Phylogeography, intraspecific structure and sex-biased dispersal of Dall's porpoise, Phocoenoides dalli, revealed by mitochondrial and microsatellite DNA analyses

Mitochondrial DNA (mtDNA) control-region sequences and microsatellite loci length polymorphisms were used to estimate phylogeographical patterns (historical patterns underlying contemporary distribution), intraspecific population structure and gender-biased dispersal of Phocoenoides dalli dalli across its entire range. One-hundred and thirteen animals from several geographical strata were sequenced over 379 bp of mtDNA, resulting in 58 mtDNA haplotypes. Analysis using F(ST) values (based on haplotype frequencies) and phi(ST) values (based on frequencies and genetic distances between haplotypes) yielded statistically significant separation (bootstrap values P < 0.05) among most of the stocks currently used for management purposes. A minimum spanning network of haplotypes showed two very distinctive clusters, differentially occupied by western and eastern populations, with some common widespread haplotypes. This suggests some degree of phyletic radiation from west to east, superimposed on gene flow. Highly male-biased migration was detected for several population comparisons. Nuclear microsatellite DNA markers (119 individuals and six loci) provided additional support for population subdivision and gender-biased dispersal detected in the mtDNA sequences. Analysis using F(ST) values (based on allelic frequencies) yielded statistically significant separation between some, but not all, populations distinguished by mtDNA analysis. R(ST) values (based on frequencies of and genetic distance between alleles) showed no statistically significant subdivision. Again, highly male-biased dispersal was detected for all population comparisons, suggesting, together with morphological and reproductive data, the existence of sexual selection. Our molecular results argue for nine distinct dalli-type populations that should be treated as separate units for management purposes.     

Sex-linked and autosomal microsatellites provide new insights into island populations of the tammar wallaby

The emerging availability of microsatellite markers from mammalian sex chromosomes provides opportunities to investigate both male- and female-mediated gene flow in wild populations, identifying patterns not apparent from the analysis of autosomal markers alone. Tammar wallabies (Macropus eugenii), once spread over the southern mainland, have been isolated on several islands off the Western Australian and South Australian coastlines for between 10 000 and 13 000 years. Here, we combine analyses of autosomal, Y-linked and X-linked microsatellite loci to investigate genetic variation in populations of this species on two islands (Kangaroo Island, South Australia and Garden Island, Western Australia). All measures of diversity were higher for the larger Kangaroo Island population, in which genetic variation was lowest at Y-linked markers and highest at autosomal markers (θ=3.291, 1.208 and 0.627 for autosomal, X-linked and Y-linked data, respectively). Greater relatedness among females than males provides evidence for male-biased dispersal in this population, while sex-linked markers identified genetic lineages not apparent from autosomal data alone. Overall genetic diversity in the Garden Island population was low, especially on the Y chromosome where most males shared a common haplotype, and we observed high levels of inbreeding and relatedness among individuals. Our findings highlight the utility of this approach for management actions, such as the selection of animals for translocation or captive breeding, and the ecological insights that may be gained by combining analyses of microsatellite markers on sex chromosomes with those derived from autosomes.     

The impact of mating systems and dispersal on fine‐scale genetic structure at maternally,paternally and biparentally inherited markers

For decades, studies have focused on how dispersal and mating systems influence genetic structure across populations or social groups. However, we still lack a thorough understanding of how these processes and their interaction shape spatial genetic patterns over a finer scale (tens—hundreds of metres). Using uniparentally inherited markers may help answer these questions, yet their potential has not been fully explored. Here, we use individual‐level simulations to investigate the effects of dispersal and mating system on fine‐scale genetic structure at autosomal, mitochondrial and Y chromosome markers. Using genetic spatial autocorrelation analysis, we found that dispersal was the major driver of fine‐scale genetic structure across maternally, paternally and biparentally inherited markers. However, when dispersal was restricted (mean distance = 100 m), variation in mating behaviour created strong differences in the comparative level of structure detected at maternally and paternally inherited markers. Promiscuity reduced spatial genetic structure at Y chromosome loci (relative to monogamy), whereas structure increased under polygyny. In contrast, mitochondrial and autosomal markers were robust to differences in the specific mating system, although genetic structure increased across all markers when reproductive success was skewed towards fewer individuals. Comparing males and females at Y chromosome vs. mitochondrial markers, respectively, revealed that some mating systems can generate similar patterns to those expected under sex‐biased dispersal. This demonstrates the need for caution when inferring ecological and behavioural processes from genetic results. Comparing patterns between the sexes, across a range of marker types, may help us tease apart the processes shaping fine‐scale genetic structure.     

