Abstract
An understanding of how extinct animals functioned underpins our understanding of past evolutionary events, including adaptive radiations, and the role of functional innovation and adaptation as drivers of both micro- and macroevolution. Yet analysis of function in extinct animals is fraught with difficulty. Hypotheses that interpret molariform teeth in fishes as evidence of durophagous (shell-crushing) diets provide a good example of the particular problems inherent in the methods of functional morphology. This is because the assumed close coupling of form and function upon which the approach is based is weakened by, among other things, behavioural flexibility and the absence of a clear one to one relationship between structures and functions. Here we show that ISO 25178-2 standard parameters for surface texture, derived from analysis of worn surfaces of molariform teeth of fishes, vary significantly between species that differ in the amount of hard-shelled prey they consume. Two populations of the Sheepshead Seabream (Archosargus probatocephalus) were studied. This fish is not a dietary specialist, and one of the populations is known to consume more vegetation and less hard-shelled prey than the other; this is reflected in significant differences in their microwear textures. The Archosargus populations differ significantly in their microwear from the specialist shell-crusher Anarhichas lupus (the Atlantic Wolffish). Multivariate analysis of these three groups of fishes lends further support to the relationship between diet and tooth microwear, and provides robust validation of the approach. Application of the multivariate models derived from microwear texture in Archosargus and Anarhichas to a third fish species—the cichlid Astatoreochromis alluaudi—successfully separates wild caught fish that ate hard-shelled prey from lab-raised fish that did not. This cross-taxon validation demonstrates that quantitative analysis of tooth microwear texture can differentiate between fishes with different diets even when they range widely in size, habitat, and in the structure of their trophic apparatus. The approach thus has great potential as an additional tool for dietary analysis in extant fishes, and for testing dietary hypotheses in ancient and extinct species.
Highlights
In the context of the past, functional morphology is widely used as an approach to inferring how ancient animals functioned, shedding light on aspects of behaviour and interactions with the environment
Our objective with this study is to explore the potential for quantitative 3D texture analysis of tooth microwear to discriminate between populations of wild-caught fishes with differences in diet by testing the following hypotheses: Hypothesis 1: Within a species, dental microwear texture analysis can discriminate between two morphologically similar populations which have different diets
Testing hypothesis 1: microwear texture does not differ between populations of Archosargus Comparing tooth surface textures in Archosargus from the IR-herb and PC-duro populations reveals that 8 ISO parameters differ significantly between populations
Summary
In the context of the past, functional morphology is widely used as an approach to inferring how ancient animals functioned, shedding light on aspects of behaviour and interactions with the environment. An understanding of function underpins our understanding of past evolutionary events, including adaptive radiations, and the role of functional innovation and adaptation as drivers of both micro- and macroevolutionary patterns and processes This approach to function, requires the relationship between form and function to be well understood, and this has been the goal of decades of functional and biomechanical analysis of extant animals. M A Purnell and L P G Darras and Chapman 2010, Binning et al 2010), and others that are not directly linked (genetic and developmental factors) In extant fishes, these morphological traits form the basis of models with which to estimate prey capture and prey processing efficiency, but prey availability (as a function of predation or seasonality) and biological interactions, like intraspecific and interspecific competition for food resources, shape the diet
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