Dispersal of aquatic organisms by waterbirds: a review of past research and priorities for future studies

1. Inland wetlands constitute ecological islands of aquatic habitat often isolated by huge areas of non-suitable terrestrial habitats. Although most aquatic organisms lack the capacity to disperse by themselves to neighbouring catchments, many species present widespread distributions consistent with frequent dispersal by migratory waterbirds.
2. A literature review indicates that bird-mediated passive transport of propagules of aquatic invertebrates and plants is a frequent process in the field, at least at a local scale. Both endozoochory (internal transport) and ectozoochory (external transport) are important processes.
3. The characteristics of the dispersed and the disperser species that facilitate such transport remain largely uninvestigated, but a small propagule size tends to favour dispersal by both internal and external transport.
4. We review the information currently available on the processes of waterbird-mediated dispersal, establishing the limits of current knowledge and highlighting problems with research methods used in previous studies. We also identify studies required in the future to further our understanding of the role of such dispersal in aquatic ecology.     

Consequences of large-scale processes for the conservation of bird populations

1.  Detailed studies of population ecology are usually carried out in relatively restricted areas in which emigration and immigration play a role. We used a modelling approach to explore the population consequences of such dispersal and applied ideas from our simulations to the conservation of wild birds.
2.  Our spatial model incorporates empirically derived variation in breeding output between habitats, density dependence and dispersal. The outputs indicate that dispersal can have considerable consequences for population abundance and distribution. The abundance of a species within a patch can be markedly affected by the surrounding habitat matrix.
3.  Dispersal between habitats may result in lower population densities at the edge of good quality habitat blocks and could partially explain why some species are restricted to large habitat fragments.
4.  Habitat deterioration may not only lead to population declines within that habitat but also in adjacent habitats of good quality. This may confound studies attempting to diagnose population declines.
5.  Although mobile species have the advantages of colonizing sites within metapopulations, dispersal into poorer quality territories may markedly reduce total populations.
6.  There are two main approaches to conservation: one is to concentrate on establishing and maintaining protected areas, while the other involves conservation of the wider countryside. If dispersal is an important process then protecting only isolated areas may be insufficient to maintain the populations within them.     

Modelling species distribution in complex environments: an evaluation of predictive ability and reliability in five shorebird species

Aim  Many wader populations around the world are declining as a consequence of habitat degradation or loss. It is therefore important to identify species-specific habitat demands accurately and to define the important factors explaining species distribution, in order to develop tools that can be used in conservation planning. The aim of this study is to create reliable, functional and ecologically interpretable predictive distribution models for five breeding wader species.
Location  The archipelago of SW Finland in the Baltic Sea.
Methods  We used multivariate adaptive regression splines (MARS) to create single-species and multiresponse distribution models based on 525 study islands and 12 abiotic and biotic environmental variables. Model evaluation was carried out on independent data not used in model building (100 + 116 islands). The models were tested for discrimination with receiver-operating characteristic statistics and for calibration with Millers calibration statistics (MCS).
Results  The single-species models for the turnstone ( Arenaria interpres ), redshank ( Tringa totanus ) and oystercatcher ( Haematopus ostralegus ) showed good predictive abilities, regarding both discrimination and calibration, when evaluated on independent data. The multiresponse models for the less prevalent species, common sandpiper ( Actitis hypoleucos ) and the common ringed plover ( Charadrius hiaticula ) had better discriminative abilities than the single-species models. The most influential predictor overall was occurrence of small larids. Exposure, area of forest and low and flat areas were also important, as well as shore habitats.
Main conclusions  We found that the ability of MARS to fit non-linear and multiresponse models makes it a useful method to quantitatively relate species occurrence to environmental characteristics of a complex environment.     

