A comparative analysis of population structuring and genetic diversity in sympatric lineages of freshwater shrimp (Atyidae: Paratya): concerted or independent responses to hydrographic factors?

1. We determined whether two sympatric mitochondrial DNA (mtDNA) lineages of freshwater shrimp (Decapoda: Atyidae: Paratya australiensis) represent biological species and if they had concerted or independent population responses to hydrographic factors in small streams (the Granite Creeks) in southeastern Australia. 2. Allozyme data indicated the presence of two gene pools at sites where the P. australiensis lineages were co‐occurring and the gene pools were statistically assigned with high probability to each respective lineage. This indicated that these mtDNA lineages in P. australiensis were reproductively isolated and thus biological species. 3. Populations of both lineages were genetically homogeneous among lowland sites within streams, but were isolated by steep stream gradients among upland sites and for lowland–upland site comparisons. However, the magnitude of differentiation was markedly different between the two lineages. Allozyme diversity also differed between the two lineages, suggesting that they have different effective population sizes. Thus, differences in the magnitude of genetic divergence among populations were probably because of different life‐history characteristics, including dispersal ability and population size. 4. Genetic population structure was mostly temporally stable, despite the extreme effects of drought during the first year and substantial stream‐flow during the second. However, stable isotope analyses revealed greater local movement in both lineages during the second year, as greater hydrological connectivity provided more opportunities for dispersal. Thus, although lowland populations within streams were genetically homogeneous, stable isotope data indicated that connections may be sporadic and result from accumulated small‐scale movements among refugial pools. 5. Both lineages were therefore found to have similar small‐scale population responses to the unstable habitats of the Granite Creeks. Results highlight the importance of refugia for the capacity of biota to recover from drought and the need for multiple restored patches to reinstate natural population processes (e.g. resilience, recolonization) in degraded systems.     

Patterns of spatial genetic structuring in a hydropsychid caddisfly (Cheumatopsyche sp. AV1) from southeastern Australia

We assessed levels of mitochondrial genetic spatial structuring in the hydropsychid caddisfly Cheumatopsyche sp. AV1 in southeastern New South Wales, Australia. No significant spatial structuring was detected within or between catchments using analysis of molecular variance, and nested clade contingency analysis suggested no strong relationship between haplotypes and geographical location, at any clade level. However, tests for association among haplotypes incorporating geographical distance in the nested clade analysis, revealed patterns of historical range expansion and recent restricted gene flow. Most likely, population fragmentation preceded range expansion, although subsequent recontact and gene flow among the previously sundered populations has apparently obscured the geographical signature of the former fragmentation. Taken together, our analyses suggest that a number of populations fragmented during the Pleistocene evolved in isolation for a time and subsequently expanded into secondary contact. Since expansion, there has apparently been substantial (albeit somewhat restricted) dispersal and gene flow of adult female Cheumatopsyche sp. AV1, throughout the study area.     

Small‐scale patterns of genetic variation in a headwater specialist mayfly: No influence of selective forest harvesting on diversity

Terrestrial environments allow the adults of some aquatic insects to disperse between headwater streams, which may be important for maintaining population connectivity and persistence. Winged adult stages of aquatic insects are particularly sensitive to degradation of terrestrial habitat, relying on it for food, reproduction and dispersal. In this study we examined the genetic pattern of the Australian mayfly Ulmerophlebia sp. AV2, in north‐eastern New South Wales, and compared the genetic diversity in forested and partially deforested sub‐catchments. Our hypotheses were (i) patterns of mitochondrial DNA (mtDNA) variation in the Leptophlebiidae mayfly Ulmerophlebia sp. AV2 show a pattern of structuring that reflects low or widespread dispersal along the stream network and across catchments; and (ii) genetic diversity will be lower in partially deforested sub‐catchments compared to forested sub‐catchments. We found gene flow was not restricted among headwater streams within sub‐catchments but was restricted at distances >15 km. Genetic diversity was high (mean haplotype diversity >0.85) in both control and harvested sub‐catchments. Instead, a historical signature of population expansion was detected which is consistent with findings for other aquatic insect taxa of eastern Australia. Our results suggest that the selective harvesting management strategy, including the use of riparian buffer zones, within these sub‐catchments does not appear to restrict dispersal between streams or erode diversity within streams for Ulmerophlebia sp. AV2. Selective harvesting therefore appears to have minimal impacts on terrestrial/aquatic links in the life cycle of this insect.     

