Development and Evolution of the Muscles of the Pelvic Fin

Locomotor strategies in terrestrial tetrapods have evolved from the utilisation of sinusoidal contractions of axial musculature, evident in ancestral fish species, to the reliance on powerful and complex limb muscles to provide propulsive force. Within tetrapods, a hindlimb-dominant locomotor strategy predominates, and its evolution is considered critical for the evident success of the tetrapod transition onto land. Here, we determine the developmental mechanisms of pelvic fin muscle formation in living fish species at critical points within the vertebrate phylogeny and reveal a stepwise modification from a primitive to a more derived mode of pelvic fin muscle formation. A distinct process generates pelvic fin muscle in bony fishes that incorporates both primitive and derived characteristics of vertebrate appendicular muscle formation. We propose that the adoption of the fully derived mode of hindlimb muscle formation from this bimodal character state is an evolutionary innovation that was critical to the success of the tetrapod transition

A comparison of morphogenesis of muscles of the forearm and hand during ontogenesis and regeneration in the axolotl ( Ambystoma mexicanum )

The morphogenesis of muscles of the forearm and hand was studied in embryonic limbs of the axolotl ( Ambystoma mexicanum ) and compared with the course of morphogenesis in the regenerating limb of adults. The first part of the paper describes the morphogenesis of muscles ontogenetic development. The course of development, from the stage of muscle blastemas through that of the independent muscle anlagen is described for each muscle. The separation of muscle anlagen and their differentiation forms a prominent proximodistal gradient. At the same time there is a clear radioulnar gradient in the formation of muscle anlagen. Phylogenetically, this radioulnar gradient is restricted to the developing limb of Urodeles. In the second part of the paper, the morphogenesis of muscles is described in the regenerating limb. The major features in regeneration recapitulate those in the embryonic limb. Proximodistal and radioulnar gradients of development are also present in the regenerating limb. This structural similarity in development supports the viewpoint that the regeneration blastema is an integrated morphogenetic unit in which muscles differentiate according to the same genetic plan as they do in the embryo. There are some differences, however, between the regenerating and embryonic limb. The regenerating limb is larger, its muscle blastemas are also larger from the beginning, and the regenerating limb has a relatively greater amount of mesenchymal cells, which are not closely integrated into the muscle or skeletal anlagen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47521/1/429_2004_Article_BF00519726.pd