Sperm whale population structure in the eastern and central North Pacific inferred by the use of single-nucleotide polymorphisms, microsatellites and mitochondrial DNA

Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla, CA 92037, USA.
Molecular Ecology Resources (Impact Factor: 3.71). 03/2011; 11 Suppl 1(s1):278-98. DOI: 10.1111/j.1755-0998.2010.02973.x
Source: PubMed


We use mitochondrial DNA (mtDNA) (400 bp), six microsatellites and 36 single-nucleotide polymorphisms (SNPs), 20 of which were linked, to investigate population structure of sperm whales (Physeter macrocephalus) in the eastern and central North Pacific. SNP markers, reproducible across technologies and laboratories, are ideal for long-term studies of globally distributed species such as sperm whales, a species of conservation concern because of both historical and contemporary impacts. We estimate genetic differentiation among three strata in the temperate to tropical waters where females are found: California Current, Hawai`i and the eastern tropical Pacific. We then consider how males on sub-Arctic foraging grounds assign to these strata. The California Current stratum was differentiated from both the other strata (P < 0.05) for mtDNA, microsatellites and SNPs, suggesting that the region supports a demographically independent population and providing the first indication that males may exhibit reproductive philopatry. Comparisons between the Hawai`i stratum and the eastern tropical Pacific stratum are not conclusive at this time. Comparisons with Alaska males were statistically significant, or nearly so, from all three strata and individuals showed mixed assignment to, and few exclusions from, the three potential source strata, suggesting widespread origin of males on sub-Arctic feeding grounds. We show that SNPs have sufficient power to detect population structure even when genetic differentiation is low. There is a need for better analytical methods for SNPs, especially when linked SNPs are used, but SNPs appear to be a valuable marker for long-term studies of globally dispersed and highly mobile species.

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    • "ses. Whether this is the case or not, there are at least 2 sperm whale clans in the range of the southwestern North Pacific stock as proposed by Kasuya and Miyashita (1988). There is no genetic information from these 2 areas and it is possible that there is a significant genetic differentiation, as reported in the eastern North Pacific (Mesnick et al. 2011). Even with a lack of genetic evidence, however, these 2 clans of sperm whales off Japan should be treated as different management units. Our findings highlight the importance of assessing vocal culture as a tool for the management of sperm whales."
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    • "A common approach is the use of genetic summary statistics. For example, in a study of North Pacific sperm whales (Physeter macrocephalus), Wright&apos;s (1943) island model F ST = 1/(4N e m + 1) was used to estimate F ST from an inferred effective population size (N e ) and fixed migration rate, and populations were defined as demographically independent if pairwise estimates of F ST were above zero (Mesnick et al. 2011). However, very few natural populations meet the assumptions of the island model (i.e. "
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    • "SNPs are increasingly being developed for use in marine mammals, where they have already provided insights into the population structure of bowhead and sperm whales [11], [12]. Because most SNP genotyping platforms only require around 120 bp of flanking sequence, SNPs are also ideally suited to genotyping historical or degraded samples such as whale bone or baleen [13], thereby facilitating new avenues of research. "
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