Scale‐dependent genetic structure of the Idaho giant salamander (Dicamptodon aterrimus) in stream networks

The network architecture of streams and rivers constrains evolutionary, demographic and ecological processes of freshwater organisms. This consistent architecture also makes stream networks useful for testing general models of population genetic structure and the scaling of gene flow. We examined genetic structure and gene flow in the facultatively paedomorphic Idaho giant salamander, Dicamptodon aterrimus, in stream networks of Idaho and Montana, USA. We used microsatellite data to test population structure models by (i) examining hierarchical partitioning of genetic variation in stream networks; and (ii) testing for genetic isolation by distance along stream corridors vs. overland pathways. Replicated sampling of streams within catchments within three river basins revealed that hierarchical scale had strong effects on genetic structure and gene flow. amova identified significant structure at all hierarchical scales (among streams, among catchments, among basins), but divergence among catchments had the greatest structural influence. Isolation by distance was detected within catchments, and in‐stream distance was a strong predictor of genetic divergence. Patterns of genetic divergence suggest that differentiation among streams within catchments was driven by limited migration, consistent with a stream hierarchy model of population structure. However, there was no evidence of migration among catchments within basins, or among basins, indicating that gene flow only counters the effects of genetic drift at smaller scales (within rather than among catchments). These results show the strong influence of stream networks on population structure and genetic divergence of a salamander, with contrasting effects at different hierarchical scales.     

Reconciling patterns of genetic variation with stream structure, earth history and biology in the Australian freshwater fish Craterocephalus stercusmuscarum (Atherinidae)

We examined the consequences of barriers, stream architecture and putative dispersal capability on levels of genetic differentiation among populations of the freshwater fish Craterocephalus stercusmuscarum. Seven polymorphic allozyme loci and sequences of a 498-bp fragment of the ATPase 6 mitochondrial DNA (mtDNA) gene were used to assess patterns of genetic variation among 16 populations from upland and lowland streams of five drainages in northern Queensland, Australia. Concordant patterns at both genetic markers revealed that there were significant levels of genetic subdivision among all populations, while an analysis of molecular variation showed that the distribution of genetic diversity was not consistent with contemporary drainage structure. There were reciprocally monophyletic mtDNA clades and fixed or large frequency differences at allozyme loci either side of instream barriers such as waterfalls. This implied barriers were effective in restricting gene flow between upland and lowland populations separated by waterfalls. However, there were two genetically distinct groups in upland areas, even within the same subcatchment, as well as high levels of genetic subdivision among lowland populations, suggesting barriers alone do not explain the patterns of genetic diversity. The data revealed a complex phylogeographic pattern, which we interpreted to be the result of one or more invasion events of independent lineages to different sections of each drainage, possibly mediated by well documented geomorphological changes. Our results highlight the importance of earth structure and history in shaping population genetic structure in stream organisms where dispersal capability may be limited, and reveal that the contemporary structure of drainages is not necessarily a good indicator of genetic relationships among populations.     

Telemetry and genetics reveal asymmetric dispersal of a lake‐feeding salmonid between inflow and outflow spawning streams at a microgeographic scale

