Landscape characteristics influence morphological and genetic differentiation in a widespread raptor (Buteo jamaicensis)

Landscape-scale population genetic structure in vagile vertebrates was commonly considered to be a contradiction in terms whereas recent studies have demonstrated behaviour and habitat associated structure in several such species. We investigate whether landscape features influence morphological and genetic differentiation in a widespread, mobile raptor. To accurately describe genetic differentiation associated with regional landscape factors, we first investigated subspecies relationships at a continental scale. We used 17 microsatellite loci and five morphological measurements to investigate differentiation between eastern and western subspecies of red-tailed hawks ( Buteo jamaicensis ) and to identify patterns between differentiation and habitat within western North America. Bayesian and frequency-based analyses of microsatellite data revealed clear distinctions between B. j. borealis (eastern) and B. j. calurus (western) samples. Furthermore, hawks sampled in Texas were stouter than those collected from the Rocky Mountains and farther west. Among western samples, birds from the Great Basin, Rocky Mountains, and Washington were significantly different in morphology than those from Oregon and California. We identified a pattern of isolation by distance among western breeding sites around the Sierra Nevada. Given the long-range dispersal capabilities of raptors, this pattern suggests that population-specific habitat preferences, corresponding with habitat breaks between eastern and western slopes of the Sierra Nevada, and/or regionally variable population densities limit migration between the Mediterranean habitat of central California and the xeric habitats of southern California and interior west. We suggest habitat preferences and regionally disparate population densities may play a role in shaping genetic structure in vagile avian taxa.     

Intact landscape promotes gene flow and low genetic structuring in the threatened Eastern Massasauga Rattlesnake

Genetic structuring of wild populations is dependent on environmental, ecological, and life‐history factors. The specific role environmental context plays in genetic structuring is important to conservation practitioners working with rare species across areas with varying degrees of fragmentation. We investigated fine‐scale genetic patterns of the federally threatened Eastern Massasauga Rattlesnake (Sistrurus catenatus) on a relatively undisturbed island in northern Michigan, USA. This species often persists in habitat islands throughout much of its distribution due to extensive habitat loss and distance‐limited dispersal. We found that the entire island population exhibited weak genetic structuring with spatially segregated variation in effective migration and genetic diversity. The low level of genetic structuring contrasts with previous studies in the southern part of the species’ range at comparable fine scales (~7 km), in which much higher levels of structuring were documented. The island population''s genetic structuring more closely resembles that of populations from Ontario, Canada, that occupy similarly intact habitats. Intrapopulation variation in effective migration and genetic diversity likely corresponds to the presence of large inland lakes acting as barriers and more human activity in the southern portion of the island. The observed genetic structuring in this intact landscape suggests that the Eastern Massasauga is capable of sufficient interpatch movements to reduce overall genetic structuring and colonize new habitats. Landscape mosaics with multiple habitat patches and localized barriers (e.g., large water bodies or roads) will promote gene flow and natural colonization for this declining species.     

Intrinsic factors drive spatial genetic variation in a highly vagile species,the wedge‐tailed eagle Aquila audax,in Tasmania

Knowledge of dispersal in a species, both its quantity and the factors influencing it, are crucial for our understanding of ecology and evolution, and for species conservation. Here we quantified and formally assessed the potential contribution of extrinsic factors on individual dispersal in the threatened Tasmanian population of wedge‐tailed eagle Aquila audax. As successful breeding by these individuals appears strongly related to habitat, we tested the effect of landscape around sampling sites on genetic diversity and spatial genetic variation, as these are influenced by patterns of dispersal. Similarly, we also tested whether habitat intervening sampling sites could explain spatial genetic variation. Twenty microsatellites were scored, but only a small proportion of spatial genetic variation (4.6%) could be explained by extrinsic factors, namely habitat suitability and elevation between sites. However, significant clinal genetic variation was evident across Tasmania, which we explain by intrinsic factors, likely high natal philopatry and occasional long‐distance dispersal. This study demonstrates that spatial genetic variation can be detected in highly vagile species at spatial scales that are small relative to putative dispersal ability, although here there was no substantial relationship with landscape factors tested.     

