A first look at using genetics to quantify reproductive success and skew in male sea otters

Background/Question/Methods

In polygynous mating systems, males compete for access to females. Male quality and competitive ability therefore influence male reproductive success. Reproductive success of male sea otters may be related to defense of small aquatic territories (most comprise 2–6 km² of shallow coastal waters), but quantifying success has been difficult in this species, as there is no male parental care (males are not observed with their pups) and it is relatively rare to observe copulation of known individuals. The objectives of this study were twofold: 1) quantify male reproductive success and calculate reproductive skew across males, and 2) determine whether territorial males have higher reproductive success than non-territorial males. We quantified male reproductive success using newly developed genetic markers and paternity analyses. To determine paternity and estimate reproductive success, tissue samples were analyzed using microsatellite nuclear DNA markers at 39 loci. We genotyped samples from 68 males and 215 females, which were collected in Monterey Bay, CA between 1999 and 2012.

Results/Conclusions

Using the genetic software programs CERVUS, FRANz, and KINGROUP, 119 animals (sires, dams, and pups) were placed in a pedigree with high confidence. As expected for a polygynous mammal, we found that males reproduce at older ages than females. Overall, reproductive skew appears to be low across male sea otters, and both territorial and non-territorial males sired pups, although mean reproductive success was significantly higher for territorial males. The most successful males were those that held exclusive mating territories for multiple years. Analyses in progress will further test the male characteristics, territory attributes (e.g. abundance of kelp canopy, benthic substrate type), and behaviors (e.g. aggressiveness, territory and resource defense) that influence reproductive success.