Abstract
Timing mechanisms play a key role in the biology of coral reef fish. Typically, fish larvae leave their reef after hatching, stay for a period in the open ocean before returning to the reef for settlement. During this dispersal, larvae use a time-compensated sun compass for orientation. However, the timing of settlement and how coral reef fish keep track of time via endogenous timing mechanisms is poorly understood. Here, we have studied the behavioural and genetic basis of diel rhythms in the clown anemonefish Amphiprion ocellaris. We document a behavioural shift from nocturnal larvae to diurnal adults, while juveniles show an intermediate pattern of activity which potentially indicates flexibility in the timing of settlement on a host anemone. qRTPCR analysis of six core circadian clock genes (bmal1, clocka, cry1b, per1b, per2, per3) reveals rhythmic gene expression patterns that are comparable in larvae and juveniles, and so do not reflect the corresponding activity changes. By establishing an embryonic cell line, we demonstrate that clown anemonefish possess an endogenous clock with similar properties to that of the zebrafish circadian clock. Furthermore, our study provides a first basis to study the multi-layered interaction of clocks from fish, anemones and their zooxanthellae endosymbionts.
Highlights
Timing mechanisms play a key role in the biology of coral reef fish
The habitat of very young larvae and adult animals is extremely different - young larvae are dispersing in the open ocean, while adults are highly sedentary in close mutualism with their host anemone
In our study we have revealed a considerable change in locomotor activity during developmental maturation of A. ocellaris from nocturnal larvae to diurnal adults
Summary
Fish larvae leave their reef after hatching, stay for a period in the open ocean before returning to the reef for settlement. During this dispersal, larvae use a time-compensated sun compass for orientation. The fascinating clown anemonefish A. ocellaris (family: Pomacentridae) represents an ideal model organism to study the contribution of the circadian clock to shaping coral reef fish biology. Like most coral reef fish, clown anemonefish have a larval dispersal stage with larvae hatching at n ight[15], leaving the natal reef immediately after hatching and staying for up to 12 days in the pelagic zone. This gene regulatory circuit thereby directs circadian rhythms of gene e xpression[21]
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