Lack of sex-biased dispersal promotes fine-scale genetic structure in alpine ungulates

Identifying patterns of fine-scale genetic structure in natural populations can advance understanding of critical ecological processes such as dispersal and gene flow across heterogeneous landscapes. Alpine ungulates generally exhibit high levels of genetic structure due to female philopatry and patchy configuration of mountain habitats. We assessed the spatial scale of genetic structure and the amount of gene flow in 301 Dall’s sheep (Ovis dalli dalli) at the landscape level using 15 nuclear microsatellites and 473 base pairs of the mitochondrial (mtDNA) control region. Dall’s sheep exhibited significant genetic structure within contiguous mountain ranges, but mtDNA structure occurred at a broader geographic scale than nuclear DNA within the study area, and mtDNA structure for other North American mountain sheep populations. No evidence of male-mediated gene flow or greater philopatry of females was observed; there was little difference between markers with different modes of inheritance (pairwise nuclear DNA F _ST = 0.004–0.325; mtDNA F _ST = 0.009–0.544), and males were no more likely than females to be recent immigrants. Historical patterns based on mtDNA indicate separate northern and southern lineages and a pattern of expansion following regional glacial retreat. Boundaries of genetic clusters aligned geographically with prominent mountain ranges, icefields, and major river valleys based on Bayesian and hierarchical modeling of microsatellite and mtDNA data. Our results suggest that fine-scale genetic structure in Dall’s sheep is influenced by limited dispersal, and structure may be weaker in populations occurring near ancestral levels of density and distribution in continuous habitats compared to other alpine ungulates that have experienced declines and marked habitat fragmentation.     

Dispersal,Mating Events and Fine-Scale Genetic Structure in the Lesser Flat-Headed Bats

Population genetic structure has important consequences in evolutionary processes and conservation genetics in animals. Fine-scale population genetic structure depends on the pattern of landscape, the permanent movement of individuals, and the dispersal of their genes during temporary mating events. The lesser flat-headed bat (Tylonycteris pachypus) is a nonmigratory Asian bat species that roosts in small groups within the internodes of bamboo stems and the habitats are fragmented. Our previous parentage analyses revealed considerable extra-group mating in this species. To assess the spatial limits and sex-biased nature of gene flow in the same population, we used 20 microsatellite loci and mtDNA sequencing of the ND2 gene to quantify genetic structure among 54 groups of adult flat-headed bats, at nine localities in South China. AMOVA and F _ST estimates revealed significant genetic differentiation among localities. Alternatively, the pairwise F _ST values among roosting groups appeared to be related to the incidence of associated extra-group breeding, suggesting the impact of mating events on fine-scale genetic structure. Global spatial autocorrelation analyses showed positive genetic correlation for up to 3 km, indicating the role of fragmented habitat and the specialized social organization as a barrier in the movement of individuals among bamboo forests. The male-biased dispersal pattern resulted in weaker spatial genetic structure between localities among males than among females, and fine-scale analyses supported that relatedness levels within internodes were higher among females than among males. Finally, only females were more related to their same sex roost mates than to individuals from neighbouring roosts, suggestive of natal philopatry in females.     

Gene flow is maintained by polyandry and male dispersal in the army ant <Emphasis Type="Italic">Eciton burchellii</Emphasis>

The combination of haplodiploidy, complementary sex determination and eusociality constrains the effective population size (N _e) of social Hymenoptera far more than in any other insect group. Additional limitations on N _e occur in army ants since they have wingless queens and colony fission, both of which are factors causing restricted maternal gene flow and high population viscosity. Therefore, winged army ant males gain a particular significance to ensure dispersal, facilitate gene flow and avoid inbreeding. Based on population genetic analyses with microsatellite markers, we studied a population of the Neotropical army ant Eciton burchellii, finding a high level of heterozygosity, weak population differentiation and no evidence for inbreeding. Moreover, by using sibship reconstruction analyses, we quantified the actual number of male contributing colonies represented in a queen’s mate sample, demonstrating that, through extreme multiple mating, the queens are able to sample the genes of males from up to ten different colonies, usually located within an approximate radius of 1 km. We finally correlated the individual mating success of each male contributing colony with the relative siring success of individual males and found a significant colony-dependent male fitness component. Our results imply that the dispersal and mating system of these army ants seem to enhance gene flow and minimise the deleterious effects associated with small effective population size. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

