Genetic variation of fish parasite populations in historically connected habitats: undetected habitat fragmentation effect on populations of the nematode Procamallanus fulvidraconis in the catfish Pelteobagrus fulvidraco

Habitat fragmentation may have some significant effects on population genetic structure because geographic distance and physical barriers may impede gene flow between populations. In this study, we investigated whether recent habitat fragmentation affected genetic structure and diversity of populations of the nematode Procamallanus fulvidraconis in the yellowhead catfish, Pelteobagrus fulvidraco. The nematode was collected from 12 localities in 7 floodplain lakes of the Yangtze River. Using 11 intersimple sequence repeat markers, analysis of molecular variance showed that genetic diversity occurred mainly within populations (70.26%). Expected heterozygosity (He) of P. fulvidraconis was barely different between connected (0.2105) and unconnected lakes (0.2083). Population subdivision (Fst) between connected lakes (0.2177) was higher than in unconnected lakes (0.1676). However, the connected and unconnected lakes did not cluster into 2 clades. A Mantel test revealed significant positive correlation between genetic and geographic distances (R = 0.5335, P < 0.01). These results suggest that habitat fragmentation did not cause genetic differentiation among populations or a reduction of diversity in isolated populations of P. fulvidraconis. At least 2 factors may increase the dispersal range of the nematode, i.e., flash flooding in summer and other species of fish that may serve as the definitive hosts. Moreover, lake fragmentation is probably a recent process; population size of the nematode in these lakes is large enough to maintain population structure.     

Population genetic structure of Vitex negundo (Verbenaceae) in Three-Gorge Area of the Yangtze River: The riverine barrier to seed dispersal in plants

Previous studies have demonstrated that large rivers can influence inter- and intra-specific gene flow for many animals. The effects of large rivers on the genetics of plant populations have focused on either hydrochoric impacts of water current on gene flow or genetic differentiation among populations from different watersheds. Few studies have explicitly tested the barrier effects on plant gene flow across banks of large rivers, especially their relative effects on pollen and seed dispersals. The Yangtze River (Changjiang River), one of the major rivers of the world, provides an excellent model to evaluate the impacts of rivers on gene flow in plants. Using RAPD (random amplified polymorphic DNA) and cpDNA (chloroplast DNA) markers, we investigated the genetic structure of 10 populations of Vitex negundo in two regions of Three-Gorge Area along the Yangtze River. Each region contained two populations on the north bank, two on the south bank and one island population along the river. The analyses indicated low RAPD between banks, and similar or a little higher differentiation between populations within the same bank. In contrast, a large proportion of chloroplast polymorphism was ascribed to among-bank variation but much lower cpDNA differentiation was among populations within the same bank. These results indicate that the Yangtze River represents a general barrier to the dispersal of seeds but not to the movement of pollen in V. negundo. The cpDNA genetic distances or differentiations between the island populations and those on either bank of the river are intermediate to those between the banks across the river, implying that the islands in the Yangtze River may serve as a stepping-stone for seed dispersal. Our results suggest that large rivers may serve as a general barrier, not only for the movement of animals, but also for the dispersal of plants, which should be of great significance for the conservation of biodiversity around the rivers.     

Population genetics and fitness in fragmented populations of the dioecious and endangered <Emphasis Type="Italic">Silene otites</Emphasis> (Caryophyllaceae)

