Neuroanatomy of the lumbosacral plexus in a highly diversified clade of South-American lizards. Evolution and phylogenetic implications

Abstract

Only few published studies that describe the neuroanatomy of lizards. Here, we describe the neuroanatomy of several Iguanian species belonging to three families (species of Liolaemus and Phymaturus belonging to Liolaemidae, Tropidurus and Stenocercus as representatives of Tropiduridae, and Diplolaemus as a representative of Leiosauridae). Based on Sudan Black B staining and conventional dissections, the neuroanatomy of the lumbosacral region is described. Among the most outstanding results is the existence of a neuronal pattern of the lumbosacral plexus characteristic of Liolaemidae. In addition, it was found that in the genus Liolaemus the lumbosacral plexus is composed of five pairs of spinal nerves while in Phymaturus, Tropidurus, Stenocercus and Diplolaemus is composed from five to six pairs of spinal nerves (from pre-sacral, sacral, and caudal vertebrae). We find differences in the origin of the spinal nerves that constitute the plexus. In some cases, the pattern of nerves involved includes even the caudal vertebrae. Variation among taxa related to the zeugopodial innervation is described, and the homology of these nervous branches is discussed. Sexual differences were found in some species studied. Based on our results and available literature, we found three different patterns of innervation of the zeugopodium. The major contribution of this study is to provide a detailed description of lumbosacral plexus nerves pathways from their origins at the vertebral column to the muscles that they innervate.