Using Species Groups to Approach the Large and Taxonomically Unresolved Freshwater Fish Family Nemacheilidae (Teleostei: Cypriniformes)

Simple Summary Since large animal families with unresolved taxonomy are difficult to study, it is better to focus on smaller units. In the present study, we test if we can define a restricted group of species within a large and unsorted fish family (Nemacheilidae). In the beginning, we selected 17 candidate species that share a rare and specific pigmentation pattern, and 29 comparative species with a different pattern. We studied their relationships and the ages of pedigree branches using molecular genetic markers. It turned out that the candidate and comparative species are intermixed in two main groups, meaning that the specific pigmentation pattern is not diagnostic. However, the genetic lineages themselves are smaller units within the large family Nemacheilidae and can be used for further studies. For example, one group revealed its evolutionary history: it expanded 12 million years ago from India into Myanmar and later further to Thailand, Laos, and China. They also revealed more than 20% of undescribed species, a very high rate in vertebrates. Our results show that species groups can be a helpful tool to approach large and unsorted animal units. This finding offers species groups as a new tool for future studies exploring the diversity of life on earth. Large animal families with unresolved taxonomy are notoriously difficult to handle with respect to their biodiversity, systematics, and evolutionary history. We approach a large and taxonomically unresolved family of freshwater fishes (Nemacheilidae, >600 species) by proposing, on the basis of morphologic data, a species group within the family and study its phylogeny with conclusions regarding its diversity, taxonomy, and biogeographic history. Phylogenetic analyses of two mitochondrial and three nuclear genes of 139 specimens, representing about 46 species (17 candidate species from the proposed species-group, plus 29 comparative species), revealed that the proposed species group does not form a distinct monophyletic lineage, but that the candidate and comparative species mixed in three different lineages. However, the results revealed more than 20% of undescribed species within the ingroup and showed that species do not cluster according to the presently recognised genera. At least one of the genetic clades shows signs of an eastward range expansion during the second half of Miocene from north India via Myanmar into Laos, western China, and western Thailand. We conclude that the approach of picking monophyletic lineages to study biodiversity, systematics, and evolutionary history helps to open the door to large animal families.