necessity to protect high-altitude aquatic habitats.