Factors shaping the range-size frequency distribution of the endemic fish fauna of the Tropical Eastern Pacific

Aim To assess the effect of habitat fragmentation and isolation in determining the range‐size frequency distribution (RFD) of the shorefish fauna endemic to a discrete biogeographical region. Location The Tropical Eastern Pacific (TEP). Methods Habitat isolation represents the separation between oceanic islands and the continental shore of the TEP and habitat fragmentation the degree of spatial continuity of habitats (i.e. reefs, soft bottom, nearshore waters) along the continental coast of the TEP. The effects of habitat isolation and fragmentation were quantified by comparing the RFDs of (1) the species found on oceanic islands vs. the continental shore, and (2) species on the continental shore that use different habitat types. Results The RFD of the entire TEP fauna was bimodal, with peaks at both small‐ and large‐range ends of the spectrum. The small‐range peak was due almost entirely to island species and the large‐range peak due mainly to species found in both the continental shore and oceanic islands. RFDs varied among species using different habitats on the continental shore: reef‐fishes had a right‐skewed RFD, soft‐bottom species a flat RFD, and coastal‐pelagic fishes a left‐skewed RFD. Main conclusions Variation in dispersal capabilities associated with habitat isolation and fragmentation in the TEP appears to be the main mechanism contributing to differences among RFD structure, although variation in tolerances arising from the dynamic regional environment may contribute to some patterns. Because diversity patterns are strongly affected by RFD structure, it is now evident that the insular and continental components of a fauna should be treated separately when analysing such patterns. Furthermore, contrasts in RFD structure among species using different habitats demonstrate that a full understanding of the causes of diversity patterns requires analyses of complete regional faunas in relation to regional geography.     

Sibling speciation by life-history divergence in Dendropoma (Gastropoda; Vermetidae)

Dendropoma meroclista has been found on six islands and one continental site between Hawaii and Kenya; it occurs in shallow-subtidal and low-intertidal habitats and has either no, or very limited, planktic development. A very similar form has been found only in the Indian Ocean (Sinai and Madagascar), where it forms gregarious masses on exposed intertidal ledges. This form also produces many more, smaller eggs than the described species and has a planktotrophic larva. While adult anatomies of the two forms are indistinguishable, the Sinai-Madagascar form has a smaller protoconch with distinctive sculpture. These apparent sibling species provide a case of speciation occurring by life-history divergence within a very conservative morphology and present a surprising example of wider distributional range in the species with little apparent capacity for dispersal.     

Cosmopolitan metapopulations of free-living microbial eukaryotes

Metapopulations of macroscopic organisms tend to be geographically restricted, but free-living protists and other microbial eukaryotes present a different picture. Here we show that most organisms smaller than 1 mm occur worldwide wherever their required habitats are realised. This is a consequence of ubiquitous dispersal driven by huge population sizes, and the consequently low probability of local extinction. Organisms larger than 10 mm are much less abundant, and rarely cosmopolitan. The supporting data, together with the discovery that the 1-10 mm size range accommodates a transition from cosmopolitan to regionally-restricted distribution, were derived from extensive inventories of eukaryotic species in a freshwater pond (1278 species), and a shallow marine bay (785 species). All accessible records were examined to establish the extent of global coverage by these species. Some groups of microbial eukaryotes are severely undersampled (e.g. naked amoebae; marine meiofauna in the southern hemisphere) but this fails to weaken evidence that metapopulations of microbial eukaryotes are cosmopolitan.     

Dormancy, dispersal and the survival of cyclopoid copepods (Cyclopoida, Copepoda) in a lowland floodplain

1. The survival of cyclopoid copepods was investigated in a floodplain for 2 years where flooding occurred during the cold season. The cyclopoid community was studied in three waterbodies with distinct hydroperiods: a permanent pond connected to the flooded area during inundation, a temporary pool that is part of the flooded area and an isolated temporary pool.
2. Field studies, including data obtained from samples of water, sediment and soil, showed the overall predominance of species with a summer diapause over those with a winter diapause or without diapause. Emergence of cyclopoid copepods at the onset of flooding, examined using emergence traps and data from recently filled or still isolated temporary pools, showed that some species can survive several months of drying.
3. The ability of the diapausing fourth copepodid stages of Cyclops strenuus and C. insignis , the two cyclopoids most abundant during winter and spring flooding, to survive terrestrial conditions was tested in laboratory experiments. Both species survived for several months, but rates differed among the species. A higher percentage of C. strenuus survived for a longer period, possibly explaining why this species was relatively more abundant in more temporary habitats.
4. Both dormancy and dispersal facilitated survival of cyclopoid copepods in transient habitats connected to each other during flood periods. Dormancy was the most important survival strategy, whereas dispersal could be more important following prolonged periods without flooding.     

