Role of male‐biased dispersal in inbreeding avoidance in the grey‐sided vole (Myodes rufocanus)

Effects of male‐biased dispersal on inbreeding avoidance were investigated in a semi‐natural population of Myodes (formerly Clethrionomys) rufocanus using a large outdoor enclosure (3 ha). Parentage of 918 voles weaned from 215 litters and relatedness of mates were analysed using microsatellite loci, and dispersal distances were obtained from mark–recapture live‐trapping data. Natal and breeding male‐biased dispersal was observed. There remained, however, chances that incestuous mating could occur, because not all males dispersed from their natal site, and 51 matings occurred between relatives (relatedness r > 0). The number of weaned juveniles from inbred litters was significantly smaller than that from non‐inbred litters. Fourteen incestuous matings occurred between close relatives (r ≥ 0.25), most of which were those between non‐littermate maternal half siblings (four cases) and those between paternal half siblings (seven cases). When comparing the observed frequencies to the expected ones generated by combining every oestrous female with a male randomly chosen from her surroundings, the observed values for inbreeding of r ≥ 0.25 were significantly smaller than the expectations, while no difference was observed for inbreeding of 0 < r < 0.25. These results suggest that male‐biased dispersal is partly effective to avoid incestuous mating, but it does not provide complete separation of male and female close relatives. Additional mechanisms such as kin discrimination based on familiarity may work in inbreeding avoidance of the vole.     

Large‐ and small‐scale geographic structures affecting genetic patterns across populations of an Alpine butterfly

Understanding factors influencing patterns of genetic diversity and the population genetic structure of species is of particular importance in the current era of global climate change and habitat loss. These factors include the evolutionary history of a species as well as heterogeneity in the environment it occupies, which in turn can change across time. Most studies investigating spatio‐temporal genetic patterns have focused on patterns across wide geographic areas rather than local variation, but the latter can nevertheless be important particularly in topographically complex areas. Here, we consider these issues in the Sooty Copper butterfly (Lycaena tityrus) from the European Alps, using genome‐wide SNPs identified through RADseq. We found strong genetic differentiation within the Alps with four genetic clusters, indicating western, central, and eastern refuges, and a strong reduction of genetic diversity from west to east. This reduction in diversity may suggest that the southwestern refuge was the largest one in comparison to other refuges. Also, the high genetic diversity in the west may result from (a) admixture of different western refuges, (b) more recent demographic changes, or (c) introgression of lowland L. tityrus populations. At small spatial scales, populations were structured by several landscape features and especially by high mountain ridges and large river valleys. We detected 36 outlier loci likely under altitudinal selection, including several loci related to membranes and cellular processes. We suggest that efforts to preserve alpine L. tityrus should focus on the genetically diverse populations in the western Alps, and that the dolomite populations should be treated as genetically distinct management units, since they appear to be currently more threatened than others. This study demonstrates the usefulness of SNP‐based approaches for understanding patterns of genetic diversity, gene flow, and selection in a region that is expected to be particularly vulnerable to climate change.     

Fine-scale genetic structure and dispersal in the common vole (Microtus arvalis)

The genetic structure and demography of local populations is tightly linked to the rate and scale of dispersal. Dispersal parameters are notoriously difficult to determine in the field, and remain often completely unknown for smaller organisms. In this study, we investigate spatial and temporal genetic structure in relation to dispersal patterns among local populations of the probably most abundant European mammals, the common vole (Microtus arvalis). Voles were studied in six natural populations at distances of 0.4-2.5 km in three different seasons (fall, spring, summer) corresponding to different life-history stages. Field observations provided no direct evidence for movements of individuals between populations. The analysis of 10 microsatellite markers revealed a persistent overall genetic structure among populations of 2.9%, 2.5% and 3% FST in the respective season. Pairwise comparisons showed that even the closest populations were significantly differentiated from each other in each season, but there was no evidence for temporal differentiation within populations or isolation by distance among populations. Despite significant genetic structure, assignment analyses identified a relatively high proportion of individuals as being immigrants for the population where they were captured. The immigration rate was not significantly lower for females than for males. We suggest that a generally low and sex-dependent effective dispersal rate as the consequence of only few immigrants reproducing successfully in the new populations together with the social structure within populations may explain the maintenance of genetic differentiation among populations despite migration.     

