Reproductive interference is stronger than expected in Heliconius butterflies

Abstract

In animals, reproductive interference associated with mimicry can result in the evolution of private communication channels, as suggested for Heliconius butterflies, where cryptic color wavelength would drive male preference for conspecific over intergeneric co-mimics. Here, we tested this hypothesis in two co-mimic pairs (intra and intergeneric) and measured the efficacy and symmetry of color pattern as a reproductive barrier in a non-co-mimic, possibly hybridizing pair of Heliconius species. We conducted pairwise experiments of preference where a group of males was presented to a conspecific and heterospecific female model made with real wings and free of chemical volatiles. We did not detect any indication of the expected use of cryptic recognition signals to mate choice in the intergeneric co-mimic pair. Additionally, we detected an unexpected male preference for heterospecific female models between intrageneric co-mimics towards the species with larger red patches, suggesting a supernormal stimulus based on a general preference for the red color. Finally, we found an asymmetry in the behavioral reproductive barrier between the non-co-mimic closely related species that also agrees with the hypothesis of a general preference for red and with an expected permeability of the reproductive barrier between them. Since the costs imposed by heterospecific courtships can limit the convergence of signaling phenotypes, our results contribute to explaining the maintenance of multiple aposematic color pattern between unpalatable and closely related sympatric Heliconius species.