The mating system of polar bears: a genetic approach

Abstract

Parentage analysis data for 583 individuals genotyped at 27 microsatellite loci were used to study the mating system of polar bears (Ursus maritimus Phipps, 1774) in the Barents Sea area. We discriminated statistically between full and half-siblings identified through only one common parent. We document for the first time multiple paternity in polar bears. We demonstrated for both sexes low fidelity to mating partners over time. We did not detect any significant difference between the age distribution of adult males at capture and the age distribution of males siring cubs. This might indicate that the male's age and size are less indicative of the reproductive success than previously thought. This is further supported by a rather long mean litter interval of 3.9 years for males siring several litters. The mating system of polar bears in the Barents Sea appears to be promiscuous, usually with a single successful father siring full siblings within a year, but with consecutive litters of a mother being fathered by different males. We discuss how population density, landscape characteristics, and adult sex ratio might influence the mating system of polar bears. This is of particular importance for management decisions such as, e.g., implementing sex ratios in hunting quotas.Résumé : Nous utilisons les résultats d'analyses de filiation portant sur 583 individus génotypés à 27 loci microsatellites, afin d'étudier le système de reproduction des ours blancs (Ursus maritimus Phipps, 1774) de la région de la Mer de Barents. Nous avons statistiquement discriminé entre les vrais-frères et soeurs et les demi-frères et soeurs identifiés par un seul parent commun. Nous documentons, pour la première fois chez les ours blancs, un cas de parenté multiple dans une même portée. Nous avons démontré une faible fidélité entre partenaires sexuels, lors de différentes reproductions, quel que soit le sexe. Nous n'avons pas détecté de différence entre la distribution des âges des mâles adultes à la capture et la distribution des âges des mâles au moment où ils sont pères. Cela pourrait indiquer que l'âge des mâles et leur taille sont une moindre indication du succès de leur reproduction qu'on ne le croyait. Cela est supporté par un intervalle moyen assez long (3,9 ans) entre les portées pour les pères ayant engendré plusieurs portées. Nos résultats indiquent que le système de reproduction des ours blancs de la mer de Barents semble lié à la promiscuité; ainsi, de manière générale, un mâle est le père de tous les petits d'une portée, mais les portées successives d'une femelle ont des pères différents. Nous discutons comment les variations de densité des populations et des caractéristiques du paysage, ainsi que le rapport des sexes des adultes peuvent influencer le système de reproduction des ours blancs. Ceci est important pour les décisions de gestion des populations, par ex. la fixation du rapport des sexes dans les quotas de chasse.

Site fidelity of Svalbard polar bears revealed by mark-recapture positions

“…While females are distributed according to prey resources, access to estrous females is the top priority for males (Sandell 1989). Polar bears have a promiscuous mating system (Zeyl et al 2009b) and males rove widely in search of estrous females (Ramsay and Stirling 1986), as predicted for species in which females are widely and unpredictably distributed (Clutton-Brock 1989). If some dominant males start to rove, it becomes the optimal strategy for all males, both dominant and subordinate (Sandell 1989).…”

Allee effect in polar bears: a potential consequence of polychlorinated biphenyl contamination

“…The representation of 10-14-year-old bears among males that sired offspring was measured in order to be compared with the observed values from Svalbard [18]. We recorded the total number of days the fertile males of defined age categories (4-9 rspb.royalsocietypublishing.org Proc.…”

“…We use computer simulations to gain qualitative insights into how contamination could affect polar bear reproductive success. We also investigate whether the comparatively low representation of prime-aged males among males siring offspring, as reported from Svalbard [18], suggests links to the heavy PCB contamination in males reported from Svalbard [3] between 1990 and 1994. Furthermore, we consider whether this phenomenon can be explained by various strategies of male-male competition for females, or by a combination of these factors.…”

“…Yet within this strongly contaminant exposed population [1][2][3], the 11-14-year-old males sired offspring during the late 1990s and early 2000s with (slightly) lower frequency than males from other age groups [18]. In comparison to the Western Hudson Bay sub-population, they can therefore be considered to have been under-represented among males who sired offspring.…”

“…Individuals were distributed randomly. The age assigned to males was based on an empirical distribution [18]. Employing a specific sub-model, PCB-dose-response, it was determined which males were sterile by applying the two dose-response relationships (equations (2.1) and (2.2)).…”