Phylogeny and biogeography of water skinks of the genus Tropidophorus (Reptilia: Scincidae): a molecular approach

Phylogenetic relationships of the Oriental semiaquatic lygosomine skinks of the genus Tropidophorus were inferred from 1219 base positions of mitochondrial 12S and 16S rRNA genes. Results of the phylogenetic analyses incorporating data for representatives of other lygosomine genera indicated that the basal phylogenetic split within Tropidophorus separated a clade of continental Indochinese species exclusive of T. cocincinensis and T. microlepis from one comprising T. cocincinensis , T. microlepis and species from Borneo, Sulawesi and the Philippines. Of the latter group, the two continental species form the sister taxon to a clade comprising the island species. Diversification among species in Indochina and among Borneo, the Philippines and Sulawesi was likely concentrated in the Miocene, with no apparent dispersal among these regions during the Pleistocene. The body depression recognized in several Indochinese species is likely to have occurred twice in parallel as an adaptation to saxicolous habitats.     

Latitudinal variation of diversity in European freshwater animals is not concordant across habitat types

Aim   We analysed the variation of species richness in the European freshwater fauna across latitude. In particular, we compared latitudinal patterns in species richness and β-diversity among species adapted to different habitat types.
Location   Europe.
Methods   We compiled data on occurrence for 14,020 animal species across 25 pre-defined biogeographical regions of European freshwaters from the Limnofauna Europaea . Furthermore, we extracted information on the habitat preferences of species. We assigned species to three habitat types: species adapted to groundwater, lotic (running water) and lentic (standing water) habitats. We analysed latitudinal patterns of species richness, the proportion of lentic species and β-diversity.
Results   Only lentic species showed a significant species–area relationship. We found a monotonic decline of species richness with latitude for groundwater and lotic habitats, but a hump-shaped relationship for lentic habitats. The proportion of lentic species increased from southern to northern latitudes. β-Diversity declined from groundwater to lentic habitats and from southern to northern latitudes.
Main conclusions   The differences in the latitudinal variation of species richness among species adapted to different habitat types are in part due to differences in the propensity for dispersal. Since lentic habitats are less persistent than lotic or groundwater habitats, lentic species evolved more efficient strategies for dispersal. The dispersal propensity of lentic species facilitated the recolonization of central Europe after the last glaciation. Overall, we stress the importance of considering the history of regions and lineages as well as the ecological traits of species for understanding patterns of biodiversity.     

The distribution of purse-web Atypus spiders (Araneae: Mygalomorphae) in central Europe is constrained by microclimatic continentality and soil compactness

Aim  Three species of primitive spiders of the genus Atypus occur in European xerothermic habitats, where they live in burrows. The aim of this study is to explain their distribution by investigating environmental variables at sites where they occur in central Europe.
Location  Over 50 sites in central Europe, Czech Republic.
Methods  Data on climatic, edaphic and vegetational parameters were collected from more than 50 sites. Phytocenological data were processed using Ellenberg's indicator values.
Results  Atypus muralis was found to occur almost exclusively in dry grassland (Festucion valesiacae), exposed to a continental microclimate. Atypus affinis usually occurred in dry sparse forests (Genisto germanicae–Quercion) that provide an Atlantic microclimate. Atypus piceus occurred in dry grassland (Bromion erecti) or forest fringes (Geranion sanguinei) characterized by an intermediate microclimate. Atypus piceus and A. muralis were restricted to agglutinate calcareous soils.
Main conclusions  Our results show that Atypus species colonized sites with different continentality in central Europe. These differences correspond to differences among their probable glacial refugia. Atypus muralis and A. piceus occur in habitats with a markedly continental climate, and are restricted to calcareous agglutinate soils that more efficiently buffer temperature and humidity extremes. Habitats of A. muralis and A. piceus are threatened by overgrowth of vegetation after a recent decline in grazing and by the decalcification of the landscape. However, habitats of A. affinis are stable in the present central European climate.     

Regional genetic diversity patterns in Antarctic hairgrass (Deschampsia antarctica Desv.)

