Evolutionary patterns of nervous plexuses in 3 iguanid families (Pleurodonta): influence of phylogeny and sexual dimorphism.

Spinal nerves emerge from the spinal cord at the cervicothoracic and lumbosacral regions, where they anastomose to form nerve plexuses. Studies on the neuroanatomy of these plexuses have traditionally focused on descriptive aspects, with little consideration of evolutionary or phylogenetic contexts. South America hosts a diverse fauna of iguanian lizards, which have been the subject of multiple studies, some of which have reported evidence of sexual dimorphism. Considering this, we investigated the evolution of nerve plexuses and compared them between sexes in species of Leiosauridae, Liolaemidae, and Tropiduridae. To visualize the plexuses, we applied differential staining with Sudan Black and performed conventional dissections. Evolutionary analyses were conducted on 8 previously studied neuroanatomical characters using Bayesian inference and parsimony approaches. Our results show congruence between both optimality criteria. The most significant evolutionary variation was observed in Leiosauridae and Liolaemidae. Characters from the brachial plexus exhibited the highest phylogenetic signal and a low evolutionary rate. In contrast, characters from the lumbar plexus showed no phylogenetic signal and varied between sexes. Lumbar plexus traits evolved faster in males than in females. Our findings suggest that brachial plexus characters evolve under a strong phylogenetic influence. Instead, the lumbar plexus in males and females may be shaped by different selective pressures. Females exhibited more conservative traits, whereas males may be influenced by additional selective forces. Phylogeny and sexual dimorphism shape the evolution of the nerve plexuses in studied Pleurodont lizards. This study constitutes a first step toward understanding nervous plexuses from both perspectives in these reptiles.