H. cydno are genetically determined and may contribute to pre-mating isolation. In the past, this likely contributed to speciation. H. pachinus is also known to hybridize with H. melpomene. The fact that both species hybridize with H. melpomene is considered significant because H. melpomene exhibits a distinct pheromonal chemistry and coloring. In fact, it has been suggested that wing preference patterns in mating may limit hybridization, a preference which is also known to limit hybridization between H. cydno and H. pachinus, which is another closely related species. Thus, divergent coloring (and therefore, mimicry), contributes to sympatric speciation. While hybridization of species is present, there is evidence to suggest that hybrids are less successful in mating than their non-hybrid counterparts. Hybrids will mate with one another; however, their mating success is 50% of that of their parents, demonstrating disruptive sexual selection against these hybrids that helps to maintain the two species as separate, sympatric species. Color patterns There are four key loci that affect wing color and pattern in H. cydno. L determines whether a given individual has melanic scales over their forewing band. The Sb and Yb loci are tightly linked in H. cydno, although the exact distance is not known. The Sb locus controls for the white submarginal band on the hindwing. The allele for the band is recessive. The Yb locus controls for a yellow band on the hindwing. The allele for this yellow band is also recessive. The K locus determines whether the medial band on the forewing, dorsally and ventrally, is yellow or white. An additional locus, G, determines the red line located on the forewing, at the base of the costal vein. Mating Coloration It has been determined, based on crosses performed between H. cydno and H. melpomene, as well as between H. cydno and H. pachinus, that there are specific linkage groups associated with both male preference and female mating outcome (red verses black in cydno/melpomene crosses and white verses yellow in cydno/pachinus crosses). Strong linkage can be seen between mate preference and dominant wing color at the locus that controls forewing coloration. This contributes to co-evolution of mimicry and mate preference while maintaining the association of different species. Iridescence and light polarization Wing iridescence is another factor in H. cydno mating. Heliconius butterflies in general use thin-film iridescence and polarized light for mate recognition. H. cydno has blue iridescence which, at some angles,