Genetic evidence for female-biased dispersal and gene flow in a polygynous primate

Many models of sex-biased dispersal predict that the direction of sex-bias depends upon a species' mating system. In agreement with this, almost all polygynous mammals show male-biased dispersal whereas largely monogamous birds show female-biased dispersal (FBD). The hamadryas baboon (Papio hamadryas hamadryas) is polygynous and so dispersal is predicted to be male biased, as is found in all other baboon subspecies, but there are conflicting field data showing both female and male dispersal. Using 19 autosomal genetic markers genotyped in baboons from four Saudi Arabian populations, we found strong evidence for FBD in post-dispersal adults but not, as expected, in pre-dispersal infants and young juveniles, when we compared male and female: population structure (F(st)), inbreeding (F(is)), relatedness (r), and the mean assignment index (mAIc). Furthermore, we found evidence for female-biased gene flow as population genetic structure (F(st)), was about four times higher for the paternally inherited Y, than for either autosomal markers or for maternally inherited mtDNA. These results contradict the direction of sex-bias predicted by the mating system and show that FBD has evolved recently from an ancestral state of male-biased dispersal. We suggest that the cost-benefit balance of dispersal to males and females is tightly linked to the unique hierarchical social structure of hamadryas baboons and that dispersal and social organization have coevolved.     

Heavily male-biased long-distance dispersal of orang-utans (genus: Pongo), as revealed by Y-chromosomal and mitochondrial genetic markers

Mating systems are thought to be an important determinant of dispersal strategies in most animals, including the great apes. As the most basal taxon of all great apes, orang-utans can provide information about the evolution of mating systems and their consequences for population structure in this Family. To assess the sex-specific population structure in orang-utans, we used a combination of paternally transmitted Y-chromosomal genetic markers and maternally transmitted mitochondrial DNA sequences. Markers transmitted through the more philopatric sex are expected to show stronger differentiation among populations than the ones transmitted through the dispersing sex. We studied these patterns using 70 genetic samples from wild orang-utans from seven Bornean and two Sumatran populations. We found pronounced population structure in haplotype networks of mitochondrial sequence data, but much less so for male-specific markers. Similarly, mitochondrial genetic differentiation was twice as high among populations compared to Y-chromosomal variation. We also found that genetic distance increased faster with geographic distance for mitochondrial than for Y-linked markers, leading to estimates of male dispersal distances that are several-fold higher than those of females. These findings provide evidence for strong male-biased dispersal in orang-utans. The transition to predominantly female-biased dispersal in the great ape lineage appears to be correlated with life in multimale groups and may reflect the associated fitness benefits of reliable male coalitions with relatives or known partners, a feature that is absent in orang-utans.     

Genetic evidence for male-biased dispersal in the three-spined stickleback (Gasterosteus aculeatus)

Sex-biased dispersal is capable of generating population structure in nonisolated populations and may affect adaptation processes when selective conditions differ among populations. Intrasexual competition for local resources and/or mating opportunities predicts a male-biased dispersal in polygynous species and a female bias in monogamous species. The patterns of sex-biased dispersal in birds and mammals are well explained by their respective mating systems, but the picture emerging from fish studies is still mixed. Using neutral genetic markers, we investigated whether there is any evidence for sex-biased dispersal among Baltic Sea populations of the three-spined stickleback ( Gasterosteus aculeatus ). The null hypothesis of non sex-biased dispersal was rejected in favour of male-biased dispersal in this species. As the three-spined stickleback has a polygynous mating system, the observed male bias in dispersal is consistent with the hypothesis that local mate competition might drive the observed pattern. Although more research both on the proximate and ultimate causes behind the observed pattern is needed, our results serve as a first step towards understanding patterns of sex-biased dispersal in this species.     

