Genetic structure in a solitary rodent (Ctenomys talarum): implications for kinship and dispersal (original) (raw)
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Molecular Ecology, 2012
The study of the spatial distribution of relatives in a population under contrasted environmental conditions provides critical insights into the flexibility of dispersal behaviour and the role of environmental conditions in shaping population relatedness and social structure. Yet few studies have evaluated the effects of fluctuating environmental conditions on relatedness structure of solitary species in the wild. The aim of this study was to determine the impact of interannual variations in environmental conditions on the spatial distribution of relatives [spatial genetic structure (SGS)] and dispersal patterns of a wild population of eastern chipmunks (Tamias striatus), a solitary rodent of North America. Eastern chipmunks depend on the seed of masting trees for reproduction and survival. Here, we combined the analysis of the SGS of adults with direct estimates of juvenile dispersal distance during six contrasted years with different dispersal seasons, population sizes and seed production. We found that environmental conditions influences the dispersal distances of juveniles and that male juveniles dispersed farther than females. The extent of the SGS of adult females varied between years and matched the variation in environmental conditions. In contrast, the SGS of males did not vary between years. We also found a difference in SGS between males and females that was consistent with male-biased dispersal. This study suggests that both the dispersal behaviour and the relatedness structure in a population of a solitary species can be relatively labile and change according to environmental conditions.
BMC Genetics, 2010
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.
Habitat islands, genetic diversity, and gene flow in a Patagonian rodent
Molecular …, 1998
The effects of terrestrial habitat islands on gene flow and genetic diversity in animal populations have been predicted and discussed in theoretical terms, but empirical data are needed to test these predictions and provide an understanding of the relationships of life-history characteristics to genetics of insular species. We studied saxicolous mice (Phyllotis xanthopygus) in Patagonia to explore genetic structure, phylogeography, and gene flow in a species inhabiting natural habitat islands. Phylogeographic analyses based on mtDNA sequences revealed two haplotype clades, which presumably reflect early Pleistocene factors that temporarily separated the mice into two geographically isolated groups. The Río Chubut, which lies within a glacial drainage basin bisecting northern Patagonia, might have affected gene flow in the species. Although we anticipated isolation by distance and founder phenomena associated with habitat islands, in some habitat patches we found evidence of high local genetic diversity. The amount of divergence in the mitochondrial cytochrome b gene (≈ 3.4%) in animals at a single locality could best be explained through a combination of historical factors and metapopulation source-sink theory. Demographic shifts, dispersal, and episodic recolonization are important in the life history and genetic population structure of P. xanthopygus.
Absence of kin structure in a population of the group-living rodent Octodon degus
Behavioral Ecology, 2011
Variation in sociality may have an important impact on population genetic structure. In highly social species, the formation of kin clusters leads to decreasing variation within but increasing genetic variation among social groups. Studies on less social species in which social groups may be more short lived have revealed a greater diversity of consequences on the genetic structure of populations. Thus, studies on populations of less social species can more precisely highlight how social structure and genetic structure covary in wild populations. We explored the relationship between natal dispersal and social structuring (i.e., whether social group are composed of kin) at the local population in a social rodent, Octodon degus, using a combination of direct (capture-mark-recapture) and indirect (codominat genetic markers) methods. Previous studies of degus indicated that social groups were characterized by high turnover rate of group members and no sex bias dispersal. As we expected, there was an absence of correlation between social and genetic structure; moreover, social groups were not characterized by high levels of genetic relatedness (R: no different form background population). Direct and indirect (corrected assignment index) methods revealed an absence of sex-biased dispersal. Moreover, this method reveled that our study population was composed of resident and immigrant individuals. Moreover, dispersal distances have no effect on kin structure as reveled by the spatial genetic autocorrelation analysis. Beside some degree of offspring association (R: among juveniles of a same group higher than background population), high turnover rate, dispersal, and perhaps a promiscuous or polyandry mating system seem to avoid a kin genetic structure, thereby limiting the opportunity for the evolution of kin-selected social behavior.
Hierarchical genetic structure and gene flow in three sympatric species of Amazonian rodents
Molecular Ecology, 1996
The population genetic structure of three species of Amazonian rodents (Oligoryzomys microtis, Oryzomys cupito, and Mesomys hispidus) is examined for mtDNA sequence haplotypes of the cytochrome b gene by hierarchical analysis of variance and gene flow estimates based on fixation indices (N,) and coalescence methods. Species samples are from the same localities along loo0 k m of the Rio Jurui in western Amazonian Brazil, but each species differs in important life history traits such as population size and reproductive rate. Average h a p l o h e differentiation, hierarchical haplotype apportionment, and gene flow estimates are contrasted in discussing the current and past population structure. Two species exhibit isolation by distance patterns wherein gene flow is largely limited to geographically adjacent localities. Mesomys exhibits this pattern throughout its range along the river. More than 75% of haplotype variation is apportioned among localities and regions, and estimates of Nm for pair-wise comparisons are nearly always less than 1. Oligoryzomys shows weak isolation by distance, but only over the largest geographical distances. N m values for this species are nearly always above 1 and most (about 80%) of haplotype variation is contained within local populations. In contrast, Oryzomys exhibits no genetic structure throughout its entire distribution; Nm values average 17 and nearly 90% of the total haplotype variance is contained within local populations. Although gene flow estimates are high, the pattern of Nm as a function of geographical distance suggests that this species experienced a more recent invasion of the region and is still in genetic disequilibrium under its current demographic conditions.
