Reproductive biology of Río Negro tuco-tuco, Ctenomys rionegrensis (Rodentia: Octodontidae)

Reproductive success depends on a precise synchronization of organisms’ activities with the environment, determining the evolution of mechanisms controlling reproductive behaviour. In temperate zones mammals exhibit pronounced seasonal reproduction because of thermoregulation costs imposed by low winter temperatures and limited food availability. Even occupying burrows that buffer external ambient conditions, these restrictions also affect subterranean rodents inhabiting these latitudes. Tuco-tucos (genus Ctenomys) are subterranean herbivorous rodents that have a Neotropical distribution between 17 and 54° of latitude S. Ctenomys rionegrensis is one of the three species occurring in Uruguay and generated interest due to chromatic polymorphism in a restricted area (50×60 km). Here we describe the timing of breeding in C. rionegrensis based on the reproductive status of free-living females and the proportion of juveniles in the population, and describe the characteristics of the estrous cycle of the species using cytological techniques. As expected, the data showed a clear seasonality in female breeding and provided evidence of the occurrence of post-partum estrous. The reproductive activity began in late austral autumn and the highest proportion of pregnant females was observed in winter. At the beginning of the austral spring, the prevalence of lactating females increased as a consequence of the first births and remained high until early summer. This pattern of breeding seasonality was clearly correlated with the annual temperature variation. The estrous cycle showed four phases characterized by both different cellular types and the abundance and appearance of mucus, which allows a clear determination of female's reproductive status.