Genotyping‐by‐sequencing analysis of Orobanche crenata populations in Algeria reveals genetic differentiation

Crenate broomrape (Orobanche crenata Forsk.) is a serious long‐standing parasitic weed problem in Algeria, mainly affecting legumes but also vegetable crops. Unresolved questions for parasitic weeds revolve around the extent to which these plants undergo local adaptation, especially with respect to host specialization, which would be expected to be a strong selective factor for obligate parasitic plants. In the present study, the genotyping‐by‐sequencing (GBS) approach was used to analyze genetic diversity and population structure of 10 Northern Algerian O. crenata populations with different geographical origins and host species (faba bean, pea, chickpea, carrot, and tomato). In total, 8004 high‐quality single‐nucleotide polymorphisms (5% missingness) were obtained and used across the study. Genetic diversity and relationships of 95 individuals from 10 populations were studied using model‐based ancestry analysis, principal components analysis, discriminant analysis of principal components, and phylogeny approaches. The genetic differentiation (F _ST) between pairs of populations was lower between adjacent populations and higher between geographically separated ones, but no support was found for isolation by distance. Further analyses identified four genetic clusters and revealed evidence of structuring among populations and, although confounded with location, among hosts. In the clearest example, O. crenata growing on pea had a SNP profile that was distinct from other host/location combinations. These results illustrate the importance and potential of GBS to reveal the dynamics of parasitic weed dispersal and population structure.     

Fine-scale genetic structure and gene dispersal inferences in 10 neotropical tree species

The extent of gene dispersal is a fundamental factor of the population and evolutionary dynamics of tropical tree species, but directly monitoring seed and pollen movement is a difficult task. However, indirect estimates of historical gene dispersal can be obtained from the fine-scale spatial genetic structure of populations at drift-dispersal equilibrium. Using an approach that is based on the slope of the regression of pairwise kinship coefficients on spatial distance and estimates of the effective population density, we compare indirect gene dispersal estimates of sympatric populations of 10 tropical tree species. We re-analysed 26 data sets consisting of mapped allozyme, SSR (simple sequence repeat), RAPD (random amplified polymorphic DNA) or AFLP (amplified fragment length polymorphism) genotypes from two rainforest sites in French Guiana. Gene dispersal estimates were obtained for at least one marker in each species, although the estimation procedure failed under insufficient marker polymorphism, limited sample size, or inappropriate sampling area. Estimates generally suffered low precision and were affected by assumptions regarding the effective population density. Averaging estimates over data sets, the extent of gene dispersal ranged from 150 m to 1200 m according to species. Smaller gene dispersal estimates were obtained in species with heavy diaspores, which are presumably not well dispersed, and in populations with high local adult density. We suggest that limited seed dispersal could indirectly limit effective pollen dispersal by creating higher local tree densities, thereby increasing the positive correlation between pollen and seed dispersal distances. We discuss the potential and limitations of our indirect estimation procedure and suggest guidelines for future studies.     

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

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 spatio-temporal 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.     

Evidence that disease-induced population decline changes genetic structure and alters dispersal patterns in the Tasmanian devil

Infectious disease has been shown to be a major cause of population declines in wild animals. However, there remains little empirical evidence on the genetic consequences of disease-mediated population declines, or how such perturbations might affect demographic processes such as dispersal. Devil facial tumour disease (DFTD) has resulted in the rapid decline of the Tasmanian devil, Sarcophilus harrisii, and threatens to cause extinction. Using 10 microsatellite DNA markers, we compared genetic diversity and structure before and after DFTD outbreaks in three Tasmanian devil populations to assess the genetic consequences of disease-induced population decline. We also used both genetic and demographic data to investigate dispersal patterns in Tasmanian devils along the east coast of Tasmania. We observed a significant increase in inbreeding (F_IS pre/post-disease −0.030/0.012, P<0.05; relatedness pre/post-disease 0.011/0.038, P=0.06) in devil populations after just 2–3 generations of disease arrival, but no detectable change in genetic diversity. Furthermore, although there was no subdivision apparent among pre-disease populations (θ=0.005, 95% confidence interval (CI) −0.003 to 0.017), we found significant genetic differentiation among populations post-disease (θ=0.020, 0.010–0.027), apparently driven by a combination of selection and altered dispersal patterns of females in disease-affected populations. We also show that dispersal is male-biased in devils and that dispersal distances follow a typical leptokurtic distribution. Our results show that disease can result in genetic and demographic changes in host populations over few generations and short time scales. Ongoing management of Tasmanian devils must now attempt to maintain genetic variability in this species through actions designed to reverse the detrimental effects of inbreeding and subdivision in disease-affected populations.     

