Maintenance of genetic diversity in cyclic populations-a longitudinal analysis in Myodes glareolus (original) (raw)

Migration and recovery of the genetic diversity during the increasing density phase in cyclic vole populations

Molecular Ecology, 2006

In cyclic populations, high genetic diversity is currently reported despite the periodic low numbers experienced by the populations during the low phases. Here, we report spatiotemporal monitoring at a very fine scale of cyclic populations of the fossorial water vole ( Arvicola terrestris ) during the increasing density phase. This phase marks the transition from a patchy structure (demes) during low density to a continuous population in high density. We found that the genetic diversity was effectively high but also that it displayed a local increase within demes over the increasing phase. The genetic diversity remained relatively constant when considering all demes together. The increase in vole abundance was also correlated with a decrease of genetic differentiation among demes. Such results suggest that at the end of the low phase, demes are affected by genetic drift as the result of being small and geographically isolated. This leads to a loss of local genetic diversity and a spatial differentiation among demes. This situation is counterbalanced during the increasing phase by the spatial expansion of demes and the increase of the effective migration among differentiated demes. We provide evidences that in cyclic populations of the fossorial water voles, the relative influence of drift operating during low density populations and migration occurring principally while population size increases interacts closely to maintain high genetic diversity.

Short-term variations in gene flow related to cyclic density fluctuations in the common vole

Molecular Ecology, 2014

In highly fluctuating populations with complex social systems, genetic patterns are likely to vary in space and time due to demographic and behavioural processes. Cyclic rodents are extreme examples of demographically instable populations that often exhibit strong social organization. In such populations, kin structure and spacing behaviour may vary with density fluctuations and impact both the composition and spatial structure of genetic diversity. In this study, we analysed the multiannual genetic structure of a cyclic rodent, Microtus arvalis, using a sample of 875 individuals trapped over three complete cycles (from 1999 to 2007) and genotyped at 10 microsatellite loci. We tested the predictions that genetic diversity and gene flow intensity vary with density fluctuations. We found evidences for both spatial scale-dependant variations in genetic diversity and higher gene flow during high density. Moreover, investigation of sex-specific relatedness patterns revealed that, although dispersal is biased toward males in this species, distances moved by both sexes were lengthened during high density. Altogether, these results suggest that an increase in migration with density allows to restore the local loss of genetic diversity occurring during low density. We then postulate that this change in migration results from local competition, which enhances female colonization of empty spaces and male dispersal among colonies.

The spatial genetic structure of bank vole (Myodes glareolus) and yellow-necked mouse (Apodemus flavicollis) populations: The effect of distance and habitat barriers

Animal Biology, 2009

Habitat barriers are considered to be an important factor causing the local reduction of genetic diversity by dividing a population into smaller sections and preventing gene fl ow between them. However, the "barrier eff ect" might be diff erent in the case of diff erent species. Th e eff ect of geographic distance and water barriers on the genetic structure of populations of two common rodent species -the yellownecked mouse ( Apodemus fl avicollis ) and the bank vole ( Myodes glareolus ) living in the area of a lake (on its islands and on two opposite shores) was investigated with the use of microsatellite fragment analysis. Th e two studied species are characterised by similar habitat requirements, but diff er with regard to the socio-spatial structure of the population, individual mobility, capability to cross environmental barriers, and other factors. Trapping was performed for two years in spring and autumn in north-eastern Poland (21 o E, 53 o N). A total of 160 yellow-necked mouse individuals (7 microsatellite loci) and 346 bank vole individuals (9 microsatellite loci) were analysed. Th e results of the diff erentiation analyses (F ST and R ST ) have shown that both the barrier which is formed by a ca. 300 m wide belt of water (between the island and the mainland) and the actual distance of approximately 10 km in continuous populations are suffi cient to create genetic diff erentiation within both species. Th e diff erences between local populations living on opposite lake shores are the smallest; diff erences between any one of them and the island populations are more distinct. All of the genetic diversity indices (the mean number of alleles, mean allelic richness, as well as the observed and expected heterozygosity) of the local populations from the lakeshores were signifi cantly higher than of the small island populations of these two species separated by the water barrier. Th e more profound "isolation eff ect" in the case of the island populations of the bank vole, in comparison to the yellow-necked mouse populations, seems to result not only from the lower mobility of the bank vole species, but may also be attributed to other diff erences in the animals' behaviour.

