What influences the worldwide genetic structure of sperm whales (Physeter macrocephalus)?

Abstract

The interplay of natural selection and genetic drift, influenced by geographic isolation, mating systems and population size, determines patterns of genetic diversity within species. The sperm whale provides an interesting example of a long-lived species with few geographic barriers to dispersal. Worldwide mtDNA diversity is relatively low, but highly structured among geographic regions and social groups, attributed to female philopatry. However, it is unclear whether this female philopatry is due to geographic regions or social groups, or how this might vary on a worldwide scale. To answer these questions, we combined mtDNA information for 1091 previously published samples with 542 newly obtained DNA profiles (394-bp mtDNA, sex, 13 microsatellites) including the previously unsampled Indian Ocean, and social group information for 541 individuals. We found low mtDNA diversity (π = 0.430%) reflecting an expansion event <80 000 years bp, but strong differentiation by ocean, among regions within some oceans, and among social groups. In comparison, microsatellite differentiation was low at all levels, presumably due to male-mediated gene flow. A hierarchical amova showed that regions were important for explaining mtDNA variance in the Indian Ocean, but not Pacific, with social group sampling in the Atlantic too limited to include in analyses. Social groups were important in partitioning mtDNA and microsatellite variance within both oceans. Therefore, both geographic philopatry and social philopatry influence genetic structure in the sperm whale, but their relative importance differs by sex and ocean, reflecting breeding behaviour, geographic features and perhaps a more recent origin of sperm whales in the Pacific. By investigating the interplay of evolutionary forces operating at different temporal and geographic scales, we show that sperm whales are perhaps a unique example of a worldwide population expansion followed by rapid assortment due to female social organization.

Kinship influences sperm whale social organization within, but generally not among, social units

“…These haplotypes differ by a single nucleotide substitution. This low level of mitochondrial diversity is consistent with previous observations on a global and mitogenome-wide scale [66]. …”

“…Two mtDNA haplotypes (A and BB) were identified in individuals from known social units, both of which have been previously observed in the western North Atlantic Ocean [66]. These haplotypes differ by a single nucleotide substitution.…”

Long-Distance Travellers: Phylogeography of a Generalist Parasite, Pholeter gastrophilus, from Cetaceans

“…This patchy distribution may perhaps indicate that the life cycle cannot be completed in low latitudes, and so the genetic connectivity between North and South Atlantic populations of P . gastrophilus would depend on trans-equatorial movements of cetaceans [109, 110]. Although there are records of tracked individuals that have undergone long-distance migrations (e.g.…”

Crowdsourcing Modern and Historical Data Identifies Sperm Whale (Physeter macrocephalus) Habitat Offshore of South-Western Australia

“…(2001)(2002) The primary dataset in this study is from the Voyage of the Odyssey-a 5-year, global, scientific expedition studying sperm whales and ocean pollution (Bohannon, 2004 Frontiers in Marine Science | www.frontiersin.orgbiopsies from sperm whales throughout the Pacific, Indian, and Atlantic Oceans and Mediterranean Sea (Wise et al, 2009;Savery et al, 2013aSavery et al, ,b, 2014. Although primarily a toxicology voyage, other opportunistic research was conducted and included sightings Clark et al, 2012;De Vos et al, 2012), acoustic studies on sperm whales and other odontocetes (Madsen et al, 2002(Madsen et al, , 2004 and genetics (Alexander et al, 2016). From December 2001 to May 2002, the RV Odyssey surveyed along 5200 km of ocean transects off the Perth Canyon, Albany Canyon, and offshore in the traditional Yankee whaling area (New Holland Grounds) when in transit to the Cocos Keeling Islands.…”