Protandry as an adaptive trait in the two Theclini species (Lepidoptera: Lycaenidae)

Abstract

Adult males emerge earlier than females in a number of insect species, a phenomenon known as a type of protandry. To clarify whether protandry is an adaptive trait or a byproduct caused by differences in developmental time between males and females, I investigated the developmental pathways of two lycaenid butterflies, Chrysozephyrus smaragdinus and Iratsume orsedice. The larvae of these species overwinter in eggshells, and hatch in the spring when their host plants undergo budding. Therefore, earlier hatching of males than females would support protandry as an adaptive trait. In addition, the mating systems of these butterflies would provide insights into the evolution of protandry. C. smaragdinus is a perching species, and males arriving at perching sites early in the adult season tend to continue occupying the site after interactions with intruding males. Consequently, males should emerge earlier than not only females but also other males. In contrast, I. orsedice is a patrolling species in which males may have to emerge earlier than females but need not emerge earlier than other conspecific males. Therefore, the degree of protandry would be greater in C. smaragdinus than in I. orsedice. I reared the butterflies in the laboratory, and found that male larvae hatched earlier than female larvae, indicating that protandry is an adaptive trait in these species. I also found that the degree of protandry was greater in C. smaragdinus than in I. orsedice, consistent with the notion that males should emerge earlier in perching species than in patrolling species.