Male Reproductive Strategy and the Importance of Maternal Status in the Antarctic Fur Seal Arctocephalus Gazella

Abstract

Abstract. Although mammalian mating systems are classically characterized in terms of male competition and polygyny, it is becoming increasingly apparent that alternative male strategies and female choice may play important roles. For example, females who mate with males from a dominant dynasty risk producing inbred offspring. Many pinnipeds are highly polygynous, but in some species alternative male strategies such as aquatic mating appear to be important, even when behavioral observations suggest strong polygyny. Here, we analyze male reproductive success in the Antarctic fur seal Arctocephalus gazella, an otariid described behaviorally as being highly polygynous, by combining a microsatellite paternity analysis spanning seven consecutive breeding seasons with detailed behavioral data on both sexes. Territorial males fathered 59% of 660 pups analyzed from our study colony. Male reproductive skew was considerable, with a quarter of all paternities assigned to just 12 top individuals on a beach where mean annual pup production was 635. Most males were successful for only a single season, but those able to return over successive years enjoyed rapidly increasing success with each additional season of tenure. We found no evidence of alternative male reproductive tactics such as aquatic or sneaky terrestrial mating. However, paternity was strongly influenced by maternal status. Females observed on the beach without a pup were significantly less likely to conceive to a sampled territorial male than equivalent females that did pup. In addition, their pups carried combinations of paternal alleles that were less likely to be found on the study beach and exhibited lower levels of shared paternity. Thus, from a territorial male's perspective, not all females offer equal opportunities for fertilization.

Does kin selection influence fostering behaviour in Antarctic fur seals (Arctocephalus gazella)?

“…Unfortunately, most studies are only able to employ of the order of 10 microsatellite markers and with this number, as here, it is difficult to distinguish between pups that are non-filial relatives and those that are filial but mismatch their true parents through genotyping errors. Thus, even after substantial experimental effort (Hoffman et al 2003) that removed many errors present in the original Gemmell dataset, we find essentially the same pattern as Gemmell (2003), the main difference being a slightly lower overall rate of fostering (9.9% compared with 11.5%). It is only after checking all single-and two-locus mismatches and then re-genotyping all cases where errors might be present that the true pattern becomes clear, specifically that fostered pups that are closely related to the female they were suckling are extremely rare.…”

“…Consequently, we attempted to drive the error rate as low as possible. First, autoradiographs for all motheroffspring pairs that mismatched at one locus were examined, revealing 15 genotyping errors (Hoffman et al 2003;Hoffman & Amos 2005). These comprised 10 scoring errors, one data-entry error and four cases of allele dropout.…”

“…(a) Study site and field methods This study was conducted at a small fur seal breeding beach at Bird Island, South Georgia (54 800 0 S, 38 802 0 W) and is based on a dataset spanning seven consecutive pupping seasons (Hoffman et al 2003;Hoffman & Amos 2005) that was subsequently expanded to incorporate an additional season (Hoffman et al 2004). Tissue samples and observational data were collected during the austral summers of 1994/1995-2001/2002 (hereafter, breeding seasons are referred to by the year in which they began).…”

“…All samples were then genotyped using a panel of nine dinucleotide-repeat microsatellite loci, previously isolated from a variety of pinniped species. These loci possessed a mean of 12 alleles (rangeZ 5-18 alleles per locus), had an average expected heterozygosity of 0.796 (rangeZ0.450-0.921) and did not deviate significantly from Hardy-Weinberg equilibrium (Hoffman et al 2003). Polymerase chain reaction (PCR) products incorporating [a 32 P]-dCTP were resolved by electrophoresis on standard 6% acrylamide sequencing gels and detected by autoradiography.…”

“…First, we examined autoradiographs for all mother-offspring pairs that mismatched at one locus and identified a small number of genotyping errors (nZ15; Hoffman et al 2003;Hoffman & Amos 2005). We then extended this approach to include all pairs mismatching at two loci.…”