Musculoskeletal Anatomical Changes That Accompany Limb Reduction in Lizards

ABDALA, V.; GRIZANTE, M.; DIOGO, R.; MOLNAR, J.; KOHLSDORF, T.

JOURNAL OF MORPHOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2015 vol. 276 p. 1290 - 1310

0362-2525

Muscles, bones, and tendons in the adult tetrapod limb are intimately integrated, both spatially and functionally. However, muscle and bone evolutiondo not always occur hand in hand. We asked, how does the loss of limb bones affect limb muscle anatomy, and do these effects vary among different lineages? To answer this question, we compared limb muscular and skeletal anatomy among gymnophthalmid lizards, which exhibit a remarkable variation in limb morphologyand different grades of digit and limb reduction. We mapped the characters onto a phylogeny of the group to assess the likelihood that they were acquiredindependently. Our results reveal patterns of reduction of muscle and bone elements that did not always coincide and examples of both, convergent and lineagespecific non-pentadactyl musculoskeletal morphologies. Among lineages in which non-pentadactyly evolved independently, the degree of convergence seems todepend on the number of digits still present. Most tetradactyl and tridactyl limbs exhibited profound differences in pattern and degree of muscle loss/reduction, and recognizable morphological convergence occurred only in extremely reduced morphologies (e.g., spike-like autopodia). We also found examples of muscles that persisted although the bones to which they plesiomorphically attach had been lost, and examples of muscles that had been lost although their normal bony attachments persisted. Our results demonstrate that muscle anatomy in reduced limbs cannot be predicted from bone anatomy alone, meaning that filling the gap between osteological and myological data is an important step toward understanding this recurrent phenomenon in the evolution of tetrapods