Gene flow counteracts the effect of drift in a Swiss population of snow voles fluctuating in size

Biological Conservation, 2015

Genetic monitoring has emerged as a useful tool to better understand evolutionary processes acting within and among natural populations. Longitudinal studies allow the examination of temporal changes in neutral genetic patterns in relation to demographic data, which is particularly interesting in populations that undergo large fluctuations in size. Taking advantage of eight years (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) of genetic survey data (18 microsatellite loci) from a snow vole (Chionomys nivalis) population in the Swiss Alps, we explore whether and how gene flow and selection shape temporal variability in genetic diversity by counteracting the effect of genetic drift, and thereby maintain the high levels of heterozygosity observed in this population. Using simulations and empirical data, we show that effective population size is small, and that genetic drift would lead to a marked decline in genetic diversity. However, this force is counterbalanced by the restoring effect of immigration. In agreement with the predictions of neutral genetic theory, we found a strong, positive association between genetic diversity and population size, which suggests positive density-dependent dispersal. This is also supported by the observed changes in genetic composition over time. Meanwhile, selection for heterozygosity was weak, overriding the effect of drift only in one out of eight years. Altogether, our results highlight the importance of gene flow as a significant evolutionary force in shaping genetic patterns in the wild, and as a crucial process for the maintenance of genetic diversity in small populations.

Genetic structure of the cyclic fossorial water vole (Arvicola terrestris): landscape and demographic influences

Molecular Ecology, 2005

Genetic structure can be strongly affected by landscape features and variation through time and space of demographic parameters such as population size and migration rate. The fossorial water vole ( Arvicola terrestris ) is a cyclic species characterized by large demographic fluctuations over short periods of time. The outbreaks do not occur everywhere at the same time but spread as a wave at a regional scale. This leads to a pattern of large areas (i.e. some hundreds of km 2 ), each with different vole abundances, at any given time. Here, we describe the abundance and genetic structures in populations of the fossorial water vole. We use the data to try to understand how landscape and demographic features act to shape the genetic structure. The spatial variability of vole abundance was assessed from surface indices, collected in spring 2002 (April) in eastern central France. Genetic variability was analysed using eight microsatellite loci at 23 localities sampled between October 2001 and April 2002. We found some congruence between abundance and genetic structures. At a regional scale, the genetic disruptions were associated with both sharp relief and transition between an area of low abundance and another of high abundance. At a local scale, we observed a variation of the isolation-by-distance pattern according to the abundance level of vole populations. From these results we suggest that the dispersal pattern in cyclic rodent populations varies throughout the demographic cycle.

Spatial genetic structure of a small rodent in a heterogeneous landscape

Molecular Ecology, 2008

Gene flow in natural populations may be strongly influenced by landscape features. The integration of landscape characteristics in population genetic studies may thus improve our understanding of population functioning. In this study, we investigated the population genetic structure and gene flow pattern for the common vole, Microtus arvalis, in a heterogeneous landscape characterised by strong spatial and temporal variation. The studied area is an intensive agricultural zone of approximately 500 km 2 crossed by a motorway. We used individual-based Bayesian methods to define the number of population units and their spatial borders without prior delimitation of such units. Unexpectedly, we determined a single genetic unit that covered the entire area studied. In particular, the motorway considered as a likely barrier to dispersal was not associated with any spatial genetic discontinuity. Using computer simulations, we demonstrated that recent anthropogenic barriers to effective dispersal are difficult to detect through analysis of genetic variation for species with large effective population sizes. We observed a slight, but significant, pattern of isolation by distance over the whole study site. Spatial autocorrelation analyses detected genetic structuring on a local scale, most probably due to the social organisation of the study species. Overall, our analysis suggests intense small-scale dispersal associated with a large effective population size. High dispersal rates may be imposed by the strong spatio-temporal heterogeneity of habitat quality, which characterises intensive agroecosystems.

Lack of concordance between mtDNA gene flow and population density fluctuations in the bank vole

Molecular Ecology, 1997

The genetic structure of bank voles Clethrionomys glareolus was determined from analyses of mitochondrial DNA (mtDNA) sequences, and compared with previous data on geographical synchrony in population density fluctuations. From 31 sample sites evenly spaced out along a 256-km transect in SE Norway a total of 39 distinct mtDNA haplotypes were found. The geographical distribution of the haplotypes was significantly nonrandom, and a cladistic analysis of the evolutionary relationship among haplotypes shows that descendant types were typically limited to a single site, whereas the ancestral types were more widely distributed geographically. This geographical distribution pattern of mtDNA haplotypes strongly indicates that the range and amount of female dispersal is severely restricted and insufficient to account for the previously observed synchrony in population density fluctuations. We conclude that geographical synchrony in this species must be caused by factors that are external to the local population, such as e.g. mobile predators.