Diet as an important factor of male status in the southern elephant seal (Mirounga leonina)

DEDDEN, A. ; BORNEMANN, H. ; NEGRETE J.; ROGERS, T. L

Conferencia; XI Conferencia Internacional sobre la Aplicación de Isótopos Estables a Estudios Ecológicos; 2018

Within polygynous breeding systems, intra-sexual selection between malesgenerally leads to the formation of a dominance hierarchy. There has beendebate over which factors favour the establishment of social dominance. Wheresome studies argue that body mass is the singular determinant of social rank,others show that rather than the males? mass, it is their length. However mostof these studies have been of males from terrestrial systems. In terrestriallybreeding polygynous species, dominant males secure not only mating access tofemales, but also to areas of high value food resources. For semi-aquaticmammals, such as the southern elephant seal, social dominance does not conferaccess to food resources as the males fast while ashore in the breedingcolonies. The males? foraging choices made at sea, prior to the breeding haulouts, reflects a male´s diet prior to dominance establishment. We ask whether amale?s diet, body mass and/or length conferred an advantage in attaining socialdominance. To reconstruct the diet of males of different social ranks we usedbulk δ15N and δ13C values of serum collected fromsexually mature male southern elephant seals (n=44) during the breeding seasonat King George Island, within the South Shetland archipelago. To identify whichfactors (diet-inferred from δ15N and δ13Cvalues, body mass, and/or standard length) influenced male social rank, weconducted a series of mixed models and took a model selection approach.Socially dominant beachmasters had a larger body mass and significantlyenriched δ15N valuescompared to less dominant males. The significant 15N enrichment (>3.4?) ofthe dominant males, suggests that they fed on higher trophic prey. There was nodifference in δ13Cvalues of the males of different ranks suggesting that both dominant andsubordinate males fed in similar regions. An interaction between diet (δ15N) and body size (both mass andlength) explained the greatest variation between males? social rank. This interactionbetween body mass and diet (δ15N) potentially infers a feedback, such that males of a larger bodymass can make deeper/longer dives, gaining access to larger prey and so confersa higher energetic efficiency.