Aim  To determine patterns in diversity of a major Antarctic plant species, including relationships of Antarctic populations with those outside the Antarctic zone.
Location  Antarctic Peninsula, Maritime Antarctica, sub-Antarctic islands, Falkland Islands and South America.
Methods  Amplified fragment length polymorphisms (AFLPs) and chloroplast sequences were used to study patterns of genetic diversity in Antarctic hairgrass ( Deschampsia antarctica Desv.) and the genetic relationships between populations over its distribution range. Thirty-eight populations were sampled from a large part of the distribution of D. antarctica , and additionally, herbarium specimens were included for areas from which we could not obtain fresh samples.
Results  A gradient in AFLP diversity was observed going from the Falklands southwards into the Antarctic. This gradient in diversity was also observed within the Antarctic Peninsula: diversity was lower further south. Diversity in the chloroplast genome of D. antarctica was low. Only three chloroplast haplotypes were found, each with a strong regional distribution.
Main conclusions  The phylogenetic construction of AFLP marker frequencies in meta-populations of D. antarctica supports a stepping-stone model of colonization, whereby gene flow mainly occurs between neighbouring populations. It is concluded that long-distance gene flow is very limited in D. antarctica . A very low diversity was found in the sub-Antarctic islands in the Indian Ocean, indicating that these populations have experienced a recent evolutionary bottleneck.     

Comparison of seastar (Asteroidea) fauna across island groups of the Scotia Arc

The Antarctic shelf fauna is isolated from other continental shelf faunas both physically by distance, and oceanographically by the Antarctic circumpolar current (ACC). To elucidate the relative importance of these two isolating mechanisms, we used the seastar fauna of the south-Atlantic sub-Antarctic islands to address the hypothesis that the ACC is dominant in controlling the distribution pattern of Antarctic fauna. We expected that seastar faunas from islands on the high latitude side of the ACC would show more similarities to each other than to faunas from islands on the low latitude side. The alternative isolation by distance model predicted that the island furthest from others would have the most unique fauna. For shelf-depth (<500 m) Asteroidea of the Scotia Arc region, assemblages were more similar between islands on each side of the ACC barrier than islands that were closer together, and this pattern was caused by differences in abundance of a few ubiquitous species.     

Searching for mechanisms of synchrony in spatially structured gamebird populations

1.  Time series data on five species of gamebird from the Dolomitic Alps were used to examine the relative importance of dispersal and common stochastic events in causing synchrony between spatially structured populations.
2.  Cross-correlation analysis of detrended time series was used to describe the spatial pattern of fluctuations in abundance, while standardized time series were used to describe both fluctuations and the trend in abundance. There were large variations in synchrony both within and between species and only weak negative relationships with distance.
3.  Species in neighbouring habitats were more likely to be in synchrony than species separated by several habitats. Species with similar density-dependent structure were more likely to be in synchrony.
4.  In order to estimate the relative importance of dispersal and environmental stochasticity, we modelled the spatial dynamics of each species using two different approaches. First, we used estimating functions and bootstrapping of time series data to calculate the relative importance of dispersal and stochastic effects for each species. Second, we estimated the intensity of environmental stochasticity from climatic records during the breeding season and then modelled the dispersal rate and dispersal distance for each species. The two models exhibited similar results for rock ptarmigan, black grouse, hazel grouse and rock partridge, while contrasting patterns were observed for capercaillie.
5.  The results suggest that environmental stochasticity plays the dominant role in synchronizing the fluctuations of these galliform species, although there will also be some dispersal between populations.     

Ecological traits influence the current distribution and range of an island endemic bird

Aim  The aim of this paper is to investigate the causes of the current restricted distribution of a narrow-range endemic bird species, the Canary Islands stonechat, Saxicola dacotiae .
Location  Eastern islands of the Canary Islands archipelago.
Methods  We compared climatic patterns (temperature and rainfall), habitat and microhabitat structure, food availability during a full annual cycle, and the abundance of native avian competitors and predators inside and outside the species' range. Three study areas, located in similar habitats on nearby islands, were studied: northern Fuerteventura, close to the northern border of the species' range; southern Lanzarote, 22 km from the nearest site occupied by stonechats; and the Lobos islet, 10 km from the nearest occupied site and 2 km from the coast of Fuerteventura.
Results  The cover of suitable habitats (slopes with high cover of large shrubs, stony fields and ravines) and microhabitats (shrubs and boulders) and the abundance of arthropods during the breeding period of Canary Islands stonechats were lower outside than inside the species' range. Temperature, rainfall and the abundance of competitors and predators inside and outside the species' range did not differ significantly.
Main conclusions  Ecological requirements explaining the distribution of the Canary Islands stonechat within its range seem to be the main factor hindering its settlement on nearby islands. Geological and palaeoclimatic processes, as well as past and current human impact, could also have constrained the distribution of this narrow-range endemic bird species.     