Genetic structure and diversity of a rare woodland bat, <Emphasis Type="Italic">Myotis bechsteinii</Emphasis>: comparison of continental Europe and Britain

The Bechstein’s bat (Myotis bechsteinii) is a rare sedentary bat considered to be highly reliant on the presence of ancient woodland. Understanding the genetic connectivity and population structure of such elusive mammals is important for assessing their conservation status. In this study, we report the genetic diversity and structure of M. bechsteinii across Britain and Europe. Assessments were made using 14 microsatellite markers and a 747 bp region of the mitochondrial cytochrome b gene. Nuclear DNA (microsatellites) showed high levels of genetic diversity and little inbreeding across the species range, though genetic diversity was slightly lower in Britain than in mainland Europe. Bayesian and spatial PCA analysis showed a clear separation between the British and European sites. Within Europe, the Italian population south of the Alps was isolated from the other sites. In Britain, there was genetic structuring between the northern and southern part of the geographical range. Despite there being little genetic divergence in mitochondrial DNA (mtDNA) sequences throughout most of Europe, the mtDNA patterns in Britain confirmed this separation of northern and southern populations. Such genetic structuring within Britain—in the absence of any obvious physical barriers—suggests that other factors such as land-use may limit gene-flow.     

Microsatellite polymorphism in the endangered snail kite reveals a panmictic,low diversity population

Genetic structure and genetic diversity are key population characteristics that can inform conservation decisions, such as delineating management units or assessing potential risks for inbreeding depression. Evidence of genetic structuring or low genetic diversity in the critically endangered snail kite (Rostrhamus sociabilis plumbeus) would have implications for monitoring and planning decisions. Recent work on understanding connectivity across the snail kite range indicated that there is less dispersal between northern and southern parts of the current range, and that dispersal is shaped by individual habitat preference. We examine whether there is neutral genetic structure and the amount of genetic variation in the population by non-lethally sampling 235 nestlings from unique nests across the entire breeding range between 2013 and 2014. Data on 15 microsatellite revealed low diversity (e.g., N _a?=?2.54, H _e?=?0.37) and range-wide panmixia based on AMOVA, Bayesian clustering, spatial autocorrelation, isolation by distance, and spatially explicit ordination analyses. Our results emphasize that long-term recovery goals and management strategies should be based on viewing snail kites as a single genetic population, despite evidence for non-random dispersal between wetlands over ecological time scales. These results also highlight the need to understand potential effects of low genetic diversity on population dynamics and viability of snail kites. More broadly, these results add to the growing evidence for potential discrepancies between dispersal and genetic patterns, emphasizing that care should be taken if using one to interpret the other, particularly for widely-ranging species.     

Population genetic structure of rock ptarmigan in the 'sky islands' of French Pyrenees: implications for conservation

Expected consequences of global warming include habitat reduction in many cool climate species. Rock ptarmigan is a Holarctic grouse that inhabits arctic and alpine tundra. In Europe, the Pyrenean ptarmigan inhabits the southern edge of the species' range and since the last glacial maximum its habitat has been severely fragmented and is restricted to high-alpine zones or 'sky islands'. A recent study of rock ptarmigan population genetic in Europe found that the Pyrenean ptarmigan had very low genetic diversity compared with that found in the Alps and Scandinavia. Habitat fragmentation and reduced genetic diversity raises concerns about the viability of ptarmigan populations in the Pyrenees. However, information on population structuring and gene flow across the Pyrenees, which is essential for designing a sound management plan, is absent. In this study, we use seven microsatellites and mitochondrial control region sequences to investigate genetic variation and differentiation among five localities across the Pyrenees. Our analyses reveal the presence of genetic differentiation among all five localities and a significant isolation-by-distance effect that is likely the result of short dispersal distances and high natal and breeding philopatry of Pyrenean ptarmigan coupled with severe habitat fragmentation. Furthermore, analysis of molecular variance, principal component analysis and Bayesian analysis of genetic structuring identified the greatest amount of differentiation between the eastern and main parts of the Pyrenean chain separated by the Sègre Valley. Our data also show that the Canigou massif may host an isolated population and requires special conservation attention. We propose a management plan which includes the translocation of birds. If a sky island structure affects genetic divergence in rock ptarmigan, it may also affect the genetic structure of other sky island species having low dispersal abilities.     

