Pigment Patterns of Larval Salamanders (Ambystomatidae, Salamandridae): The Role of the Lateral Line Sensory System and the Evolution of Pattern-Forming Mechanisms

AbstractIn many species of salamanders, pigment cells derived from the neural crest give rise to a horizontal stripe pattern in hatchling larvae. A defining element of these horizontal stripe patterns is a region over the middle of the myotomes that is relatively free of melanophores. This study shows that formation of a “melanophore-free region” and horizontal stripe pattern inAmbystoma tigrinum tigrinum(family Ambystomatidae) correlates with the development of the trunk lateral line sensory system. Moreover, prevention of lateral line development results in greater densities of melanophores in the middle of the flank, essentially eliminating the melanophore-free region in this taxon. A phylogenetic survey also revealed that ablation of the lateral lines has qualitatively similar effects on melanophores in seven of eight additional taxa (Ambystomatidae:A. barbouri, A. maculatum, A. talpoideum;Salamandridae:Notophthalmus viridescens, Pleurodeles waltl, Taricha granulosa, T. rivularis). InTaricha torosa,however, a superficially similar melanophore-free region forms prior to lateral line development, and ablation of the lateral lines does not perturb the horizontal stripe pattern. Finally, heterospecific grafting experiments demonstrated thatT. torosalateral lines are competent to generate a melanophore-free region, andT. torosamelanophores are competent to respond to cues associated with the lateral lines. These results indicate that lateral line-dependent pattern-forming mechanisms are common and probably ancestral within the families Ambystomatidae and Salamandridae and suggest that these ancestral mechanisms have been retained inT. torosaas redundant, lateral line-independent mechanisms for stripe formation have evolved