Behavioral and physiological differences between two parapatric Heliconiusspecies

The behavior and physiology of two parapatric sibling species, Heliconius e rato cyrbia Godt. and H. himera Hew., were investigated to assess if enviro nmental adaptation enabled stable morphological, generic, and ecological di fferences to exist in the face of hybridization. Morning and evening activi ty, egg production, and Larval development time of H. himera and H. erato i n 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 of H; himera. H. h imera was considerably more active than H. erato, flying earlier in the mor ning and later in the evening, even when both species were collected in sym patry. Similarly, H. himera laid more eggs, and the hatched larvae develope d more rapidly The results suggest that physiological constraints are an im portant selective force that may have been important in speciation and coun teracts hybridization in the maintenance of the H. himera/H. erato contact zone. Ecological selection, arising from adaptation to low temperatures, ma y help explain the competitive exclusion of H. erato by H. himera in the dr ier, cooler montane habitat favored by the latter species.