Heliconius cydno

Experiments performed pertaining to H. cydno oviposition reveal that they utilize chemoreception, not visual cues, when choosing their egg-laying sites.[11] H. cydno's oviposition sites are generally the tendrils of their Passiflora host plants, and eggs are placed singly.[1]

While leaf shape experiments and egg mimics do not have significant effects on oviposition, chemical cues from methanol render sites less appealing to H. cydno. Their lack of preference for leaf shape can be attributed to their varied usage of Passiflora hosts. H. cydno also does not participate in larval cannibalism, which plays a role in their indifference to egg mimics.[11]

The eggs of H. cydno are yellow, 1.1 mm in height and 0.9 mm wide.[1]

In the Schönbrunn Zoo aquarium house

Early instar larvae of this species have a white body and black spines.

Mature larvae are characterized by an orange head topped by two black horns 1.2 cm long. Their bodies are brownish pink, with black scoli (spines with multiple points) and black spots. The caterpillars of H. cydno are known to form small groups, demonstrating social behavior.[1]

Pupae of H. cydno are characterized by antennae, an abdomen with long spines, and a general dark brown color. They have two rectangular gold patches that decorate the thorax.[1]

Adults have forewings and hindwings which are black with either yellow or white bands/spots. Their hindwings have bars on their ventral surface, distinguishing themselves from mimics. Wing coloration is dependent on location.[1]

H. cydno engages in the predator defense mechanism of Müllerian mimicry with H. eleuchia (specifically in Ecuador) and H. sapho by adopting colors that warn a predator of their bad taste, deterring attacks.[1] For instance, H. cydno alithea, which has two potential colorings, mimics H. eleuchia in its yellow form, and mimics H. sapho in its white form. In contrast, H. cydno's close relative, H. melpomene, mimics H. erato.[4]

It is a species well known and widely researched for its tendency to hybridize with the closely related H. melpomene, from which it diverged around 1.5 million years ago.[1][10] They are sympatric for much of the geographic range of H. cydno, from Central America to northern South America, and exhibit a low level of hybridization and gene flow in nature.[12] Hybrids between the two species occur at a frequency of less than 0.1%.[12] Their low levels of hybridization can, in part, be attributed to pre-mating isolation, as H. melpone is found in more open habitats, while H. cydno lives in a closed-forest environment.[10] Studies suggest that changes in host use and mimicry in H. melpomene and H. cydno are genetically determined and may contribute to pre-mating isolation. In the past, this likely contributed to speciation.[3][10] H. pachinus is also known to hybridize with H. melpomene.[12] The fact that both species hybridize with H. melpomene is considered significant because H. melpomene exhibits a distinct pheromonal chemistry and coloring.[6]

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.[4]

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.[12]

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.[13]

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).[4] Strong linkage can be seen between mate preference and dominant wing color at the locus that controls forewing coloration.[5] This contributes to co-evolution of mimicry and mate preference while maintaining the association of different species.

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, is 90% polarized. In experiments investigating polarized light as a signal in mating, it was found that when a female's wings were shown behind a depolarizing filter, she was approached at a significantly lower rate than when her wings were shown behind a non-depolarizing filter. It has been suggested that the high degree of iridescence displayed by H. cydno can be attributed to their forest understory habitat, which generally has less-direct sunlight.[14]

H. cydno females are known to mate multiply, thus engaging in polyandry. There are many possible benefits to females mating multiply that may conclude more robust progeny, more allocation of resources, or other benefits.

Research done on H. cydno in Costa Rica suggests that the species has 12- and 14-membered macrolide scent gland extracts which have a C-18 skeleton. They are derived from linolenic, linoleic, and oleic acids and have an S configuration. According to the study, other species' desire and ability to hybridize with H. cydno was not affected by their possession of macrolide scent gland extracts.[6]