Genetic differentiation in bottlenose dolphins from South Australia: association with local oceanography and coastal geography

Abstract

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.

Environmental and social influences on the genetic structure of bottlenose dolphins (Tursiops aduncus) in Southeastern Australia

“…Conversely, there was no evidence for male-biased dispersal for communities along the continuous coastal habitat (Eden, Hunter coast and Ballina). These results are also similar to other studies in which bottlenose dolphin populations sampled in homogenous environments are connected through both male and female dispersal (Natoli et al 2005(Natoli et al , 2008Parsons et al 2006;Bilgmann et al 2007a;Quérouil et al 2007). The consistency of sex-specific dispersal patterns across geographically distant populations demonstrates the significant environmental influences on a highly mobile, generalist predator.…”

“…Analysis of sex-specific dispersal patterns using a larger sample size than that in Möller and Beheregaray (2004) supported a pattern of male-biased dispersal for the Port Stephens and Jervis Bay populations. These results are similar to those reported in several other embayment populations, which indicate that dispersal of females occurs less frequently than for males (Krützen et al 2004;Sellas et al 2005;Bilgmann et al 2007a). By remaining in their natal habitats, females can potentially increase their reproductive fitness through greater familiarity with local prey resources and opportunities to associate with familiar females as a collective defence mechanism against predators and coercing males (Connor et al 2000;Möller and Beheregaray 2004).…”

“…The fact that the Bayesian clustering approach in STRUCTURE did not detect these partitions most likely results from the limitations of the program to detect genetic differentiation when F ST values are low (Latch et al 2006) or when populations are not in HardyWeinberg equilibrium. Concordant patterns of genetic differentiation emerging from this study and Möller et al (2007) (Sellas et al 2005), while in South Australia, bottlenose dolphins sampled in the Spencer Gulf were genetically distinct from those ranging along the open coast (Bilgmann et al 2007a). Natoli et al (2005) further showed that the two ecologically distinct Mediterranean Sea basins also hold genetically differentiated bottlenose dolphin populations.…”

“…Genetic discontinuities in some bottlenose dolphin populations coincide with breaks in oceanographic features, such as water depth, bottom topography, primary productivity, sea surface temperature and salinity. For example, in South Australia, Bilgmann et al (2007a) attributed high genetic differentiation between dolphins in the Spencer Gulf and the adjacent coastal population to the strong temperature and salinity differential caused by the oceanographic front at the mouth of the gulf. Similar correlations have been documented in bottlenose dolphins from the Black Sea to Scotland (Natoli et al 2005) and between coastal and offshore ecotypes in the North-West Atlantic .…”

New Evidence for Bottlenose Dolphin (Tursiops spp.) Population Connectivity between Kangaroo Island and South Australian Mainland Waters

“…Baseline information regarding the ecology, distribution and movements on this species and the potential connectivity between local populations in this region is, however, still very limited, with most information based upon stranding records [2] [3]. However, previous studies have provided evidence of bottlenose dolphins occurring within both Spencer and Gulf St. Vincent as well as in the vicinity of Adelaide [5] [6] [7] and in particular the Port River-Barker Inlet estuary (The Adelaide Dolphin Sanctuary) where they are known to be resident all year round [4] [5].…”