A trade-off between reproduction and a condition-dependent sexually selected ornament in the house sparrow Passer domesticus

Reproductive effort was manipulated in a free-living population of house sp arrows (Passer domesticus) to investigate the trade-off between reproductiv e investment and the expression of a condition-dependent sexually selected ornament. Phenotypic plasticity in the expression of this trait was related to the experimentally manipulated size of the brood reared by a male. Male s that invested more in current reproduction subsequently became more attra ctive to females in this population as they showed a preference for males w ith smaller badges. This supports the argument that direct benefits are a p rimary focus for mate choice by females. Trade-offs between reproductive ef fort and the expression of sexual ornaments are a potentially important sou rce of phenotypic variation in both sexual ornaments and life-history trait s.