Setting a morphological framework for the genus Verhoeffiella (Collembola, Entomobryidae) for describing new troglomorphic species from the Dinaric karst (Western Balkans)

Abstract

Recent research of cave Collembola in Dinaric karst resulted in discovery of high regional diversification of the genus Verhoeffiella Absolon, 1900. The most striking feature of Verhoeffiella species is the high number of troglomorphic traits, which makes this genus a good model for studying morphological diversification and adaptation in subterranean environments. We explore the expression of various morphological modifications assumed to be linked to subterranean life, through detailed descriptions of four new species and redescription of two species including the type species of the genus. Species delimitations are confirmed by single locus (cytochrome c oxidase I) tree-based (Poisson tree processes) and distance-based (automatic barcode gap discovery) species delimitation approaches, which gave identical results. Morphological changes classically considered as adaptive for cave life and new, potentially troglomorphic characters for Collembola are discussed. For several of these characters, high morphological diversity between species and large decoupling in the development of different traits within species are recorded. Such a decoupling is also illustrated in the finding of two cases of Verhoeffiella species pairs at different levels of troglomorphy living in syntopy. We further provide several new differential characters of specific and possibly generic or supra-generic importance and describe for the first time among Collembola an original ‘distal organ’ on Ant. IV.