The degree of natal philopatry relative to natal dispersal in animal populations has important demographic and genetic consequences and often varies substantially within species. In salmonid fishes, lakes have been shown to have a strong influence on dispersal and gene flow within catchments; for example, populations spawning in inflow streams are often reproductively isolated and genetically distinct from those spawning in relatively distant outflow streams. Less is known, however, regarding the level of philopatry and genetic differentiation occurring at microgeographic scales, for example, where inflow and outflow streams are separated by very small expanses of lake habitat. Here, we investigated the interplay between genetic differentiation and fine‐scale spawning movements of brown trout between their lake‐feeding habitat and two spawning streams (one inflow, one outflow, separated by <100 m of lake habitat). Most (69.2%) of the lake‐tagged trout subsequently detected during the spawning period were recorded in just one of the two streams, consistent with natal fidelity, while the remainder were detected in both streams, creating an opportunity for these individuals to spawn in both natal and non‐natal streams. The latter behavior was supported by genetic sibship analysis, which revealed several half‐sibling dyads containing one individual that was sampled as a fry in the outflow and another that was sampled as fry in the inflow. Genetic clustering analyses in conjunction with telemetry data suggested that asymmetrical dispersal patterns were occurring, with natal fidelity being more common among individuals originating from the outflow than the inflow stream. This was corroborated by Bayesian analysis of gene flow, which indicated significantly higher rates of gene flow from the inflow into the outflow than vice versa. Collectively, these results reveal how a combination of telemetry and genetics can identify distinct reproductive behaviors and associated asymmetries in natal dispersal that produce subtle, but nonetheless biologically relevant, population structuring at microgeographic scales.     

Population structure in the freshwater shrimp (Paratya australiensis) inferred from allozymes and mitochondrial DNA

In 1995, an allozyme study was conducted on the genetic structure of a population of the common atyid shrimp, Paratya australiensis, in the Conondale Range, south-eastern Queensland with two subcatchments each within two river drainages sampled. The allozyme study revealed a high degree of population structure, with the data interpreted as reflecting a pattern of restricted contemporary gene flow, primarily between streams within subcatchments. High levels of differentiation occurred between all subcatchments. In this study, we analysed a partial fragment of the mitochondrial COI gene in order to further test and verify these results. The mtDNA data largely conflicted with the hypothesis of restricted gene flow indicating that contemporary dispersal was highly unlikely, even between streams within subcatchments, with many sites fixed for unique mtDNA haplotypes. Additionally, the level of divergence between the Stony Creek subcatchment and all other sampling sites indicated that it had been isolated for approximately 2-3 million years, while low levels of divergence were detected across the Conondale Range between the Kilcoy and Booloumba Creek subcatchments. The sharing of alleles at certain allozyme loci between all subcatchments is, therefore, likely to be the result of ancestral retention and possibly because of the effects of balancing selection.     

Biogeographic history of an Australian freshwater shrimp, Paratya australiensis (Atyidae): the role life history transition in phylogeographic diversification

The widespread distribution of the freshwater shrimp Paratya australiensis in eastern Australia suggests that populations of this species have been connected in the past. Amphidromy is ancestral in these shrimps, although many extant populations are known to be restricted to freshwater habitats. In this study, we used a fragment of the cytochrome c oxidase I mitochondrial DNA (mtDNA) gene to examine diversity within P. australiensis and to assess the relative importance of amphidromy in its evolutionary history. We hypothesized that if transitions from an amphidromous to a freshwater life history were important, then we would find a number of divergent lineages restricted to single or groups of nearby drainages. Alternatively, if amphidromy was maintained within the species historically, we expected to find lineages distributed over many drainages. We assumed that the only way for divergence to occur within amphidromous lineages was if dispersal was limited to between nearby estuaries, which, during arid periods in the earth's history, became isolated from one another. We found nine highly divergent mtDNA lineages, estimated to have diverged from one another in the late Miocene/early Pliocene, when the climate was more arid than at present. Despite this, the geographic distribution of lineages and haplotypes within lineages did not support the notion of a stepping-stone model of dispersal between estuaries. We conclude that the extensive divergence has most likely arisen through a number of independent amphidromy-freshwater life history transitions, rather than via historical isolation of amphidromy populations. We also found evidence for extensive movement between coastal and inland drainages, supporting the notion that secondary contact between lineages may have occurred as a result of drainage rearrangements. Finally, our data indicate that P. australiensis is likely a complex of cryptic species, some of which are widely distributed, and others geographically restricted.     