Phylogeography of the world's tallest angiosperm, Eucalyptus regnans: evidence for multiple isolated Quaternary refugia

Aim There is a need for more Southern Hemisphere phylogeography studies, particularly in Australia, where, unlike much of Europe and North America, ice sheet cover was not extensive during the Last Glacial Maximum (LGM). This study examines the phylogeography of the south‐east Australian montane tree species Eucalyptus regnans. The work aimed to identify any major evolutionary divergences or disjunctions across the species’ range and to examine genetic signatures of past range contraction and expansion events. Location South‐eastern mainland Australia and the large island of Tasmania. Methods We determined the chloroplast DNA haplotypes of 410 E. regnans individuals (41 locations) based on five chloroplast microsatellites. Genetic structure was examined using analysis of molecular variance (AMOVA), and a statistical parsimony tree was constructed showing the number of nucleotide differences between haplotypes. Geographic structure in population genetic diversity was examined with the calculation of diversity parameters for the mainland and Tasmania, and for 10 regions. Regional analysis was conducted to test hypotheses that some areas within the species’ current distribution were refugia during the LGM and that other areas have been recolonized by E. regnans since the LGM. Results Among the 410 E. regnans individuals analysed, 31 haplotypes were identified. The statistical parsimony tree shows that haplotypes divided into two distinct groups corresponding to mainland Australia and Tasmania. The distribution of haplotypes across the range of E. regnans shows strong geographic patterns, with many populations and even certain regions in which a particular haplotype is fixed. Many locations had unique haplotypes, particularly those in East Gippsland in south‐eastern mainland Australia, north‐eastern Tasmania and south‐eastern Tasmania. Higher haplotype diversity was found in putative refugia, and lower haplotype diversity in areas likely to have been recolonized since the LGM. Main conclusions The data are consistent with the long‐term persistence of E. regnans in many regions and the recent recolonization of other regions, such as the Central Highlands of south‐eastern mainland Australia. This suggests that, in spite of the narrow ecological tolerances of the species and the harsh environmental conditions during the LGM, E. regnans was able to persist locally or contracted to many near‐coastal refugia, maintaining a diverse genetic structure.     

Evolution and maintenance of divergent lineages in an endangered freshwater fish, <Emphasis Type="Italic">Macquaria australasica</Emphasis>

Variable hydrological regimes and habitat availability are factors that affect the distribution of freshwater dependent species and are expected to influence their levels of genetic diversity. Although geologically relatively stable, the south eastern region of Australia has experienced significant changes in hydrological conditions during the Quaternary. This area has also been recently affected by anthropogenic activities, resulting in dramatic population declines of Macquarie Perch (Macquaria australasica). We conducted a range-wide phylogeographic study of this endangered fish to assess the relationship between landscape and freshwater fish evolution in south eastern Australia and infer levels of genetic diversity and population structure. Surprisingly, we detected high genetic diversity, with 46 mtDNA control region haplotypes found across 37 sampling locations. Some lineages were remarkably divergent; one represents a putative undescribed species that probably went extinct during the period of this study. Our reconstruction of population history using a combination of coalescent and phylogenetic methods indicates that the species originated on the coast, east of the Great Dividing Range (GDR), with subsequent colonisation of the Murray-Darling basin, west of the GDR. Nested clade and IM analyses inferred a series of range expansions and fragmentations across the species range consistent with the history of climatic oscillations in south eastern Australia during the Pleistocene. We conclude that the unexpected high levels of diversity and divergence observed in M. australasica may be due to specific habitat requirements, localised recruitment, and Pleistocene climate fluctuations. Under expectations of a drier climate and increased sea levels due to global warming, populations of this and other freshwater species may be expected to experience increased habitat fragmentation and loss of genetic diversity. Conservation management should focus on habitat protection, the maintenance of genetic diversity and taxonomic review.     