Kinship in colonial tuco-tucos: evidence from group composition and population structure
Behavioral Ecology, 2004
Kinship plays a significant role in shaping the social and genetic structures of many vertebrate populations. Evidence of kinship, however, may be substantially influenced by the spatial and temporal scales over which co-ancestry is monitored. For example, while data on social group composition may yield little indication of relatedness among reproductive partners, data on the demographic structure of a population may reveal considerable shared ancestry among mates. We explored relationships among social group composition, individual movements, and population-level patterns of kinship using data from a 7-year field study of the colonial tuco-tuco (Ctenomys sociabilis), a group-living subterranean rodent that is endemic to southwestern Argentina. Our analyses indicate that social groups are composed of 1-4 generations of closely related females and a single, immigrant male, suggesting that reproductive partners are not related to one another. Monitoring individual movements, however, revealed that (1) most male dispersal occurs within the local population and (2) most new social groups are founded by females born in the study population, indicating that individuals reared in different burrow systems may share considerable co-ancestry. Simulation analyses revealed that up to 67% of reproductive partnerships consist of animals that share co-ancestry within the last 5-7 generations. Thus, while analyses of social group composition provide little evidence of kinship among reproductive partners, population-level analyses of dispersal and group formation suggest that co-ancestry among mates is common. These findings have important implications for interpreting social interactions and genetic structure in this species.
Identifying factors and the extent of their roles in the differentiation of populations is of great importance for understanding the evolutionary process in which a species is involved. Ctenomys minutus is a highly karyotype-polymorphic subterranean rodent, with diploid numbers ranging from 42 to 50 and autosomal arm numbers (ANs) ranging from 68 to 80, comprising a total of 45 karyotypes described so far. This species inhabits the southern Brazilian coastal plain, which has a complex geological history, with several potential geographical barriers acting on different time scales. We assessed the geographical genetic structure of C. minutus, examining 340 individuals over the entire distributional range and using information from chromosomal rearrangements, mitochondrial DNA (mtDNA) sequences and 14 microsatellite loci. The mtDNA results revealed seven main haplogroups, with the most recent common ancestors dating from the Pleistocene, whereas clustering methods defined 12 populations. Some boundaries of mtDNA haplogroups and population clusters can be associated with potential geographical barriers to gene flow. The isolation-by-distance pattern also has an important role in fine-scale genetic differentiation, which is strengthened by the narrowness of the coastal plain and by common features of subterranean rodents (that is, small fragmented populations and low dispersal rates), which limit gene flow among populations. A step-by-step mechanism of chromosomal evolution can be suggested for this species, mainly associated with the metapopulation structure, genetic drift and the geographical features of the southern Brazilian coastal plain. However, chromosomal variations have no or very little role in the diversification of C. minutus populations.
Genetica, 2020
Understanding the processes and patterns of local adaptation and migration involves an exhaustive knowledge of how landscape features and population distances shape the genetic variation at the geographical level. Ctenomys australis is an endangered subterranean rodent characterized by having a restricted geographic range immerse in a highly fragmented sand dune landscape in the Southeast of Buenos Aires province, Argentina. We use 13 microsatellite loci in a total of 194 individuals from 13 sampling sites to assess the dispersal patterns and population structure in the complete geographic range of this endemic species. Our analyses show that populations are highly structured with low rates of gene flow among them. Genetic differentiation among sampling sites was consistent with an isolation by distance pattern, however, an important fraction of the population differentiation was explained by natural barriers such as rivers and streams. Although the individuals were sampled at locations distanced from each other, we also use some landscape genetics approaches to evaluate the effects of landscape configuration on the genetic connectivity among populations. These analyses showed that the sand dune habitat availability (the most suitable habitat for the occupation of the species), was one of the main factors that explained the differentiation patterns of the different sampling sites located on both sides of the Quequén Salado River. Finally, habitat availability was directly associated with the width of the sand dune landscape in the Southeast of Buenos Aires province, finding the greatest genetic differentiation among the populations of the Northeast, where this landscape is narrower.
Molecular Ecology, 2013
To better understand evolutionary pathways leading to eusociality, interspecific comparisons are needed, which would use a common axis, such as that of reproductive skew, to array species. African mole-rats (Bathyergidae, Rodentia) provide an outstanding model of social evolution because of a wide range of social organizations within a single family; however, their reproductive skew is difficult to estimate, due to their cryptic lifestyle. A maximum skew could theoretically be reached in groups where reproduction is monopolized by a stable breeding pair, but the value could be decreased by breeding-male and breeding-female turnover, shared reproduction and extra-group mating. The frequency of such events should be higher in species or populations inhabiting mesic environments with relaxed ecological constraints on dispersal. To test this prediction, we studied patterns of parentage and relatedness within 16 groups of Ansell's mole-rat (Fukomys anselli) in mesic miombo woodland. Contrary to expectation, there was no shared reproduction (more than one breeder of a particular sex) within the studied groups, and proportion of immigrants and offspring not assigned to current breeding males was low. The within-group parentage and relatedness patterns observed resemble arid populations of 'eusocial' Fukomys damarensis, rather than a mesic population of 'social' Cryptomys hottentotus. As a possible explanation, we propose that the extent ecological conditions affect reproductive skew may be markedly affected by life history and natural history traits of the particular species and genera.