A PERSISTENT DIURNAL RHYTHM IN CHAOBORUS LARVAE. I. THE NATURE OF THE RHYTHMICITY1

Abstract

Larvae of Chaoborus punctipennis Say (Diptera: Culicidae) were maintained under constant conditions in two 152‐ × 10‐cm columns containing lake water and sediments. Visual counts of the larvae in the columns were made hourly with a flashlight equipped with a red filter and darkened reflector. Activity was observed during dark periods; however, no activity was observed during light periods. A diurnal rhythm of activity persisted up to 10 days in constant darkness. The phase of the rhythm was reset by entrainment under differing light regimes, as well as by temperatures of 5C or less. These critical low temperatures also abolished activity. The offset of light was demonstrated to be the Zeitgeber for this rhythm; therefore it is necessary that under natural conditions these larvae receive some offset stimulus from the setting sun.

Light control of evening vertical migrations by Chaoborus punctipennis larvae

“…LaRow (1968) suggested that within the sediments the larvae undergo a circadian pattern of movements that brings the animals to the mud surface near dusk, where they enter the water in response to a threshold light intensity (Swift and Forward 1988) or other factors as suggested in this study.…”

Comparaison des communautés d'invertébrés entre des lacs avec et sans omble de fontaine (Salvelinus fontinalis) /

“…While C. flavicans and C. trivittatus larvae co-occurred with fish, C. americanus larvae were strongly associated with fishless lakes. The first instar larvae can benefit from a size refuge and escape prédation, but larger final instars adopt predator avoidance behaviours such as diel vertical migration (LaRow 1968(LaRow , 1969. However, this behaviour is not observed in C americanus larvae, and so it only occurs in fishless lakes von Ende 1979;Wissel et al 2003).…”

“…As in the limnetic area, in this study it was observed that Daphnia pulex was more abundant in presence of fish rather than in absence and this could be correlated with the high density of Chaoborus larvae present into the water column during daytime. Fish are known to influence Chaoborus larvae composition and distribution , von Ende 1979, Wissel et al 2003 and some Chaoborus species make diurnal migration to avoid fish prédation (LaRow 1968(LaRow , 1969. Their absence from the nekton samples offishpresent lakes may result from direct prédation by brook trout or from behavioural change as a response to fish prédation.…”

A laboratory method for studying zooplankton swimming behaviors

“…Zooplankton cultures were exposed to continuous light of a constant intensity in order to dampen LaRow (1968LaRow ( , 1969, Hagerman (1969), Hart & Allanson (1976), and others have found endogenous rhythms of swimming activity in cladoceran, copepod and ostracod zooplankton, and Buchanan & Goldberg (1981) observed a strong relationship between the prestimulus swimming activity and the strength of the phototactic response for Daphnia after a stimulus is applied . The spectral distribution of the light source to which zooplankton are adapted can influence the photosensitivity of the animals .…”