Landscape genetics of the Tasmanian devil: implications for spread of an infectious cancer

Emerging infectious diseases are increasingly recognized in species’ declines and extinctions. Landscape genetics can be used as a tool to predict disease emergence and spread. The Tasmanian devil is threatened with extinction by a nearly 100% fatal transmissible cancer, which has spread across 95% of the species’ geographic range in 20 years. Here, we present a landscape genetic analysis in the last remaining uninfected parts of the Tasmanian devil’s geographic range to: describe population genetic structure, characterize genetic diversity, and test the influence of landscape variables on Tasmanian devil gene flow to assess the potential for disease spread. In contrast to previous genetic studies on Tasmanian devils showing evidence for two genetic populations island-wide, our genetic based assignment tests and spatial principal components analyses suggest at least two, and possibly three, populations in a study area that is approximately 15% of the size of the overall species’ geographic range. Positive spatial autocorrelation declined at about 40 km, in contrast to 80 km in eastern populations, highlighting the need for range-wide genetic studies. Strong genetic structure was found between devils in the northern part of the study area and those found south of Macquarie Harbor, with weaker structure found between the northeastern and northwestern portion of our study area. Consistent with previous work, we found low overall genetic diversity, likely owing to a combination of founder effects and extreme weather events thousands of years ago that likely caused large-scale population declines. We also found possible signs of recent bottlenecks, perhaps resulting from forest clearing for dairy farming in the central part of the study area. This human disturbance also may have contributed to weak genetic structuring detected between the northeastern and northwestern part of the study area. Individual-based least cost path modeling showed limited influence of landscape variables on gene flow, with weak effects of variation in elevation in the northeast. In the northwest, however, landscape genetic models did not perform better than the null isolation-by-distance model. At the larger spatial scale of the northern part of the study area, elevation and temperatures were negatively correlated with gene flow, consistent with low dispersal suitability of higher elevation habitats that have lower temperatures and dense, wet vegetation. Overall, Tasmanian devils are a highly vagile species for which dispersal and gene flow appear to be influenced little by landscape features, and spread of devil facial tumor disease to the remaining portion of the devil’s geographic range seems imminent. Nonetheless, strong genetic structure found between the northern and southern portions of our study area, combined with low densities and limited possible colonization of DFTD from the east suggest there is some time for implementation of management strategies.     

Response of a southern temperate marsupial, the Tasmanian pademelon (Thylogale billardierii), to historical and contemporary forest fragmentation

Despite only limited Pleistocene glacial activity in the southern hemisphere, temperate forest species experienced complex distributional changes resulting from the combined effects of glaciation, sea level change and increased aridity. The effects of these historical processes on population genetic structure are now overlain by the effects of contemporary habitat modification. In this study, 10 microsatellites and 629 bp of the mitochondrial control region were used to assess the effects of historical forest fragmentation and recent anthropogenic habitat change on the broad-scale population genetic structuring of a southern temperate marsupial, the Tasmanian pademelon. A total of 200 individuals were sampled from seven sites across Tasmania and two islands in Bass Strait. High mitochondrial and nuclear genetic diversity indicated the maintenance of large historical population sizes. There was weak phylogeographical structuring of haplotypes, although all King Island haplotypes and three Tasmanian haplotypes formed a divergent clade implying the mid-Pleistocene isolation of a far northwestern population. Both the mitochondrial and nuclear data indicated a division of Tasmanian populations into eastern and western regions. This was consistent with a historical barrier resulting from increased aridity in the lowland 'midlands' region during glacial periods, and with a contemporary barrier resulting from recent habitat modification in that region. In Tasmania, gene flow appears to have been relatively unrestricted during glacial maxima in the west, while in the east there was evidence for historical expansion from at least one large glacial refuge and recolonization of Flinders Island.     

