THE EVOLUTION OF BEGGING - SIGNALING AND SIBLING COMPETITION

In many species, young solicit food from their parents, which respond by feeding them, Because of the difference in genetic make-up between parents and their offspring and the consequent conflict, this interact ion is often studied as a paradigm for the evolution of communication, Existent theoretical models demonstrate that chick signaling and pare nt responding can be stable if solicitation is a costly signal, The ma rginal cost of producing stronger signals allows the system to converg e to an equilibrium: young beg with intensity that reflects their need , and parents use this information to maximize their own inclusive fit ness, However, we show that there is another equilibrium where chicks do not beg and parents' provisioning effort is optimal with respect to the statistically probable distribution of chicks' states, Expected f itness for parents and offspring at the nonsignaling equilibrium is hi gher than at the signaling equilibrium, Because nonsignaling is stable and it is Likely to be the ancestral condition, we would like to know how natural systems evolved from nonsignaling to signaling, We sugges t that begging may have evolved through direct sibling fighting before the establishment of a parental response, that is, that nonsignaling squabbling leads to signaling. In multiple-offspring broods, young fol lowing a condition-dependent strategy in the contest for resources pro vide information about their condition. Parents can use this informati on even though it is not an adaptation for communication, and evolutio n will lead the system to the signaling equilibrium, This interpretati on implies that signaling evolved in multiple-offspring broods, but gi ven that signaling is evolutionarily stable, it would also be favored in species which secondarily evolved single-chick broods.