Genetic diversity and sex‐biased dispersal in the brown spotted pitviper (Protobothrops mucrosquamatus): Evidence from microsatellite markers

Dispersal plays a vital role in the geographical distribution, population genetic structure, quantity dynamics, and evolution of a species. Sex‐biased dispersal is common among vertebrates and many studies have documented a tendency toward male‐biased dispersal in mammals and female‐biased dispersal in birds. However, dispersal patterns in reptiles remain poorly understood. In this study, we explored the genetic diversity and dispersal patterns of the widely distributed Asian pitviper Protobothrops mucrosquamatus. In total, 16 polymorphic microsatellite loci were screened in 150 snakes (48 males, 44 females, 58 samples without sex information) covering most of their distribution. Microsatellite analysis revealed high genetic diversity in P. mucrosquamatus. Bayesian clustering of population assignment identified two major clusters for all populations, somewhat inconsistent with the mitochondrial DNA phylogeny of P. mucrosquamatus reported in previous research. Analyses based on 92 sex‐determined and 37 samples of P. mucrosquamatus from three small sites in Sichuan, China (Mingshan, Yibin, and Zizhong) consistently suggested female‐biased dispersal in P. mucrosquamatus, which is the first example of this pattern in snakes. The female‐biased dispersal patterns in P. mucrosquamatus may be explained by local resource competition.     

Pollen dispersal and genetic structure of the tropical tree Dipteryx panamensis in a fragmented Costa Rican landscape

In the face of widespread deforestation, the conservation of rainforest trees relies increasingly on their ability to maintain reproductive processes in fragmented landscapes. Here, we analysed nine microsatellite loci for 218 adults and 325 progeny of the tree Dipteryx panamensis in Costa Rica. Pollen dispersal distances, genetic diversity, genetic structure and spatial autocorrelation were determined for populations in four habitats: continuous forest, forest fragments, pastures adjacent to fragments and isolated pastures. We predicted longer but less frequent pollen movements among increasingly isolated trees. This pattern would lead to lower outcrossing rates for pasture trees, as well as lower genetic diversity and increased structure and spatial autocorrelation among their progeny. Results generally followed these expectations, with the shortest pollen dispersal among continuous forest trees (240 m), moderate distances for fragment (343 m) and adjacent pasture (317 m) populations, and distances of up to 2.3 km in isolated pastures (mean: 557 m). Variance around pollen dispersal estimates also increased with fragmentation, suggesting altered pollination conditions. Outcrossing rates were lower for pasture trees and we found greater spatial autocorrelation and genetic structure among their progeny, as well as a trend towards lower heterozygosity. Paternal reproductive dominance, the pollen contributions from individual fathers, did not vary among habitats, but we did document asymmetric pollen flow between pasture and adjacent fragment populations. We conclude that long-distance pollen dispersal helps maintain gene flow for D. panamensis in this fragmented landscape, but pasture and isolated pasture populations are still at risk of long-term genetic erosion.     

东方田鼠种群扩散及活动对外部因子的反应格局

在野外围栏条件下,采用2×2×2析因实验,测定外部因子食物、捕食,以及同域分布物种黑线姬鼠的种间竞争对东方田鼠扩散和活动距离的独立作用及其交互作用的效应。研究结果表明,在所有的扩散个体中,幼体扩散的比例为71.0%。雄体扩散的比例为80.5%。东方田鼠扩散的趋势与其种群密度及补充量的变动一致。食物对扩散具有显著独立作用;捕食对扩散的作用接近显著;种间竞争对扩散的直接效应不显著;食物、捕食与种间竞争交互作用对扩散的效应亦不显著。在诱捕期内雄性的长距离活动比例及其诱捕期间长距离活动比例均显著大于诱捕期内雌性及其诱捕期间的长距离活动比例。不同处理种群间,仅雄体在诱捕期间的长距离活动比例具有显著差异;食物对雄体的长距离活动具有直接和间接(通过密度)的效应;而预防捕食者和竞争物种对不同处理种群雄体的长距离活动则无一致的效应。     

