Linking micro and macroevolution of head shape in an island radiation

Phenotypic traits have been shown to evolve in response to variation in
the environment. However, the evolutionary processes underlying the
emergence of phenotypic diversity can typically only be understood at the
population level. Consequently, how subtle phenotypic differences at the
intraspecific level can give rise to larger-scale changes in performance
and ecology remains poorly understood. We here tested for the covariation
between ecology, bite force, jaw muscle architecture, and the
three-dimensional shape of the cranium and mandible in 16 insular
populations of the lizards Podarcis melisellensis and P. sicula. We then
compared the patterns observed at the among-population level with those
observed at the interspecific level. We found that three-dimensional head
shape as well as jaw musculature evolve similarly under similar ecological
circumstances. Depending on the type of food consumed or on the level of
sexual competition, different muscle groups were more developed and
appeared to underlie changes in cranium and mandible shape. Our findings
show that the local selective regimes are primary drivers of phenotypic
variation resulting in predictable patterns of form and function.
Moreover, intraspecific patterns of variation were generally consistent
with those at the interspecific level, suggesting that microevolutionary
variation may translate into macroevolutionary patterns of
ecomorphological diversity.