RESUMEN
Incomplete lineage sorting (ILS) and introgression have been increasingly recognized as important processes involved in biological differentiation. Both ILS and introgression result in incongruences between gene trees and species trees, consequently causing difficulties in phylogenetic reconstruction. This is particularly the case for rapid radiations, as short internodal distances and incomplete reproductive isolation increase the likelihood of both ILS and introgression. Estimation of the relative frequency of these processes requires assessments across many genomic regions. We use transcriptomics to test for introgression and estimate the frequency of ILS in a set of three closely related and geographically adjacent South American tuco-tucos species (Ctenomys), a genus comprising 64 species resulting from recent, rapid radiation. After cleaning and filtering, 5764 orthologous genes strongly support paraphyly of C. pearsoni relative to C. brasiliensis (putatively represented by the population of Villa Serrana). In line with earlier phylogenetic work, the C. pearsoni - C. brasiliensis pair is closely related to C. torquatus, whereas C. rionegrensis is more distantly related to these three nominal species. Classical Patterson's d-statistic shows significant signals of introgression from C. torquatus into C. brasiliensis. However, a 5-taxon test shows no significant results. ILS was estimated to have involved about 9% of the loci, suggesting it represents an important process in the incipient diversification of tuco-tucos.