Relatedness and other finescale population genetic analyses in the threatened eastern box turtle (Terrapene c. carolina) suggest unexpectedly high vagility with important conservation implications

Genetic analyses of populations are essential to the conservation of threatened and cryptic taxa such as Chelonians. Turtles and tortoises are among the most imperiled vertebrate taxa worldwide, yet many of the natural history traits remain unknown leaving management decisions ill- or improperly informed. The eastern box turtle Terrapene c. carolina is no exception, with many gaps in our knowledge about traits such as juvenile dispersal and patterns of relatedness across the landscape, especially as it is a species not particularly tied to water and vulnerable to human disturbance. In addition, all long-term studies of this species have documented demographic population declines, even in protected habitats. In this study we explore finescale population structuring, gene flow, dispersal, and relatedness at four sites across the species range. These sites vary in habitat fragmentation and surrounding habitat quality. Many radiotelemtery and mark-recapture studies suggest that Terrapene spp. have a sedentary natural history, with small and temporally conserved home ranges and little propensity for dispersal. Based on these data we predicted that populations would be highly structured at fine geographic scales, closely related individuals (1st- and 2nd-degree relatives) would coexist in close proximity, and individuals exhibiting transient behavior would be true transients. All sites had low levels of population structuring, mean pairwise relatedness values were statistically zero, over 90 % of pairs of individuals were unrelated, 4.4–8.7 % were half-siblings, and fewer than 1.0 % were full siblings or parent-offspring pairs. These patterns were consistent across all four sites, regardless of habitat fragmentation. Furthermore, while some related pairs were found within a few meters of each other, others ranged up to 33 km apart. We found that one of two individuals with transient behavior was indeed a true genetic transient. These findings suggest that box turtles may be much more vagile than current management practices recognize. As most turtle species are strongly affected by anthropogenic disturbance, many may require much larger contiguous blocks of intact habitat for species persistence as the box turtle likely does. Management plans may therefore need to be updated to allow for safe and effective long-distance dispersal at the appropriate spatial scales in order to maintain genetic health of these species.     

Genetic diversity and population structure of Tasmanian devils, the largest marsupial carnivore

Genetic diversity and population structure were investigated across the core range of Tasmanian devils (Sarcophilus laniarius; Dasyuridae), a wide-ranging marsupial carnivore restricted to the island of Tasmania. Heterozygosity (0.386-0.467) and allelic diversity (2.7-3.3) were low in all subpopulations and allelic size ranges were small and almost continuous, consistent with a founder effect. Island effects and repeated periods of low population density may also have contributed to the low variation. Within continuous habitat, gene flow appears extensive up to 50 km (high assignment rates to source or close neighbour populations; nonsignificant values of pairwise FST), in agreement with movement data. At larger scales (150-250 km), gene flow is reduced (significant pairwise FST) but there is no evidence for isolation by distance. The most substantial genetic structuring was observed for comparisons spanning unsuitable habitat, implying limited dispersal of devils between the well-connected, eastern populations and a smaller northwestern population. The genetic distinctiveness of the northwestern population was reflected in all analyses: unique alleles; multivariate analyses of gene frequency (multidimensional scaling, minimum spanning tree, nearest neighbour); high self-assignment (95%); two distinct populations for Tasmania were detected in isolation by distance and in Bayesian model-based clustering analyses. Marsupial carnivores appear to have stronger population subdivisions than their placental counterparts.     

Bloodlines: mammals,leeches, and conservation in southern Asia

Southern Asia is a biodiversity hotspot both for terrestrial mammals and for leeches. Many small-mammal groups are under-studied in this region, while other mammals are of known conservation concern. In addition to standard methods for surveying mammals, it has recently been demonstrated that residual bloodmeals within leeches can be sequenced to find mammals in a given area. While these invertebrate-parasite-derived DNA (iDNA) methods are promising, most of the leech species utilized for this type of survey remain unevaluated, notwithstanding that their diversity varies substantially. Here we examine approximately 750 individual leech specimens in the genus Haemadipsa across a large range in southern Asia (Bangladesh, Cambodia, and China), specifically reviewing the diversity of mammals they feed on and their own genetic structuring. Leeches were found to feed on a considerable variety of mammals, corroborating prior studies. Additionally, leeches were found to have fed both on bats and on birds, neither of which has previously been recorded with this method. The genetic structuring of the leeches themselves revealed 15 distinct clades of which only two precisely corresponded to previously characterized species, indicating that much work is needed to finalize classifications in this genus. Most importantly, with regards to mammal conservation, leeches in these clades appear to feed on a broad range of mammals.     

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.     

