Common dolphins (Delphinus delphis) are widespread and highly mobile marine mammals. They inhabit coastal and pelagic environments in temperate and subtropical waters in both the northern and southern hemisphere. In these environments they form regional subpopulations that are discernible on a genetic basis, despite the fact that individuals can migrate between populations. An understanding of the geographic locations of the regional subpopulations is important for the long-term conservation and management of the species.
Previous research has identified three distinct regional populations of common dolphins in Australasian waters; a single population inhabits the southern coast of Australia, a different one is found along the eastern coast while a third lives in the waters around Tasmania and New Zealand. However, there are numerous subpopulations in all these areas, and little information exists about the factors that separate them or the genetic characteristics of the groups.
In marine environments, it is difficult to identify the specific barriers and conditions that separate genetically distinct populations. These may include factors such as spatial distance, oceanographic features such as currents, upwellings or environmental gradients, or ecological differences that require specific feeding or behavioural strategies. The complexity of these factors makes it difficult to disentangle them in order to identify appropriate policies for conservation and management.
A new, comprehensive study from Flinders University has now undertaken the first, widespread census of the genetic diversity of common dolphin populations living along 3000km of Australia’s southern coastline. The study, published in BMC Ecology and Evolution, aims to quantify the genetic diversity of the dolphin subpopulations and to understand what oceanic conditions act as barriers between the groups. The authors hope that their results will help inform conservation and management strategies that will support long-term gene flow between the populations.
Study first author Dr. Andrea Barceló says high levels of genomic variation can play an important part in the long-term survival of these wide-ranging marine mammals and other species, particularly during the ongoing habitat changes associated with climate change and human activities.
“Information about how the environment affects DNA diversity of marine populations can assist with the population management and in forecasting how they may cope with climate change and other anthropogenic impacts,” said Dr. Barceló.
In addition, researchers from Flinders and Macquarie Universities stress the importance of maintaining connectivity between the different groups to promote gene flow and long-term genomic variation. This will, in turn, enhance population viability under anthropogenic impacts, including unfavorable climatic events.
“While so many breeding and feeding conditions are still unknown, it’s important for managers of our coastal environments to consider the importance of DNA diversity, particularly in the event of changes in key environmental conditions such as water temperatures, salinity, and food sources,” said study co-author Professor Luciana Möller.
The genomic analysis of more than 200 dolphins from along the southern coast of Australia revealed the presence of five dolphin populations between Western Australia and Victoria. The adaptive divergence was compared with the key environmental conditions and available fish food supplies, fueled by oceanic upwellings and local seasonal circulations.
The results indicated that genomic variation in dolphins of the southern coast of Western Australia was associated with local currents, while genomic differentiation of common dolphins from sites along the continental shelf break was impacted by fluctuations of primary productivity and sea surface temperatures. In contrast, genomic differentiation of dolphin populations from protected coastal habitats and more enclosed embayment areas was associated mainly with fluctuations in salinity and local environmental temperatures.
Common dolphin subpopulations appear to show localized site fidelity and adaptations to feeding and living in environments with specific conditions. This enhances genetic variation of the species on a global scale, and is likely to enable adaptation to changing conditions as long as there is genetic exchange between subpopulations.
The researchers conclude that such seascape genomic assessment allows the identification of candidate genes for future comparative studies of common dolphins and potentially other delphinid species that share similar dynamic environments around the world.