SEX-BIASED GENE FLOW IN SPECTACLED EIDERS (ANATIDAE): INFERENCES FROM MOLECULAR MARKERS WITH CONTRASTING MODES OF INHERITANCE

Abstract Genetic markers that differ in mode of inheritance and rate of evolution (a sex‐linked Z‐specific micro‐satellite locus, five biparentally inherited microsatellite loci, and maternally inherited mitochondrial [mtDNA] sequences) were used to evaluate the degree of spatial genetic structuring at macro‐ and microgeographic scales, among breeding regions and local nesting populations within each region, respectively, for a migratory sea duck species, the spectacled eider (Somateria fisheri). Disjunct and declining breeding populations coupled with sex‐specific differences in seasonal migratory patterns and life history provide a series of hypotheses regarding rates and directionality of gene flow among breeding populations from the Indigirka River Delta, Russia, and the North Slope and Yukon‐Kuskokwim Delta, Alaska. The degree of differentiation in mtDNA haplotype frequency among breeding regions and populations within regions was high (φ_CT= 0.189, P < 0.01; φ_SC= 0.059, P < 0.01, respectively). Eleven of 17 mtDNA haplotypes were restricted to a single breeding region. Genetic differences among regions were considerably lower for nuclear DNA loci (sex‐linked: φ_ST= 0.001, P > 0.05; biparentally inherited microsatellites: mean θ= 0.001, P > 0.05) than was observed for mtDNA. Using models explicitly designed for uniparental and biparentally inherited genes, estimates of spatial divergence based on nuclear and mtDNA data together with elements of the species' breeding ecology were used to estimate effective population size and degree of male and female gene flow. Differences in the magnitude and spatial patterns of gene correlations for maternally inherited and nuclear genes revealed that females exhibit greater natal philopatry than do males. Estimates of generational female and male rates of gene flow among breeding regions differed markedly (3.67 × 10^‐4 and 1.28 × 10^‐2, respectively). Effective population size for mtDNA was estimated to be at least three times lower than that for biparental genes (30,671 and 101,528, respectively). Large disparities in population sizes among breeding areas greatly reduces the proportion of total genetic variance captured by dispersal, which may accelerate rates of inbreeding (i.e., promote higher coancestries) within populations due to nonrandom pairing of males with females from the same breeding population.     

Population- and sociogenetic structure of the leaf-cutter ant <Emphasis Type="Italic">Atta colombica</Emphasis> (Formicidae,Myrmicinae)

Relatedness and genetic variability in colonies of social insects are strongly influenced by the number of queens present and the number of matings per queen, but also by the genetic variability in the population. Thus, multiple paternity will enhance within-colony genetic variability more strongly when the males a queen mates with are unrelated. To study the kin-structure within colonies of the leaf-cutter ant Atta colombica and the population structure of this species around Barro Colorado Island, Panama, we developed five polymorphic microsatellite loci with a range of three to 17 alleles in At. colombica, all of which cross-amplify in other higher attines as well. The average effective mating frequency calculated from four-locus microsatellite genotypes was 1.89 ± 0.12 (harmonic mean ± SE) and thus slightly lower than the average observed mating frequency of 2.50 ± 0.11 (arithmetic mean ± SE) over the 55 colonies studied, confirming former studies that utilized fewer loci. The discrepancy between observed mating frequency and effective mating frequency is most probably due to paternity skew within colonies. The study population proved to be genetically diverse and in Hardy-Weinberg equilibrium, suggesting random mating within the study area. No population substructure was observed, neither considering nuclear (global F _ST = 0.011 ± 0.003 SE) nor mitochondrial markers (mean Φ_ST = 0.008). Consequently, gene flow is obviously promoted by both sexes across the range investigated here. Thus, multiple mating and long-distance dispersal appear to be two interconnected behavioural mechanisms to create and maintain genetic diversity in At. colombica. The advantages of this system are partly offset by paternity skew and the non-zero relatedness among colony fathers found in the study population. Received 18 March 2008; revised 14 July 2008; accepted 18 July 2008.     

