A team of scientists has solved the mystery of orchid mantis evolution. Orchid mantises, which blend in with flowers, show sexual dimorphism—with the males being smaller and less conspicuous. The research team found that this was largely due to the predatory success of larger females. The details are in a paper that was just published in the journal Scientific Reports.
The orchid mantis (Hymenopus coronatus) is an unusual insect that has camouflage resembling a flower. The females are large, colorful, and tend to hang around their host flower. The males, however, are quite small, inconspicuous, and mobile. This is an example of sexual dimorphism, in which the sexes have major differences in size and or appearance. In insects and other arthropods, it’s common for females to be much larger than males. This allows the females to carry more eggs while the tiny males can blend in and stay mobile to look for mating opportunities. Until now, it was assumed that the sexual dimorphism of orchid mantises had evolved for similar reasons.
Researchers from the Cleveland Museum of Natural History and the Palatinate Museum of Natural History in Germany worked together with other scientists to solve the orchid mantis puzzle once and for all. Previous research had already showed that female orchid mantises were not blending in to avoid predation—they were actually mimicking flowers in an attempt to attract and prey on pollinating insects. By combining evolutionary, ecological, and observational data, the research team began to piece together the puzzle. Unlike other mantids, the females weren’t larger for reproductive reasons but rather because it gave them better success as a predator. The males, on the other hand, stayed small and inconspicuous. This gave them a better chance of finding a female to mate with while avoiding predation. This is a very unusual case of sexual size dimorphism being caused by predatory success and not reproductive motivations, at least for the females.
The team’s findings finally provide a real explanation for sexual dimorphism in orchid mantises. The authors believe there are probably similar examples in the animal kingdom. Their study will help scientists fully understand how sexually dimorphic traits evolve.
Svenson et al. Selection for predation, not female fecundity, explains sexual size dimorphism in the orchid mantises. Scientific Reports (2016).