Reproductive effort of male northern elephant seals: estimates from mass loss

Abstract

The energetic component of reproductive effort of male northern elephant seals, Mirounga angustirostris, was estimated from mass loss over the breeding season and correlated with dominance rank and age. Fifty-four unrestrained bulls were weighed on a platform scale by luring them with a model of a female seal or moving them with a tarpaulin and using playback of male aggressive vocalizations. Adult males weighed up to 2300 kg upon arrival at the breeding rookery. Mean rate of mass loss during the breeding season was 7.1 ± 1.5 (SD) and 4.6 ± 0.8 kg per day for 17 adults and 13 subadults, respectively. Rate of mass loss was positively correlated with body size (mass or length) for both age-classes. Mass-specific rate of mass loss did not differ between age-classes but increased with increasing dominance rank among adult males. Reproductive effort, expressed as percentage of body mass lost over the 3-month breeding season, was greater for high-ranking bulls (mean 41.4%) than for low-ranking adults (33.8%), but was not related to age-class or body size. High-ranking males experienced higher mating success and expended more energy than subordinate males. Comparison with a previous study on conspecific females indicates that mass-specific energetic investment in reproduction is similar for both sexes, despite marked sex differences in reproductive strategy and duration of effort.

Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris)

“…Nineteen adult male seals from Año Nuevo State Reserve, CA were studied during the 1998 breeding season. Animals were considered adult based on body mass and development of secondary sexual characteristics (Le Boeuf, 1974;Deutsch et al, 1990). Individuals were identified by pre-existing flipper tags and dye marks (Lady Clairol, Stamford, CT, USA).…”

“…However, male pinnipeds often maintain high rates of energy expenditure while fasting in the process of maintaining territory or controlling access to females (Crocker et al, 2012). The ability to minimize protein loss over extended fasts may positively impact sustainable levels of energy expenditure and tenure in breeding adult males, both of which are directly associated with reproductive success (Anderson and Fedak, 1985;Deutsch et al, 1990;Lidgard et al 2005). However, the regulation of metabolism during these high-energy fasts is poorly understood.…”

Metabolic responses to adrenocorticotropic hormone (ACTH) vary with life-history stage in adult male northern elephant seals

“…The three month breeding fast is energetically costly and incorporates terrestrial movement and combative male-male competition to establish access to females. During this time, body mass decreases by approximately 40% in dominant males and 30% in subordinate males [39,40]. Dominant males experience higher mating success, but at the cost of increased energy expenditure, with successful males having sustained fasting energy expenditures approaching 4 times their standard metabolic rates [38].…”

Angiotensin II and Aldosterone Increase with Fasting in Breeding Adult Male Northern Elephant Seals (Mirounga angustirostris)

“…In addition, pups maintain a state of metabolic quiescence similar to that of hibernators during their postweaning fast, which allows them to further reduce energetic expenditures and metabolic water losses. In contrast, adult male seals are physically more active during their fasting period associated with the breeding season, exhibiting high rates of mass loss and energy expenditure (Deutsch et al 1990). This increase in activity could potentially impede their ability to maintain ionic and osmotic homeostasis, which is observed in the relatively inactive fasting pups.…”