Phylogeographic Structure of the Fossorial Long-Clawed Mouse Chelemys macronyx (Cricetidae: Sigmodontinae)

We present a phylogeographic study of the fossorial sigmodontine mouse Chelemys macronyx. Analyses were based on mitochondrial DNA sequences of specimens collected over most of distributional range of the species. Results showed that C. macronyx has a shallow genealogy that is geographically structured into 2 main clades: one in the northern part of the species distribution, at high-Andean localities in the Argentinean provinces of Mendoza and northern Neuquén, and the other covering the majority of its distributional range at medium- to low-elevation localities from northwestern Neuquén to the south. The northern clade appears to have been demographically stable, while the southern clade presents signals of demographic expansion. These results suggest that current genetic variation of C. macronyx may have originated from 2 refugia.Fil: Alarcón, Oriet. Universidad de Concepción; ChileFil: D'elía, Guillermo. Universidad Austral de Chile; Chile. Centro de Investigación en Ecosistemas de la Patagonia; ChileFil: Lessa, Enrique P.. Universidad de la República. Facultad de Ciencias; UruguayFil: Pardiñas, Ulises Francisco J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin

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

Living on the edge: Exploring the role of coastal refugia in the Alexander Archipelago of Alaska

Although islands are of long‐standing interest to biologists, only a handful of studies have investigated the role of climatic history in shaping evolutionary diversification in high‐latitude archipelagos. In this study of the Alexander Archipelago (AA) of Southeast Alaska, we address the impact of glacial cycles on geographic genetic structure for three mammals co‐distributed along the North Pacific Coast. We examined variation in mitochondrial and nuclear loci for long‐tailed voles (Microtus longicaudus), northwestern deermice (Peromyscus keeni), and dusky shrews (Sorex monticola), and then tested hypotheses derived from Species Distribution Models, reconstructions of paleoshorelines, and island area and isolation. In all three species, we identified paleoendemic clades that likely originated in coastal refugia, a finding consistent with other paleoendemic lineages identified in the region such as ermine. Although there is spatial concordance at the regional level for endemism, finer scale spatial and temporal patterns are less clearly defined. Demographic expansion across the region for these distinctive clades is also evident and highlights the dynamic history of Late Quaternary contraction and expansion that characterizes high‐latitude species

Evolution of morphological adaptations for digging in living and extinct ctenomyid and octodontid rodents

To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We mapped morphological specializations of the digging apparatus onto our phylogenetic hypothesis and attempted to match morphological diversity with information on the ecology and behaviour of octodontoid taxa. Burrowing for sheltering and rearing is the rule among octodontids and ctenomyids, and adaptations for digging have been known from the Early Pliocene onward. However, only a few taxa have evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages, and morphological changes associated with scratch-digging are not restricted to subterranean lineages. By contrast, various adaptations for chisel-tooth digging are restricted to some subterranean lineages and are combined differently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Hence, we suggest that, during the early evolution of those branches giving rise to fully subterranean ctenomyids and octodontids, a change in behaviour probably preceded the origin of structural adaptations.Facultad de Ciencias Naturales y Muse

Evolution of morphological adaptations for digging in living and extinct ctenomyid and octodontid rodents

To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We mapped morphological specializations of the digging apparatus onto our phylogenetic hypothesis and attempted to match morphological diversity with information on the ecology and behaviour of octodontoid taxa. Burrowing for sheltering and rearing is the rule among octodontids and ctenomyids, and adaptations for digging have been known from the Early Pliocene onward. However, only a few taxa have evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages, and morphological changes associated with scratch-digging are not restricted to subterranean lineages. By contrast, various adaptations for chisel-tooth digging are restricted to some subterranean lineages and are combined differently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Hence, we suggest that, during the early evolution of those branches giving rise to fully subterranean ctenomyids and octodontids, a change in behaviour probably preceded the origin of structural adaptations.Facultad de Ciencias Naturales y Muse

Genetic analyses suggest burrow sharing by Río Negro tuco-tucos (Ctenomys rionegrensis)