Characteristics of dispersal in the eastern mosquitofish Gambusia holbrooki

The demographic and genetic characteristics of dispersing Gambusia holbrooki were examined relative to changes in stream flow velocity, flow direction, and rapid saltwater inundation. Dispersal of all G. holbrooki sex classes decreased as flow velocity increased, dispersal for a given flow velocity being greater in female, than male and juvenile fish respectively. Juveniles and males dispersed at low (9 mm s⁻¹) but not high (109 mm s ¹) flow. Females dispersed at both flow rates. Dispersing adults were not larger than non-dispersing adults of the same sex. Direction of dispersal was sex and size dependent, but independent of flow velocity. Larger females (>22 mm) moved preferentially downstream, while smaller females (17–22 mm) remained stationary or moved in the upstream direction. Males dispersed equally in both directions. No relationship was found between dispersal characteristics and the presence of high salt concentrations. Movement patterns at high flow were independent of glucose-6-phosphate isomerase ( GPI-2* ) alleles carried by dispersing individuals. Significant non-random dispersal of sex or size cohorts, and the interaction of dispersal with flow velocity have significant implications for the maintenance of genetic diversity in stream ecosystems, particularly where localized selection or genetic drift may alter the genetic constitution of specific sex or size cohorts. The applicability of these results to field populations is discussed.     

Population genetic structure of the bank vole Myodes glareolus within its glacial refugium in peninsular Italy

It is now well established that Southern European peninsulas have been major glacial refugia for temperate species during Pleistocene climatic oscillations. However, substantial environmental changes occurred also within these peninsulas throughout the Pleistocene, raising questions about the role and interplay of various microevolutionary processes in shaping patterns of intraspecific diversity within these areas. Here, we investigate the patterns of genetic variation in the bank vole Myodes glareolus within the Italian peninsula. By using a panel of 13 microsatellite loci, we found more intraspecific variation than expected based on previous assessments. Indeed, both Bayesian and ordination‐based clustering analyses of variation recovered five main geographic/genetic clusters along the peninsula, with three clusters geographically restricted to the southern portion of the peninsula. This clustering is supported by previous evidences of some morphological distinctiveness among these populations. This pattern can be explained by a refugia‐within‐refugia scenario, with the occurrence of multiple sub‐refugia for the bank vole within the Italian peninsula, likely promoted by the major palaeo‐environmental changes which affected forested habitats within this area during the Pleistocene. Moreover, our results support a scenario whereby the high levels of intraspecific diversity observed within major Pleistocene refugia are better explained by dynamic microevolutionary processes occurred within these areas, rather than by long‐term demographic stability of refugial population. Finally, the narrow and isolated distribution of some of the identified lineages suggests the need for future assessments of their conservation and taxonomic status.     

Variation in fine‐scale genetic structure and local dispersal patterns between peripheral populations of a South American passerine bird

The distribution of suitable habitat influences natal and breeding dispersal at small spatial scales, resulting in strong microgeographic genetic structure. Although environmental variation can promote interpopulation differences in dispersal behavior and local spatial patterns, the effects of distinct ecological conditions on within‐species variation in dispersal strategies and in fine‐scale genetic structure remain poorly understood. We studied local dispersal and fine‐scale genetic structure in the thorn‐tailed rayadito (Aphrastura spinicauda), a South American bird that breeds along a wide latitudinal gradient. We combine capture‐mark‐recapture data from eight breeding seasons and molecular genetics to compare two peripheral populations with contrasting environments in Chile: Navarino Island, a continuous and low density habitat, and Fray Jorge National Park, a fragmented, densely populated and more stressful environment. Natal dispersal showed no sex bias in Navarino but was female‐biased in the more dense population in Fray Jorge. In the latter, male movements were restricted, and some birds seemed to skip breeding in their first year, suggesting habitat saturation. Breeding dispersal was limited in both populations, with males being more philopatric than females. Spatial genetic autocorrelation analyzes using 13 polymorphic microsatellite loci confirmed the observed dispersal patterns: a fine‐scale genetic structure was only detectable for males in Fray Jorge for distances up to 450 m. Furthermore, two‐dimensional autocorrelation analyzes and estimates of genetic relatedness indicated that related males tended to be spatially clustered in this population. Our study shows evidence for context‐dependent variation in natal dispersal and corresponding local genetic structure in peripheral populations of this bird. It seems likely that the costs of dispersal are higher in the fragmented and higher density environment in Fray Jorge, particularly for males. The observed differences in microgeographic genetic structure for rayaditos might reflect the genetic consequences of population‐specific responses to contrasting environmental pressures near the range limits of its distribution.     