Eroding abodes and vanished bridges: historical biogeography of the substrate specialist pebble-mound mice (Pseudomys)

Aim  To determine whether the pronounced ecological importance of pebble mounds to pebble-mound mice ( Pseudomys ) is manifest in their continental biogeography.
Location  Northern Australia.
Methods  A GIS-based comparison was made between the habitats contained within the potential climatic distributions of mice, representing a null hypothesis of no habitat selection, and their actual distributions based on all known location records.
Results  All species had a clear preference for hilly, rocky landscapes with a surficial cover dominated by bedrock. Simple vegetation communities with relatively open eucalypt overstorey and grassy understorey were preferred. Highly degraded rocks and aggradational surfaces and plains were avoided. The extent of the summer monsoon may be important in determining the southern limits of the group's distribution. Major disjunctions between species were attributable to the presence of clay plains and sand sheets.
The behavioural requirement of pebble-mound mice for mounds determines their population distribution pattern and the distribution of the different species within the genus.
Main conclusions  The behavioural need for pebble mounds drives the distributional pattern of populations and species of pebble-mound mice. The initial spread of pebble-mound mice probably occurred during the late Pliocene or earliest Pleistocene. There has predominantly been degradation of the potential distribution of the group since that time due to the stability of Australian landscapes and Pleistocene planation and sand sheet development over large areas of northern Australia. This process is ongoing, and past regions of rocky contact between current distributions have disappeared, while the distributional limits of several species are steadily being reduced by erosion of hills and the spread of dune fields.     

Open-ocean barriers to dispersal: a test case with the Antarctic Polar Front and the ribbon worm Parborlasia corrugatus (Nemertea: Lineidae)

Open-ocean environments provide few obvious barriers to the dispersal of marine organisms. Major currents and/or environmental gradients potentially impede gene flow. One system hypothesized to form an open-ocean dispersal barrier is the Antarctic Polar Front, an area characterized by marked temperature change, deep water, and the high-flow Antarctic Circumpolar current. Despite these potential isolating factors, several invertebrate species occur in both regions, including the broadcast-spawning nemertean worm Parborlasia corrugatus. To empirically test for the presence of an open-ocean dispersal barrier, we sampled P. corrugatus and other nemerteans from southern South America, Antarctica, and the sub-Antarctic islands. Diversity was assessed by analyzing mitochondrial 16S rRNA and cytochrome c oxidase subunit I sequence data with Bayesian inference and tcs haplotype network analysis. Appropriate neutrality tests were also employed. Although our results indicate a single well-mixed lineage in Antarctica and the sub-Antarctic, no evidence for recent gene flow was detected between this population and South American P. corrugatus. Thus, even though P. corrugatus can disperse over large geographical distances, physical oceanographic barriers (i.e. Antarctic Polar Front and Antarctic Circumpolar Current) between continents have likely restricted dispersal over evolutionary time. Genetic distances and haplotype network analysis between South American and Antarctic/sub-Antarctic P. corrugatus suggest that these two populations are possibly two cryptic species.     

Movement patterns of Rhyssomatus lineaticollis Say (Coleoptera: Curculionidae) within and among Asclepias syriaca (Asclepiadaceae) patches in a fragmented landscape

Abstract.  1. Dispersal capabilities of organisms are critical in determining the landscape population structure of species as well as their likelihood of survival in fragmented landscapes. Using mark–recapture techniques on the monophagous weevil Rhyssomatus lineaticollis Say (Curculionidae), within- and between-patch dispersal capabilities, landscape level population structure, and the role of beetle density and host patch characteristics in setting distances, amounts, and timing of dispersal were studied.
2. The data indicate that R. lineaticollis is sedentary, with 50% of recaptured beetles moving < 1 m and the maximum distance moved < 1 km. Within- and between-patch movement of beetles was unrelated to host plant patch characteristics and beetle densities.
3. Despite limited dispersal, R. lineaticollis probably functions as a patchy population in east-central Iowa, U.S.A. because dispersals between patches are common and because all host patches surveyed contained this herbivore, indicating a lack of suitable vacant patches, a prerequisite for metapopulation structure.
4. Between-patch distances are well within the dispersal capabilities of R. lineaticollis , although this may be the result of an increase in the density of patches of its host, Asclepias syriaca , in the landscape over the last 150 years as a result of human disturbance and this species' weedy habit.
5. Metapopulation structure in monophagous prairie herbivores may be most likely in species whose non-weedy host plants form highly predictable resources in space and time, but which are now widely scattered in habitat fragments.     

