Dispersal and population structure at different spatial scales in the subterranean rodent Ctenomys australis

This study was funded by grants from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, PIP5838), Agencia de Promoción Científica y Tecnológica de la Argentina (PICTO1-423, BID-1728/OC-AR), and the programme ECOS-Sud France/Argentina (A05B01).Background: 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). 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. Results: Our results show that dispersal in C. australis is not restricted at regional spatial scales (similar to 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. Conclusions: Overall, the assignment-based approaches were able to detect population substructure at fine geographical scales. Additionally, the maintenance of a significant genetic structure at regional (similar to 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.Publisher PDFPeer reviewe

Extreme flooding increases poaching mortality in the southernmost stronghold of the endangered marsh deer

Extreme stochastic perturbations can affect population dynamics, but quantitative assessments are scarce for threatened species. The 2015-2016 El Niño-Southern Oscillation (ENSO) caused extreme flooding in the Delta of the Paraná River in Argentina where the southernmost population of the regionally endangered marsh deer (Blastocerus dichotomus) occurs. Using field surveys and data from informants, we studied the impact of this flood on the mortality, distribution, and abundance of this marsh deer population in an area of 1 236 km2. The occurrence of this extreme flood significantly increased marsh deer mortality. One hundred forty-two marsh deer deaths were recorded over the seven-month flood duration, with poaching accounting for 86.6% of deaths. Mortality of marsh deer was significantly higher near urban areas, embankments, and dirt roads, while mortality from poaching was higher in plantations and permanently inundated lands. Two areas of high spatial clustering of poaching mortality were detected, encompassing plantations with easy access or in proximity to urban areas, while embankments appeared to act as attractive population sinks. Flood-related mortality significantly decreased the occurrence of the species in the study area after the flood, but changes in relative abundance between periods were heterogeneous across the landscape, probably because of local migrations. Since climate change is expected to increase the global frequency and magnitude of extreme flood events, our study provides valuable information for mitigating the negative synergistic effects of extreme flooding on marsh deer, as well as for global wildlife populations subjected to periodic extreme floods.Las perturbaciones estocásticas extremas pueden afectar la dinámica de las poblaciones, pero las evaluaciones cuantitativas son escasas para las especies amenazadas. El fenómeno de “El Niño” de 2015-2016 causó inundaciones extremas en el Delta del río Paraná en Argentina, donde se encuentra la población más austral del ciervo de los pantanos (Blastocerus dichotomus), categorizada como En Peligro a nivel regional. En base a relevamientos de campo y datos de informantes, estudiamos el impacto de esta inundación sobre la mortalidad, distribución y abundancia de esta población de ciervo de los pantanos dentro de un área de 1 236 km2. La ocurrencia de esta inundación incrementó signicativamente la mortalidad del ciervo de los pantanos. Hemos registrado 142 individuos muertos durante los siete meses de duración de la inundación, y la caza furtiva representó el 86.6% de las muertes. La mortalidad del ciervo de los pantanos fue signicativamente mayor en proximidad a áreas urbanas, terraplenes y caminos vehiculares, mientras que la mortalidad por cacería fue mayor en plantaciones y terrenos permanentemente inundados. Se detectaron dos áreas de alta concentración espacial de mortalidad por cacería, que abarcaron plantaciones de fácil acceso o próximas a áreas urbanas, mientras que los terraplenes parecen haber funcionado como sumideros atractivos para los ciervos. La mortalidad relacionada con las inundaciones disminuyó signicativamente la presencia de la especie dentro del área de estudio luego de la inundación, pero los cambios en la abundancia relativa entre períodos fueron heterogéneos en todo el paisaje, probablemente como resultado de migraciones locales. Dado que se espera que el cambio climático aumente la frecuencia global y la magnitud de las inundaciones extremas, nuestro estudio proporciona información valiosa para mitigar los efectos sinérgicos negativos de las inundaciones extremas tanto en el ciervo de los pantanos como en poblaciones de otras especies sujetas a inundaciones extremas periódicas.EEA Delta del ParanáFil: Pereira, Javier A. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Pereira, Javier Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Varela, Diego. Universidad Nacional de Misiones. Instituto de Biología Subtropical; ArgentinaFil: Varela, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología Subtropical; ArgentinaFil: Varela, Diego. Asociación Civil Centro de Investigaciones del Bosque AtlánticoFil: Thompson, Jeffrey J. Consejo Nacional de Ciencia y Tecnología. Guyra Paraguay; ParaguayFil: Thompson, Jeffrey J. Instituto Saite; ParaguayFil: Lartigau, Bernardo V. Asociación para la Conservación y el Estudio de la Naturaleza; ArgentinaFil: Fracassi, Natalia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Delta del Paraná; ArgentinaFil: Kittlein, Marcelo J. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biología. Instituto de Investigaciones Marinas y Costeras (IIMyC); ArgentinaFil: Kittlein, Marcelo J. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Marinas y Costeras (IIMyC); Argentin