Molecular population genetics of the red kangaroo (Macropus rufus): mtDNA variation

The genetic population structure of a large, wide-ranging marsupial, the red kangaroo ( Macropus rufus ) was assessed using sequence and haplotype frequency data of mitochondrial DNA (mtDNA) from locations across the species range in Australia. Results from sequence data revealed extensive haplotype diversity within the red kangaroo (32/34 sequences were unique). Sequence diversity was distributed within rather than between geographical regions across the species range. Genetic connectivity across the range of the species has therefore been maintained over the long term. On a smaller within-region scale, significant genetic structuring was evident from heterogeneity of haplotype frequencies amongst sampling sites. The geographical scale of panmictic populations differed across the continent with more restricted genetic populations occurring in areas with greater topographic and habitat complexity. We propose that these differences in area of genetic populations are the result of population responses to limiting ecological factors during drought.     

Limited Population Structure,Genetic Drift and Bottlenecks Characterise an Endangered Bird Species in a Dynamic,Fire-Prone Ecosystem

Fire is a major disturbance process in many ecosystems world-wide, resulting in spatially and temporally dynamic landscapes. For populations occupying such environments, fire-induced landscape change is likely to influence population processes, and genetic patterns and structure among populations. The Mallee Emu-wren Stipiturus mallee is an endangered passerine whose global distribution is confined to fire-prone, semi-arid mallee shrublands in south-eastern Australia. This species, with poor capacity for dispersal, has undergone a precipitous reduction in distribution and numbers in recent decades. We used genetic analyses of 11 length-variable, nuclear loci to examine population structure and processes within this species, across its global range. Populations of the Mallee Emu-wren exhibited a low to moderate level of genetic diversity, and evidence of bottlenecks and genetic drift. Bayesian clustering methods revealed weak genetic population structure across the species'' range. The direct effects of large fires, together with associated changes in the spatial and temporal patterns of suitable habitat, have the potential to cause population bottlenecks, serial local extinctions and subsequent recolonisation, all of which may interact to erode and homogenise genetic diversity in this species. Movement among temporally and spatially shifting habitat, appears to maintain long-term genetic connectivity. A plausible explanation for the observed genetic patterns is that, following extensive fires, recolonisation exceeds in-situ survival as the primary driver of population recovery in this species. These findings suggest that dynamic, fire-dominated landscapes can drive genetic homogenisation of populations of species with low-mobility and specialised habitat that otherwise would be expected to show strongly structured populations. Such effects must be considered when formulating management actions to conserve species in fire-prone systems.     

Connectivity and gene flow among Eastern Tiger Salamander (Ambystoma tigrinum) populations in highly modified anthropogenic landscapes

Fragmented landscapes resulting from anthropogenic habitat modification can have significant impacts on dispersal, gene flow, and persistence of wildlife populations. Therefore, quantifying population connectivity across a mosaic of habitats in highly modified landscapes is critical for the development of conservation management plans for threatened populations. Endangered populations of the eastern tiger salamander (Ambystoma tigrinum) in New York and New Jersey are at the northern edge of the species’ range and remaining populations persist in highly developed landscapes in both states. We used landscape genetic approaches to examine regional genetic population structure and potential barriers to migration among remaining populations. Despite the post-glacial demographic processes that have shaped genetic diversity in tiger salamander populations at the northern extent of their range, we found that populations in each state belong to distinct genetic clusters, consistent with the large geographic distance that separates them. We detected overall low genetic diversity and high relatedness within populations, likely due to recent range expansion, isolation, and relatively small population sizes. Nonetheless, landscape connectivity analyses reveal habitat corridors among remaining breeding ponds. Furthermore, molecular estimates of population connectivity among ponds indicate that gene flow still occurs at regional scales. Further fragmentation of remaining habitat will potentially restrict dispersal among breeding ponds, cause the erosion of genetic diversity, and exacerbate already high levels of inbreeding. We recommend the continued management and maintenance of habitat corridors to ensure long-term viability of these endangered populations.     