Phylogeny and colonization history of Pringlea antiscorbutica (Brassicaceae), an emblematic endemic from the South Indian Ocean Province

The origins and evolution of sub-Antarctic island floras are not well understood. In particular there is uncertainty about the ages of the contemporary floras and the ultimate origins of the lineages they contain. Pringlea R. Br. (Brassicaceae) is a monotypic genus endemic to four sub-Antarctic island groups in the southern Indian Ocean. Here we used sequences from both the chloroplast and nuclear genomes to examine the phylogenetic position of this enigmatic genus. Our analyses confirm that Pringlea falls within the tribe Thelypodieae and provide a preliminary view of its relationships within the group. Divergence time estimates and ancestral area reconstructions imply Pringlea diverged from a South American ancestor ～5Myr ago. It remains unclear whether the ancestor of Pringlea dispersed directly to the South Indian Ocean Province (SIOP) or used Antarctica as a stepping-stone; what is clear, however, is that following arrival in the SIOP several additional long-distance dispersal events must be inferred to explain the current distribution of this species. Our analyses also suggest that although Pringlea is likely to have inherited cold tolerance from its closest relatives, the distinctive morphology of this species evolved only after it split from the South American lineage. More generally, our results lend support to the hypothesis that angiosperms persisted on the sub-Antarctic islands throughout the Pliocene and Pleistocene. Taken together with evidence from other sub-Antarctic island plant groups, they suggest the extant flora of sub-Antarctic is likely to have been assembled over a broad time period and from lineages with distinctive biogeographic histories.     

Evidence for a lacustrine faunal refuge in the Larsemann Hills, East Antarctica, during the Last Glacial Maximum

Aim  There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c . 130,000 yr bp , i.e. prior to the LGM.
Location  Lake Reid, Larsemann Hills, East Antarctica (76°23' E; 69°23' S).
Methods  Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c . 130,000 yr bp .
Results  Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM.
Main conclusion  The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent.     

Persistent genetic signatures of historic climatic events in an Antarctic octopus

Repeated cycles of glaciation have had major impacts on the distribution of genetic diversity of the Antarctic marine fauna. During glacial periods, ice cover limited the amount of benthic habitat on the continental shelf. Conversely, more habitat and possibly altered seaways were available during interglacials when the ice receded and the sea level was higher. We used microsatellites and partial sequences of the mitochondrial cytochrome oxidase 1 gene to examine genetic structure in the direct‐developing, endemic Southern Ocean octopod Pareledone turqueti sampled from a broad range of areas that circumvent Antarctica. We find that, unusually for a species with poor dispersal potential, P. turqueti has a circumpolar distribution and is also found off the islands of South Georgia and Shag Rocks. The overriding pattern of spatial genetic structure can be explained by hydrographic (with ocean currents both facilitating and hindering gene flow) and bathymetric features. The Antarctic Peninsula region displays a complex population structure, consistent with its varied topographic and oceanographic influences. Genetic similarities between the Ross and Weddell Seas, however, are interpreted as a persistent historic genetic signature of connectivity during the hypothesized Pleistocene West Antarctic Ice Sheet collapses. A calibrated molecular clock indicates two major lineages within P. turqueti, a continental lineage and a sub‐Antarctic lineage, that diverged in the mid‐Pliocene with no subsequent gene flow. Both lineages survived subsequent major glacial cycles. Our data are indicative of potential refugia at Shag Rocks and South Georgia and also around the Antarctic continent within the Ross Sea, Weddell Sea and off Adélie Land. The mean age of mtDNA diversity within these main continental lineages coincides with Pleistocene glacial cycles.