Fine‐scale genetic population structure in a mobile marine mammal: inshore bottlenose dolphins in Moreton Bay, Australia

Abstract

Highly mobile marine species in areas with no obvious geographic barriers are expected to show low levels of genetic differentiation. However, small-scale variation in habitat may lead to resource polymorphisms and drive local differentiation by adaptive divergence. Using nuclear microsatellite genotyping at 20 loci, and mitochondrial control region sequencing, we investigated fine-scale population structuring of inshore bottlenose dolphins (Tursiops aduncus) inhabiting a range of habitats in and around Moreton Bay, Australia. Bayesian structure analysis identified two genetic clusters within Moreton Bay, with evidence of admixture between them (F(ST) = 0.05, P = 0.001). There was only weak isolation by distance but one cluster of dolphins was more likely to be found in shallow southern areas and the other in the deeper waters of the central northern bay. In further analysis removing admixed individuals, southern dolphins appeared genetically restricted with lower levels of variation (AR = 3.252, π = 0.003) and high mean relatedness (r = 0.239) between individuals. In contrast, northern dolphins were more diverse (AR = 4.850, π = 0.009) and were mixing with a group of dolphins outside the bay (microsatellite-based STRUCTURE analysis), which appears to have historically been distinct from the bay dolphins (mtDNA Φ(ST) = 0.272, P < 0.001). This study demonstrates the ability of genetic techniques to expose fine-scale patterns of population structure and explore their origins and mechanisms. A complex variety of inter-related factors including local habitat variation, differential resource use, social behaviour and learning, and anthropogenic disturbances are likely to have played a role in driving fine-scale population structure among bottlenose dolphins in Moreton Bay.

Causes and consequences of fine-scale population structure in a critically endangered freshwater seal

“…Hence, large and mobile mammals tend to exhibit coarse-grained or widely clinal genetic structures, except when differentiation follows from behaviourally mediated dispersal limitation caused by, for example, individual-level habitat or resource specialization [87,107] or spatial clustering of related individuals [4,81]. Our analyses uncovered cryptic and remarkably fine-scaled genetic structure within the Saimaa ringed seal population, despite potentially high individual dispersal ability [19,21].…”

“…Gene flow among populations is often restricted or even prevented by geographic barriers, but assessing what constitutes an obstacle for a given species is not always straightforward [11,87,88]. In analyses of spatial genetic variation, a clear benefit of the Saimaa ringed seal population is that the topography of the lake unambiguously determines possible routes of dispersal among subpopulations, and the level of differentiation then depends on the migration rates through these routes.…”

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

“…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).…”

Patterns of population structure at microsatellite and mitochondrial DNA markers in the franciscana dolphin (Pontoporia blainvillei)

“…Additionally, although the genetic population structure of many species may be characterized by a pattern of IBD (e.g., Ansmann, Parra, Lanyon, & Seddon, 2012; Hoelzel et al., 2007; Natoli et al., 2005), we did not observe a significant correlation between genetic differentiation and geographic distance among populations (Figure 4). If equilibrium between the loss of alleles due to genetic drift and their replacement by gene flow between populations exists, the genetic distance between populations will increase with geographic distance due to the changing influence of gene flow and genetic drift as populations become more or less geographically separated (Hutchison & Templeton, 1999).…”