Postglacial climate changes and rise of three ecotypes of harbour porpoises, Phocoena phocoena, in western Palearctic waters

Abstract

Despite no obvious barriers to gene flow in the marine realm, environmental variation and ecological specializations can lead to genetic differentiation in highly mobile predators. Here, we investigated the genetic structure of the harbour porpoise over the entire species distribution range in western Palearctic waters. Combined analyses of 10 microsatellite loci and a 5085 base-pair portion of the mitochondrial genome revealed the existence of three ecotypes, equally divergent at the mitochondrial genome, distributed in the Black Sea (BS), the European continental shelf waters, and a previously overlooked ecotype in the upwelling zones of Iberia and Mauritania. Historical demographic inferences using approximate Bayesian computation (ABC) suggest that these ecotypes diverged during the last glacial maximum (c. 23-19 kilo-years ago, kyrBP). ABC supports the hypothesis that the BS and upwelling ecotypes share a more recent common ancestor (c. 14 kyrBP) than either does with the European continental shelf ecotype (c. 28 kyrBP), suggesting they probably descended from the extinct populations that once inhabited the Mediterranean during the glacial and post-glacial period. We showed that the two Atlantic ecotypes established a narrow admixture zone in the Bay of Biscay during the last millennium, with highly asymmetric gene flow. This study highlights the impacts that climate change may have on the distribution and speciation process in pelagic predators and shows that allopatric divergence can occur in these highly mobile species and be a source of genetic diversity.

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

“…Interestingly, these conditions were also probably suitable for harbour porpoises (Phocoena phocoena), a small cetacean with high energetic needs. The end of the Sapropel period likely led to the fragmentation of harbour porpoise populations as waters became too oligotrophic and warm for this cold-water affiliated species [48,49]. By contrast, bottlenose dolphins, having a wider range and lower energetic costs [50] are still currently observed in the Mediterranean Sea.…”

Defining management units for cetaceans by combining genetics, morphology, acoustics and satellite tracking

“…Block et al, 2011). In the last decades, harbour porpoises (Phocoena phocoena) have been studied intensely in European waters to identify population delimitations and to monitor the status of the species (e.g., Siebert et al, 2006, Evans and Teilmann, 2009, Wiemann et al, 2010Alfonsi et al, 2012;Fontaine et al, 2014). The main driver for this effort has been the fact that several thousand harbour porpoises are bycaught each year and drown in European gillnet fisheries (Tregenza et al, 1997;Vinther and Larsen, 2004;Bjørge et al, 2013).…”

First circumglobal assessment of Southern Hemisphere humpback whale mitochondrial genetic variation and implications for management

“…Further testing of hypotheses regarding the origin of ASHW using samples from BSC and BSD is required (e.g. using approximate Bayesian computation analysis; Fontaine et al 2014). Highly asymmetric gene flow from populations in East Africa to Arabia has also been observed for humpback dolphins (Mendez et al 2011) and has been attributed in part to the dominant oceanographic current systems of these coasts, which facilitate northward connectivity but not southward movement.…”