Novel hatching cue in the neotropical damselfly Megaloprepus caerulatus: larval adaptation and maternal constraint

Abstract

The evolution of sibling cannibalism as a maternal strategy is particularly challenging to explain when nurseries are shared among multiple females. Such is the case for the damselfly, Megaloprepus caerulatus, whose females lay eggs in bark above the water line in large, water-filled tree holes. Asynchronous egg hatching appears to be a maternal bet-hedging strategy to increase the chances that cannibalistic offspring hatch during windows of opportunity, which occur after the remaining large larvae emerge, having eaten all others. We investigated the proximate causes of asynchronous hatching. By monitoring the pattern of egg hatching under ambient temperature in an insectary, we found that egg hatching co-occurred with lower ambient temperatures, which decreased with increasing rainfall. Treating fully developed eggs to a lower temperature for two hours triggered increased hatching relative to controls at ambient temperature. Dissection of control clutches indicated that embryonic development of siblings was asynchronous. Results suggested that the hatching trigger is adaptive. Rainfall assures a recharge of the larval habitat with water and provides wet conditions essential for neonate mobility on bark. Only 40% of neonates in a 4-day drying treatment survived; none survived the 8- and 14-day treatments. This novel hatching trigger should increase the number of neonates entering the nursery after rains, constraining a mother’s control over the timing of egg hatch, while increasing the competition among related and unrelated offspring for limited windows of opportunity in the shared nursery.