The first objective of the project was to figure out whether coral reef fishes that live in complex groups are related. In other animals such as birds, mammals and insects, group formation is often explained by the group members being close relatives, such as siblings or parents/offspring. In coral reef fishes we assumed for a long time that group members would not be related, because most coral reef fishes have a larval dispersal phase where they travel long distances in the open ocean before settling onto a reef. It is not clear whether the larvae, after they travelled for so long, have a chance to settle close to their close relatives. To address this question, I travelled to Papua New Guinea and took genetic samples from 17 groups of emerald coral gobies and 200 groups of clown anemonefish. I used DNA fingerprinting to find out how closely related the fish were. The results were surprising, because I did find that fish in the same group are closer related than fish that are further apart. This helps us understand why dominant breeders might accept the non-breeding subordinates: they are relatives that will eventually inherit the territory they live on. The first study, on emerald gobies, is already published, the second study, concerning anemonefish, is in preparation.
To address the second objective of the project, I wrote a literature review to summarize the current state of the art in social evolution of coral reef fishes, and to identify crucial knowledge gaps and the most interesting future research directions. For this review I worked together with colleagues from Australia and the US. We summarized what we know about social evolution in coral reef fishes and all the experiments that have been done on anemonefish, gobies and other species that live in complex social systems. We identified some crucial research directions that deserve more attention, such as addressing the question of why dominant breeders accept subordinate non-breeders in their territories, how different species compare to each other, using new analysis techniques to understand more complex groups, and addressing how climate change will impact the social live of coral reef fishes. The review is published, already widely read and will help move this research field forward.
For the third objective, I used laboratory experiments to find out if vertebrates can adjust their growth rate in response to their mutualistic partner. Anemonefish and anemones live in a close mutualistic relationship. The fish and the anemone exchange nutrients and they protect each other from predators. There is a lot about this relationship we do not understand yet and we do not know how this mutualism might impact the social evolution of the fish. By looking at the growth rate of juveniles in different sized anemones, we can begin to understand what effect a larger healthier host (anemone) has on the fish. I found that clownfish do change their growth depending on how large the anemone is that they live in. The juveniles in the larger anemones grew faster than the ones in the smaller anemones. This is the first time this flexibility in response to a mutualistic partner has been shown in any animal and it helps us to understand the big impact fish and anemones have on each other. This study was published.
These results of all objectives so far were published (or are under review) in high impact journals, and they were disseminated through press releases, news reports, conference talks and invited seminars, both for the scientific community and the wider public.
