The intertidal marine midge, Pontomyia oceana, was found to use 2 clocks on eclosion day to concentrate their mass emergence. Experiments were designed to test whether the function of 2 clocks is accuracy or precision. Since the mean eclosion time at night may follow sunset from 0-5 hours depending on season, and may precede the time of low tide from 0-5 hours depending on lunar phase, the accuracy hypothesis is not supported. Under the precision hypothesis, the midges use 2 clocks to reduce the variation in eclosion time between individuals so everyone emerge at the same time; encountering mates is obviously a strong selective force behind the mechanism of the diel timing of emergence.
On the other hand, the marine midge also increases probability of total reproductive failure by concentrating the emergence of their offspring to a short period. We discovered that a batch of fertilized eggs have 2 peaks of emergence days, about 30 and 45 days later. Among the 3 hypotheses proposed to explain this dimorphism in duration of life cycle, the bet-hedging hypothesis is supported. The midge “strategically” allocates their offspring to emerge at both the first and the second peaks, so the risk of total mortality could be spread and reduced. The loss in mean fitness due to longer life cycle in some offspring is presumably compensated by lower fitness variation between generations.
Species 1: Diptera Chironomidae Pontomyia oceana (marine midge)
Keywords: marine midge
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA