Résumé
Species coexistence involves the evolution of reproductive barriers
opposing gene flow. Heliconius butterflies display colorful patterns
affecting mate choice and survival through warning signaling and mimicry.
These patterns are called “magic traits” for speciation because divergent
natural selection may promote mimicry shifts in pattern whose role as
mating cue facilitates reproductive isolation. By contrast, between
comimetic species, natural selection promotes pattern convergence. We
addressed whether visual convergence interferes with reproductive
isolation by testing for sexual isolation between two closely related
species with similar patterns, H. timareta thelxinoe and H. melpomene
amaryllis. Experiments with models confirmed visual attraction based on
wing phenotype, leading to indiscriminate approach. Nevertheless, mate
choice experiments showed assortative mating. Monitoring male behavior
toward live females revealed asymmetry in male preference, H. melpomene
males courting both species equally while H. timareta males strongly
preferred conspecifics. Experiments with hybrid males suggested an
important genetic component for such asymmetry. Behavioral observations
support a key role for short-distance cues in determining male choice in
H. timareta. Scents extracts from wings and genitalia revealed
interspecific divergence in chemical signatures, and hybrid female scent
composition was significantly associated with courtship intensity by H.
timareta males, providing candidate chemical mating cues involved in
sexual isolation.