Short-lived intertidal midge Pontomyia oceana have semilunar eclosion rhythm entrained by night light

Abstract

Semilunar or lunar rhythms are common in intertidal organisms. Some are controlled by endogenous oscillators that are entrained by environmental factors. This study investigates whether the semilunar eclosion rhythm of the short-lived (~1 mo) marine midge Pontomyia oceana may be controlled by a night-light entrained endogenous rhythm. Mating midges were collected in southern Taiwan. Their fertilized eggs and larvae were cultured following various treatments in the laboratory until eclosion. A cohort, i.e. those fertilized on the same evening, later exhibited, under different light conditions without lunar cues, 2 modes in eclosion days. The periods of the circasemilunar eclosion rhythms under the no-cue conditions were between 12 to 15 d. Four successive evenings of nightlight synchronized the eclosion of midges into 2 concentrated peaks. Shifting the evenings of the entraining night-light resulted in a shift in the evenings of eclosion, although the degree of response was only ~50%. Night light in the first few days of life also had a concentration effect. Damping of the rhythm depended on the days in the life cycle during which the night-light was applied. The circa semilunar period of the rhythm was resistant to environmental changes as demonstrated by the low Q10 estimated from temperature treatments. This is the most short-lived species with demonstrated endogenous semilunar rhythm.