The genetic population structure of two socially parasitic ants: “the active slave-maker” Myrmoxenus ravouxi and the “degenerate slave-maker” M. kraussei

Slave-making ants exploit the societies of host ant species and are typically rare and patchily distributed. IUCN considers almost all slave-making ants as vulnerable, but solid data on their actual abundance are uncommon. Here we examine the genetic structure of populations of two species of the socially parasitic genus Myrmoxenus, which differ strongly in dispersal behavior and the occurrence of slave-raids. Microsatellite genotypes suggest strong differentiation even among neighboring populations of both species. F_ST-, G″_ST-, and D-values were considerably higher in the “degenerate slave-maker” M. kraussei from Northern Italy than in the active slavemaker M. ravouxi from Southern Germany. This matches observations that sexuals of M. kraussei mate in their natal nest and queens disperse on foot while sexuals of M. ravouxi engage in mating and dispersal flights. Allelic richness was surprisingly high in both species and did not suggest recent bottlenecks, indicating that populations are larger and less vulnerable than expected from the difficulties of locating nests. Despite of considerable inbreeding, only very few diploid males were detected, supporting the view that at least in M. kraussei sex is not determined by single locus complementary sex determination unlike most other social Hymenoptera. The mismatch between the genetic and social structure of M. ravouxi colonies indicates occasionally fusion of slave-maker colonies in the field, mutual raids, or queen replacement. Complementary analyses of the host species of the two social parasites, Temnothorax unifasciatus and T. recedens, revealed low levels of population differentiation and confirmed the colony structure with a single, singly-mated queen.     

Conservation genetics of the short-beaked common dolphin (<Emphasis Type="Italic">Delphinus delphis</Emphasis>) in the Mediterranean Sea and in the eastern North Atlantic Ocean

Mediterranean Sea common dolphins have recently been listed as ‘endangered’ in the IUCN Red list, due to their reported decline since the middle of the 20th century. However, little is know about the number or distribution of populations in this region. We analysed 118 samples from the Black Sea, Mediterranean Sea and eastern North Atlantic at nine microsatellite nuclear loci and for 428 bps of the mtDNA control region. We found small but significant population differentiation across the basin between the eastern and the western Mediterranean populations at both nuclear and mtDNA markers (microsatellite F _ST = 0.052, mtDNA F _ST = 0.107, P values ≤ 0.001). This matched the differential distribution and habitat use patterns exhibited by this species in the eastern and the western parts of the Mediterranean Sea. The assignment test of a small number of samples from the central Mediterranean could not exclude further population structure in the central area of the basin. No significant genetic differentiation at either marker was observed among the eastern north Atlantic populations, though the Alboran population (inhabiting the Mediterranean waters immediately adjacent the Atlantic ocean) showed significant mtDNA genetic differentiation compared to the Atlantic populations. Directional estimates of gene flow suggested movement of females out of the Mediterranean, which may be relevant to the population decline. Phylogenetic analysis suggested that the observed population structure evolved recently.     

Insights into the biodiversity of the Succulent Karoo hotspot of South Africa: the population genetics of a rare and endemic halictid bee,Patellapis doleritica

Population genetic analyses are especially relevant for species considered threatened or highly endemic and for which other forms of biological information are lacking. Patellapis doleritica is a recently described communally nesting halictid bee of conservation concern because it is rare and endemic to the Succulent Karoo of South Africa. Moreover, its dispersal is considered to be restricted by its specialised nesting requirements and inclement weather conditions during its limited annual flight period, traits which may be common to other bee species of the region. We hypothesised that gene flow in P. doleritica was low, leading to marked genetic differentiation. Using 7 microsatellites, we investigated its mating and population genetic structure in 258 individuals (171 females and 87 males) from 7 populations spanning most of its known range. Deviation from Hardy–Weinberg equilibrium (F_IS = + 0.254) suggested P. doleritica to be inbred, as in many other communal nesting bee species. Global F_ST (0.028) and global G′_ST (0.216) revealed modest but significant differentiation between most populations, even across the very limited range of the species (ca. 25 km), with one genetically extreme outlier population. Despite inbreeding, we detected a surprisingly low frequency of diploid males (2 %). Patellapis doleritica nevertheless deserves special conservation attention since it is an endemic species with a low overall abundance and therefore possibly prone to environmental change and local extinction.     

