Evolution and ecology of developmental processes and of the resulting morphology: directional asymmetry in hindlimbs of Agamidae and Lacertidae (Reptilia: Lacertilia)

Abstract

In this paper, the evolution and ecology of directional asymmetry (DA) during the developmental trajectory (DT) is compared with that of its product, morphological DA (MDA). DT and MDA are calculated for two bilateral morphological scale characters of lizards, the number of subdigital lamellae beneath the fourth toe in 10 agamid and 28 lacertid taxa, and the number of rows of ventral scales in 12 lacertid taxa. MDA, the subtraction between left and right sides (classical measure of DA), is functional in adult animals. Results confirm the hypothesis that, in DT, the regression parameters a (constant) and b (regression slope) of counts on the right side with those on the left describe a developmental process. No phylogenetic or environmental effects were observed on a and b, but analyses considering both a andb together show non-random phyletic patterns. Independent analyses deduced the same ancestral DT in Agamidae and Lacertidae. In Lacertidae, distance between pairs of taxa in a+b (standardized values) correlates positively with the phylogenetic distance between taxa. Phyletic trends in MDA are indirect, and due to the link of MDA witha +b. The MDA of species is more dissimilar in sympatry than in allopatry. The phyletic trends suggest evolution of DT, while the association of MDA with sympatry suggests that ecological pressures shape MDA in adult animals. Evolution of DT is independent from that of its product, MDA—adaptive determinism defines the result of, but not the mechanistic process of, development. Deterministic environmental processes define MDA, and deterministic evolutionary processes define the interactive result of a and b, but not each separately. According to circumstances, different DTs produce similar or different MDA, and a particular DT can produce different MDAs.