Paternity, polygyny and alternative mating tactics in humpback whales (<italic>Megaptera novaeangliae</italic>).

Polygynous mating systems are common among terrestrial mammals, and are typically characterized by a skewed operational sex ratio, competition among males for females, variation in reproductive success (RS) among males and the evolution of alternative mating tactics. Little is known about mating systems of marine taxa due to difficulty of observing individual behavior and determining paternity. Humpback whales are thought to be polygynous with differences in reproduction among males related to alternative mating tactics. However, there is currently a lack of data on male RS. I tested predictions regarding male RS in humpback whales using the molecular assessment of paternity in a population in the Mexican Pacific. Parentage analysis for 125 mother-calf pairs and a sample of 297 males, genotyped for 13 polymorphic microsatellite loci, resulted in putative paternities for 30--50% of calves. The distribution of male RS deviated significantly from a random mating model. However, reproductive skew was not severe: most fathers sired only one calf and no male was assigned more than three calves. Most current measures of skew report a single value that describes variance but not the underlying statistical distribution of RS. I describe a procedure to estimate reproductive skew in terms of the population-wide distribution of RS using a simple simulation of mating, specifically for datasets with incomplete sampling of offspring and males. For my humpback whale data, I found that the best-fit mating model was an approximation of a gamma distribution, only slightly skewed beyond a Poisson distribution. Therefore I conclude that this population has a polygynous mating system, but without the large variation in male RS typical of some systems of this type. Successful males employed diverse mating tactics, with significant variation among the proportions of four alternative tactics used by fathers. Most fathers were observed to employ all tactics to varying degrees, although some appeared to favor specific tactics such as physically competing for females or escorting mothers. The latter, a tactic generally considered low pay-off, may in fact contribute significantly to overall male RS. Implications of these new findings are discussed in relation to the current understanding of this mating system.Ph.D.Animal PhysiologyBiological SciencesZoologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123554/2/3096064.pd