Evidence for multiple historical colonizations of an endoreic drainage basin by an Australian freshwater fish

The contemporary and historical colonization capacity of an Australian freshwater fish, north-west glassfish Ambassis sp., was tested using mtDNA sequence data and six newly developed microsatellite loci in an endoreic basin in central Australia. Overall, Ambassis sp. exhibited weak genetic structure within catchments, suggesting some capacity to recolonize extirpated waterholes after disturbance. Genetic structure revealed that the historical pattern of connectivity among catchments in the Lake Eyre Basin was dramatically different from other species studied in this region. Two highly divergent clades were detected in separate catchments in the basin. mtDNA from individuals sampled in catchments north of the Lake Eyre Basin suggest that Ambassis sp. has colonized on two separate occasions from catchments in northern Australia, subsequently generating two highly divergent lineages.     

Spatial genetic structure of aquatic bryophytes in a connected lake system

Using genetic markers, we investigated the genetic structure of three clonal aquatic moss species, Calliergon megalophyllum Mikut., Fontinalis antipyretica Hedw. and F. hypnoides Hartm. on two scales: among populations in a connected lake system (large‐scale spatial genetic structure) and among individuals within populations (fine‐scale spatial genetic structure). Mean genetic diversities per population were 0.138, 0.247 and 0.271, respectively, and total diversities equalled 0.223, 0.385 and 0.421, respectively. Relative differentiation levels (F_ST values of 0.173, 0.280 and 0.142, respectively) were significant but showed that there is a moderate amount of gene flow taking place within the lake system connected with narrow streams. Bayesian STRUCTURE analysis provided some indication that the direction of water flow influences population genetic structuring in the studied aquatic mosses. We propose that dispersal leading to gene flow in C. megalophyllum, F. antipyretica and F. hypnoides takes place both along water via connecting streams and by animal vectors, such as waterfowl. Nevertheless, the slight genetic structuring pattern along the direction of water flow suggests that dispersal of shoots or their fragments along water is a means of dispersal in these mosses. The absence of sexual reproduction and spores may have caused the observed spatial genetic structure within populations, including aggregations of similar genotypes (clones or closely related genotypes) at short distances in populations otherwise showing an isolation by distance effect. Regardless of the results pointing to the dominance of vegetative propagation, it is impossible to completely rule out the potential role of rare long‐distance spore dispersal from areas where the species are fertile.     

Molecular Phylogeography and Population Genetic Structure of an Endangered Species Pachyhynobius shangchengensis (hynobiid Salamander) in a Fragmented Habitat of Southeastern China

The salamander Pachyhynobius shangchengensis (Hynobiidae) is a vulnerable species restricted to a patchy distribution associated with small mountain streams surrounded by forested slopes in the Mount Dabieshan region in southeastern China. However, molecular phylogeography and population genetic structure of P. shangchengensis remain poorly investigated. In this study, we explored the genetic structure and phylogeography of P. shangchengensis based on partial sequences of the mitochondrial DNA (mtDNA) cytochrome b and cytochrome c oxidase subunit I genes. Fifty-one haplotypes and four clades were found among 93 samples. Phylogenetic analyses revealed four deeply divergent and reciprocally monophyletic mtDNA lineages that approximately correspond to four geographic regions separated by complicated topography and long distances. The distinct geographic distributions of all lineages and the estimated divergence time suggest spatial and temporal separation coinciding with climatic changes during the Pleistocene. Analysis of molecular variance indicated that most of the observed genetic variation occurred among the four groups, implying long-term interruption of gene flow, and the possible separation of P. shangchengensis into four management units for conservation.     

Patterns of gene flow in two species of eel-tailed catfish, Neosilurus hyrtlii and Porochilus argenteus (Siluriformes: Plotosidae), in western Queensland's dryland rivers

Using genetic techniques (mtDNA, microsatellites and allozymes), this study investigated patterns of gene flow in two plotosid catfish species ( Neosilurus hyrtlii and Porochilus argenteus ), at various hierarchical scales in the dryland rivers of western Queensland, Australia. The study area constituted two major catchments, Cooper and Darling, representing arid and semiarid systems, respectively. Results generally conformed to expectations, with high levels of gene flow observed within catchments and limited contemporary gene flow evident across catchment boundaries. However, the isolation between catchments was more recent than expected, occurring approximately 40 000–72 000 years ago. Also contrary to predictions, genetic structure within the Cooper catchment did not fit the stream hierarchy model of genetic differentiation, which there was evidence of in the Darling catchment. This was hypothesized to relate to the different climatic regimes and hydrological inputs in each system, leading to a more genetically homogeneous system in the Cooper than in the Darling system.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 457–467.     