Occasional recombination of a selfish X‐chromosome may permit its persistence at high frequencies in the wild

The sex‐ratio X‐chromosome (SR) is a selfish chromosome that promotes its own transmission to the next generation by destroying Y‐bearing sperm in the testes of carrier males. In some natural populations of the fly Drosophila neotestacea, up to 30% of the X‐chromosomes are SR chromosomes. To investigate the molecular evolutionary history and consequences of SR, we sequenced SR and standard (ST) males at 11 X‐linked loci that span the ST X‐chromosome and at seven arbitrarily chosen autosomal loci from a sample of D. neotestacea males from throughout the species range. We found that the evolutionary relationship between ST and SR varies among individual markers, but genetic differentiation between SR and ST is chromosome‐wide and likely due to large chromosomal inversions that suppress recombination. However, SR does not consist of a single multilocus haplotype: we find evidence for gene flow between ST and SR at every locus assayed. Furthermore, we do not find long‐distance linkage disequilibrium within SR chromosomes, suggesting that recombination occurs in females homozygous for SR. Finally, polymorphism on SR is reduced compared to that on ST, and loci displaying signatures of selection on ST do not show similar patterns on SR. Thus, even if selection is less effective on SR, our results suggest that gene flow with ST and recombination between SR chromosomes may prevent the accumulation of deleterious mutations and allow its long‐term persistence at relatively high frequencies.     

Genetic evidence for dispersal by both sexes in the Central American Squirrel Monkey, Saimiri oerstedii citrinellus

Sex-biased dispersal (SBD) is common in many vertebrates, including primates. However, dispersal patterns in New World primates may vary among closely related taxa or populations in different local environments. Here, we test for SBD in an endangered New World primate, the Central American Squirrel Monkey (Saimiri oerstedii citrinellus). Previous studies of behavioral ecology suggest predominantly female dispersal in S.o. oerstedii in the Southern Pacific region of Costa Rica. However, our genetic data do not support strongly female-biased dispersal in S.o. citrinellus in the Central Pacific region. Our tests for SBD using microsatellite data including comparisons of isolation-by-distance, AI(c) , and F(ST) values between males and females were not significant. Also, we found greater population genetic structure in mitochondrial markers than in microsatellite markers, indicative of predominantly male dispersal. We conclude that both sexes disperse in S.o. citrinellus, and that males probably disperse over longer distances. We discuss how spatial and temporal variation among local populations should be taken into account when studying dispersal patterns and especially sex bias.     

Evidence for female-biased dispersal in the protandrous hermaphroditic Asian Seabass, Lates calcarifer

Movement of individuals influences individual reproductive success, fitness, genetic diversity and relationships among individuals within populations and gene exchange among populations. Competition between males or females for mating opportunities and/or local resources predicts a female bias in taxa with monogamous mating systems and a male-biased dispersal in polygynous species. In birds and mammals, the patterns of dispersal between sexes are well explored, while dispersal patterns in protandrous hermaphroditic fish species have not been studied. We collected 549 adult individuals of Asian seabass (Lates calcarifer) from four locations in the South China Sea. To assess the difference in patterns of dispersal between sexes, we genotyped all individuals with 18 microsatellites. Significant genetic differentiation was detected among and within sampling locations. The parameters of population structure (F(ST)), relatedness (r) and the mean assignment index (mAIC), in combination with data on tagging-recapture, supplied strong evidences for female-biased dispersal in the Asian seabass. This result contradicts our initial hypothesis of no sex difference in dispersal. We suggest that inbreeding avoidance of females, female mate choice under the condition of low mate competition among males, and male resource competition create a female-biased dispersal. The bigger body size of females may be a cause of the female-biased movement. Studies of dispersal using data from DNA markers and tagging-recapture in hermaphroditic fish species could enhance our understanding of patterns of dispersal in fish.     

Reduced introgression of the Y chromosome between subspecies of the European rabbit (Oryctolagus cuniculus) in the Iberian Peninsula

The role of the Y chromosome in speciation is unclear. Hybrid zones provide natural arenas for studying speciation, as differential introgression of markers may reveal selection acting against incompatibilities. Two subspecies of the European rabbit (Oryctolagus cuniculus) form a hybrid zone in the Iberian Peninsula. Previous work on mitochondrial DNA (mtDNA), Y- and X-linked loci revealed the existence of two divergent lineages in the rabbit genome and that these lineages are largely subspecies-specific for mtDNA and two X-linked loci. Here we investigated the geographic distribution of the two Y chromosome lineages by genotyping two diagnostic single nucleotide polymorphisms in a sample of 353 male rabbits representing both subspecies, and found that Y chromosome lineages are also largely subspecies-specific. We then sequenced three autosomal loci and discovered considerable variation in levels of differentiation at these loci. Finally, we compared estimates of population differentiation between rabbit subspecies at 26 markers and found a surprising bimodal distribution of F(ST)values. The vast majority of loci showed little or no differentiation between rabbit subspecies while a few loci, including the SRY gene, showed little or no introgression across the hybrid zone. Estimates of population differentiation for the Y chromosome were surprisingly high given that there is male-biased dispersal in rabbits. Taken together, these data indicate that there is a clear dichotomy in the rabbit genome and that some loci remain highly differentiated despite extensive gene flow following secondary contact.     