Population fragmentation is often correlated with loss of genetic diversity and reduced fitness. Obligate out-crossing (dioecy) is expected to enhance genetic diversity, reduce genetic differentiation, and avoid inbreeding depression through frequent gene flow. However, in highly fragmented populations dioecy has only diminishing effects upon genetic structure as pollination limitations (e.g. flight distance of pollinators) most often restrict inter-population gene flow in insect pollinated species. In fragmented dry grasslands in northeastern Germany, we analysed genetic structure, fitness, and habitat quality of the endangered dioecious Silene otites (Caryophyllaceae). Using AFLP markers, a high level of differentiation among ten populations was found (F _st = 0.36), while the intra-population genetic diversities (H _E = 0.165–0.240) were similar as compared to hermaphroditic species. There was neither a correlation between geographic and genetic distance nor between genetic diversity and population size, which indicates reduced gene flow among populations and random genetic drift. Plant size was positively correlated with genetic diversity. Seed set and number of juveniles were positively related to population size. Higher total coverage resulted in reduced plant fitness, and the number of juveniles was negatively correlated to cryptogam cover. Additionally, we found a sex ratio bias towards more male plants in larger populations. Overall, our results indicate that on a regional geographic scale dioecy does not necessarily prevent genetic erosion in the case of habitat fragmentation, especially in the absence of long distance seed and pollen dispersal capacity.     

Patterns of range-wide genetic variation in six North American bumble bee (Apidae: Bombus) species

The increasing evidence for population declines in bumble bee (Bombus) species worldwide has accelerated research efforts to explain losses in these important pollinators. In North America, a number of once widespread Bombus species have suffered serious reductions in range and abundance, although other species remain healthy. To examine whether declining and stable species exhibit different levels of genetic diversity or population fragmentation, we used microsatellite markers to genotype populations sampled across the geographic distributions of two declining (Bombus occidentalis and Bombus pensylvanicus) and four stable (Bombus bifarius; Bombus vosnesenskii; Bombus impatiens and Bombus bimaculatus) Bombus species. Populations of declining species generally have reduced levels of genetic diversity throughout their range compared to codistributed stable species. Genetic diversity can be affected by overall range size and degree of isolation of local populations, potentially confounding comparisons among species in some cases. We find no evidence for consistent differences in gene flow among stable and declining species, with all species exhibiting weak genetic differentiation over large distances (e.g. >1000 km). Populations on islands and at high elevations experience relatively strong genetic drift, suggesting that some conditions lead to genetic isolation in otherwise weakly differentiated species. B. occidentalis and B. bifarius exhibit stronger genetic differentiation than the other species, indicating greater phylogeographic structure consistent with their broader geographic distributions across topographically complex regions of western North America. Screening genetic diversity in North American Bombus should prove useful for identifying species that warrant monitoring, and developing management strategies that promote high levels of gene flow will be a key component in efforts to maintain healthy populations.     

Diversity and structure of fragmented populations of a threatened endemic cyprinodontid (Aphanius sophiae) inferred from genetics and otolith morphology: Implications for conservation and management

The assessment of population structure and genetic diversity is crucial for the management and conservation of threatened species. Natural and artificial barriers to dispersal (i.e., gene flow) increase populations’ differentiation and isolation by reducing genetic exchange and diversity. Freshwater ecosystems are highly fragmented because of human activities. Threatened species with small population sizes are more sensitive to habitat fragmentation effects. Here, we investigate the genetic population structure and gene flow among seven populations of Aphanius sophiae in the Kor Basin by using sequences of the complete Cyt b gene and otolith morphometry. The Cyt b gene showed low level of genetic variation, only 4.12% of the identified sites were variable, and 2.42% were parsimony informative. Overall, haplotype diversity was low to moderate and nucleotide diversity was low to extremely low. Fish populations exhibited high levels of genetic differentiation, suggesting limited gene flow among them. These differences were obtained not only among geographically distant populations, but also among neighboring localities. Genetic population structure was supported by the AMOVA analysis and by the haplotype network (only one of 21 haplotypes were shared by two localities). Otolith morphometric analysis was in agreement with genetic results, the two most distant and isolated populations were clearly separated, and genetically close populations showed less differences in morphometry. A significant pattern of isolation by distance was also detected among A. sophiae populations, with genetic distance more correlated with hydrological distance than with geographic distance. Results suggested that limited gene flow due to habitat fragmentation is an important factor contributing to genetic structuring and to the loss of genetic variation of A. sophiae populations. Aphanius sophiae population structure seems to be the result of habitat fragmentation and water pollution, but other factors such as introduced species should be considered. Given the high degree of genetic structuring, the definition of conservation groups is of particular importance for A. sophiae, which should be considered endangered according to the IUCN criteria. Conservation plans must recognize the genetic independence of populations and manage separately preventing the loss of locally adapted genotypes.     