Dynamics of populations with individual variation in dispersal on bounded domains

Most classical models for the movement of organisms assume that all individuals have the same patterns and rates of movement (for example, diffusion with a fixed diffusion coefficient) but there is empirical evidence that movement rates and patterns may vary among different individuals. A simple way to capture variation in dispersal that has been suggested in the ecological literature is to allow individuals to switch between two distinct dispersal modes. We study models for populations whose members can switch between two different nonzero rates of diffusion and whose local population dynamics are subject to density dependence of logistic type. The resulting models are reaction–diffusion systems that can be cooperative at some population densities and competitive at others. We assume that the focal population inhabits a bounded region and study how its overall dynamics depend on the parameters describing switching rates and local population dynamics. (Traveling waves and spread rates have been studied for similar models in the context of biological invasions.) The analytic methods include ideas and results from reaction–diffusion theory, semi-dynamical systems, and bifurcation/continuation theory.     

Limited seed dispersal shapes fine-scale spatial genetic structure in a Neotropical dioecious large-seeded palm

Seed and pollen dispersal contribute to gene flow and shape the genetic patterns of plants over fine spatial scales. We inferred fine-scale spatial genetic structure (FSGS) and estimated realized dispersal distances in Phytelephas aequatorialis, a Neotropical dioecious large-seeded palm. We aimed to explore how seed and pollen dispersal shape this genetic pattern in a focal population. For this purpose, we genotyped 138 seedlings and 99 adults with 20 newly developed microsatellite markers. We tested if rodent-mediated seed dispersal has a stronger influence than insect-mediated pollen dispersal in shaping FSGS. We also tested if pollen dispersal was influenced by the density of male palms around mother palms in order to further explore this ecological process in large-seeded plants. Rodent-mediated dispersal of these large seeds occurred mostly over short distances (mean 34.76 ± 34.06 m) while pollen dispersal distances were two times higher (mean 67.91 ± 38.29 m). The spatial extent of FSGS up to 35 m and the fact that seed dispersal did not increase the distance at which male alleles disperse suggest that spatially limited seed dispersal is the main factor shaping FSGS and contributes only marginally to gene flow within the population. Pollen dispersal distances depended on the density of male palms, decreasing when individuals show a clumped distribution and increasing when they are scattered. Our results show that limited seed dispersal mediated by rodents shapes FSGS in P. aequatorialis, while more extensive pollen dispersal accounts for a larger contribution to gene flow and may maintain high genetic diversity. Abstract in Spanish is available with online material.     

The influence of seed dispersal mechanisms on the genetic structure of tropical tree populations

Seed dispersal mechanisms should have a direct impact on the genetic structure of populations. Species whose seeds are dispersed near the maternal plant (e.g. gravity or wind dispersal) or species whose seeds are deposited in clumps or patches should have more fine-scale genetic structure than species whose seeds are dispersed singly by mobile animals. Furthermore, due to the overlap of seed shadows, species with high adult densities should have less genetic structure than species with lower densities. Allozyme analyses of three tropical tree species belonging to the moist tropical forest of Barro Colorado Island, Republic of Panama, were used to describe variation in the scale and intensity of genetic structure within their populations. The genetic structure of seedlings and immature trees in the low-density, wind-dispersed species (Platypodium elegans) was the coarsest and strongest whereas genetic structure in a population of Swartzia simplex var. ochnacea (high density, bird-dispersed) was both the finest and the weakest. The genetic structure of Alseis blackiana, a high-density, wind-dispersed species was intermediate in both degree and scale. In P. elegans and A. blackiana, which had J shaped size distributions, the significant genetic structure seen in the smaller and intermediate diameter classes disappeared in the largest diameter class. The loss of genetic structure was not observed in S. simplex, a species with a more even size distribution.     

Long-distance seed and pollen dispersal inferred from spatial genetic structure in the very low-density rainforest tree, Baillonella toxisperma Pierre, in Central Africa

We analysed the spatial distribution of genetic diversity to infer gene flow for Baillonella toxisperma Pierre (Moabi), a threatened entomophilous pollinated and animal-dispersed Central African tree, with typically low density (5-7 adults trees/km(2)). Fifteen nuclear and three universal chloroplast microsatellites markers were used to type 247 individuals localized in three contiguous areas with differing past logging intensity. These three areas were within a natural forest block of approximately 2886 km(2) in Gabon. Expected heterozygosity and chloroplast diversity were He(nuc) = 0.570 and H(cp) = 0.761, respectively. F(IS) was only significant in one area (F(IS) = 0.076, P < 0.01) and could be attributed to selfing. For nuclear loci, Bayesian clustering did not detect discrete gene pools within and between the three areas and global differentiation (F(STnuc) = 0.007, P > 0.05) was not significant, suggesting that they are one population. At the level of the whole forest, both nuclear and chloroplast markers revealed a weak correlation between genetic relatedness and spatial distance between individuals: Sp(nuc) = 0.003 and Sp(cp) = 0.015, respectively. The extent of gene flow (σ) was partitioned into global gene flow (σ(g)) from 6.6 to 9.9 km, seed dispersal (σ(s)) from 4.0 to 6.3 km and pollen dispersal (σ(p)) from 9.8 to 10.8 km. These uncommonly high dispersal distances indicate that low-density canopy trees in African rainforests could be connected by extensive gene flow, although, given the current threats facing many seed disperser species in Central Africa, this may no longer be the case.     

