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, 7 (3), e33654

Weak Polygyny in California Sea Lions and the Potential for Alternative Mating Tactics


Weak Polygyny in California Sea Lions and the Potential for Alternative Mating Tactics

Ramona Flatz et al. PLoS One.

Erratum in

  • PLoS One. 2012;7(4): doi/10.1371/annotation/03fdf5e5-b986-49c7-aa43-202bdedd3a36


Female aggregation and male territoriality are considered to be hallmarks of polygynous mating systems. The development of genetic parentage assignment has called into question the accuracy of behavioral traits in predicting true mating systems. In this study we use 14 microsatellite markers to explore the mating system of one of the most behaviorally polygynous species, the California sea lion (Zalophus californianus). We sampled a total of 158 female-pup pairs and 99 territorial males across two breeding rookeries (San Jorge and Los Islotes) in the Gulf of California, Mexico. Fathers could be identified for 30% of pups sampled at San Jorge across three breeding seasons and 15% of sampled pups at Los Islotes across two breeding seasons. Analysis of paternal relatedness between the pups for which no fathers were identified (sampled over four breeding seasons at San Jorge and two at Los Islotes) revealed that few pups were likely to share a father. Thirty-one percent of the sampled males on San Jorge and 15% of the sampled males on Los Islotes were assigned at least one paternity. With one exception, no male was identified as the father of more than two pups. Furthermore, at Los Islotes rookery there were significantly fewer pups assigned paternity than expected given the pool of sampled males (p<0.0001). Overall, we found considerably lower variation in male reproductive success than expected in a species that exhibits behavior associated with strongly polygynous mating. Low variation in male reproductive success may result from heightened mobility among receptive females in the Gulf of California, which reduces the ability of males to monopolize groups of females. Our results raise important questions regarding the adaptive role of territoriality and the potential for alternative mating tactics in this species.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Map of the study sites at two sea lion rookeries in the Gulf of California.
Insets indicate sampled study areas within each rookery. 1) San Jorge Island measures approximately 2.0 km between the northern islet and southern tip and 0.2 km at the widest point. Here, the marked area includes the study site and sampled adjacent areas. 2) Los Islotes Island is approximately 0.5 km long and 0.1 km at its widest point.
Figure 2
Figure 2. Distribution of cumulative male reproductive success.
Bars represent the number of paternities assigned over a three year period to each of a) 65 territorial males on San Jorge including males both within the study site and along adjacent areas and b) 21 territorial males on San Jorge including only those males within the study site, and c) the number of paternities assigned over a two year period to each of 35 territorial males on Los Islotes. Solid bars include only those paternities where the father was identified at the rookery the year of conception, whereas hatched bars include all paternity assignments.
Figure 3
Figure 3. Observed paternal relatedness compared with expected values over a range of polygyny levels.
Expected values of average paternal relatedness (r-values) between pups if each successful male sires 1, 2, 3, 4 or 5 pups. Error bars represent +/− one standard deviation. Horizontal lines represent the observed r-values for each pool of sampled pups. At each of the two rookeries, separate analyses were done for pups that were assigned fathers (known paternities) and pups whose fathers could not be assigned (unknown paternities). In all cases observed r-values fall between what would be expected if each successful male sired just one or two pups.

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