A box of chocolates is nice enough, but if you really want to win a girl's heart, you might take a cue from male guppies and go one step further. Boy guppies woo females by looking like their favorite food, a study has found. The authors say females go wild for males with big orange spots simply because the markings resemble the bright orange fruits they like to eat. The research challenges the standard theory of sexual selection, which maintains that sexy traits reveal the quality of a prospective mate's genes.
Scientists theorized that male guppies' orange spots reflected their health and food-finding prowess--important considerations for females picking a mate. But that failed to explain why females from some populations are more responsive to orange spots than are females from other populations. "Maybe this is a stimulus that just attracts their attention," says Helen Rodd, a zoologist at the University of Toronto. When Rodd noticed that the guppy spots were the same color as fruit that falls into the water from trees onshore, she wondered if the species first evolved extra sensitivity to orange to help find food--and males later exploited that sensitivity to catch the eye of females.
To test her hypothesis, Rodd and colleagues placed colored disks in guppy-rich streams in Trinidad and noted the sex and age of each fish that approached or pecked each disk. Back in the lab, the team did similar experiments with lab-raised guppies bred from different populations. In all experiments, fish of both sexes pecked at the orange disks most often, with the occasional exception of red disks, suggesting that the orange bias goes beyond potential mates. The team also found that the sex appeal of the males' orange spots was greater in populations in which both sexes showed a strong attraction to orange, the team reports in the 7 March issue of the Proceedings of the Royal Society of London, Series B.
The work adds to a handful of studies in other species that have identified sexy traits that reveal little about a potential mate's worth, says Anne Houde, an evolutionary biologist at Lake Forest College in Illinois. But she says Rodd's study is one of the first to get at how sexual preferences get started in the first place. Still, both Houde and Rodd point out that orange appeal is just one factor in the mating game. The spots may first catch a lady's eye, but she'll soon check out traits more reflective of mates' genetics. So don't buy that chocolate shirt unless you've got the goods to back it up.