Exaggeration of a sexual ornament – not by female choice

JOHN H. CHRISTY; PABLO D. RIBEIRO

Cornell

Congreso; ISBE 2008 – 12th International Behavioral Ecology Congress; 2008

Cornell University, Ithaca, New York, USA

Exaggeration of the size of male sexual ornaments is thought to be driven by female preferences, while natural selection limits ornament size. We studied whether this was true for sand structures called hoods which are built by courting male fiddler crabs Uca terpsichores next to the entrances to their burrows to which they attract females for mating.  We measured the effect of hood size on male attractiveness to females and on the ability of males to quickly and reliably relocate their burrows and escape predators.  We replaced males´ hoods with replicas made of cement that were ½, ¾, full (average) and super-sized and recorded the rate with which they attracted females. We experimentally introduced errors in males non-visual path maps to their burrows´ locations and measured the time it took them to find their burrows on which we had placed hood replicas of the different sizes.  The female preference curve leveled off at hoods the were ¾ of average hood size while male borrow relocation ability continued to increase for hoods larger than they ever build. Hence males build hoods, a sexually selected signal, larger than they need to be to be maximally attractive to females but smaller than is best to aid in burrow relocation.  The relatively close distance at which females, compared to male burrow owners, respond to hoods as guidepost to burrows may explain the former, while loss of hood structural integrity with increasing size may explain the later