Range‐wide population genetic structure of the Caribbean sea fan coral,Gorgonia ventalina

The population structure of benthic marine organisms is of central relevance to the conservation and management of these often threatened species, as well as to the accurate understanding of their ecological and evolutionary dynamics. A growing body of evidence suggests that marine populations can be structured over short distances despite theoretically high dispersal potential. Yet the proposed mechanisms governing this structure vary, and existing empirical population genetic evidence is of insufficient taxonomic and geographic scope to allow for strong general inferences. Here, we describe the range‐wide population genetic structure of an ecologically important Caribbean octocoral, Gorgonia ventalina. Genetic differentiation was positively correlated with geographic distance and negatively correlated with oceanographically modelled dispersal probability throughout the range. Although we observed admixture across hundreds of kilometres, estimated dispersal was low, and populations were differentiated across distances <2 km. These results suggest that populations of G. ventalina may be evolutionarily coupled via gene flow but are largely demographically independent. Observed patterns of differentiation corroborate biogeographic breaks found in other taxa (e.g. an east/west divide near Puerto Rico), and also identify population divides not discussed in previous studies (e.g. the Yucatan Channel). High genotypic diversity and absence of clonemates indicate that sex is the primary reproductive mode for G. ventalina. A comparative analysis of the population structure of G. ventalina and its dinoflagellate symbiont, Symbiodinium, indicates that the dispersal of these symbiotic partners is not coupled, and symbiont transmission occurs horizontally.     

Weak genetic structuring indicates ongoing gene flow across White-ruffed Manakin (<Emphasis Type="Italic">Corapipo altera</Emphasis>) populations in a highly fragmented Costa Rica landscape

We explored the effects of recent forest fragmentation on fine-scale patterns of population structuring and genetic diversity in populations of White-ruffed Manakins (Corapipo altera) inhabiting premontane forest fragments of varying size in southwestern Costa Rica. Habitat fragmentation is a major conservation concern for avian populations worldwide, but studies of the genetic effects of fragmentation on Neotropical birds are limited. We sampled 159 manakins from nine forest fragments of varying size within an 18 km radius, and genotyped these birds at 13 microsatellite loci. Bayesian clustering methods revealed that birds from all fragments comprised a single genetic population, and an MCMC approach showed that the fragments were likely to be at migration-drift equilibrium. F-statistics showed only modest levels of differentiation between forest fragments. We calculated allelic diversity indices for each fragment but found no correlation between genetic diversity and fragment size. These results suggest that manakins may retain substantial connectivity via inter-fragment dispersal despite habitat fragmentation.     

Absence of isolation by distance patterns at the regional scale in the fungal plant pathogen Leptosphaeria maculans

Outcomes of host-pathogen coevolution are influenced by migration rates of the interacting species. Reduced gene flow with increasing spatial distance between populations leads to spatial genetic structure, as predicted by the isolation by distance (IBD) model. In wind-dispersed plant-pathogenic fungi, a significant spatial genetic structure is theoretically expected if local spore dispersal is more frequent than long-distance dispersal, but this remains to be documented by empirical data. For 29 populations of the oilseed rape fungus Leptosphaeria maculans sampled from two French regions, genetic structure was determined using eight minisatellite markers. Gene diversity (H = 0.62-0.70) and haplotypic richness (R = 0.96-1) were high in all populations. No linkage disequilibrium was detected between loci, suggesting the prevalence of panmictic sexual reproduction. Analysis of molecular variance showed that > 97% of genetic diversity was observed within populations. Genetic differentiation was low among populations (F(st) < 0.05). Although direct methods previously revealed short-distance dispersal for L. maculans, our findings of no correlation between genetic and geographic distances among populations illustrate that the IBD model does not account for dispersal of the fungus at the spatial scale we examined. These results indicate high gene flow among French populations of L. maculans, suggesting high dispersal rates and/or large effective population sizes, two characteristics giving the pathogen high evolutionary potential against the deployment of resistant oilseed rape cultivars.     

