Cryptic, sibling or neither of the two? Integrative species delimitation ofPsylliodesflea beetles with overlapping ranges

Abstract

Species identification and delimitation are particularly challenging for morphologically similar and geographically overlapping species, such as in the case of Western Palaearctic flea beetle species Psylliodes kiesenwetteri Kutschera, 1864 and Psylliodes ruffoi Leonardi, 1975. In this study, we implemented an integrative taxonomic approach based on a comprehensive geographic assessment of morphological and genetic variation, including 142 adult specimens from 15 sympatric and allopatric populations. Results of species delimitation methods using the barcode marker COI show that molecular identification and delimitation between P. kiesenwetteri and P. ruffoi are straightforward. Single-locus and multi-locus phylogenetic analyses indicate these two species have a large genetic divergence and belong to two distinct clades of the Psylliodes gibbosa species group. Morphological identification based on qualitative characters shows great differences in identification success depending on the character used. Characters of male and female genitalia perform very well, but can only be assessed on fully sclerified individuals, whereas the colour of antennae was discovered as a new reliable diagnostic character both for teneral and fully sclerified individuals.Morphological identification is particularly sharp when multiple characters are used in combination or when a morphometric approach is performed. In conclusion, despite overall morphological similarity, P. kiesenwetteri and P. ruffoi are not cryptic species neither they are sibling species, as they belong to distinct clades within the gibbosa species group, and they can be reliably distinguished by morphological characters. This study substantiates the relevance of a range-wide assessment of morphological and genetic variation, including individuals from the type locality, and both sympatric and allopatric populations, for taxonomic assessment of morphologically similar species with overlapping ranges.