Population genetic structure and long-distance dispersal among seabird populations: implications for colony persistence

Dramatic local population decline brought about by anthropogenic-driven change is an increasingly common threat to biodiversity. Seabird life history traits make them particularly vulnerable to such change; therefore, understanding population connectivity and dispersal dynamics is vital for successful management. Our study used a 357-base pair mitochondrial control region locus sequenced for 103 individuals and 18 nuclear microsatellite loci genotyped for 245 individuals to investigate population structure in the Atlantic and Pacific populations of the pelagic seabird, Leach's storm-petrel Oceanodroma leucorhoa leucorhoa. This species is under intense predation pressure at one regionally important colony on St Kilda, Scotland, where a disparity between population decline and predation rates hints at immigration from other large colonies. AMOVA, F(ST), Φ(ST) and Bayesian cluster analyses revealed no genetic structure among Atlantic colonies (Global Φ(ST) = -0.02 P > 0.05, Global F(ST) = 0.003, P > 0.05, STRUCTURE K = 1), consistent with either contemporary gene flow or strong historical association within the ocean basin. The Pacific and Atlantic populations are genetically distinct (Global Φ(ST) = 0.32 P < 0.0001, Global F(ST) = 0.04, P < 0.0001, STRUCTURE K = 2), but evidence for interocean exchange was found with individual exclusion/assignment and population coalescent analyses. These findings highlight the importance of conserving multiple colonies at a number of different sites and suggest that management of this seabird may be best viewed at an oceanic scale. Moreover, our study provides an illustration of how long-distance movement may ameliorate the potentially deleterious impacts of localized environmental change, although direct measures of dispersal are still required to better understand this process.     

Fine-scale spatial genetic correlation analyses reveal strong female philopatry within a brush-tailed rock-wallaby colony in southeast Queensland

We combine spatial data on home ranges of individuals and microsatellite markers to examine patterns of fine-scale spatial genetic structure and dispersal within a brush-tailed rock-wallaby (Petrogale penicillata) colony at Hurdle Creek Valley, Queensland. Brush-tailed rock-wallabies were once abundant and widespread throughout the rocky terrain of southeastern Australia; however, populations are nearly extinct in the south of their range and in decline elsewhere. We use pairwise relatedness measures and a recent multilocus spatial autocorrelation analysis to test the hypotheses that in this species, within-colony dispersal is male-biased and that female philopatry results in spatial clusters of related females within the colony. We provide clear evidence for strong female philopatry and male-biased dispersal within this rock-wallaby colony. There was a strong, significant negative correlation between pairwise relatedness and geographical distance of individual females along only 800 m of cliff line. Spatial genetic autocorrelation analyses showed significant positive correlation for females in close proximity to each other and revealed a genetic neighbourhood size of only 600 m for females. Our study is the first to report on the fine-scale spatial genetic structure within a rock-wallaby colony and we provide the first robust evidence for strong female philopatry and spatial clustering of related females within this taxon. We discuss the ecological and conservation implications of our findings for rock-wallabies, as well as the importance of fine-scale spatial genetic patterns in studies of dispersal behaviour.     

Relative information content of polymorphic microsatellites and mitochondrial DNA for inferring dispersal and population genetic structure in the olive sea snake, Aipysurus laevis

Polymorphic microsatellites are widely considered more powerful for resolving population structure than mitochondrial DNA (mtDNA) markers, particularly for recently diverged lineages or geographically proximate populations. Weaker population subdivision for biparentally inherited nuclear markers than maternally inherited mtDNA may signal male-biased dispersal but can also be attributed to marker-specific evolutionary characteristics and sampling properties. We discriminated between these competing explanations with a population genetic study on olive sea snakes, Aipysurus laevis. A previous mtDNA study revealed strong regional population structure for A. laevis around northern Australia, where Pleistocene sea-level fluctuations have influenced the genetic signatures of shallow-water marine species. Divergences among phylogroups dated to the Late Pleistocene, suggesting recent range expansions by previously isolated matrilines. Fine-scale population structure within regions was, however, poorly resolved for mtDNA. In order to improve estimates of fine-scale genetic divergence and to compare population structure between nuclear and mtDNA, 354 olive sea snakes (previously sequenced for mtDNA) were genotyped for five microsatellite loci. F statistics and Bayesian multilocus genotype clustering analyses found similar regional population structure as mtDNA and, after standardizing microsatellite F statistics for high heterozygosities, regional divergence estimates were quantitatively congruent between marker classes. Over small spatial scales, however, microsatellites recovered almost no genetic structure and standardized F statistics were orders of magnitude smaller than for mtDNA. Three tests for male-biased dispersal were not significant, suggesting that recent demographic expansions to the typically large population sizes of A. laevis have prevented microsatellites from reaching mutation-drift equilibrium and local populations may still be diverging.     

