The formation of new species has become one of the most controversial subjects in evolutionary theory. Fosorial rodents of the genus Ctenomys are an interesting biological model to test hypothesis on this subject, as they have suffered an explosive speciation process. C. rionegrensis has different fur colorations in a restricted and homogeneous area, and has been studied in recent years from a microevolutionay perspective. Sexual selection, as a mate choice mechanism, has an important role in population differentiation. Studies on mating behavior and choice will constitute a major contribution to the population and genetic results of this species.
Objetive: To understand the reproductive dynamic of C. rionegrensis' populations, determining mating systems, as well as the influence of sexual selection in chromatic polymorphism dynamics.
Sigmodontine rodents represent a diverse and endemic of new world group with about 71 extant genera. Two main areas of study exist in this research:
Macrosystematic, classification and biogeography: traditionally sigmodontine have been classified by skull and morphological characteristics. The research on this topic is based on molecular evidence (DNA sequences, nuclear and mitochondrial) that is analyzed by cladistics methods. The aim of this research is to 1) generate phylogenetic hypothesis, 2) define natural groups, 3) test biogeography hypothesis. Many relevant result on the matter have been addressed changing classical concept on historical biogeography of the group.
Alpha taxonomy and diversification processes: biological limits of species are in most of the cases poorly understood. That is why many species status are doubted and discussed. Moreover, processes leading diversification in this group remains poorly study. Studies involve taxa distributed along Argentina, Brasil, Paraguay and Uruguay. The objectives of this study are: 1) determine the diversity at a species level, 2) understand processes that generat that diversity. Field work is a important part of the work together with a phylogenetic analysis using mitochondrial sequences. Results in this area show a higher diversity than expected and discard rivers as vicariate agents.
Problem description and primary results: In uruguay, the tucu-tucu Ctenomys pearsoni is highly distributed along Rio de la Plata and Atlantic ocean coasts. One major characteristic is important chromosome diversity. The status of some chromosome forms are still unknown, with a common form with 2n=70 distributed along Colonia and San José departments. This thesis finished on 2003 showed a polyphyletic relationship between populations at mitochondrial DNA level. Results are compatible with a isolation by distance model, with no departure from neutrality and low estimations of gene flow. No support exists for more than one species in pearsoni's complex. No classical scenarios for chromosome speciation were found in light of the results of mitochondrial DNA.
Problem: South American rodents have been proposed to be a great example for explosive speciation. Recent studies carried out in our laboratory using cyt b gene of mitochondrial DNA confirm this hypothesis. However, only one molecular marker was used and it has a particular evolutionary rite and possible submitted to directional selection in history. In this project we try to solve this issue using nuclear genes introns.
Main results: introns sequences have been generated for two independent genes and compeared to mitochondrial results. Until now all molecular markers show some evidence of an increase in diversification rates of tucu-tucus in the base of radiation. Meanwhile, introns showed to be an excellent marker because of easy models adjustment, including molecular clock and show very low levels of homoplasy.