Chromosomal assignment of the canine melanophilin gene (MLPH): a candidate gene for coat color dilution in Pinschers

Pinschers affected by coat color dilution show a specific pigmentation phenotype. The dilute pigmentation phenotype leads to a silver-blue appearance of the eumelanin-containing fur and a pale sandy color of pheomelanin-containing fur. In Pinscher breeding, dilute black-and-tan dogs are called "blue," and dilute red or brown animals are termed "fawn" or "Isabella fawn." Coat color dilution in Pinschers is sometimes accompanied by hair loss and a recurrent infection of the hair follicles. In human and mice, several well-characterized genes are responsible for similar pigment variations. To investigate the genetic cause of the coat color dilution in Pinschers, we isolated BAC clones containing the canine ortholog of the known murine color dilution gene Mlph. RH mapping of the canine MLPH gene was performed using an STS marker derived from BAC sequences. Additionally, one MLPH BAC clone was used as probe for FISH mapping, and the canine MLPH gene was assigned to CFA25q24.

Can ancient colour polymorphisms explain why some cichlid lineages speciate rapidly under disruptive sexual selection?

It is not sufficiently understood why some lineages of cichlid fishes have proliferated in the Great Lakes of East Africa much more than anywhere else in the world, and much faster than other cichlid lineages or any other group of freshwater fish. Recent field and experimental work on Lake Victoria haplochromines suggests that mate choice-mediated disruptive sexual selection on coloration, that can cause speciation even in the absence of geographical isolation, may explain it. We summarize the evidence and propose a hypothesis for the genetics of coloration that may help understand the phenomenon. By detl ning colour patterns by hue and arrangement of hues on the body, we could assign almost all observed phenotypes of Lake Victoria cichlids to one of three female («plain», «orange blotched», «black and white») and three male («blue», «red-ventrum», «reddorsum») colour patterns. These patterns diagnose species but frequently eo-occur also as morphs within the same population, where they are associated with variation in mate preferences, and appear to be transient stages in speciation. Particularly the male patterns occur in almost every genus of the species flock. We propose that the patterns and their association into polymorphisms express an ancestral trait that is retained across speciation. Our model for male colour pattern assumes two structural loci. When both are switched off, the body is blue. When switched on by a cascade of polymorphic regulatory genes, one expresses a yellow to red ventrum, the other one a yellow to red dorsum. The expression of colour variation initiates speciation. The blue daughter species will inherit the variation at the regulatory genes that can, without new mutational events, purely by recombination, again expose the colour polymorphism, starting the process anew. Very similar colour patterns also dominate among the Mbuna of Lake Malawi. In contrast, similar colour polymorphisms do not exist in the lineages that have not proliferated in the Great Lakes. The colour pattern polymorphism may be an ancient trait in the lineage (or lineages) that gave rise to the two large haplochromine radiations. We propose two tests of our hypothesis.