SHOULD ADVERTISING PARENTAL CARE BE HONEST

Species with paternal care show less exaggerated sexual ornamentation than those in which males do not care, although direct benefits from p aternal care can vastly exceed the indirect benefits of mate choice. W hether condition-dependent handicaps can signal parenting ability is c ontroversial. The good-parent process predicts the evolution of honest signals of parental investment, whereas the differential-allocation m odel suggests a trade-off between the attractiveness of a mate and his care-provisioning. I show that both alternatives can arise from optim al allocations to advertisement, parental investment and future reprod uctive value of the male, and that the male's marginal fitness gain fr om multiple matings determines which option should apply. The marginal gain is diminishing if opportunities for polygyny or extra-pair copul ations are limited. Advertisement is then expected to be modest and ho nest, indicating genetic quality and condition-dependent parental inve stment simultaneously. Increasing marginal gains are likely to be rela ted to cases where genetic quality has a significant influence on offs pring fitness. This alternative leads to differential allocation with stronger advertisement, more frequent extra-pair copulations, and dimi nished male care. Reliability is also reduced if allocation benefits h ave thresholds, e.g. if there is a minimum body condition required for survival, or if females use a polygyny-threshold strategy of mate cho ice.