Cryptic Diversity of the European Blind Mole Rat Nannospalax leucodon Species Complex: Implications for Conservation

Simple Summary Cryptic species, hidden by morphological uniformity, represent a significant part of the diversity in some taxonomic groups, and pose a real challenge for conservation planning. Here, we explore cryptic speciation in blind mole rats of the genus Nannospalax-comprehensively studied mammals for many unusual features (cancer resistance, longevity, etc.). Intensive chromosomal changes are one of these peculiarities. In the European N. leucodon species complex, 25 lineages with different karyotypes have been described, comprising undetected/cryptic species. As some of them are endangered, taxonomic revision is urgent for conservation purposes. Using 36-60-year-old archived teeth samples and newly captured animals, we analysed the nucleotide polymorphism of two mitochondrial gene sequences among 17 out of 25 chromosomal forms-the highest number studied so far-and provided molecular genetic records for 5 of them for the first time. Eleven chromosomal forms were separated into distinct clades in phylogenetic trees. High evolutionary divergence values among several chromosomal forms overlapped with those acquired for higher taxonomic categories. By integrating the results of previous karyological analyses and crossbreeding experiments that revealed complete reproductive isolation of seven chromosomal forms, with our new findings, we propose conservation strategies to preserve their genetic diversity. We explored the cryptic speciation of the Nannospalax leucodon species complex, characterised by intense karyotype evolution and reduced phenotypic variability that has produced different lineages, out of which 25 are described as chromosomal forms (CFs), so many cryptic species remain unnoticed. Although some of them should be classified as threatened, they lack the official nomenclature necessary to be involved in conservation strategies. Reproductive isolation between seven CFs has previously been demonstrated. To investigate the amount and dynamics of genetic discrepancy that follows chromosomal changes, infer speciation levels, and obtain phylogenetic patterns, we analysed mitochondrial 16S rRNA and MT-CYTB nucleotide polymorphism among 17 CFs-the highest number studied so far. Phylogenetic trees delineated 11 CFs as separate clades. Evolutionary divergence values overlapped with acknowledged higher taxonomic categories, or sometimes exceeded them. The fact that CFs with higher 2n are evolutionary older corresponds to the fusion hypothesis of Nannospalax karyotype evolution. To participate in conservation strategies, N. leucodon classification should follow the biological species concept, and proposed cryptic species should be formally named, despite a lack of classical morphometric discrepancy. We draw attention towards the syrmiensis and montanosyrmiensis CFs, estimated to be endangered/critically endangered, and emphasise the need for detailed monitoring and population survey for other cryptic species.