Evidence that sensory traps can evolve into honest signals

Conventional models(1-4) explaining extreme sexual ornaments propose that these reflect male genetic quality(2-4) or are arbitrary results of genetic linkage between female preference and the ornament(1). The chase-away model(5) emphasizes sexual conflict: male signals attract females because they exploit receiver biases(6-9). As males gain control of mating decisions, females may experience fitness costs through suboptimal mating rates or post-copulatory exploitation. Elaboration of male signals is expected if females increase their response threshold to resist such exploitation. If ornaments target otherwise adaptive biases such as feeding responses(8-10), selection on females might eventually separate sexual and non-sexual responses to the signal. Here we show that the terminal yellow band (TYB) of several Goodeinae species evokes both feeding and sexual responses; sexual responsiveness phylogenetically pre-dates the expression of the TYB in males and is comparable across taxa, yet feeding responsiveness decreases in species with more elaborated TYBs. Displaying a TYB is costly, and thus provides an example where a trait arose as a sensory trap but has evolved into an honest signal.