Contrasting spatial genetic structure in Annona crassiflora populations from fragmented and pristine savannas

In continuous populations, fine-scale genetic structure tends to be stronger in species with restricted pollen and seed dispersal. However, habitat fragmentation and disturbances can affect genetic diversity and spatial genetic structure due to disruption in ecological processes, such as plant reproduction and seed dispersal. In this study, we compared the genetic diversity and fine-scale spatial genetic structure (SGS) in two populations of Annona crassiflora (Annonaceae) in a pristine savanna Reserve (ESECAE) and in a fragmented disturbed savanna area (PABE), both in Cerrado biome in Central Brazil. The analyses were based on the polymorphism at 10 microsatellite loci. Our working hypothesis was that SGS is stronger and genetic diversity is lower in population at fragmented area (PABE) than at pristine area (ESECAE). Both populations presented high levels of polymorphism and genetic diversity and showed no sign of bottleneck for both Wilcoxon sign-rank test for heterozygosity excess (p > 0.05) and coalescent analyses (growth parameter g not different from zero), but population at fragmented area showed higher fixation index and stronger SGS. Besides, populations are significantly differentiated (F _ST = 0.239, R _ST = 0.483, p < 0.001 for both). Coalescent analyses showed high historical effective population sizes for both populations, high gene flow between ESECAE and PABE and recent time to most recent common ancestor (~37 k year BP). Our results suggest that despite the high genetic diversity, fragmentation and disturbance may have been affecting populations of this species increasing mating between closely related individuals leading to high fixation index and strong SGS.     

Population structure and conservation implications for the loggerhead sea turtle of the Cape Verde Islands

The Cape Verde Islands harbour the second largest nesting aggregation of the globally endangered loggerhead sea turtle in the Atlantic. To characterize the unknown genetic structure, connectivity, and demographic history of this population, we sequenced a segment of the mitochondrial (mt) DNA control region (380 bp, n = 186) and genotyped 12 microsatellite loci (n = 128) in females nesting at three islands of Cape Verde. No genetic differentiation in either haplotype or allele frequencies was found among the islands (mtDNA F _ST = 0.001, P > 0.02; nDNA F _ST = 0.001, P > 0.126). However, population pairwise comparisons of the mtDNA data revealed significant differences between Cape Verde and all previously sequenced Atlantic and Mediterranean rookeries (F _ST = 0.745; P < 0.000). Results of a mixed stock analysis of mtDNA data from 10 published oceanic feeding grounds showed that feeding grounds of the Madeira, Azores, and the Canary Islands, in the Atlantic Ocean, and Gimnesies, Pitiüses, and Andalusia, in the Mediterranean sea, are feeding grounds used by turtles born in Cape Verde, but that about 43% (±19%) of Cape Verde juveniles disperse to unknown areas. In a subset of samples (n = 145) we evaluated the utility of a longer segment (~760 bp) amplified by recently designed mtDNA control region primers for assessing the genetic structure of Atlantic loggerhead turtles. The analysis of the longer fragment revealed more variants overall than in the shorter segments. The genetic data presented here are likely to improve assignment and population genetic analyses, with significant conservation and research applications.     

Population stock structure of leatherback turtles (Dermochelys coriacea) in the Atlantic revealed using mtDNA and microsatellite markers

This study presents a comprehensive genetic analysis of stock structure for leatherback turtles (Dermochelys coriacea), combining 17 microsatellite loci and 763 bp of the mtDNA control region. Recently discovered eastern Atlantic nesting populations of this critically endangered species were absent in a previous survey that found little ocean-wide mtDNA variation. We added rookeries in West Africa and Brazil and generated longer sequences for previously analyzed samples. A total of 1,417 individuals were sampled from nine nesting sites in the Atlantic and SW Indian Ocean. We detected additional mtDNA variation with the longer sequences, identifying ten polymorphic sites that resolved a total of ten haplotypes, including three new variants of haplotypes previously described by shorter sequences. Population differentiation was substantial between all but two adjacent rookery pairs, and F _ST values ranged from 0.034 to 0.676 and 0.004 to 0.205 for mtDNA and microsatellite data respectively, suggesting that male-mediated gene flow is not as widespread as previously assumed. We detected weak (F _ST = 0.008 and 0.006) but significant differentiation with microsatellites between the two population pairs that were indistinguishable with mtDNA data. POWSIM analysis showed that our mtDNA marker had very low statistical power to detect weak structure (F _ST < 0.005), while our microsatellite marker array had high power. We conclude that the weak differentiation detected with microsatellites reflects a fine scale level of demographic independence that warrants recognition, and that all nine of the nesting colonies should be considered as demographically independent populations for conservation. Our findings illustrate the importance of evaluating the power of specific genetic markers to detect structure in order to correctly identify the appropriate population units to conserve.     