Landscape, habitat characteristics and the genetic population structure of two caddisflies

1. In a region of south‐eastern England, we investigated the hierarchical genetic structure of populations of two stream‐dwelling caddisflies (Trichoptera: Polycentropodidae) with contrasting distributions: Plectrocnemia conspersa inhabits numerous small, patchily distributed seeps and streams, while the confamilial Polycentropus flavomaculatus is found in fewer but larger streams and rivers. We also contrasted the genetic structure of P. conspersa in the lowland south‐east with that in an upland region in the north west. 2. Microsatellite genotypes were obtained from samples of both species taken from a ‘core area’ and at sites 15, 40 and 100 km from this core (two regions for P. conspersa, totalling 45 sites and 1405 larvae; one region for P. flavomaculatus, totalling 10 sites and 269 larvae). 3. The genetic structure of P. conspersa differed in the two regions. In the upland north‐west, significant genetic differentiation was observed at a spatial scale of around 40 km from the core, while there was no structure in the lowland south‐east up to around 100 km. Areas of high altitude did not appear directly to reduce gene flow, whereas other potential landscape barriers, including particular geological formations, large urban areas and the sea had a pronounced effect. 4. Weak genetic differentiation in P. conspersa across large distances, particularly in the lowland south‐east, suggests that it disperses strongly, facilitating gene flow within and between catchments. Conversely, for P. flavomaculatus we found strong genetic differentiation between almost all sites, suggesting that dispersal is much more limited. 5. Greater dispersal in the patchily distributed P. conspersa than in P. flavomaculatus, which occupies larger and presumably more persistent habitats, could be a general feature of other similarly distributed aquatic insects. While higher relief is potentially a partial barrier to dispersal, P. conspersamust have effective gene flow through such apparently inhospitable terrain, perhaps attributable to dispersal between neighbouring small and ephemeral populations. Indeed, its exploitation of headwaters and seeps requires the ability to disperse between such sites. Apparently it cannot, however, overcome more continuous barriers, consisting of large tracts of landscape with few habitable larval sites. Such landscapes, including those created by humans, may have a stronger effect on population connectivity and colonization in the longer term.     

Phylogeography and Population Genetic Structure of the Ornate Dragon Lizard, Ctenophorus ornatus

Species inhabiting ancient, geologically stable landscapes that have been impacted by agriculture and urbanisation are expected to have complex patterns of genetic subdivision due to the influence of both historical and contemporary gene flow. Here, we investigate genetic differences among populations of the granite outcrop-dwelling lizard Ctenophorus ornatus, a phenotypically variable species with a wide geographical distribution across the south-west of Western Australia. Phylogenetic analysis of mitochondrial DNA sequence data revealed two distinct evolutionary lineages that have been isolated for more than four million years within the C. ornatus complex. This evolutionary split is associated with a change in dorsal colouration of the lizards from deep brown or black to reddish-pink. In addition, analysis of microsatellite data revealed high levels of genetic structuring within each lineage, as well as strong isolation by distance at multiple spatial scales. Among the 50 outcrop populations’ analysed, non-hierarchical Bayesian clustering analysis revealed the presence of 23 distinct genetic groups, with outcrop populations less than 4 km apart usually forming a single genetic group. When a hierarchical analysis was carried out, almost every outcrop was assigned to a different genetic group. Our results show there are multiple levels of genetic structuring in C. ornatus, reflecting the influence of both historical and contemporary evolutionary processes. They also highlight the need to recognise the presence of two evolutionarily distinct lineages when making conservation management decisions on this species.     

