Can a handicapped parent rely on its partner? An experimental study within Adélie penguin pairs

Keywords: Adé lie penguin begging biparental care breeding effort chick compensation Pygoscelis adeliae In biparental species, the response of parents when their mates are disadvantaged is highly variable. Moreover, experimental studies on parental effort have mainly focused on short-lived birds whose breeding constraints largely differ from those of long-lived species such as seabirds. We investigated the short-and long-term consequences of handicapping one parent within Adé lie penguin, Pygoscelis adeliae, pairs. We also examined whether handicapped mates and offspring could convey cues informing the other parent of the need to increase breeding effort and whether this parent adjusted its behaviour accordingly. While handicapped penguins foraged for longer and lost more mass than controls, partners, fasting for longer at the nest, did not change their behaviour or lose more mass suggesting that they compensated at least for themselves. Information exchange was increased between mates after the return of handicapped females from foraging. However, partner males did not respond to this. Handicapped pair chicks, which were smaller than control chicks, did not increase their solicitation rate for food. In the subsequent breeding season, compared to controls, 40% of previously handicapped females laid fewer eggs, the resight rate of previously handicapped males was lower and pair instability was higher. No additional cues seemed to be detected by Adé lie penguins when their mates were handicapped and, for handicapped-pair offspring, the cost associated wih a higher solicitation rate was probably too high for these small chicks to support. Consequently, we found no compensatory behaviour from partners in this long-lived species: handicapped individuals and offspring both supported the whole additional cost in both the short term and the long term. In species where both parents provide parental care, a conflict of interest may arise between partners which are both expected to minimize current reproductive effort but are none the less forced to cooperate to breed (Houston et al. 2005). Many experimental studies on parental effort, mainly carried out on passerines (Houston & Davies 1985), have shown that parents could respond to a reduction in care by their partners, by modifying their own effort. However, depending on the species, the partners' responses may show discrepancies and vary from a decreased effort (Sanz et al. 2000) or no response (Sanz et al. 2000; Schwagmeyer et al. These species and sex-specific differences may be determined by: (1) the availability of proximate cues that indicate the reduced effort of the …