Glenn Almany, Suzanne Mills & Ricardo Beldade
Environmental changes have caused the destabilization of many of the world's ecosystems. In order to cope with environmental change, organisms may adapt by selection or adjust their phenotypes. Phenotypic plasticity, the development of alternative phenotypes by given genotypes, and the induced expression of a different phenotype via parental effects in offspring, are powerful means by which individuals can rapidly adjust to environmental change; a phenomenon known as phenotypic tracking. An additional response involves organisms altering the dispersive potential of their offspring to track the movement of favorable environments in space and time; a phenomenon known as habitat tracking.
Marine species produce larval offspring that develop in the open water for hours to months before settling to a suitable habitat patch, and this larval phase provides the main opportunity for dispersal. Theory predicts that selection should favor dispersal in habitats that are spatially or temporally variable, or that remain near their carrying capacity. Different dispersal strategies are widespread in animals and plants, enabling species to respond to environmental change. However, despite extreme temporal and spatial variability in coral reef environments, phenotypic plasticity associated with dispersal is virtually unknown among coral reef organisms.
Dispersal in the marine environment is largely determined by larval traits such as size and energy reserves, which are in turn correlated with swimming speed, a trait that likely plays an important role in determining whether a larva can remain near its natal population (i.e., restricted dispersal resulting in self-recruitment). Variation in larval traits may arise due to environmental factors, the parental phenotype or both. Parental effects are known to impact larval traits, but whether such traits also influence dispersal is unknown. Larger clownfish mothers produce more offspring that come back home (to the same population) (Beldade et al 2012). Certain areas of a coral reef islands are more likely to harbour clownfish mothers that produce larvae that come back home (Beldade et al 2016). This project seeks to understand if the final destination of larvae, return to their natal reef or disperse to other reefs, depends on the environment at the natal reef mediated through parental effects on offspring phenotype.
We are using the clownfish as a model species and are combining both laboratory and field experiments to unravel the causal mechanisms underlying dispersal. Our first aim is to test for effects of parental phenotype on egg and larval traits associated with dispersal. Our second aim is to then test how environmental conditions influence these dispersal-associated traits mediated through parental effects. Our third aim is to test the performance of different dispersal phenotypes after settlement under different environmental conditions. Whilst previous research has highlighted the importance of parental phenotype on larval dispersal, whether these effects influence survival after the larval period is unknown. As a result, there is strong evidence for important links between environmental conditions, parental effects, larval dispersal and subsequent performance after settlement, but no study has attempted to unravel this complex relationship. Our fourth aim is to conduct large-scale, manipulative experiments on a natural population to test the insights we gained in the first three aims and provide data to accurately model dispersal.
Because of the fundamental importance of larval dispersal and its influence on metapopulation dynamics, population replenishment and evolution, understanding how environmental conditions influence dispersal is critical and timely given the rapidly changing environment brought on by human actions. The results of this project will contribute to mitigate such impacts and improve the management of marine fisheries in general, and coral reefs specifically, two globally valuable resources that have significant impacts on human wellbeing.