Spatial genetic structure among and within populations of Primula sieboldii growing beside separate streams

We investigated the hierarchical genetic structure of SSR (simple sequence repeats) and cpDNA (chloroplast DNA) polymorphisms among and within populations of Primula sieboldii, a heterostylous clonal herb. Seven out of eight populations at the study site, located in a mountainous region of Nagano Prefecture, had each developed alongside a different stream, and the other occurred on a flat area 70 m from the nearest stream. The magnitude of genetic differentiation among streamside populations in maternally inherited cpDNA (Phi = 0.341) was much higher than that in biparentally inherited SSRs (Phi = 0.011). This result suggests that seed dispersal among streams was restricted, and pollen was the primary agent of gene flow among streamside populations. In contrast, genetic differentiation among subpopulations within streams were low at both markers (Phi = 0.053 for cpDNA, Phi = 0.025 for SSR). This low differentiation among subpopulations in cpDNA compared with that among streamside populations suggest that seed dispersal occur along the stream probably during flooding. This hypothesis was supported by the fact that in cpDNA haplotypes, no clear genetic structure was detected within the streamside population, while a significant genetic structure was found within 20 m in the nonstreamside population. Furthermore, within the streamside populations, two pairs of ramets with identical multilocus genotypes for eight SSR loci were distantly (> 50 m) distributed along the same streamside, suggesting dispersal of clonal propagule. Our study showed that the heterogeneity of the landscape can influence gene flow and hence spatial genetic structure.     

Dispersal and recruitment of Tasiagma ciliata (Trichoptera: Tasimiidae) in rainforest streams, south-eastern Australia

1. This study examined genetic variation within and among populations of the caddis fly Tasiagma ciliata (Tasimiidae: Trichoptera) from rainforest streams in south-east Queensland, Australia.
2. Very low levels of genetic differentiation at large spatial scales, between subcatchments and between catchments, indicated that dispersal by the winged adults is widespread. However, significant genetic differentiation at the smallest spatial scale examined, within reaches in a single stream, suggested limited movement by larvae within streams.
3. A patchy distribution of deviations from Hardy–Weinberg equilibrium and differences in patterns among allozyme loci suggested that populations in particular reaches were the result of only a few matings.
4. These results are surprising, given the large numbers of larvae present within a single reach. We suggest that stochastic effects of recruitment may underlie much of the spatial and temporal variation in population numbers in these rainforest streams.     

Quantifying Spatial Genetic Structuring in Mesophotic Populations of the Precious Coral Corallium rubrum

While shallow water red coral populations have been overharvested in the past, nowadays, commercial harvesting shifted its pressure on mesophotic organisms. An understanding of red coral population structure, particularly larval dispersal patterns and connectivity among harvested populations is paramount to the viability of the species. In order to determine patterns of genetic spatial structuring of deep water Corallium rubrum populations, for the first time, colonies found between 58–118 m depth within the Tyrrhenian Sea were collected and analyzed. Ten microsatellite loci and two regions of mitochondrial DNA (mtMSH and mtC) were used to quantify patterns of genetic diversity within populations and to define population structuring at spatial scales from tens of metres to hundreds of kilometres. Microsatellites showed heterozygote deficiencies in all populations. Significant levels of genetic differentiation were observed at all investigated spatial scales, suggesting that populations are likely to be isolated. This differentiation may by the results of biological interactions, occurring within a small spatial scale and/or abiotic factors acting at a larger scale. Mitochondrial markers revealed significant genetic structuring at spatial scales greater then 100 km showing the occurrence of a barrier to gene flow between northern and southern Tyrrhenian populations. These findings provide support for the establishment of marine protected areas in the deep sea and off-shore reefs, in order to effectively maintain genetic diversity of mesophotic red coral populations.     