Spatial genetic structuring in a vagile species, the European wood mouse

We examined the genetic structure of natural populations of the European wood mouse Apodemus sylvaticus at the microgeographic (<3 km) and macrogeographic (>30 km) scales. Ecological and behavioural studies indicate that this species exhibits considerable dispersal relative to its home-range size. Thus, there is potential for high gene flow over larger geographic areas. As levels of population genetic structure are related to gene flow, we hypothesized that population genetic structuring at the microgeographic level should be negligible, increasing only with geographic distance. To test this, four sites were sampled within a microgeographic scale with two additional samples at the macrogeographic level. Individuals ( n =415) were screened and analysed for seven polymorphic microsatellite loci. Contrary to our hypothesis, significant levels of population structuring were detected at both scales. Comparing genetic differentiation with geographic distance suggests increasing genetic isolation with distance. However, this distance effect was non-significant being confounded by surprisingly high levels of differentiation among microgeographic samples. We attribute this pattern of genetic differentiation to the effect of habitat fragmentation, splitting large populations into components with small effective population sizes resulting in enhanced genetic drift. Our results indicate that it is incorrect to assume genetic homogeneity among populations even where there is no evidence of physical barriers and dispersal can occur freely. In the case of A. sylvaticus , it is not clear whether dispersal does not occur across habitat barriers or behavioural dispersal occurs without consequent gene flow.     

Can small wildlife conservancies maintain genetically stable populations of large mammals? Evidence for increased genetic drift in geographically restricted populations of Cape buffalo in East Africa

The Cape buffalo (Syncerus caffer caffer) is one of the dominant and most widespread herbivores in sub‐Saharan Africa. High levels of genetic diversity and exceptionally low levels of population differentiation have been found in the Cape buffalo compared to other African savannah ungulates. Patterns of genetic variation reveal large effective population sizes and indicate that Cape buffalos have historically been interbreeding across considerable distances. Throughout much of its range, the Cape buffalo is now largely confined to protected areas due to habitat fragmentation and increasing human population densities, possibly resulting in genetic erosion. Ten buffalo populations in Kenya and Uganda were examined using seventeen microsatellite markers to assess the regional genetic structure and the effect of protected area size on measures of genetic diversity. Two nested levels of genetic structure were identified: a higher level partitioning populations into two clusters separated by the Victoria Nile and a lower level distinguishing seven genetic clusters, each defined by one or two study populations. Although relatively small geographic distances separate most of the study populations, the level of genetic differentiation found here is comparable to that among pan‐African populations. Overall, correlations between conservancy area and indices of genetic diversity suggest buffalo populations inhabiting small parks are showing signs of genetic erosion, stressing the need for more active management of such populations. Our findings raise concerns about the future of other African savannah ungulates with lower population sizes and inferior dispersal capabilities compared with the buffalo.     

Nuclear genetic variation of <Emphasis Type="Italic">Rosa odorata</Emphasis> var. <Emphasis Type="Italic">gigantea</Emphasis> (Rosaceae): population structure and conservation implications

Rosa odorata var. gigantea is one of the most important ancestors of modern roses, which owns many merit traits including large flower, early flowering, and tea scent. Due to habitat loss and fragmentation, it has been listed as a rare and endangered species in China. In this study, a total of 424 accessions from 27 locations across its major distribution range were sampled. Its genetic diversity and population structure were assessed using a combination of seven nuclear microsatellite markers and one single-copy nuclear gene. Moderate to high within-population genetic diversity and moderate differentiation among populations were revealed despite its narrow distribution. The sampled 27 populations were resolved into two genetic clusters with limited contemporary and historical gene flows. The Red River Fault Zone was inferred to be a physical or geographical barrier to gene flow between these two genetic clusters. Genetic distances were significantly associated with geographic distances, indicating the isolation-by-distance model. Our ecological niche modeling indicated that R. odorata var. gigantea had high current potential areas in the central Yunnan province and substantial losses of high potential distribution areas in the western Yunnan in the future. Two detected clusters showed significant genetic differentiation and represented two separate evolutionary lineages, which should be recognized as two evolutionary significant units (ESUs) for conservation concerns. These results could be applied for the decision-making and conservation planning for this important species.     

