Evolution along allometric lines of least resistance: Morphological differentiation in Pristurus geckos

Species living in distinct habitats often experience unique ecological
selective pressures, which can drive phenotypic divergence. However, how
ecophenotypic patterns are affected by allometric trends and trait
integration levels is less well understood. Here we evaluate the role of
allometry in shaping body size and body form diversity in Pristurus geckos
utilizing differing habitats. We found that patterns of allometry and
integration in body form were distinct in species with different habitat
preferences, with ground-dwelling Pristurus displaying the most divergent
allometric trend and high levels of integration. There was also strong
concordance between intraspecific allometry across individuals and
evolutionary allometry among species, revealing that differences in body
form among individuals were predictive of evolutionary changes across the
phylogeny at macroevolutionary scales. This suggested that phenotypic
evolution occurred along allometric lines of least resistance, with
allometric trajectories imposing a strong influence on the magnitude and
direction of size and shape changes across the phylogeny. When viewed in
phylomorphospace, the largest rock-dwelling species were most similar to
the smallest ground-dwelling species, and vice versa. Thus, in Pristurus,
phenotypic evolution along the differing habitat-based allometric
trajectories resulted in similar body forms at differing body sizes in
distinct ecological habitats.