Indo-West Pacific patterns of genetic differentiation in the high-dispersal starfish Linckia laevigata

Genetic variation in four natural populations of the starfish Linckia laevigata from the Indo-West Pacific was examined using restriction fragment analysis of a portion of the mtDNA including the control region. Digestion with seven restriction enzymes identified 47 haplotypes in a sample of 326 individuals. Samples collected from reef sites within each location were not significantly differentiated based on Φ_ST or spatial distribution of haplotypes, indicating that dispersal is high over short to moderate distances. Evidence of gene flow is further supported by the low divergence among haplotypes and the lack of any clear geographical structuring among different haplotypes in the gene phylogeny. However, analysis of molecular variance ( AMOVA ), Φ_ST and contingency χ² analyses of the spatial distribution of haplotypes demonstrate the presence of significant broad scale population genetic structure among the four widespread locations examined. RFLP data are consistent with high gene flow between the Philippines and Western Australia and moderate gene flow between the Great Barrier Reef (GBR) and Fiji, but only limited gene flow between either the Philippines or Western Australia and either the GBR or Fiji. The presence of mtDNA structure contrasts with previous allozyme data which suggest that dispersal among widely separated locations is equivalent to dispersal among populations within the highly connected GBR studies. This discordance between patterns of gene flow inferred from these two markers cannot be fully accounted for by differences in effective population size for mtDNA. This might suggest that while mtDNA variation may represent contemporary patterns of gene flow, allozyme variation among populations is yet to reach equilibrium between drift and migration over the range surveyed.     

Glacial vicariance and historical biogeography of rock ptarmigan (Lagopus mutus) in the Bering region

In this paper, we address alternative hypotheses for the evolution of subspecies of rock ptarmigan (Lagopus mutus) endemic to the Aleutian Archipelago. To do this we examined patterns of genetic differentiation among populations of rock ptarmigan in the Aleutian Islands and parts of both Alaska and Siberia. Variation in mitochondrial control region sequences of 105 rock ptarmigan from 10 subspecies within the Bering region revealed three major phylogenetic lineages, two of which are endemic to the Aleutian Islands. Accordingly, haplotype and nucleotide diversities of rock ptarmigan within the archipelago are much higher than within mainland Alaska or Siberia. For Aleutian rock ptarmigan, analyses of molecular variance indicated significant genetic structuring and low estimates of gene flow among populations, despite small interisland distances within the archipelago. However, isolation by distance did not describe the pattern of gene flow or differentiation at this scale. Our estimates of divergence times of lineages suggest that Aleutian rock ptarmigan became isolated prior to the most recent Pleistocene glaciation event (late Wisconsin Stade) and that current patterns of genetic variation reflect the postglacial redistribution of divergent lineages and subsequent limited gene flow. In addition, genetic divergence among lineages was concordant with the distribution of plumage types among subspecies. The patterns of genetic variation described here for rock ptarmigan provide evidence for the role of glacial vicariance in contributing to genetic diversity within this and other Bering region species.     

Restricted mating dispersal and strong breeding group structure in a mid-sized marsupial mammal (Petrogale penicillata)

Ecological genetic studies have demonstrated that spatial patterns of mating dispersal, the dispersal of gametes through mating behaviour, can facilitate inbreeding avoidance and strongly influence the structure of populations, particularly in highly philopatric species. Elements of breeding group dynamics, such as strong structuring and sex-biased dispersal among groups, can also minimize inbreeding and positively influence levels of genetic diversity within populations. Rock-wallabies are highly philopatric mid-sized mammals whose strong dependence on rocky terrain has resulted in series of discreet, small colonies in the landscape. Populations show no signs of inbreeding and maintain high levels of genetic diversity despite strong patterns of limited gene flow within and among colonies. We used this species to investigate the importance of mating dispersal and breeding group structure to inbreeding avoidance within a 'small' population. We examined the spatial patterns of mating dispersal, the extent of kinship within breeding groups, and the degree of relatedness among brush-tailed rock-wallaby breeding pairs within a colony in southeast Queensland. Parentage data revealed remarkably restricted mating dispersal and strong breeding group structuring for a mid-sized mammal. Breeding groups showed significant levels of female kinship with evidence of male dispersal among groups. We found no evidence for inbreeding avoidance through mate choice; however, anecdotal data suggest the importance of life history traits to inbreeding avoidance between first-degree relatives. We suggest that the restricted pattern of mating dispersal and strong breeding group structuring facilitates inbreeding avoidance within colonies. These results provide insight into the population structure and maintenance of genetic diversity within colonies of the threatened brush-tailed rock-wallaby.