Journal of Heredity Advance Access originally published online on February 17, 2006
Journal of Heredity 2006 97(3):226-234; doi:10.1093/jhered/esj018
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The Influence of Maternal Lineages on Social Affiliations among Humpback Whales (Megaptera novaeangliae) on Their Feeding Grounds in the Southern Gulf of Maine
From the Whale Center of New England, PO Box 159, Gloucester, MA 01930 (Weinrich and Blackmer); WCS/AMNH Cetacean Conservation and Research Program, International Conservation-Marine, c/o Wildlife Conservation Society, 2300 Southern Blvd, Bronx, NY 10460, and the Conservation Genetics Program and Center for Biodiversity and Conservation, American Museum of Natural History, 79th Street and Central Park West, New York, NY 10024 (Rosenbaum); the School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand (Baker); the Department of Neurobiology, Physiology, and Behavior, University of California, Davis, Davis, CA (Blackmer); and the Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada (Whitehead)
Address correspondence to M. T. Weinrich at the address above, or e-mail: mason{at}whalecenter.org.
Humpback whales on their feeding grounds in the Gulf of Maine typically form fluid fission/fusion groups of two to three individuals characterized by noncompetitive and, at times, cooperative behavior. Here we test the hypothesis that, despite the apparent absence of close kinship bonds, the fluid associations between feeding whales are influenced by "maternal lineages" as represented by mtDNA haplotypes. Using skin samples collected with a biopsy dart, variation in the hypervariable segment of the mtDNA control region identified 17 unique haplotypes among 159 individually identified whales from the southern Gulf of Maine. The haplotypes of a further 143 individuals were inferred from known direct maternal (cow-calf) relationships. The frequencies of associations among these 302 individuals were calculated from 21,617 sighting records collected from 1980 to 1995, excluding associations between a cow and her dependent calf. For groups of two where the haplotypes of both individuals were known (n = 3,151), individuals with the same haplotype were together significantly more often (26%) than expected by random association (20%). To account for different group sizes and associations with individuals of unknown haplotype and sex, we used Monte Carlo simulations to test for nonrandom associations in the full data set, as well as known female-only (n = 1,512), male-only (n = 730), and mixed-sex (n = 2,745) groups. Within-haplotype associations were significantly more frequent than expected at random for all groups (P = .002) and female-only groups (P = .011) but not male-only groups, while mixed-sex groups approached significance (P = .062). A Mantel test of individual pairwise association indices and haplotype identity confirmed that within-haplotype associations were more frequent than expected for all sex combinations except male-male associations, with females forming within-haplotype associations 1.7 times more often than expected by random assortment. Partial matrix correlations and permutation analyses indicated that the skew toward within-haplotype associations could not be accounted for by short-term temporal co-occurrence or fine-scale spatial distributions of individuals with shared haplotypes. While the mechanism by which individuals with a common mtDNA haplotype assort remains unknown, our results strongly suggest an influence of maternal lineages on the social organization of humpback whales within a regional feeding ground.