Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins

MELINA BARRIONUEVO; VALENTINA FERRETTI; JAVIER CIANCIO; ESTEBAN FRERE

MARINE BIOLOGY

SPRINGER

Lugar: Berlin; Año: 2021

0025-3162

In birds, possibleexplanations for a bias in brood sex ratio include differential cost of rearingnestlings of different sexes, and different parental fitness returns related tooffspring sex. We studied brood sex ratio of Magellanic penguins, Spheniscusmagellanicus, in Puerto Deseado for three years. Our objectives were tocompare the growth curves and energetic costs of rearing nestlings of differentsexes, and to evaluate the possible implications of environmental and parentalcondition in the establishment of a bias in the brood sex ratio. We alsoinvestigated the relationship between hatching order and sex, and its impact onbrood survival. Asymptotic mass was 11.41% higher for males than for females. Theenergetic cost of feeding male nestlings was slightly higher than for feeding females,but the difference in energy requirements was only 2.6% of the total energybudget. During the threeyears, brood sex ratio was 0.53, and almost constant within years over theraising period, showing no sex allocation during feeding. Sea surfacetemperature, which is linked to higher prey abundance when colder, explained broodsex ratio at fledging. The sex ratio was male-biased during the coldest year. Parentalbody condition was not an important variable explaining brood sex ratio. There was no bias in nestling sex withrespect to hatching order and nestling survival was not related to nestling sex.We conclude that, even though the cost of feeding male offspring is higher, itonly involves a small fraction of total cost of raising nestlings and might notbe responsible for an adaptive bias in the sex ratioof nestlings for this species. However, during good oceanic conditions, femalesmight bias their brood sex ratio towards males, thereby potentially gaining anadvantage by raising good quality males.