Genetic diversity in fragmented populations of the critically endangered spider orchid Caladenia huegelii: implications for conservation

The Orchidaceae is characterised by a diverse range of life histories, reproductive strategies and geographic distribution, reflected in a variety of patterns in the population genetic structure of different species. In this study, the genetic diversity and structure was assessed within and among remnant populations of the critically endangered sexually deceptive orchid, Caladenia huegelii. This species has experienced severe recent habitat loss in a landscape marked by ancient patterns of population fragmentation within the Southwest Australian Floristic Region, a global biodiversity hotspot. Using seven polymorphic microsatellite loci, high levels of within-population diversity (mean alleles/locus = 6.73; mean H _E = 0.690), weak genetic structuring among 13 remnant populations (F _ST = 0.047) and a consistent deficit of heterozygotes from Hardy–Weinberg expectation were found across all populations (mean F _IS = 0.22). Positive inbreeding coefficients are most likely due to Wahlund effects and/or inbreeding effects from highly correlated paternity and typically low fruit set. Indirect estimates of gene flow (Nm = 5.09 using F _ST; Nm = 3.12 using the private alleles method) among populations reflects a historical capacity for gene flow through long distance pollen dispersal by sexually deceived wasp pollinators and/or long range dispersal of dust-like orchid seed. However, current levels of gene flow may be impacted by habitat destruction, fragmentation and reduced population size. A genetically divergent population was identified, which should be a high priority for conservation managers. Very weak genetic differentiation indicates that the movement and mixing of seeds from different populations for reintroduction programs should result in minimal negative genetic effects.     

Genetic diversity and population structure of a cyprinid fish (Ancherythroculter nigrocauda) in a highly fragmented river

In this study, samples of Ancherythroculter nigrocauda, an endemic fish in the upper Yangtze River, were collected above and below dams in the Longxi River, a tributary of the upper Yangtze River, China, to investigate the genetic impacts of dams. The mitochondrial cytochrome b gene (cyt b) and 13 microsatellite (SSR) loci were used to analyze whether dams have resulted in loss of genetic diversity of the two fragmented populations or caused genetic differentiation between them. The results showed that the haplotype diversity (0.488; 0.486), nucleotide diversity (0.084%; 0.082%) and average expected heterozygosity (0.652; 0.676) of the two populations were all at a low level, and recent bottlenecks were detected. However, there was no genetic differentiation detected by the low genetic differentiation index (F_st, cyt b: ?0.1677, p = 0.99707; SSR: 0.00259, p = 0.81427). Besides, 11 pairs of half‐sibling relationship were found between the two populations indicating that there were individual movements and gene flow between them. This could be the larvae moving from upstream to downstream when water spilled over dams in flooding season. Therefore, our analysis showed that the dams have caused a loss of genetic diversity of the populations of A. nigrocauda in the Longxi River, blocked the active upstream movement but allowing passive downstream drift of larvae.     

