Abstract
BackgroundThe population genetic structure of subterranean rodent species is strongly affected by demographic (e.g. rates of dispersal and social structure) and stochastic factors (e.g. random genetic drift among subpopulations and habitat fragmentation). In particular, gene flow estimates at different spatial scales are essential to understand genetic differentiation among populations of a species living in a highly fragmented landscape. Ctenomys australis (the sand dune tuco-tuco) is a territorial subterranean rodent that inhabits a relatively secure, permanently sealed burrow system, occurring in sand dune habitats on the coastal landscape in the south-east of Buenos Aires province, Argentina. Currently, this habitat is threatened by urban development and forestry and, therefore, the survival of this endemic species is at risk. Here, we assess population genetic structure and patterns of dispersal among individuals of this species at different spatial scales using 8 polymorphic microsatellite loci. Furthermore, we evaluate the relative importance of sex and habitat configuration in modulating the dispersal patterns at these geographical scales.ResultsOur results show that dispersal in C. australis is not restricted at regional spatial scales (~ 4 km). Assignment tests revealed significant population substructure within the study area, providing support for the presence of two subpopulations from three original sampling sites. Finally, male-biased dispersal was found in the Western side of our study area, but in the Eastern side no apparent philopatric pattern was found, suggesting that in a more continuous habitat males might move longer distances than females.ConclusionsOverall, the assignment-based approaches were able to detect population substructure at fine geographical scales. Additionally, the maintenance of a significant genetic structure at regional (~ 4 km) and small (less than 1 km) spatial scales despite apparently moderate to high levels of gene flow between local sampling sites could not be explained simply by the linear distance among them. On the whole, our results support the hypothesis that males disperse more frequently than females; however they do not provide support for strict philopatry within females.
Highlights
The population genetic structure of subterranean rodent species is strongly affected by demographic and stochastic factors
Characterising dispersal patterns is difficult in the case of solitary species with territorial behaviour living in complex landscapes in which spatial structure can be described as a more or less continuous habitat, irregularly interrupted by discontinuities [4,5]
The local population FST was largest for the Western site and lowest for the Eastern site being intermediate for the central one (Table 3). These results suggest stronger genetic drift and/or lower immigration rate for the Western sampling site than for the two other sampling sites
Summary
The population genetic structure of subterranean rodent species is strongly affected by demographic (e.g. rates of dispersal and social structure) and stochastic factors (e.g. random genetic drift among subpopulations and habitat fragmentation). Ctenomys australis (the sand dune tuco-tuco) is a territorial subterranean rodent that inhabits a relatively secure, permanently sealed burrow system, occurring in sand dune habitats on the coastal landscape in the south-east of Buenos Aires province, Argentina This habitat is threatened by urban development and forestry and, the survival of this endemic species is at risk. Many species of subterranean rodents fit in this description and represent a real challenge to the study of migration patterns These species occupy fragmented habitats and present limited dispersal abilities in relation to the spatial scale of the habitat discontinuities [3]. They occupy small population units with low genetic variation and high inter-population divergence [6]. This is the case of the subterranean rodents of the genus Ctenomys (tuco-tucos), which present restricted mobility and are usually distributed in patches with low local effective population numbers [6,7]
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