Behavioral and Physiological Differences between Two Parapatric Heliconius Species1

The behavior and physiology of two parapatric sibling species,i Heliconius erato cyrbiaGodt. andH. himeraHew., were investigated to assess if environmental adaptation enabled stable morphological, genetic, and ecological differences to exist in the face of hybridization. Morning and evening activity, egg production, and larval development time ofH. himeraandH. eratoin insectaries were recorded; individuals were collected in allopatry and in sympatry from a hybrid zone in which the species overlapped. Studies were performed at ambient conditions within the natural range ofH. himera. H. himerawas considerably more active thanH, eratoflying earlier in the morning and later in the evening, even when both species were collected in sympatry. Similarly,H. himeralaid more eggs, and the hatched larvae developed more rapidly. The results suggest that physiological constraints are an important selective force that may have been important in speciation and counteracts hybridization in the maintenance of theH. himeral H. eratocontact zone. Ecological selection, arising from adaptation to low temperatures, may help explain the competitive exclusion ofH. eratobyH. himerain the drier, cooler montane habitat favored by the latter species.