Influence of environmental heterogeneity on the distribution and persistence of a subterranean rodent in a highly unstable landscape

O.E.G was supported by the Marine Alliance for Science and Technology for Scotland.In this study we combine information from landscape characteristics, demographic inference and species distribution modelling to identify environmental factors that shape the genetic distribution of the fossorial rodent Ctenomys. We sequenced the mtDNA control region and amplified 12 microsatellites from 27 populations distributed across the Iberá wetland ecosystem. Hierarchical Bayesian modelling was used to construct phylogenies and estimate divergence times. We developed species distribution models to determine what climatic variables and soil parameters predicted species presence by comparing the current to the historic and predicted future distribution of the species. Finally, we explore the impact of environmental variables on the genetic structure of Ctenomys based on current and past species distributions. The variables that consistently correlated with the predicted distribution of the species and explained the observed genetic differentiation among populations included the distribution of well-drained sandy soils and temperature seasonality. A core region of stable suitable habitat was identified from the Last Interglacial, which is projected to remain stable into the future. This region is also the most genetically diverse and is currently under strong anthropogenic pressure. Results reveal complex demographic dynamics, which have been in constant change in both time and space, and are likely linked to the evolution of the Paraná River. We suggest that any alteration of soil properties (climatic or anthropic) may significantly impact the availability of suitable habitat and consequently the ability of individuals to disperse. The protection of this core stable habitat is of prime importance given the increasing levels of human disturbance across this wetland system and the threat of climate change.PostprintPeer reviewe

Dispersal and population structure at different spatial scales in the subterranean rodent Ctenomys australis

<p>Abstract</p> <p><b>Background</b></p> <p>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). 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. <it>Ctenomys australis </it>(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.</p> <p>Results</p> <p>Our results show that dispersal in <it>C. australis </it>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.</p> <p>Conclusions</p> <p>Overall, 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.</p

Interactions between environmental factors can hide isolation by distance patterns: a case study of Ctenomys rionegrensis in Uruguay

Identifying the factors responsible for the structuring of genetic diversity is of fundamental importance for biodiversity conservation. However, arriving at such understanding is difficult owing to the many factors involved and the potential interactions between them. Here, we present an example of how such interactions can preclude us from arriving at a complete characterization of the demographic history and genetic structure of a species. Ctenomys rionegrensis is a species with restricted dispersal abilities and, as such, should exhibit an isolation by distance (IBD) pattern, which previous studies were unable to uncover. It was therefore concluded that this species underwent a recent population expansion. Using a novel hierarchical Bayesian method, we show that the inability to detect the IBD pattern is due to the interaction between elevation and geographical distance. We posit that populations in low areas suffer periodic floods that may reduce local population sizes, increasing genetic drift, a process that masks the effect of distance on genetic differentiation. Our results do not refute the possibility that the populations of C. rionegrensis underwent a recent population expansion but they indicate that an alternative scenario described by a metapopulation model at or near migration-drift equilibrium cannot be excluded either.</p