Switch from nocturnal to diurnal activity identified
An international team around the doctoral candidates Gregor Schalm and Kristina Bruns investigated the behavioural and genetic basis of diel rhythms in anemonefish and thus was able to identify the internal clock of the animals. Schalm and Bruns, who do their research at the ICBM associated research group for Animal Biodiversity and Evolutionary Biology (IBU), headed by Prof. Dr Gabriele Gerlach at the Institute for Biology and Environmental Sciences at the University of Oldenburg, were supported by colleagues from Germany, Italy and Australia. Their findings have been published in the recent issue of Scientific Reports.
On hearing the name „Nemo“, many people associate a particular image, for a fish named that way being the hero of a highly successful animation movie of 2003. In fact, (false) clown anemonefish (Amphiprion ocellaris) from the eastern Indian and West Pacific Oceans formed the natural template for the movie‘s protagonist. Adult anemonefish have a symbiotic relationship with sea anemones. The so-called flower animals provide shelter with their stinging tentacles for the fish, as the adults are relatively poor swimmers, whereas the fish prevent the anemones from being attacked by predators.
As in most coral reef fish, timing mechanisms play a biological key role in clown anemonefish. Usually, the larvae leave their natal reef immediately after hatching to continue living in the open ocean. After a while, they return to their home reef where they eventually settle down. Knowledge remains incomplete what determines dispersal duration of the larvae and how they manage to find their way back to the natal reef. It is known, for example, that cardinal fish (Ostorhinchus doederleini) larvae use celestial cues in combination with a time-compensated compass to find back home. The researchers suppose similar mechanisms in clownfish, which underlines the necessity for the animals to have a proper timing system.
The scientists substantiated a behavioural shift of the clownfish as a function of their respective age from nocturnal larvae to diurnal adults. Juveniles exhibited an intermediate pattern. The researchers interpret this particular feature as a potential flexibility in the timing of settlement on a host anemone.
A genetic analysis of six core circadian clock genes revealed comparable rhythmic expression patterns in larvae and juvenile clownfish. Therefore, the age-dependent activity patterns could not be contributed to these genes. On the basis of embryonic cell lines in cell cultures, the scientists eventually succeeded in demonstrating that clown anemonefish possess an endogenous timer similar to the well-studied internal clock of the zebrafish (Brachydanio rerio). „Our study provides a first basis to understand the migratory behaviour of coral reef fish and to elucidate the multi-layered interaction of anemone fish, sea anemones as well as their zooxanthellae endosymbionts“, Gabriele Gerlach, head of the resarch group, points out.
Gregor Schalm; Kristina Bruns; Nina Drachenberg; Nathalie Geyer; Nicholas S. Foulkes; Cristiano Bertolucci; Gabriele Gerlach: „Finding Nemo’s clock reveals switch from nocturnal to diurnal activity“, Scientific Reports, doi: 10.1038/s41598-021-86244-9.