Population genetic structure of the endangered Eastern Bristlebird, Dasyornis brachypterus; implications for conservation

For species that are habitat specialists or sedentary, population fragmentation may lead to genetic divergence between populations and reduced genetic diversity within populations, with frequent inbreeding. Hundreds of kilometres separate three geographical regions in which small populations of the endangered Eastern Bristlebird, Dasyornis brachypterus, a small, ground-dwelling passerine that occurs in fire-prone bushland in eastern Australia, are currently found. Here, we use mitochondrial and microsatellite DNA markers to: (i) assess the sub-specific taxonomy designated to northern range-edge, and central and southern range-edge D. brachypterus, respectively, and (ii) assess levels of standing genetic variation and the degree of genetic subdivision of remnant populations. The phylogenetic relationship among mtDNA haplotypes and their spatial distribution did not support the recognised subspecies boundaries. Populations in different regions were highly genetically differentiated, but in addition, the two largest, neighboring populations (located within the central region and separated by ~50 km) were moderately differentiated, and thus are likely closed to migration (microsatellites, F _ST = 0.06; mtDNA, F _ST = 0.12, ?? _ST = 0.08). Birds within these two populations were genotypically diverse and apparently randomly mating. A long-term plan for the conservation of D. brachypterus??s genetic diversity should consider individual populations as separate management units. Moreover, managers should avoid actively mixing birds from different populations or regions, to conserve the genetic integrity of local populations and avoid outbreeding depression, should further translocations be used as a recovery tool for this species.     

The Evolution of Extreme Polyandry in Social Insects: Insights from Army Ants

The unique nomadic life-history pattern of army ants (army ant adaptive syndrome), including obligate colony fission and strongly male-biased sex-ratios, makes army ants prone to heavily reduced effective population sizes (N _e). Excessive multiple mating by queens (polyandry) has been suggested to compensate these negative effects by increasing genetic variance in colonies and populations. However, the combined effects and evolutionary consequences of polyandry and army ant life history on genetic colony and population structure have only been studied in a few selected species. Here we provide new genetic data on paternity frequencies, colony structure and paternity skew for the five Neotropical army ants Eciton mexicanum, E. vagans, Labidus coecus, L. praedator and Nomamyrmex esenbeckii; and compare those data among a total of nine army ant species (including literature data). The number of effective matings per queen ranged from about 6 up to 25 in our tested species, and we show that such extreme polyandry is in two ways highly adaptive. First, given the detected low intracolonial relatedness and population differentiation extreme polyandry may counteract inbreeding and low N _e. Second, as indicated by a negative correlation of paternity frequency and paternity skew, queens maximize intracolonial genotypic variance by increasingly equalizing paternity shares with higher numbers of sires. Thus, extreme polyandry is not only an integral part of the army ant syndrome, but generally adaptive in social insects by improving genetic variance, even at the high end spectrum of mating frequencies.     

Molecular detection of intra-population structure in a threatened potoroid,Potorous tridactylus: conservation management and sampling implications

Fine-scale genetic structure was investigated in three regional populations of the long-nosed potoroo (Potorous tridactylus) a threatened endemic marsupial. Two populations were from the Australian mainland and one from an island. Populations were sub-sampled at two sites, 6–8 km apart, connected by suitable habitat for dispersal. Factors influencing fine-scale structure were investigated by genotyping 157 individuals at 10 microsatellite loci and sequencing a ~621 bp region of the mtDNA control region. Results indicated that P. tridactylus populations exhibit significant intra-population structure, with significant F _ST and Φ _ST values recorded between subpopulations. This structure appeared mediated by small neighbourhood size, female philopatry and limited dispersal over 6–8 km, predominantly by males. Results highlighted several important features of P. tridactylus populations that have implications for conservation. Firstly, the small neighbourhood size suggests any investigations of intra-population structure should be conducted on a finer scale (e.g. 25–50 m) than many current monitoring programs. Secondly, the island populations were genetically depauperate, which may reflect processes occurring in many isolated ‘mainland island’ populations. Thirdly, the lower gene flow identified between populations separated by anthropogenically modified habitat suggests P. tridactylus is sensitive to changes in habitat configuration.     

