Linking morphology to behaviour
Uncovering the genetic basis of behavioural and morphological traits and the factors influencing their evolution is undoubtedly of great significance, yet this only provides one half of the story; it is one thing to establish the mechanisms of evolution and their phenotypic consequences, but another entirely to elucidate the functional link between them. The associations between morphology and behaviour are perhaps the best-studied of the three integrative pathways discussed here as in a broad sense uncovering these associations is the express goal of functional morphology (Wainwright, 1994). Several experimental studies have addressed the functional significance of chondrichthyan morphology (Wilga and Lauder, 2004a). As a result, the contribution of structures such as the dorsal, caudal, and pectoral fins to locomotor performance in elasmobranchs is relatively well understood (Maia and Wilga, 2013; Wilga and Lauder, 2001; Wilga and Lauder, 2004b). There are however several major limitations of this approach that constrain integration between morphological and behavioural studies. This experimental approach rarely captures ecologically relevant complex behaviours, and where it does, influence of the laboratory setting on expressed behaviour cannot be ruled out (Moore and Biewener, 2015). Moreover, population and species-specific morphologies (Grover, 1972; Keeney and Heist, 2006; Sternes and Shimada, 2020) mean that there is little reason to suggest that existing kinematic studies should be representative of all – or even a substantial proportion of extant chondrichthyan diversity. The lack of studies linking morphology to complex behaviours in wild populations fundamentally constrains our understanding of evolution as without such studies the true adaptive value of morphology. This in turn constrains our understanding of ecological interactions, the evolution of complex behaviours such as foraging strategies, and how future environmental change may influence them. Novel technological advancements are increasingly enabling quantitative study of chondrichthyan behaviour in wild populations (Butcher et al., 2021; Renshaw et al., 2023) and thus with sufficient research effort this knowledge gap is likely to decrease, however significant further study combining experimental and observational approaches will be required in order to achieve this goal.