Evidence of genetic differentiation for Hawai‘i insular false killer whales (Pseudorca crassidens)

Citation

Chivers, S.J., R.W. Baird, K.M. Martien, B.L. Taylor, E. Archer, A.M. Gorgone, B.L. Hancock, N.M. Hedrick, D. Matilla, D.J. McSweeney, E.M. Oleson, C.L. Palmer, V. Pease, K.M. Robertson, J. Robbins, J.C. Salinas, G.S. Schorr, M. Schultz, J.L. Theileking, and D.L. Webster. 2010. Evidence of genetic differentiation for Hawai‘i insular false killer whales (Pseudorca crassidens). NOAA Technical Memorandum NMFS-SWFSC-458, 46p.

Abstract

Chivers et al. (2007) found Hawai‘i insular false killer whales to be distinct from other strata within the Indo-Pacific Ocean using mitochondrial DNA (mtDNA) control region sequence data. Here, we add new samples and eight nuclear DNA (nDNA) microsatellite markers to that study. After extensive quality checking, some haplotypes and duplicate individuals were removed from the 2007 mtDNA data set. A strong phylogeographic signal consistent with local haplotype evolution was evident for Hawai‘i insular false killer whales with all but one individual having one of 2 closely related haplotypes found only in this population. The mtDNA characteristics of the Hawai‘i insular false killer whales (n = 81) differed significantly (all p-values for Fisher exact and ΦST <0.0001) from both broad-scale strata (Central North Pacific (n = 13) and Eastern North Pacific (n = 39)), and all fine-scale strata (Hawai‘i pelagic (n = 9), Mexico (n = 19), Panama (n = 15) and American Samoa (n = 6)). The magnitude of mtDNA differentiation (all ΦST >0.68) was consistent with less than one migrant per generation. The nDNA marker results were highly significant with all Fisher exact p-values ≤ 0.001 for comparisons of the Hawai‘i insular stratum (n = 69) to the broad-scale strata (Central North Pacific (n = 13) and Eastern North Pacific (n = 36)), and fine-scale strata (Hawai‘i pelagic (n = 9), Mexico (n = 19), Panama (n = 12) and American Samoa (n = 6)). The magnitude of differentiation was much less for nDNA (0.01 < FST < 0.08, 0.01 < Jost’s D < 0.06) than for mtDNA, indicating the potential for some male-mediated gene flow although the possibility that FST is low because of the high mutation rate of microsatellites or the influence of selection operating to counter gene flow cannot be excluded. Inferences from these data are limited by sample distribution, with pelagic false killer whales near the Hawaiian Islands inadequately sampled. However, the small number of Hawai‘i insular false killer whales (around 120) together with an estimated effective population size of 44.3 (95% CI = 31.2-67.2) are causes for concern about loss of genetic diversity.

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