AN ANALYSIS OF THE DYNAMIC FACTORS RESPONSIBLE FOR THE PHENOMENON OF PIGMENT SUPPRESSION IN SALAMANDER LARVAE

Open Access
Publisher Website
Google Scholar
Abstract
Embryos of 5 spp. of salamanders (Ambystoma tigrinum A. mexicanum, A. punctatum, Triturus torosus, and T. rivularis) were used in examining the fact that the temporary suppression of pigmentation in slowly developing pro-pigment cells is optimally realized when the difference between the developmental rates of donor and host pigment cells is only moderately large. It was found by (1) culturing two fragments of neural crest of different age in single drops of medium, (2) by grafting neural crest on the flanks of hosts of graded age, and (3) by orthotopic transplantation of neural folds between donor and host neurulae of different age, that partially differentiated pigment cells are more effective in preventing migration by young pro-pigment cells than are fully differentiated pigment cells. The results of in vivo and in vitro studies designed to demonstrate the role of other environmental factors in the suppression phenomenon were not conclusive but suggested that the decline in melanogenic strength of the epidermis with age might secondarily prolong the suppression of differentiation in slowly developing cells. Observations on the manner in which trunk regions deprived of neural crest become invaded by melanophores revealed that melanophore differentiation is essentially a continuous process in T. rivularis, A. mexicanum, and A. punctatum embryos, whereas in T. torosus and A. tigrinum the sequence of pigmentation is interrupted and consists of distinct "primary" and "secondary" melanophore generations. It was noted that removal of one trunk neural fold from T. rivularis embryos had no noticeable effect upon the number of pigment cells that later appeared. In similarly treated T. torosus embryos, however, this resulted in a 30-40% reduction in the number of cells normally appearing.