A recent quantitative genetic study representing 10 years of research on the coral reefs of Papua New Guinea has some very bad news for Nemo - Nemo doesn’t have the genetic capacity to adapt to rapid change in his natural environment. This study, published in the journal Ecology Letters by researchers from France’s National Centre for Scientific Research (CRIOBE USR3278 PSL University Paris : EPHE-UPVD-CNRS, Perpignan, France), Australia (James Cook University/ARC Centre of Excellence for Coral Reef Studies), Saudi Arabia (KAUST), Chile (Universidad Austral de Chile), and the United States (WHOI) shows that an anemone fish’s reproductive success, which guarantees a population ‘s ability to renew itself, depends almost entirely on its habitat, in particular the quality of its anemone. Nemo's future lies not in his genes, but our ability to preserve his habitat.
To date, the genetic capacity of a natural population to adapt, mathematically evaluated by the fundamental theorem of natural selection, had only been measured in about fifteen terrestrial species around the world. According to one of the study’s authors, Serge Planes, research director at France’s National Centre of Scientific Research, ‘It is not surprising that genetic capacity had yet to be measured for a marine population. Sampling within the marine environment is extremely challenging and long-term datasets for individuals within a marine population are incredibly rare'. According to Benoit Pujol, a permanent researcher at CNRS and also author of this study "to date, we just haven’t had the data required to answer this question yet."
Clownfish (Amphiprion percula) on their anemone in the lagoon around Kimbe Island in Papua New Guinea. © Simon Thorrold (WHOI)
Problem solved! An international team led by France’s CNRS (CRIOBE USR3278 PSL University Paris : EPHE-UPVD-CNRS, Perpignan, France) in collaboration with researchers from Saudi Arabia (KAUST), Australia (JCU/ARC Centre of Excellence for Coral Reef Studies), Chile (Universidad Austral de Chile), and the United States (WHOI), have monitored clownfish in the lagoons of Kimbe Bay, a biodiversity hot spot in Papua New Guinea, for over ten years. In this long-term research project, scientists identified each fish individually and sampled its DNA, making it possible to have the data necessary to perform quantitative genetic analyses on a marine population. After reconstructing Kimbe Island’s clownfish family tree, the researchers were able to calculate this population’s genetic evolutionary potential, and more, their ability to renew their population. Unfortunately for Nemo, this potential is almost nil, as evidenced by its low genetic variation – it’s so low in fact, it’s almost non-existent! “For a clownfish, it’s not “who” you are, but “where” you are that matters for your future reproductive success” says Geoff Jones, another author from James Cook University. “Big families that extend over many generations are linked to high quality habitats, not their shared genes”.
Clownfish (Amphiprion percula) coming out of their anemone to greet scientific divers, or more likely to defend their habitat. © Morgan Bennett-Smith (KAUST)
The quality of the anemone that provides the clownfish its home contributes significantly – on average 50% - to the ability of the clownfish to renew its population. If the population of high quality anemones remains healthy, this will ensure that the clownfish population will persist. However, anemones, and coral reefs in general, are under direct threat from climate change! According to Pujol: "Clownfish depend upon the quality of their habitat, because to adapt genetically to constraints will be extremely difficult, if not impossible. Maintaining their habitat in a good shape is therefore essential." According to Planes: "To expect a clownfish to genetically adapt at pace which would allow it to persist in the lagoons would be unreasonable, and thus the ability of these fish to remain in the lagoons over time will depend partly on our ability to maintain the quality of its habitat”.
Salles O, Almany G, Berumen M, Jones G, Saenz-Agudelo P, Srinivasan M, Thorrold S, Pujol B, Planes S (2019). Strong habitat and weak genetic effects shape the lifetime reproductive success in a wild clownfish population. Ecology Letters. 26 November 2019.