Genetic analyses of kinship can generate important insights into social structure, particularly forspecies for which direct observations of social relationships are challenging. We used molecular markersto characterize the kin structure of a population of the Río Negro tuco-tuco (Ctenomys rionegrensis), asubterranean species of rodent that is rarely observed above ground. Previous research has revealed thatadults of this species engage in at least periodic episodes of burrow sharing, indicating thatC. rionegrensismaynot be strictly solitary. To explore the kin structure of this species, we used variability at 10 microsatellite locito determine if (1) adults and juveniles captured at the same burrow entrance were parents and o spring and(2) kinship among adults captured together di ered from that among randomly sampled pairs of individuals inour study population. Our analyses revealed that adults and juveniles captured together were not typicallyparents and o spring, suggesting potential mixing of litters among burrow systems. Relatedness among adultscaptured together did not di er from background levels of genetic similarity, providing no evidence thatspatial proximity was associated with kin structure. Collectively, our ndings support the hypothesis thatC. rionegrensisis not strictly solitary but instead engages in burrow sharing by adults and associated litters ofyoung.Los análisis genéticos de parentesco pueden generar importantes ideas sobre la estructura social, particularmente en especies donde las observaciones directas de las relaciones sociales son aún muy discutidas. Utilizamos marcadores moleculares para caracterizar la estructura de parentesco en una población de los tuco-tucos de Río Negro (Ctenomys rionegrensis), una especie de roedores subterráneos que rara vez se observa sobre la super cie. Investigaciones anteriores han revelado que los adultos de esta especie pueden compartir madrigueras, al menos por periodos, indicando que esta especie puede no ser estrictamente solitaria. Para explorar la estructura de parentesco de esta especie utilizamos la variabilidad presente en 10 loci de microsatélites para determinar si (1) adultos y juveniles capturados en la misma madriguera son padres e hijos y (2) el parentesco entre los adultos capturados en las mismas cuevas di ere del de pares de individuos muestreados al azar en la población estudiada. Nuestros análisis revelaron que los adultos y los juveniles capturados juntos típicamente no están emparentados, lo que sugiere una posible mezcla de camadas dentro del sistema de madrigueras. El parentesco entre los adultos capturados juntos, sin embargo, no di rió de los niveles medios de similitud genética, sin proporcionar evidencia de que la proximidad espacial estuviera asociada con la estructura de parentesco. En conjunto, nuestros hallazgos apoyan la hipótesis de que C. rionegrensis no es una especie estrictamente solitaria, sino que existe intercambio de madrigueras entre los adultos y sus camadas asociadas

Scorched mussels (Brachidontes spp., Bivalvia: Mytilidae) from the tropical and warm-temperate southwestern Atlantic: the role of the Amazon River in their speciation

Antitropicality is a distribution pattern where closely related taxa are separated by an intertropical latitudinal gap. Two potential examples include Brachidontes darwinianus (south eastern Brazil to Uruguay), considered by some authors as a synonym of B. exustus (Gulf of Mexico and the Caribbean), and B. solisianus, distributed along the Brazilian coast with dubious records north of the intertropical zone. Using two nuclear (18S and 28S rDNA) and one mitochondrial gene (mtDNA COI), we aimed to elucidate the phylogeographic and phylogenetic relationships among the scorched mussels present in the warm-temperate region of the southwest Atlantic. We evaluated a divergence process mediated by the tropical zone over alternative phylogeographic hypotheses. Brachidontes solisianus was closely related to B. exustus I, a species with which it exhibits an antitropical distribution. Their divergence time was approximately 2.6 Ma, consistent with the intensification of Amazon River flow. Brachidontes darwinianus, an estuarine species is shown here not to be related to this B. exustus complex. We suspect ancestral forms may have dispersed from the Caribbean to the Atlantic coast via the Trans-Amazonian seaway (Miocene). The third species, B rodriguezii is presumed to have a long history in the region with related fossil forms going back to the Miocene. Although scorched mussels are very similar in appearance, their evolutionary histories are very different, involving major historical contingencies as the formation of the Amazon River, the Panama Isthmus, and the last marine transgressio