Inconsistency Between Socio-Spatial and Genetic Structure in a Coastal Dolphin Population

Abstract

Identifying population structure and boundaries among communities of wildlife exposed to anthropogenic threats is key to successful conservation management. Previous studies on the demography, social and spatial structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) suggested four nearly discrete behavioral communities in Perth metropolitan waters, Western Australia. We investigated the genetic structure of these four communities using highly polymorphic microsatellite markers and part of the hypervariable segment of the mitochondrial control region. Overall, there was no evidence of spatial genetic structure. We found significant, yet very small genetic differentiation between some communities, most likely due to the presence of highly related individuals within these communities. Our findings of high levels of contemporary migration and highly related individuals among communities point toward a panmictic genetic population with continuous gene flow among each of the communities. In species with slow life histories and fission-fusion dynamics, such as Tursiops spp., genetic and socio-spatial structures may reflect different timescales. Thus, despite genetic similarity, each social community should be considered as a distinct ecological unit to be conserved because they are exposed to different anthropogenic threats and occur in different ecological habitats, social structure being as important as genetic information for immediate conservation management. The estuarine community, in particular, is highly vulnerable and appropriate conservation measures are needed in order to maintain its connectivity with the adjacent, semi-enclosed coastal communities.

Patterns of association and distribution of estuarine-resident common bottlenose dolphins (Tursiops truncatus) in North Carolina, USA

“…Concurrence of fine-scale genetic and social structure in T. truncatus, as well as T. aduncus, has been reported in estuarine and coastal waters [e.g., 5,36,[82][83][84][85][86][87][88][89][90][91][92]. In contrast, social structuring has been reported in the absence of detected genetic differentiation [9,25,93,94]. There are three possible interpretations of the current results.…”

“…aduncus , has been reported in estuarine and coastal waters [e.g., 5 , 36 , 82 – 92 ]. In contrast, social structuring has been reported in the absence of detected genetic differentiation [ 9 , 25 , 93 , 94 ]. There are three possible interpretations of the current results.…”

“…Habitat partitioning on small spatial scales has been identified or confirmed by recent genetic, telemetry, and photo-ID results [ 14 , 135 , 136 ], as has been mixing of genetically distinct groups within those small areas [ 36 ]. In the US, stocks have yet to be designated using results from social network results, however, given the relatively small size of many stocks or communities of bottlenose dolphins, Chabanne et al [ 25 ] and Bonneville et al [ 7 ] suggested that each social community, although not necessarily demographically independent, may still warrant separate management considerations due to different exposers to anthropogenic threats. Ultimately, however, a reevaluation of the stock designation of estuarine-resident common bottlenose dolphins in NC is needed.…”

“…In estuarine and nearshore habitats, dolphins are exposed to numerous anthropogenic threats, such as interactions with and bycatch in fishing gear, vessel strikes, provisioning, and acoustic disruption [e.g., 8, [15][16][17][18][19][20], and environmental contaminants that are sufficiently severe as to cause demographic effects [e.g., [21][22][23][24]. As a result, it has been suggested that management and conservation measures be applied at an appropriate spatial scale for the fine-scale population structure [7,25].…”

Fine‐scale social and genetic structure of common bottlenose dolphins (Tursiops truncatus) in the Barataria Basin, Louisiana, USA

“…Higher levels of genetic relatedness have been reported for social groups of bottlenose dolphins (Tursiops spp.) in other studies (Diaz-Aguirre et al, 2019;Chabanne et al, 2021). In this study, two of the four social clusters had large enough sample size to investigate genetic relatedness.…”