Endangered species in small habitat patches can possess high genetic diversity: the case of the Tana River red colobus and mangabey

We used mtDNA sequence data from the Tana River red colobus and mangabey to determine how their population genetic structure was influenced by dispersal and habitat fragmentation. The colobus and mangabey are critically endangered primates endemic to gallery forests in eastern Kenya. The forests are a Pliocene–Pleistocene refugium that has recently undergone significant habitat loss and fragmentation due to human activities. We expected both primates to exhibit low levels of genetic diversity due to elevated genetic drift in their small populations, and to show a strong correspondence between genetic and geographic distance due to disruption of gene flow between forests by habitat fragmentation. Additionally, because mangabey females are philopatric, we expected their mtDNA variation to be homogeneous within forest patches but to be heterogeneous between patches. In contrast, colobus have a female-biased dispersal and so we expected their mtDNA variation to be homogeneous within and between forest patches. We found high levels of haplotype and nucleotide diversity as well as high levels of sequence divergence between haplotype groups in both species. The red colobus had significantly higher genetic variation than the mangabey did. Most of the genetic variation in both primates was found within forest fragments. Although both species showed strong inter-forest patch genetic structure we found no correspondence between genetic and geographic distances for the two primates. We attributed the high genetic diversity to recent high effective population size, and high sequence divergence and strong genetic structures to long-term habitat changes in the landscape.     

Population structure and genetic variation in the endangered Giant Kangaroo Rat (<Emphasis Type="Italic">Dipodomys ingens</Emphasis>)

Populations of the endangered giant kangaroo rat, Dipodomys ingens (Heteromyidae), have suffered increasing fragmentation and isolation over the recent past, and the distribution of this unique rodent has become restricted to 3% of its historical range. Such changes in population structure can significantly affect effective population size and dispersal, and ultimately increase the risk of extinction for endangered species. To assess the fine-scale population structure, gene flow, and genetic diversity of remnant populations of Dipodomys ingens, we examined variation at six microsatellite DNA loci in 95 animals from six populations. Genetic subdivision was significant for both the northern and southern part of the kangaroo rat’s range although there was considerable gene flow among southern populations. While regional gene diversity was relatively high for this endangered species, hierarchical F-statistics of northern populations in Fresno and San Benito counties suggested non-random mating and genetic drift within subpopulations. We conclude that effective dispersal, and therefore genetic distances between populations, is better predicted by ecological conditions and topography of the environment than linear geographic distance between populations. Our results are consistent with and complimentary to previous findings based on mtDNA variation of giant kangaroo rats. We suggest that management plans for this endangered rodent focus on protection of suitable habitat, maintenance of connectivity, and enhancement of effective dispersal between populations either through suitable dispersal corridors or translocations.     

Specialization to cold‐water upwellings may facilitate gene flow in seabirds: new evidence from the Peruvian pelican Pelecanus thagus (Pelecaniformes: Pelecanidae)

Recent research has shown that tropical seabirds specialized to feed on cold water upwellings exhibit low population genetic differentiation and high gene flow across large geographic distances. This pattern is opposite to the general pattern of differentiation reported for tropical seabirds, and led us to hypothesize that specialization to cold‐water upwellings facilitates gene flow between colonies. As a test of this hypothesis we characterized population differentiation and gene flow across the range of the Peruvian pelican Pelecanus thagus, an upwelling specialist endemic to the Humboldt Current, using an 838 base pair segment of the mitochondrial control region and seven microsatellite loci. In support of our hypothesis we report genetic panmixia across the geographic range of this species and inferred high gene flow between colonies. The high dispersal propensity of upwelling specialist seabirds (adults and/or juveniles) may reduce loss of genetic diversity during population declines, and increase the ability of these species to colonize new islands.     

Low genetic differentiation between populations of an endemic prairie katydid despite habitat loss and fragmentation

Tallgrass prairie habitats within North America have suffered severe fragmentation and habitat loss as land has been converted for agricultural purposes. Habitat loss and fragmentation can affect gene flow and the genetic structure of insect populations. Neoconocephalus bivocatus is a prairie obligate katydid found only in isolated prairie patches. We compared genetic diversity and population differentiation using AFLP markers in N. bivocatus and N. robustus, a grassland generalist that is not isolated to prairie fragments and occupies a more contiguous range. Similar levels of genetic diversity were present within populations of both species. While population genetic structure was found in both species, there was no relationship between assigned genotypes and sampling localities. This genetic structure may instead be evidence of a past barrier to gene flow that has since been removed. Genetic differentiation within both species was low, with no evidence of a correlation with geographic distance, indicating neither species is dispersal limited at these distances. We see no significant reduction in genetic diversity or genetic differentiation within N. bivocatus when compared to N. robustus. We therefore conclude that while N. bivocatus utilizes a fragmented landscape, long-distance dispersal likely maintains gene flow between isolated prairie patches.     

