Underground speciation: Unraveling the systematics and evolution of the highly diverse tuco-tucos (genus Ctenomys) with genomic data.

Subterranean rodents of the genus Ctenomys (tuco-tucos) are endemic to South America and have experienced relatively recent radiation. There are about 67 recognized species that originated in approximately 1-2 MY. They stand out for their species richness, extraordinary chromosomal diversity, and wide range of habitat they occupy in the continent. Phylogenetic relationships among species of tuco-tucos have been challenging to resolve. Groups of closely-related species have been suggested, but their relationships must be resolved. This study estimates the phylogeny of the genus using massive sequencing, generating thousands of independent molecular markers obtained by RADseq, with a taxonomic sampling that includes 66% of the recognized species. The sequences obtained were mapped against the C. sociabilis genome, recovering up to 1,215 widely shared RAD loci with more than 19,000 polymorphic sites. Our new phylogenetic hypothesis corroborated the species groups previously proposed with cytochrome b gene sequences and provided a much greater resolution of the relationships among species groups. The frater group is sister to all other tuco-tucos, whereas some of the earlierliest proposals placed the sociabilis group as sister to all other tuco-tucos. Ctenomys leucodon, previously proposed as an independent lineage, is associated with the frater group with moderate statistical support. The magellanicus and mendocinus are sister groups in a major clade formed by the boliviensis, talarum, tucumanus, torquatus, and opimus groups. Ctenomys viperinus, included in the phylogeny for the first time, belongs to the tucumanus group. This multi-locus phylogenetic hypothesis provides insights into the historical biogeography of understanding this highly diverse genus.