SUMMARY Seals have adapted to the high heat transfer coefficient in the aquatic environment by effective thermal insulation of the body core. While swimming and diving, excess metabolic heat is supposed to be dissipated mainly over the sparsely insulated body appendages, whereas the location of main heat sinks in hauled-out seals remains unclear. Here, we demonstrate thermal windows on the trunk of harbour seals, harp seals and a grey seal examined under various ambient temperatures using infrared thermography. Thermograms were analysed for location, size and development of thermal windows. Thermal windows were observed in all experimental sessions, shared some common characteristics in all seals and tended to reappear in similar body sites of individual seals. Nevertheless, the observed variations in order and location of appearance,number, size and shape of thermal windows would imply no special anatomical site for this avenue of heat loss. Based on our findings, we suggest that, in hauled-out seals, heat may be transported by blood flow to a small area of the wet body surface where the elevation of temperature facilitates evaporation of water trapped within the seals' pelages due to increased saturation vapour pressure. The comparatively large latent heat necessary for evaporation creates a temporary hot spot for heat dissipation.

For many marine organisms, including large, long-lived predators, the factors affecting connectivity between populations are still largely unknown. We assessed levels of genetic differentiation and dispersal patterns of bottlenose dolphins Tursiops sp. across Spencer Gulf and coastal areas west of the gulf in the Great Australian Bight, South Australia (SA), using data from mitochondrial DNA control region sequences and 6 microsatellite loci. Marked genetic differentiation and low migration were detected between dolphins of Spencer Gulf and those inhabiting coastal areas west of the gulf. We hypothesise that the restriction to dolphin gene flow is influenced by an oceanographic front at the mouth of Spencer Gulf that builds up over the austral summer and exhibits strong differences in water temperatures and salinity levels. It appears that the genetic subdivision reported here is a recent phenomenon, a finding consistent with the known geomorphologic history of the region. Coastal bottlenose dolphins from SA are evolutionarily divergent from other bottlenose dolphin species and are potentially under threat due to ongoing human-related mortality. The information from this study can, therefore, be used for the development of much-needed conservation management strategies.

Identifying which factors shape the distribution of intraspecific genetic diversity is central in evolutionary and conservation biology. In the marine realm, the absence of obvious barriers to dispersal can make this task more difficult. Nevertheless, recent studies have provided valuable insights into which factors may be shaping genetic structure in the world's oceans. These studies were, however, generally conducted on marine organisms with larval dispersal. Here, using a seascape genetics approach, we show that marine productivity and sea surface temperature are correlated with genetic structure in a highly mobile, widely distributed marine mammal species, the short-beaked common dolphin. Isolation by distance also appears to influence population divergence over larger geographical scales (i.e. across different ocean basins). We suggest that the relationship between environmental variables and population structure may be caused by prey behaviour, which is believed to determine common dolphins' movement patterns and preferred associations with certain oceanographic conditions. Our study highlights the role of oceanography in shaping genetic structure of a highly mobile and widely distributed top marine predator. Thus, seascape genetic studies can potentially track the biological effects of ongoing climate-change at oceanographic interfaces and also inform marine reserve design in relation to the distribution and genetic connectivity of charismatic and ecologically important megafauna.

Climatic oscillations during the Pleistocene have greatly influenced the distribution and connectivity of many organisms, leading to extinctions but also generating biodiversity. While the effects of such changes have been extensively studied in the terrestrial environment, studies focusing on the marine realm are still scarce. Here we used sequence data from one mitochondrial and five nuclear loci to assess the potential influence of Pleistocene climatic changes on the phylogeography and demographic history of a cosmopolitan marine predator, the common dolphin (genus Delphinus). Population samples representing the three major morphotypes of Delphinus were obtained from 10 oceanic regions. Our results suggest that short-beaked common dolphins are likely to have originated in the eastern Indo-Pacific Ocean during the Pleistocene and expanded into the Atlantic Ocean through the Indian Ocean. On the other hand, long-beaked common dolphins appear to have evolved more recently and independently in several oceans. Our results also suggest that short-beaked common dolphins had recurrent demographic expansions concomitant with changes in sea surface temperature during the Pleistocene and its associated increases in resource availability, which differed between the North Atlantic and Pacific Ocean basins. By proposing how past environmental changes had an effect on the demography and speciation of a widely distributed marine mammal, we highlight the impacts that climate change may have on the distribution and abundance of marine predators and its ecological consequences for marine ecosystems.

Interactions between short-beaked common dolphins Delphinus delphis and the fishing industry of South Australia (SA) have lead to serious concerns over the long-term viability of the local dolphin population. Common dolphins are gregarious animals with high vagility and are expected to display limited genetic differentiation over large spatial scales. Here, we investigate population genetic structure of southern Australian common dolphins using mitochondrial DNA control region sequences and seven microsatellite markers. We found unexpected levels of genetic differentiation for short-beaked common dolphins over a distance of $1500 km. Although no genetic structure was observed in common dolphins along the coast of SA, we detected marked differentiation between dolphins from SA and south-eastern Tasmania, suggesting a minimum of two genetic populations in southern Australia. We hypothesize that the ephemeral distribution of small pelagic fish enhances movement and dispersal between dolphin groups at a local level. However, clear differences in water temperature, habitat features and fish abundance between SA and Tasmania may contribute to the contemporary isolation observed between dolphin populations. Our findings have important consequences for developing conservation management strategies, because SA has the largest purse-seine fishery by weight in Australia, and substantial numbers of fatal common dolphin interactions have occurred. In 2004/2005 alone, an estimated 1728 common dolphins were encircled and 377 died over a 7-month period. If these impacts lead to a reduction in population size, it is unlikely that dolphins from the adjacent south-eastern Tasmanian population will replace the lost individuals. Recommendations for assessing the impacts of the fishery are presented. The information herein may also have implications for fisheries-marine mammal interactions in coastal and neritic habitats in other areas of the world. Moreover, we demonstrate that a species commonly thought to be wide ranging can show an unexpected degree of genetic differentiation.