Habitat‐driven population structure of bottlenose dolphins, Tursiops truncatus, in the North‐East Atlantic

Abstract

Despite no obvious barrier to gene flow, historical environmental processes and ecological specializations can lead to genetic differentiation in highly mobile animals. Ecotypes emerged in several large mammal species as a result of niche specializations and/or social organization. In the North-West Atlantic, two distinct bottlenose dolphin (Tursiops truncatus) ecotypes (i.e. 'coastal' and 'pelagic') have been identified. Here, we investigated the genetic population structure of North-East Atlantic (NEA) bottlenose dolphins on a large scale through the analysis of 381 biopsy-sampled or stranded animals using 25 microsatellites and a 682-bp portion of the mitochondrial control region. We shed light on the likely origin of stranded animals using a carcass drift prediction model. We showed, for the first time, that coastal and pelagic bottlenose dolphins were highly differentiated in the NEA. Finer-scale population structure was found within the two groups. We suggest that distinct founding events followed by parallel adaptation may have occurred independently from a large Atlantic pelagic population in the two sides of the basin. Divergence could be maintained by philopatry possibly as a result of foraging specializations and social organization. As coastal environments are under increasing anthropogenic pressures, small and isolated populations might be at risk and require appropriate conservation policies to preserve their habitats. While genetics can be a powerful first step to delineate ecotypes in protected and difficult to access taxa, ecotype distinction should be further documented through diet studies and the examination of cranial skull features associated with feeding.

Ecological opportunities and specializations shaped genetic divergence in a highly mobile marine top predator

“…This dolphin, which was photo-identified in a coastal area over a 2-year period, had coastal-like isotopic signatures but had been genetically identified as belonging to the pelagic group. Current migration rates are very low between ecotypes [22]. However, as haplotypes are shared between coastal and pelagic dolphins, this individual could possibly be a migrant.…”

“…In the NEA, several hypotheses might explain the weak morphological differences. First, haplotype network and coalescent-based estimations of divergence times suggested that the differentiation between the two ecotypes occurred more recently in the NEA than in the NWA [22,63], giving less time for morphological divergence. Moreover, coastal and pelagic habitats might be less contrasted in the NEA than in the NWA.…”

“…Population history analyses were based on 355 biopsy-sampled or stranded bottlenose dolphins, which were analysed for 25 microsatellites and a 681 base-pair portion of the mitochondrial DNA control region (N ¼ 343) in [22]. In this previous study, each individual was genetically assigned to one of four populations using Bayesian clustering analyses (figure 1).…”

“…mainly sighted in deeper waters). They are hierarchically structured, with two populations within each ecotype [22]. In the coastal ecotype, the Coastal North (CN) population includes individuals sampled around the UK and Ireland, while the Coastal South (CS) population includes individuals of the French and Spanish coasts.…”

Population Structure and Dynamics

“…(e.g., LeDuc et al 2008;Morin et al 2010;Foote et al 2009Foote et al , 2010Foote et al , 2011Parsons et al 2013; see also Chapter 6). Microsatellite and mtDNA used in combination suggest that bottlenose dolphins in the Northeast Atlantic comprise isolated populations, despite no obvious physical barriers to gene flow (Louis et al 2014). Historical environmental processes and subsequent ecological specialization appear to have created distinct groups that are likely maintained via philopatry, combined with different social organizations and foraging specializations.…”