Genetic diversity,differentiation and conservation in <Emphasis Type="Italic">Araucaria bidwillii</Emphasis>(Araucariaceae), Australia's Bunya pine

Habitat fragmentation has resulted in many species becoming geographically restricted, as dispersal among subsequent isolates becomes compromised. This study investigated the effects of historical fragmentation on the genetic diversity and differentiation of Australia's Bunya Pine (Araucaria bidwillii) using random amplified DNA (RAPD) markers. High diversity characterises all Bunya populations sampled, regardless of population size or degree of isolation, which may be either due to similar effective population size among populations, or the lagging effects of the detection of contemporary genetic signal in long-lived conifer species. Large genetic differentiation characterises the northern and southern populations, although all sampled populations are significantly differentiated from each other. The northern population, at Mt Lewis, is responsible for the majority of variation detected among populations, and as such represents a significant genetic reservoir. The conservation of the genotypes of the Mt Lewis population may be imperative for the future of the species, given predicted models of accelerated climate change over the coming decades.     

Population fragmentation leads to isolation by distance but not genetic impoverishment in the philopatric Lesser Kestrel: a comparison with the widespread and sympatric Eurasian Kestrel

Population fragmentation is a widespread phenomenon usually associated with human activity. As a result of habitat transformation, the philopatric and steppe-specialist Lesser Kestrel Falco naumanni underwent a severe population decline during the last century that increased population fragmentation throughout its breeding range. In contrast, the ubiquitous Eurasian Kestrel Falco tinnunculus did not suffer such adverse effects, its breeding range still remaining rather continuous. Using microsatellites, we tested the effects of population fragmentation on large-scale spatial patterns of genetic differentiation and diversity by comparing these two sympatric and phylogenetically related species. Our results suggest that habitat fragmentation has increased genetic differentiation between Lesser Kestrel populations, following an isolation-by-distance pattern, while the population of Eurasian Kestrels is panmictic. Contrary to expectations, we did not detect significant evidence of reduced genetic variation or increased inbreeding in Lesser Kestrels. Although this study reports genetic differentiation in a species that has potential for long-distance dispersal but philopatry-limited gene flow, large enough effective population sizes and migration may have been sufficient to mitigate genetic depauperation. A serious reduction of genetic diversity in Lesser Kestrels would, therefore, only be expected after severe population bottlenecks following extreme geographic isolation.     

Genetic diversity in Crambe maritima along the English Channel: the role of ocean currents in determining population structure

We utilised genetic markers (ISSR's) to investigate population structuring in Crambe maritima , a coastal perennial found in isolated populations on either side of the English Channel. Despite the expectation that smaller populations would contain lower levels of genetic diversity, we found no correlation with total population size or the number of flowering plants and genetic diversity. Although populations were genetically differentiated from each other, isolation by distance was not apparent in the whole data set or within the UK samples.
Despite being sampled from a wide geographic range, the majority of diversity (71%) was contained within populations, with no unique genotype, or even allele, identifying any population. When genetic distances were plotted using MDS techniques, samples from each population had a tendency to cluster, but the spread of points was wide indicating high levels of gene flow. High levels of gene flow, through the dispersal of seeds, were verified by assignment testing, which showed that 8.7% of individuals were assigned to a population other than the one they were collected from. The pattern of genetic variation can be explained by examining the direction of currents in the English Channel and Bay of Biscay. Gene flow, via seed dispersal, is possible between UK and French populations on either side of the English Channel. In contrast, French populations on the Bay of Biscay coast are effectively isolated by the direction of currents and consequently show a greater degree of genetic differentiation.