Integrative phenotyping reveals new insights into the anemonefish adaptive radiation.

Evolutionary radiations are fundamental to the generation of biodiversity, occurring when organisms rapidly diversify to exploit various ecological niches. Symbiosis can serve as a powerful catalyst for such diversification, as illustrated by the iconic association of anemonefish and sea anemones. However, a critical gap in our understanding of adaptive radiations lies in determining how ecological opportunities drive adaptive morphological, behavioral, and physiological traits and how these traits, in turn, influence diversification. Using anemonefish (Amphiprion spp.) as a model, we investigated the phenotypic diversification accompanying their evolutionary history following symbiosis with giant sea anemones. While host specificity has traditionally been viewed as the primary driver of anemonefish adaptive radiation, we present an alternative perspective, showing that distinct ecological strategies-independent of host species-may also significantly contribute to their diversification. By examining half of the described anemonefish species, we combined field observations, swimming tunnel experiments, computational simulations, and morphological analyses to empirically reveal the presence of eco-morphotypes that exist independently of host specificity. Our findings provide novel insights into the evolutionary history and processes shaping anemonefish diversity. We show that, beyond sea anemone hosts, multiple drivers significantly contributed to their diversification. Integrative phenotyping, combining in situ and laboratory observations, reveals the forces driving adaptive radiations. It uncovers an unexpected, fine-tuned diversification in anemonefish, exemplifying how natural selection precisely shapes biodiversity during radiative bursts and highlighting the complexity of ecological interactions and evolutionary mechanisms.