Occurrence of protandry in an aseasonal multivoltine moth: Implications for body-size evolution

摘要

The behaviour of males emerging/maturing/arriving earlier than females is called protandry. Among insects, protandry has been reported only in those that are seasonal. This is probably because discrete generations, a requisite for protandry, are often reported in insects from seasonal environments. In what may be the first evidence for aseasonal multivoltine insects, we report protandry in Opisina arenosella, a tropical moth with discrete generations. The mean emergence time for males of Opisina was significantly earlier than that of females and the proportion of females in the population increased with progress in the flight period, suggesting protandry. Field-activity pattern of moths, monitored using light traps, showed that the peak activity period for males was earlier than that of females, a trend similar to that of the emergence pattern. Further, through laboratory studies on developmental biology, protandry was consistently observed over a range of temperatures (22-34 degrees C) normally prevalent in the study area, suggesting that protandry per se may not be a function of seasonality. We attribute protandry in Opisina to sexual selection for early male emergence. We discuss why protandry among aseasonal insects cannot result from selection for body size in males or females, and suggest that protandry and smaller male body size should not be related to availability of food. The evidences provided in this communication may open opportunities for exploring reproductive asynchrony in general, and protandry in particular, among aseasonal insects.