Influences of past climatic changes on historical population structure and demography of a cosmopolitan marine predator, the common dolphin (genus Delphinus)

Abstract

Climatic oscillations during the Pleistocene have greatly influenced the distribution and connectivity of many organisms, leading to extinctions but also generating biodiversity. While the effects of such changes have been extensively studied in the terrestrial environment, studies focusing on the marine realm are still scarce. Here we used sequence data from one mitochondrial and five nuclear loci to assess the potential influence of Pleistocene climatic changes on the phylogeography and demographic history of a cosmopolitan marine predator, the common dolphin (genus Delphinus). Population samples representing the three major morphotypes of Delphinus were obtained from 10 oceanic regions. Our results suggest that short-beaked common dolphins are likely to have originated in the eastern Indo-Pacific Ocean during the Pleistocene and expanded into the Atlantic Ocean through the Indian Ocean. On the other hand, long-beaked common dolphins appear to have evolved more recently and independently in several oceans. Our results also suggest that short-beaked common dolphins had recurrent demographic expansions concomitant with changes in sea surface temperature during the Pleistocene and its associated increases in resource availability, which differed between the North Atlantic and Pacific Ocean basins. By proposing how past environmental changes had an effect on the demography and speciation of a widely distributed marine mammal, we highlight the impacts that climate change may have on the distribution and abundance of marine predators and its ecological consequences for marine ecosystems.

Post-glacial habitat release and incipient speciation in the genus Delphinus

“…If the mutation rate was an order of Habitat release and incipient speciation I Segura-García et al magnitude slower, the time of divergence would be an order of magnitude older. A previous study used a rate of 9.86 × 10 − 9 for the cytb mtDNA locus to conclude that divergence between sbENP and lbENP took place during the Pleistocene (Amaral et al, 2012). In a comparison between control region and cytb mutation rates in cetaceans, Alter and Palumbi (2009) suggested that the control region evolved 4-5 times faster than cytb.…”

“…A third morphotype with an even longer rostrum and greater number of teeth was identified in the Indian Ocean and off China, and was nominally identified as a subspecies of D. capensis, D. capensis tropicalis (Jefferson and van Waerebeek, 2002). This putative subspecies is genetically differentiated from the two proposed species (Amaral et al, 2012).…”

“…However, independent studies comparing populations elsewhere could not find support for two genetic lineages representing distinguishable 'long-beaked' and 'shortbeaked' species worldwide based on 199 samples analyzed for microsatellite DNA and mtDNA control region sequences (Natoli et al, 2006), mtDNA cytochrome b (cytb) sequences for 343 samples and nuclear sequence data at 5 loci for 90 samples (Amaral et al, 2012) and mtDNA cytb sequences for an additional 37 samples (Cunha et al, 2015). Instead, it was suggested that the long-and shortbeaked phenotypes showed convergent adaptation to coastal and pelagic habitat, respectively (Natoli et al, 2006), divergent selection with incomplete lineage sorting (Amaral et al, 2012) or phenotypic plasticity within the species D. delphis (Cunha et al, 2015). A third morphotype with an even longer rostrum and greater number of teeth was identified in the Indian Ocean and off China, and was nominally identified as a subspecies of D. capensis, D. capensis tropicalis (Jefferson and van Waerebeek, 2002).…”

“…It is in the ENP among the populations of these two forms where genetic differentiation is most pronounced (Rosel et al, 1994;Natoli et al, 2006;Amaral et al, 2012). We focused on this region using robust sample sets and both nuclear and mtDNA markers to better understand the mechanisms that may be supporting incipient speciation and to assess the timing and pattern of differentiation within this genus.…”

Phylogenomics of the killer whale indicates ecotype divergence in sympatry

“…In some cases there is a correlation between population structure and apparent habitat boundaries, as for the bottlenose dolphin (Tursiops truncatus) populations in European waters (Natoli et al, 2005) or with resource specializations as for the killer whale (Orcinus orca) populations in the North Pacific (Hoelzel et al, 2007). Environmental cycles releasing habitat or opening/closing dispersal corridors may also influence the evolution of population structure in these species (Amaral et al, 2012;Moura et al, 2013). For killer whales, some well-studied populations show strong resource specializations based on consistent prey choice (ecotypes) within stable, matrifocal social groups (pods), together with genetic and phenotypic differentiation (Hoelzel et al, 1998;Pitman and Ensor, 2003;Hoelzel et al, 2007;Morin et al, 2010).…”