2013 年 88 巻 3 号 p. 143
One of the long term goals in the field of evolutionary genetics is to integrate our understanding of “evolution” at macro to micro scale, i.e., ecology, genetics, and molecular biology. Many ecologically relevant traits are now studied at the molecular level. Body color is one of such traits that are highly relevant to ecological factors and also suitable for genetic analyses in many organisms. In this issue of Genes and Genetic Systems, three review papers on body color evolution in fish, mammals, and insects, by R. Miyagi and Y. Terai, H. Suzuki, and A. Takahashi, respectively, are provided.
Body color variation could have large impact on individual fitness through numerous factors such as adjustment to physical environment, camouflage, and sexual selection. For instance, highly divergent body color variation among Lake Victoria cichlids is known to be an important trait for sexual selection, which could potentially lead to reproductive isolation among closely related species. In this respect, changes in color vision to adapt to different ambient light conditions in the lake may be a key factor affecting the nuptial coloration in male fish. Miyagi and Terai (in this issue) review studies related to diversity in body color and color vision in these cichlids and the underlying molecular changes, which could have potentially driven species diversification in these lakes.
In mammals, camouflage appears to be the most important factor determining the evolutionary changes in coat color. The studies on the coat color variation in wild animals have centered around two essential genes, melanocortin-1 receptor (Mc1r) and agouti signaling protein (Asip). Studies have repeatedly shown that changes in these genes affect the coat color in a number of different mammalian species. Suzuki (in this issue) addresses this issue by describing the molecular variation and evolutionary features of these genes, and also discusses some of the phylogeographic studies conducted by his own group and other authors using these genes.
In the third review by Takahashi (in this issue), I focus on the pigmentation variation in the fruitfly, Drosophila. In D. melanogaster, geographic clines of thoracic and abdominal pigmentation intensity in adults are observed in populations from different continents, which suggest that this trait is under some kind of natural selection. The genetic difference of the naturally occurring variation in pigmentation intensity is attributed to a gene encoding an enzyme in the melanin biosynthesis pathway known as ebony. I summarize the studies on cis-regulatory variation that controls the transcription level of this gene in the developing epidermis, which affects the intensity of cuticular pigmentation intensity. Various pleiotropic features of this gene are emphasized including those related to neuronal functions, suggesting a potential association of pigmentation and behavior in this insect species.
Overall, these reviews on body color variations in species from three different animal taxa highlight some of the well-documented key molecular factors underlying the phenotypic changes. The detailed knowledge on these factors certainly elucidates the recent advancement in the field of evolutionary genetics in understanding the genetic bases of ecologically relevant traits. Perhaps seeking new approaches integrating genomics and gene network analyses for studying species divergence may be a next area to be explored.
Finally, I would like to close this preface by thanking the editors of Genes and Genetic Systems for providing me the opportunity to organize this special review issue. I also would like to express my thanks to The Genetic Society of Japan for the Young Investigator Award (2012) and for allowing me to undertake this honorable task.