Biodiversity loss caused by human activities (habitat degradation, over-exploitation) mainly affects top predators and generates trophic cascades in both terrestrial and aquatic biomes (Duffy et al. 2003; Estes et al. 2011). In parallel, a growing number of studies have shown that, before extinction, a rapid evolution to earlier maturation at smaller body size occurs (e.g. Conover and Munch 2002). Surprisingly, even if over-exploitation is stopped, some populations seem incapable to recover, suggesting a loss of their resilience potential (e.g. Neubaeur et al. 2013). This resilience loss could be linked to an impairment of population adaptative capacity through an erosion of genetic variances for adaptative traits, and/or to a change in the naturally-selected adaptative optimum. Anthropogenic selection against large individuals induces a parallel decrease in both density and size in populations, which may both induce trophic cascades in the ecosystem, and result in a displacement of the natural adaptative optimum. Management and conservation of biodiversity therefore requires to better understand whether and how such eco-evolutionary feedbacks are implicated in the resilience loss.
In my Ph.D., I investigate the eco-evolutionary mechanisms involved in trophic cascades at several scales (from gene to ecosystem). I apply a size-dependent divergent selection on medaka fish (Oryzias latipes) in laboratory to obtain a “dwarf” line, a “giant” line and a “control” line. This will permit to measure experimentally (1) the evolutionary response to selection in terms of life history traits, trait genetic architecture, and candidate gene expression (that is realized in BOREA), (2) the contribution of evolution to trophic cascades (by quantifying the respective contributions of evolution and density), and (3) whether and how a medaka-driven trophic cascade alters the form of natural selection acting on medaka (eco-evolutionary feedback loop).