Population Differentiation and Hybridisation of Australian Snubfin (Orcaella heinsohni) and Indo-Pacific Humpback (Sousa chinensis) Dolphins in North-Western Australia

Abstract

Little is known about the Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins (‘snubfin’ and ‘humpback dolphins’, hereafter) of north-western Australia. While both species are listed as ‘near threatened’ by the IUCN, data deficiencies are impeding rigorous assessment of their conservation status across Australia. Understanding the genetic structure of populations, including levels of gene flow among populations, is important for the assessment of conservation status and the effective management of a species. Using nuclear and mitochondrial DNA markers, we assessed population genetic diversity and differentiation between snubfin dolphins from Cygnet (n = 32) and Roebuck Bays (n = 25), and humpback dolphins from the Dampier Archipelago (n = 19) and the North West Cape (n = 18). All sampling locations were separated by geographic distances >200 km. For each species, we found significant genetic differentiation between sampling locations based on 12 (for snubfin dolphins) and 13 (for humpback dolphins) microsatellite loci (F ST = 0.05–0.09; P<0.001) and a 422 bp sequence of the mitochondrial control region (F ST = 0.50–0.70; P<0.001). The estimated proportion of migrants in a population ranged from 0.01 (95% CI 0.00–0.06) to 0.13 (0.03–0.24). These are the first estimates of genetic diversity and differentiation for snubfin and humpback dolphins in Western Australia, providing valuable information towards the assessment of their conservation status in this rapidly developing region. Our results suggest that north-western Australian snubfin and humpback dolphins may exist as metapopulations of small, largely isolated population fragments, and should be managed accordingly. Management plans should seek to maintain effective population size and gene flow. Additionally, while interactions of a socio-sexual nature between these two species have been observed previously, here we provide strong evidence for the first documented case of hybridisation between a female snubfin dolphin and a male humpback dolphin.

HERPESVIRUS-ASSOCIATED GENITAL LESIONS IN A STRANDED STRIPED DOLPHIN (STENELLA COERULEOALBA) IN THE CANARY ISLANDS, SPAIN

“…The similarity between the sequences from our study with those of wild bottlenose dolphins suggests interspecific transmission by sexual contact. Many species of delphinids co-occur, and sexual interactions between species can occur (Schaurich et al 2012;Brown et al 2014). The sequences we obtained have high homology with those from genital lesions of free-living Mediterranean and Atlantic bottlenose dolphins (Smolarek Benson et al 2006).…”

Site-Specific Assessments of the Abundance of Three Inshore Dolphin Species to Inform Conservation and Management

“…Nonetheless, genetic studies offer supporting evidence of limited connectivity between local populations for these species. Low levels of gene flow have been observed between local populations of snubfin and humpback dolphins separated by > 200 km, including snubfin dolphins at Roebuck and Cygnet Bays, to the extent that those local populations should be considered separate management units (Cagnazzi, 2011;Brown et al, 2014). Fine-scale population genetic structure appears to be common in coastal populations of bottlenose dolphins (e.g., Ansmann et al, 2012;Kopps et al, 2014) and, despite evidence of individual movement between the two sites, significant genetic differentiation has been reported between bottlenose dolphins at Cygnet Bay and Beagle Bay (Allen, 2015).…”

“…Globally, their distribution is restricted to shallow coastal and estuarine waters of northern Australia and southern New Guinea (Parra et al, 2002(Parra et al, , 2004Beasley et al, 2005Beasley et al, , 2016Jefferson and Rosenbaum, 2014). Available data suggest that both species are discontinuously distributed as small populations of 50-200 (e.g., Parra et al, 2006a;Palmer et al, 2014; Table 1), which exhibit site fidelity (Parra et al, 2006a;Cagnazzi et al, 2011Cagnazzi et al, , 2013a, limited gene flow between populations (Cagnazzi, 2011;Brown et al, 2014), and are reliant upon near-shore habitats (Parra et al, 2006b;Parra and Jedensjö, 2014). While snubfin and humpback dolphins are data deficient, both species have been assigned precautionary "near threatened" 1 statuses by the International Union for Conservation of Nature (IUCN) in light 1 The IUCN Red List status assessment of "near threatened" for humpback dolphins in Australia was prior to the description of S. sahulensis (Jefferson and Rosenbaum, 2014) and, therefore, considered both S.sahulensis and S.chinensis as a single species (Reeves et al, 2008a).…”

Marine Mammal Behavior: A Review of Conservation Implications

“…However, hybridization, a spontaneous phenomenon which is suspected in several cetacean (Brown et al, 2014;Hodgins et al, 2014) and pinniped (Lancaster et al, 2010) species also has conservation implications. Depending on the fitness of the hybrids, hybridization may alter gene flow and species boundaries (Lancaster et al, 2010).…”