Effects of gene dosage and hormones on the expression of Dr in the platyfish,Xiphophorus maculatus(Poeciliidae)

Abstract

SUMMARYPlatyfish, Xiphophorus maculatus, are polymorphic for the patterns red-dorsal (Dr) and spotted-dorsal (Sd) fins, both controlled by closely linked loci on the X chromosome of Jamapa strain, Jp 163A. The intensity of red pigment looks the same in males and females, but spectrophotometric analysis of dorsal fin extracts showed that heterozygous intact males have significantly more red pigment (drosopterin) than homozygous or heterozygous females or castrated males. The mechanism of Dr expression in Jamapa is, thus, similar to the one present in the Belize stock, where a sex difference is readily apparent that is known to be under androgenic control. The Sd phenotype is identical in both sexes. Sd and Dr are not restricted to the X chromosome, and no evidence for gene dosage compensation has been obtained. Within the Jamapa stock the expression of Sd and Dr are best described in terms of dominance and recessiveness. Dr is strongly augmented by a testicular hormone. Dr and Sd have been separated by crossing-over. In natural populations both genes can occur by themselves, linked to each other or to other pigment genes. The development of the Sd macromelanophores is not contingent upon the presence of pterinophores (Dr) in the dorsal fin or elsewhere in the body.

Genetic Linkage and Color Polymorphism in the Southern Platyfish (Xiphophorus maculatus): A Model System for Studies of Color Pattern Evolution

“…Studies of pigment cells in platyfish have established that a number of types of coloration are expressed, including black melanins, red, orange, and yellow carotenoids, and yellow, orange, red, and reddish brown pterins. 20,24,[26][27][28]34 These studies have also characterized the genetic basis of at least 42 different color patterns (Table 1). (The adult expression of these patterns and the pertinent references are given in the Appendix.)…”

“…34,42,43 The distribution of the pigments in pterinophores, as Valenti and Kallman 34 termed them, was lutein at the center and pterinosomes containing drosopterin at the periphery. They concluded that the red coloration stems from the pterin, drosopterin.…”

“…can be artificially produced and are common in the aquarium trade. While the origin of the fish studied by Kallman and Valenti 34 was known, the origin of the fish studied by the Goodrich group is not clear. If they were hybrids, an allele or alleles coding for erythropterin could have been introduced by hybridization into the platyfish that they studied.…”

“…4,49 Black macromelanophore body and dorsal fin coloration Four sex-linked black color patterns have been described, all of which are expressed to the same degree in males and females. 20,28,34,37 (However, one of the 12 spot-sided alleles, Sp8, is expressed to a greater degree in males. 20 ) These color patterns appear to be controlled by several tightly linked loci, each having several alleles.…”