Rotifer cryptic diversity: case study Keratella cochlearis

Traditional taxonomy may underestimate biodiversity because of the occurrence of cryptic species (i.e. different morphologically indistinguishable species). This seems to be especially true for microscopic animals such as rotifers. The merging of different cryptic species that have different environmental preferences in one taxon may hinder our understanding of species-environment relationships. Here wWe investigated the occurrence of cryptic diversity within the monogonont rotifer Keratella cochlearis. Keratella cochlearis is a ubiquitous species occurring across environmental gradients and the presence of cryptic species can be suspected. We sampled 17 lakes of differenting in their trophic state, chemical parameters and altitude in the region Trentino-South Tyrol region (North Italy). We measured the main morphological characteristics of the lorica for each single individual of K. cochlearis prior to sequencing that was also investigated genetically. We sequenced the partial cytochrome c oxidase subunit 1 and inferred cryptic species by the Generalized Mixed Yule Coalescence (GMYC) model. We found 8 GMYC entities (cryptic species) whose lorica measurements showed a large phenotypic plasticity. Furthermore, most cryptic species occurred in many lakes with few exceptions. We discuss our results in relation to ecological key variables such as trophic state, conductivity, altitude and chemical parameters.