Comparative development of limb musculature in phylogenetically and ecologically divergent lizards

Abstract

Background Squamate reptiles (lizards, snakes, and amphisbaenians) exhibit incredible diversity in their locomotion, behavior, morphology, and ecological breadth. Although they often are used as models of locomotor diversity, surprisingly little attention has been given to muscle development in squamate reptiles. In fact, the most detailed examination was conducted almost 80 years ago and solely focused on the proximal limb regions. Herein, we present forelimb and hindlimb muscle morphogenesis data for three lizard species with different locomotion and feeding strategies: the desert grassland whiptail lizard, the central bearded dragon, and the veiled chameleon. This study fills critical gaps in our understanding of muscle morphogenesis in squamate reptiles and presents a comparative and temporospatial analysis of muscle development. Results Our results reveal a conserved pattern of early muscle development among lizards with different adult morphologies and ecologies. The variations that exist are concentrated in distal regions, particularly the specialized autopodia of chameleons, where differentiation of muscles associated with the digits is delayed. Conclusions The chameleon autopod provides an example of major evolutionary modifications to the skeleton with only minor disruption of the conserved order and pattern of limb muscle development. This robustness of muscle patterning facilitates the evolution of extreme yet functional phenotypes.

Candidate Regulatory Genes for Hindlimb Development in the Embryos of the Chinese Alligator (Alligator sinensis)

“…Despite the differences in the adult muscle morphology among various reptile species, muscle development is highly conserved. Limb muscles are mainly derived from the paraxial mesoderm, which differentiates to form somites during development [34,35]. The dorsal somites develop into the myotome, which further develops into the skeletal muscles of the body and limbs [36].…”

Limb development, evolution, and regeneration and repair: Part two

“…Only mutants for both Pax3 and Pax7 genes show an absence of muscle in their fins. The evolutionary aspect of limb muscles is also addressed in a study performed by Diaz et al, 7 where they perform a comparative analysis of muscle development in three different lizards (the desert grassland whiptail lizard, the central bearded dragon and the veiled chameleon). They describe that despite a major rearrangement in the skeleton of the veiled chameleon, which displays a bifurcated autopod adapted to arboreal locomotion, minor yet functional changes occurred in muscle development.…”