Two decades of genetic consistency in a reproductive population in the face of exploitation: patterns of adult and larval walleye (<Emphasis Type="Italic">Sander vitreus</Emphasis>) from Lake Erie’s Maumee River

Analyses of genetic variability and allelic composition in a species exhibiting reproductive fidelity to natal sites may provide important ecological indication of temporal population dynamics, facilitating understanding responses to past disturbances and future climate change. The walleye is an ecologically and economically valuable species, whose largest fishery centers in Lake Erie of the Laurentian Great Lakes; it exhibits reproductive site fidelity, despite otherwise wide-ranging dispersal. We tested whether genetic composition and diversity have remained temporally stable in Lake Erie’s Maumee River, which is the largest and most highly fished spawning run. This population has experienced over a century of exploitation, habitat alterations, and pollution, which may have affected genetic structure and might influence future sustainability. Fourteen nuclear DNA microsatellite loci were analyzed from 744 spawning run walleye to test genetic patterns across: (1) years (N = 12, spanning 1995–2013), (2) birth year cohorts, (3) the sexes, (4) those reproducing earlier (ages 2–6) versus later (7 or older) in life, and (5) the adults versus larvae. Results indicated stability in genetic diversity levels (mean H _O = 0.76 ± 0.03) and allelic composition across years (F _ST = 0.000–0.006, NS), cohorts (F _ST = 0.000–0.013, NS), sexes (F _ST = 0.000, NS), earlier versus later reproduction (F _ST = 0.000, NS), and between the larvae and adults (F _ST = 0.000–0.004, NS). Number of breeders and effective population size were substantial and consistent. This reproductive population thus has maintained genetic stability and high diversity, despite intensive anthropogenic pressures.     

Population genetics and fine-scale genetic structure of Rhizopogon roseolus in the Tottori sand dune

We investigated the population genetics and fine-scale genetic structure of Rhizopogon roseolus. A total of 173 R. roseolus sporocarps were collected from two stands in the Tottori sand dune. We developed and applied five novel polymorphic microsatellite (SSR; simple sequence repeat) markers for sporocarp genotyping. In total, we identified 110 genets, most of which were small in size. Spatial autocorrelation analyses revealed a significantly positive genetic structure in short-distance classes. The inbreeding coefficient value was significant in both stands (F_IS = 0.18), while the F_ST value (F_ST = 0.020) indicated little genetic differentiation between the two populations. The majority of alleles were distributed in both stands with similar frequencies. These results suggest that short-distance spore dispersal plays a dominant role in generating new genets, and eventually increases the frequency of inbreeding in the Tottori sand dune, whereas rare gene flow between the two stands, possibly associated with spore dispersal by mycophagous animals, could reduce genetic differentiation.     

Remarkably low genetic diversity and strong population structure in common bottlenose dolphins (Tursiops truncatus) from coastal waters of the Southwestern Atlantic Ocean

Knowledge about the ecology of bottlenose dolphins in the Southwestern Atlantic Ocean is scarce. Increased by-catch rates over the last decade in coastal waters of southern Brazil have raised concerns about the decline in abundance of local dolphin communities. Lack of relevant data, including information on population structure and connectivity, have hampered an assessment of the conservation status of bottlenose dolphin communities in this region. Here we combined analyses of 16 microsatellite loci and mitochondrial DNA (mtDNA) control region sequences to investigate genetic diversity, structure and connectivity in 124 biopsy samples collected over six communities of photographically identified coastal bottlenose dolphins in southern Brazil, Uruguay and central Argentina. Levels of nuclear genetic diversity were remarkably low (mean values of allelic diversity and heterozygosity across all loci were 3.6 and 0.21, respectively), a result that possibly reflects the small size of local dolphin communities. On a broad geographical scale, strong and significant genetic differentiation was found between bottlenose dolphins from southern Brazil–Uruguay (SB–U) and Bahía San Antonio (BSA), Argentina (AMOVA mtDNA Φ_ST = 0.43; nuclear F_ST = 0.46), with negligible contemporary gene flow detected based on Bayesian estimates. On a finer scale, moderate but significant differentiation (AMOVA mtDNA Φ_ST = 0.29; nuclear F_ST = 0.13) and asymmetric gene flow was detected between five neighbouring communities in SB–U. Based on the results we propose that BSA and SB–U represent two distinct evolutionarily significant units, and that communities from SB–U comprise five distinct Management Units (MUs). Under this scenario, conservation efforts should prioritize the areas in southern Brazil where dolphins from three MUs overlap in their home ranges and where by-catch rates are reportedly higher.     

