Species status and population structure of the newly described Tursiops australis (the Burrunan dolphin)and Tursiops truncatus (the common bottlenose dolphin)in southern Australian waters, assessed using genetic markers and morphology.
2017-02-14T01:48:40Z (GMT) by
Taxonomic relationships and affinities within the cetacean genus Tursiops have been plagued with controversy, with historically upwards of 20 species being described and later all synonymised with the common bottlenose dolphin T. truncatus. Numerous studies have demonstrated that Tursiops is polyphyletic. Tursiops truncatus is morphologically and genetically diverse and exhibits distinct 'ecotypes' with coastal/inshore popUlations often distinct from offshore populations. Recently, a 'worldwide distribution form' of T. truncatus has been hypothesised, suggesting interconnection on an evolutionary time-scale and long¬distance dispersal. However, a second distinct Tursiops species, the Indo-Pacific bottlenose dolphin T. aduncus has recently been formally recognised, based on morphological and mitochondrial DNA data. Similar to other regions, south-eastern Australia has two 'bottlenose' dolphin types, a small coastal form being distinct from a larger offshore form. My thesis examines the specific affinities of these south-eastern Australian dolphins using morphology and genetic analyses, and examines the genetic population structure and potential drivers of population differentiation of these marine mammals, with a particular view to assisting with appropriate conservation management for threatened inshore populations. Small coastal dolphins endemic to south-eastern Australia have variously been assigned to described species Tursiops truncatus, T. aduncus or T. maugeanus; however the specific affinities of these animals is controversial and have recently been questioned. Historically 'the southern Australian Tursiops' was identified as unique and was formally named Tursiops maugeanus, but was later synonymised with T. truncatus. Morphologically, these coastal dolphins share some characters with both aforementioned recognised Tursiops species, however they also possess unique characters not found in either. Recent mitochondrial DNA and microsatellite genetic evidence indicated deep evolutionary divergence between this dolphin and the two currently recognised species. I describe the macro-morphological, colouration and cranial characters of these coastal dolphins, assess the available and new genetic data, and conclude that multiple lines of evidence clearly indicate a new species of dolphin. Together with colleagues, we demonstrate that the syntype material of T. maugeanus comprises two different species, one of which is genetically most similar to T. truncatus, and the other is representative of the new species and requires formal classification. These coastal dolphins are now described as Tursiops australis, with the common name of 'Burrunan Dolphin' following Australian aboriginal narrative (Chapter Two -Charlton-Robb et al. 2011). The recognition of T. australis is particularly significant given the endemism of this new species to a small geographic region of southern and south-eastern Australia, where only two small resident populations in close proximity to a major urban and agricultural centre are known, giving them a high conservation value and making them susceptible to numerous anthropogenic threats. The two resident populations of T. australis at the eastern end of their range occur in Port Phillip Bay and the Gippsland Lakes, both of which are semi-enclosed water bodies along coastal Victoria. While T. australis is also found in South Australia and Tasmania, little is known about the population status and migration of these animals across their known range. To better understand breeding and movement patterns that would aid conservation management, I apply genetic tools to examine population structure, migration and family structure of T. australis (Chapter Three). Two regions of the mitochondrial DNA (the control region (-450bp) and cytochrome b (-1200bp)) and ten chromosomal microsatellite regions are used to assess population structure. Biopsy samples were collected from Port Phillip Bay, the Gippsland Lakes live populations and from beach-cast strandings across both Victoria and Tasmania (n=159). Genetic analyses, using both the maternal and bi-parental markers, revealed two distinct populations across the south-eastern Australian region; the Port Phillip Bay population being significantly differentiated from the Gippsland Lakes and Tasmanian popUlation. The data also suggest female philopatry and male biased dispersal across the region. Common bottlenose dolphins, T. truncatus, also reside in south-eastern Australian waters. Chapter Four examines the genetic diversity and population structure of T. truncatus in south¬eastern Australia using biopsy samples from free-ranging animals and samples from stranded animals (ranging from single to mass strandings) (n=83). Ten micro satellite markers and two mtDNA sequences (control region and cytochrome b) revealed high levels of genetic diversity. Two groups with overlapping ranges were found; animals stranding on King Island (in central Bass Strait, north west of Tasmania) and at Point Hibbs (on the south-western tip of Tasmania) formed one group that was differentiated from the second group consisting of all remaining samples corning from widespread Tasmanian and Victorian coastal regions. These two groups most likely represent an 'offshore' and a 'coastal' ecotype of T. truncatus in this region, respectively. I found a greater proportion of parent-offspring and/or full-sibling pairs within, as opposed to between, sampling events, indicating natal philopatry within pods and/or populations. In addition, control region haplotypes were compared with 77 haplotypes from numerous populations and ocean basins worldwide. Similarly to other worldwide studies on T. truncatus, a complex phylogenetic network with no distinct clustering of the south-eastern dolphins was discovered, suggesting whilst these animals are clearly forming two distinct populations within this region, on a worldwide scale they both represent the 'world-wide distribution form'. In addition, I contributed to three other collaborative studies: the first presents the genetic data that first highlighted T. australis as a potential new species, based on a small sample size of the mtDNA control region (Charlton et al. 2006); the second was a study investigating Tursiops and Delphinus species along eastern, south-eastern and southern Australia that presents multi-gene evidence for a distinct new species (Moller et al. 2008), and the final study used stable isotope signatures of both T. australis (reported as SABD) and T. truncatus from south-eastern Australia to demonstrate species level distinction in isotope signatures indicating the two species are feeding on different prey and likely foraging in different areas (Owen et aI., 2011). Lastly, in order to conserve and protect T. australis popUlations in Victorian waters, I submitted a nomination for threatened species listing of T. australis under the Flora and Fauna Guarantee Act 1988 (Department of Sustainability and Environment: Victorian Sate Government). These four documents are provided as attachments to this thesis.