The complex biogeographic history of a widespread tropical tree species

Many tropical forest tree species have broad geographic ranges, and fossil records indicate that population disjunctions in some species were established millions of years ago. Here we relate biogeographic history to patterns of population differentiation, mutational and demographic processes in the widespread rainforest tree Symphonia globulifera using ribosomal (ITS) and chloroplast DNA sequences and nuclear microsatellite (nSSR) loci. Fossil records document sweepstakes dispersal origins of Neotropical S. globulifera populations from Africa during the Miocene. Despite historical long-distance gene flow, nSSR differentiation across 13 populations from Costa Rica, Panama, Ecuador (east and west of Andes) and French Guiana was pronounced (F(ST)= 0.14, R(ST)= 0.39, P < 0.001) and allele-size mutations contributed significantly (R(ST) > F(ST)) to the divergences between cis- and trans-Andean populations. Both DNA sequence and nSSR data reflect contrasting demographic histories in lower Mesoamerica and Amazonia. Amazon populations show weak phylogeographic structure and deviation from drift-mutation equilibrium indicating recent population expansion. In Mesoamerica, genetic drift was strong and contributed to marked differentiation among populations. The genetic structure of S. globulifera contains fingerprints of drift-dispersal processes and phylogeographic footprints of geological uplifts and sweepstakes dispersal.     

Sex-biased gene flow and colonization in the Formosan lesser horseshoe bat: inference from nuclear and mitochondrial markers

Sex-biased behaviours are expected to play an important role in partitioning genetic variance in animal populations. Comparing genetic structure at markers with different modes of inheritance provides a means of detecting these behaviours and their consequences for population genetic structure. In colonially breeding mammals, the common combination of female philopatry and male vagility can promote contrasting patterns of genetic differentiation between the sexes, both via their effects on recurrent gene flow and on colonization. We examined sex differences in gene flow and structure by comparing maternally inherited mitochondrial DNA (mtDNA) and biparentally inherited autosomal loci in the Formosan lesser horseshoe bat Rhinolophus monoceros . We found that genetic partitioning was higher at mtDNA than autosomal markers in both sexes, indicative of female-biased philopatry and male-biased dispersal. Across Taiwan, isolation-by-distance was detected for all sex/marker combinations but was steeper for mtDNA than for nuclear markers. We suggest that isolation-by-distance shown from mtDNA at large scales is likely to reflect the stepwise founding of new breeding colonies by females during colonization. In contrast, no isolation-by-distance was found at smaller distances of up to 100 km, indicating that gene flow and/or recent shared ancestry homogenises genetic structure among nearby sites. Our results highlight the value of an indirect genetic approach to understanding sex-biased behaviours and their consequences in a little-studied species.     

Divergent selection as revealed by P(ST) and QTL-based F(ST) in three-spined stickleback (Gasterosteus aculeatus) populations along a coastal-inland gradient

Three measures of divergence, estimated at nine putatively neutral microsatellite markers, 14 quantitative traits, and seven quantitative trait loci (QTL) were compared in eight populations of the three-spined stickleback (Gasterosteus aculeatus L.) living in the Scheldt river basin (Belgium). Lowland estuarine and polder populations were polymorphic for the number of lateral plates, whereas upland freshwater populations were low-plated. The number of short gill rakers and the length of dorsal and pelvic spines gradually declined along a coastal-inland gradient. Plate number, short gill rakers and spine length showed moderate to strong signals of divergent selection between lowland and upland populations in comparison between P(ST) (a phenotypic alternative for Q(ST)) and neutral F(ST). However, such comparisons rely on the unrealistic assumption that phenotypic variance equals additive genetic variance, and that nonadditive genetic effects and environmental effects can be minimized. In order to verify this assumption and to confirm the phenotypic signals of divergence, we tested for divergent selection at the underlying QTL. For plate number, strong genetic evidence for divergent selection between lowland and upland populations was obtained based on an intron marker of the Eda gene, of which the genotype was highly congruent with plate morph. Genetic evidence for divergent selection on short gill rakers was limited to some population pairs where F(ST) at only one of two QTL was detected as an outlier, although F(ST) at both loci correlated significantly with P(ST). No genetic confirmation was obtained for divergent selection on dorsal spine length, as no outlier F(ST)s were detected at dorsal spine QTL, and no significant correlations with P(ST) were observed.     

