Health and immune response of the critically endangered Burrunan dolphins, assessed via immune gene markers and skin microbiome
The Marine Mammal Foundation is undertaking genetic research to determine the immune capacity and overall health of the Burrunan dolphin. This project will be conducted by PhD candidate Grace Day, supervised by MMF’s Director and Head of Research Dr Kate Robb, and Deakin University’s associate professor Beata Ujvari.
Recent mortality events of the Burrunan dolphin have highlighted a trend that has been observed across the world; there has been a rise in the prevalence of disease in cetaceans, alongside a decrease in cetacean immune health. Prompted by this, the project is investigating the genetic diversity of key immune genes, as well as the skin microbiome to determine the Burrunan dolphin’s immune capacity and ability to adapt to a changing environment.
Cetaceans (whales, dolphins and porpoises) have been described as marine ecosystem ‘sentinels’, meaning that their health is also a reflection of the ecosystem's overall health. With that, the risk factors that influence disease outcomes of cetaceans often involve changes in their habitat. For instance, terrestrial runoff is commonly identified as contributing to cetacean disease, with disease prevalence in marine mammals being associated with proximity to land and runoff. Over the last 40 years, disease outbreaks among marine mammals have increased due to eutrophication and terrestrial pathogens spreading to the ocean.
While there is a rise in incidences of marine mammal diseases, there is also a reduction in their immune health. Reduced immune health may be due to chronic stress, caused by factors such as vessel activity, lack of prey, and habitat degradation, as well as through toxin accumulation and low genetic diversity. Burrunan dolphins have experienced two mass mortality events in the Gippsland Lakes due to Fresh Water Skin Disease (FWSD). The first event was in 2006-07, while the second began in 2020 and is ongoing.
It is well known that low genetic diversity can be detrimental to the health and fitness of a population or species, with preservation of genetic diversity identified as a key conservation outcome in Australia’s Biodiversity Conservation Strategy (2010-2030). Previous studies have established that the populations of Burrunan dolphins have low genetic diversity. The low number of genetic haplotypes observed indicates that the resident populations are likely inbred, meaning that their ability to adapt to environmental challenges is lessened. To link immune fitness with genetic diversity, we are therefore investigating the immune genes of Burrunan dolphins.
Using genes to assess dolphin health
This project focuses on key regions of the genome that are frequently targeted in conservation biology studies. These regions include genes associated with the innate and adaptive immune systems, such as the Major Histocompatibility Complex (MHC) gene family.
The MHC genes provide instructions to make receptors found on the surface cells. These receptors serve as a marker, distinguishing the body’s own cells from foreign entities, including pathogens (disease-causing agents), like bacteria and viruses. Foreign particles entering the body are displayed on the MHC receptors, eliciting an immune response. To effectively recognise a wide range of pathogens, the receptor relies on structural diversity, which, in turn, is dictated by the genetic diversity of the genes encoding them.
The diversity of these genes has been linked to immune fitness, overall fitness and even mate choice, underscoring their significance for investigation. Our research is dedicated to assessing the genetic diversity of the MHC genes in Burrunan dolphins, aiming to evaluate their immune capacity and ability to adapt to a changing environment.
Using the dolphin’s microbiome to assess health
The skin is the first line of immune defence, it provides a physical barrier to prevent entry of pathogens into the body and is home to a community of microbes (bacteria, fungi, archaea, viruses) which modulate the immune system. The community of ‘friendly’ microbes on the skin are described as commensals due to their beneficial and homeostatic relationship with the host. There is a signalling conversation between the commensals and skin cells that assists in wound healing and toleration of the beneficial microbes. Commensal microbes also outcompete pathogens, and create an acidic environment which prevents pathogenic colonisation and infection.. Disruption in the balance of beneficial microbes (dysbiosis) can have adverse health effects for the host. Research of the skin microbiome is a growing and exciting field, however it is still fairly novel in marine mammals, despite their susceptibility to skin diseases and lesions. Therefore, this project also aims to characterise the composition and diversity of the microbes that exist on Burrunan dolphin skin. This project will give an exhaustive insight into the population health of Burrunan dolphins through the analysis of their immune gene genetic diversity, as well as the association between their genotypes and commensal microbiomes.
To conduct this study, biopsy samples from live and deceased animals are collected, which consist of skin and blubber tissue. This is then used to extract DNA using molecular laboratory techniques. To sequence the DNA, we use a combination of traditional Sanger sequencing, as well as Next Generation Sequencing technology. In doing so, we can target immune genes of interest or microbial DNA that exists due to the microbes on the skin. Bioinformatic analysis is then undertaken to determine gene evolution and to generate population genetic indices.
Special thanks to our research supporters
Meet the researcher!
Grace Day is a second year PhD candidate at Deakin University working in collaboration with Marine Mammal Foundation. She began genetic research on Burrunan dolphins in 2021 during her Honours year. Grace has always had an interest in molecular biology and evolutionary ecology and hopes that her research will contribute to a body of information that will ultimately be used for the conservation and preservation of Burrunan dolphins.
Publications and presentations
Day, G., Robb, K., Oxley, A., Telonis-Scott, M., Ujvari, B. Organisation and evolution of major histocompatibility complex in cetaceans (iScience, under review).
Charlton-Robb, K., Taylor, A.C., McKechnie, S.W. (2016) Population genetic structure of the Burrunan dolphin (Tursiops australis) in coastal waters of south-eastern Australia: conservation implications. Conservation Genetics. DOI 10.1007/s10592-014-0652-6
Charlton-Robb, K., Gershwin L., Thompson, R., Austin, J., Owen, K., and McKechnie, S.W. (2011) A New Dolphin Species, the Burrunan Dolphin Tursiops australis sp. nov., Endemic to Southern Australian Coastal Waters. PLoS ONE 6(9): e24047. doi:10.1371/journal.pone.0024047.
Charlton, K., Taylor, A.C., McKechnie, S.W. (2006) A note on divergent mtDNA lineages of “bottlenose” dolphins from coastal waters of southern Australia. J. Cetacean Res. Manage 8(2), 173-179.
Presentations
Day, G. (2023) Organisation and evolution of major histocompatibility complex in cetaceans. Lightning Talk. XXIIIrd International Congress of Genetics and Genomics lightning talk. Melbourne, Australia. – awarded with the Jenny Graves prize for best student lightning talk
3CR Out of the Blue show interview “Melbourne’s very own dolphin”
Ecological Society of Australia blog “Bacteria on Burrunans: The Micro Building Blocks of Immunity”
3 Minute Thesis (3MT) “Deep Dive into Dolphin Immune Genes”