Effective size of density‐dependent populations in fluctuating environments

Reliable estimates of effective population size are of central importance in population genetics and evolutionary biology. For populations that fluctuate in size, harmonic mean population size is commonly used as a proxy for (multi‐) generational effective size. This assumes no effects of density dependence on the ratio between effective and actual population size, which limits its potential application. Here, we introduce density dependence on vital rates in a demographic model of variance effective size. We derive an expression for the ratio in a density‐regulated population in a fluctuating environment. We show by simulations that yearly genetic drift is accurately predicted by our model, and not proportional to as assumed by the harmonic mean model, where N is the total population size of mature individuals. We find a negative relationship between and N. For a given N, the ratio depends on variance in reproductive success and the degree of resource limitation acting on the population growth rate. Finally, our model indicate that environmental stochasticity may affect not only through fluctuations in N, but also for a given N at a given time. Our results show that estimates of effective population size must include effects of density dependence and environmental stochasticity.     

Long‐distance dispersal and genetic structure of natural populations: an assessment of the inverse isolation hypothesis in peat mosses

It is well accepted that the shape of the dispersal kernel, especially its tail, has a substantial effect on the genetic structure of species. Theory predicts that dispersal by fat‐tailed kernels reshuffles genetic material, and thus, preserves genetic diversity during colonization. Moreover, if efficient long‐distance dispersal is coupled with random colonization, an inverse isolation effect is predicted to develop in which increasing genetic diversity per colonizer is expected with increasing distance from a genetically variable source. By contrast, increasing isolation leads to decreasing genetic diversity when dispersal is via thin‐tailed kernels. Here, we use a well‐established model group for dispersal biology (peat mosses: genus Sphagnum) with a fat‐tailed dispersal kernel, and the natural laboratory of the Stockholm archipelago to study the validity of the inverse isolation hypothesis in spore‐dispersed plants in island colonization. Population genetic structure of three species (Sphagnum fallax, Sphagnum fimbriatum and Sphagnum palustre) with contrasting life histories and ploidy levels were investigated on a set of islands using microsatellites. Our data show (, amova , IBD) that dispersal of the two most abundant species can be well approximated by a random colonization model. We find that genetic diversity per colonizer on islands increases with distance from the mainland for S. fallax and S. fimbriatum. By contrast, S. palustre deviates from this pattern, owing to its restricted distribution in the region, affecting its source pool strength. Therefore, the inverse isolation effect appears to hold in natural populations of peat mosses and, likely, in other organisms with small diaspores.     

The effect of dispersal ability in winter and summer stoneflies on their genetic differentiation

Abstract.  1. Plecopteran species disperse less than most other aquatic insects. Within stoneflies, members of different families vary in the degree of wing morphology and season of adult emergence.
2. Dispersal limitations were tested to determine if there were increased differences among the nearby, Chagrin and Grand River populations in north-eastern Ohio, by comparing genetic variation within the 16s rRNA region of mitochondrial DNA in two stoneflies. Allocapnia recta emerges in winter and often has rudimentary wings, and Leuctra tenuis emerges in summer with fully developed wings.
3. There was significant genetic variability between the samples of A. recta from two adjacent rivers (FST = 0.20), but not between samples of L. tenuis (FST = 0.07).
4. Distinct clades in A. recta were found to occur within the minimum spanning tree specific to the Chagrin River, which contributed to a significant difference in gene diversity between the two rivers. Haplotypes in L. tenuis appeared randomly distributed between the two rivers; however, nucleotide diversity was significantly less in samples from the Grand River.
5. Shared haplotypes of both species illustrate the inter-connectedness of the Chagrin and Grand River populations, and the lower genetic variability of L. tenuis between the two rivers is indicative of its greater dispersal capability.