Global phylogeography with mixed-marker analysis reveals male-mediated dispersal in the endangered scalloped hammerhead shark (Sphyrna lewini)

Background

The scalloped hammerhead shark, Sphyrna lewini, is a large endangered predator with a circumglobal distribution, observed in the open ocean but linked ontogenetically to coastal embayments for parturition and juvenile development. A previous survey of maternal (mtDNA) markers demonstrated strong genetic partitioning overall (global Φ_ST = 0.749) and significant population separations across oceans and between discontinuous continental coastlines.

Methodology/Principal Findings

We surveyed the same global range with increased sample coverage (N = 403) and 13 microsatellite loci to assess the male contribution to dispersal and population structure. Biparentally inherited microsatellites reveal low or absent genetic structure across ocean basins and global genetic differentiation (F _ST = 0.035) over an order of magnitude lower than the corresponding measures for maternal mtDNA lineages (Φ_ST = 0.749). Nuclear allelic richness and heterozygosity are high throughout the Indo-Pacific, while genetic structure is low. In contrast, allelic diversity is low while population structure is higher for populations at the ends of the range in the West Atlantic and East Pacific.

Conclusions/Significance

These data are consistent with the proposed Indo-Pacific center of origin for S. lewini, and indicate that females are philopatric or adhere to coastal habitats while males facilitate gene flow across oceanic expanses. This study includes the largest sampling effort and the most molecular loci ever used to survey the complete range of a large oceanic predator, and findings emphasize the importance of incorporating mixed-marker analysis into stock assessments of threatened and endangered shark species.     

Pronounced differences in genetic structure despite overall ecological similarity for two Ambystoma salamanders in the same landscape

Studies linking genetic structure in amphibian species with ecological characteristics have focused on large differences in dispersal capabilities. Here, we test whether two species with similar dispersal potential but subtle differences in other ecological characteristics also exhibit strong differences in genetic structure in the same landscape. We examined eight microsatellites in marbled salamanders (Ambystoma opacum) from 29 seasonal ponds and spotted salamanders (Ambystoma maculatum) from 19 seasonal ponds in a single geographic region in west-central Massachusetts. Despite overall similarity in ecological characteristics of spotted and marbled salamanders, we observed clear differences in the genetic structure of these two species. For marbled salamanders, we observed strong overall genetic differentiation (F _ST = 0.091, F′ _ST = 0.375), three population-level clusters of populations (K = 3), a strong pattern of isolation by distance (r = 0.58), and marked variation in family-level structure (from 1 to 23 full-sibling families per site). For spotted salamanders, overall genetic differentiation was weaker (F _ST = 0.025, F′ _ST = 0.102), there was no evidence of population-level clustering (K = 1), the pattern of isolation by distance (r = 0.17) was much weaker compared to marbled salamanders, and there was less variation in family-level structure (from 10 to 36 full-sibling families per site). We suspect that a combination of breeding site fidelity, effective population size, and generation interval is responsible for these marked differences. Our results suggest that marbled salamanders, compared to spotted salamanders, are more sensitive to fragmentation from various land-use activities and would be less likely to recolonize extirpated sites on an ecologically and conservation-relevant time frame.     

Unspecific histological and hematological alterations in anadromous and resident <Emphasis Type="Italic">Salvelinus malma</Emphasis> induced by volcanogenic pollution

Knowledge of larval dispersal and connectivity in coral reef species is crucial for understanding population dynamics, resilience, and evolution of species. Here, we use ten microsatellites and one mitochondrial marker (cytochrome b) to investigate the genetic population structure, genetic diversity, and historical demography of the powder-blue tang Acanthurus leucosternon across more than 1000 km of the scarcely studied Eastern African region. The global AMOVA results based on microsatellites reveal a low but significant F _ST value (F _ST = 0.00252 P < 0.001; D _EST = 0.025 P = 0.0018) for the 336 specimens sampled at ten sample sites, while no significant differentiation could be found in the mitochondrial cytochrome b dataset. On the other hand, pairwise F _ST, PCOA, and hierarchical analysis failed to identify any genetic breaks among the Eastern African populations, supporting the hypothesis of genetic homogeneity. The observed genetic homogeneity among Eastern African sample sites can be explained by the lengthy post-larval stage of A. leucosternon, which can potentiate long-distance dispersal. Tests of neutrality and mismatch distribution signal a population expansion during the mid-Pleistocene period.