Pleistocene refugia in an arid landscape: analysis of a widely distributed Australian passerine

While many studies have documented the effect that glacial cycles have had on northern hemisphere species, few have attempted to study the associated effect of aridification at low latitudes in the southern hemisphere. We investigated the past effects that cyclic aridification may have had on the population structure and history of a widespread endemic Australian bird species, the Australian magpie (Gymnorhina tibicen). One thousand one hundred and sixty-six samples from across its native range were analysed for mitochondrial control region sequence variation and variation at six microsatellite loci. Analysis of mitochondrial control region sequence data indicated monophyletic clades that were geographically congruent with an eastern and western region. The contemporary distribution of east and west clades is nonoverlapping but in close proximity. Populations were estimated to have diverged in the Pleistocene around 36,000 years ago. The putative Carpentarian and Nullarbor arid barriers appear to be associated with the divergence between east and west mainland populations. Nested clade analysis indicated a signature of range expansion in the eastern region suggesting movement possibly inland and northward subsequent to the last period of aridity. The island population of Tasmania was of very recent origin, possibly since sea levels rose 16,000 years ago. Given the east-west structure, there was no congruence between morphology and recent history of this species indicating a lack of support for morphological taxa. Overall mitochondrial DNA and microsatellite variation suggest that increasing aridity and Pleistocene refugia played a role in structuring populations of the Australian magpie; however, the dispersal ability and generalist habitat requirements may have facilitated the movement of magpies into an almost contiguous modern distribution across the continent. This study supports the idea that Pleistocene aridification played an important role in structuring intraspecific variation in low latitudinal southern hemisphere avian species.     

Vagility and the Monsoon Rain Forest Archipelago of Northern Australia: Patterns of Genetic Diversity in Syzygium nervosum (Myrtaceae)1

Syzygium nervosum is a common monsoon rain forest tree. Its habitat in Australia consists of small rain forest patches that are scattered through a savanna matrix. It is a mast flowering canopy species that produces large quantities of fruits fed on by mobile frugivores such as birds and fruit bats. The genetic diversity of this species was investigated, especially in relation to rain forest patch size, geographic isolation, and geographic distribution. Syzygium nervosum was found to have high levels of genetic diversity within populations (H_e= 0.307). Diversity among populations, however, was relatively low (Fsr = 0.118), and was not spatially structured across its geographic range in Australia. This is thought to have been caused by relatively frequent gene flow among populations (N_m= 1.67), mediated primarily by mobile frugivores. Genetic diversity was not correlated with patch size or isolation. It is thought that seed dispersal by frugivores has acted to expand the effective population size of this species beyond the individual rain forest patch, and thus has prevented the substantial loss of genetic diversity that otherwise would have been observed. Thus this species is dependent upon these frugivores for the maintenance of its genetic diversity and hence its long-term viability. These results lend support to theories of post-Holocene expansion of rain forest by vagile species in northern Australia.     

Historical demography and colonization pathways of the widespread intertidal seaweed Hormosira banksii (Phaeophyceae) in southeastern Australia

The palaeoceanography of southern Australia has been characterized by fluctuating sea levels during glacial periods, changing temperature regimes and modified boundary currents. Previous studies on genetic structuring of species in southeastern Australia have focused mainly on the differentiation of eastern and western populations while the potential role of Bass Strait as a region of overlap for three biogeographic provinces (Peronia, Maugea, and Flindersia) has been largely ignored. This study aimed to explore the likely roles of historic and contemporary factors in determining divergence patterns in the habitat‐forming intertidal seaweed Hormosira banksii in southeastern Australia with a special focus on postglacial dispersal into Bass Strait. We examined the genetic diversity of 475 Hormosira specimens collected from 19 sites around southern Australia using DNA sequence analysis of cytochrome oxidase 1. Three major haplotype groups were identified (western, centre and eastern) corresponding with the three existing biogeographical provinces in this region. Historic break points appeared to be retained and reinforced by modern day dispersal barriers. Phylogeographic grouping of Hormosira reflected a combination of historic and contemporary oceanography. As western and eastern group haplotypes were largely absent within Bass Strait, re‐colonization after the last glacial maximum appeared to have originated from refuges within or near present day Bass Strait. Patterns of genetic structure for Hormosira are consistent with other marine species in this region and highlight the importance of biogeographical barriers in contributing to modern genetic structure.