Elevating perceived predation risk modifies the relationship between parental effort and song complexity in the song sparrow Melospiza melodia.

Adult-directed predation risk elevates costs of parental care, and may modify relationships between sexually selected ornaments and parental effort by accentuating the tradeoff between survival and parental investment. We assessed multiple hypotheses regarding the relationship between maternal effort, paternal effort, and the sexually selected trait of male song complexity in the song sparrow Melospiza melodia. Further, we explored whether experimentally elevating perceived adult-directed predation risk near nests affected these relationships. We quantified two dimensions of song complexity: song repertoire size and residual syllable number (the relative number of syllables for a given song repertoire size). Under elevated perceived predation risk, but not in the absence of the predator stimuli, females mated to males with higher residual syllable number displayed higher nestling provisioning rates and performed a greater proportion of nestling provisioning trips. In other words, elevating perceived predation risk induced a pattern of maternal investment consistent with differential allocation. In contrast, under elevated perceived predation risk, only, females performed a lesser proportion of provisioning trips when mated to males with large song repertoire sizes. Further, consistent with the good parent hypothesis, males with large song repertoire sizes displayed lower latencies to return to the nest, independent of the predator stimuli. Results suggest that residual syllable number may reflect some aspect of male genetic quality, such that females are more willing to maintain maternal effort while facing heightened predation risk. On the other hand, females may gain paternal benefits when mated to males with large song repertoires. Our study supports the hypothesis that increased costs of parental care associated with predation risk may induce relationships between sexually selected traits and parental behavior, which may increase the strength of sexual selection. Additionally, results suggest that different aspects of song complexity may fulfill non-equivalent signaling roles. [ABSTRACT FROM AUTHOR]