Sex-biased dispersal and natal philopatry in the diamondback terrapin, Malaclemys terrapin

Nesting ecology and population studies indicate that diamondback terrapins (Malaclemys terrapin) exhibit nest site fidelity and high habitat fidelity. However, genetic studies indicate high levels of gene flow. Because dispersal affects the genetics and population dynamics of a species, we used six highly polymorphic microsatellite markers to investigate sex-biased dispersal and natal philopatry of M. terrapin in Barnegat Bay, NJ. We compared results of spatial autocorrelation analysis, assignment methods and Wright's F(ST) estimators to a mark-recapture analysis. Mark-recapture analysis over a 4-year period indicated that most individuals have relatively small home ranges (<2 km), with mature females displaying greater home ranges than males. Goodness of fit analysis of our mark-recapture study indicated that some juvenile males were likely transient individuals moving through our study location. Mean assignment indices and first-generation migrant tests indicated that mature males were more prone to disperse than mature females, but first-generation migrant tests indicated that per capita there are more female than male dispersers. Thus, the relative importance of males and females on gene flow in terrapin populations may change in relation to population sex ratios. Spatial autocorrelation analysis indicated that mature females exhibited natal philopatry to nesting beaches, but first-generation migrant tests indicated that a small number of females failed to nest on natal beaches. Finally, we discuss the important conservation implications of male-biased dispersal and natal philopatry in the diamondback terrapin.     

Population structure of Aphis spiraecola (Hemiptera: Aphididae) on pear trees in China identified using microsatellites

The spiraea aphid (Aphis spiraecola Patch) is a primary pest of fruit trees, particularly pear trees in China. Despite the economic importance of this pest, little is known about its genetic structure or its patterns of dispersal at local and regional scales; however, knowledge of these characteristics is important for establishing effective control strategies for this pest. The genetic variability of 431 individuals from 21 populations on pear trees in China was investigated using eight polymorphic microsatellite loci. The high polymorphism of these markers was evident from the expected heterozygosity value (He = 0.824) and the Polymorphism Information Content (PIC = 0.805), indicating that the spiraea aphid maintains a high level of genetic diversity. The analysis of molecular variance revealed a middle level of population differentiation (F(ST) = 0.1478) among A. spiraecola populations. This result is consistent with the results of the STRUCTURE analysis (K = 3), the unweighted pair-group method with arithmetic average tree and the Mantel test (r = 0.6392; P < 0.05). Our results indicate high levels of genetic exchange in the spiraea aphid, possibly facilitated by geography and climate. Our findings emphasize the importance of considering regional differences in studies of population structure, even when strong isolation-by-distance influences the genetic population structure of species.     

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.     

Joint estimation of contemporary seed and pollen dispersal rates among plant populations

There are few statistical methods for estimating contemporary dispersal among plant populations. A maximum-likelihood procedure is introduced here that uses pre- and post-dispersal population samples of biparentally inherited genetic markers to jointly estimate contemporary seed and pollen immigration rates from a set of discrete external sources into a target population. Monte Carlo simulations indicate that accurate estimates and reliable confidence intervals can be obtained using this method for both pollen and seed migration rates at modest sample sizes (100 parents/population and 100 offspring) when population differentiation is moderate (F(ST) ≥ 0.1), or by increasing pre-dispersal samples (to about 500 parents/population) when genetic divergence is weak (F(ST) = 0.01). The method exhibited low sensitivity to the number of source populations and achieved good accuracy at affordable genetic resolution (10 loci with 10 equifrequent alleles each). Unsampled source populations introduced positive biases in migration rate estimates from sampled sources, although they were minor when the proportion of immigration from the latter was comparatively low. A practical application of the method to a metapopulation of the Australian resprouter shrub Banksia attenuata revealed comparable levels of directional seed and pollen migration among dune groups, and the estimate of seed dispersal was higher than a previous estimate based on conservative assignment tests. The method should be of interest to researchers and managers assessing broad-scale nonequilibrium seed and pollen gene flow dynamics in plants.