A gene for color differences between sexes

doi:10.1126/science.abc2242

GSTDTAP > 气候变化

DOI	10.1126/science.abc2242
	A gene for color differences between sexes
	Nancy Chen
	2020-06-12
发表期刊	Science
出版年	2020
英文摘要	Sexual dimorphism—phenotypic differences between sexes of the same species—is a widespread yet puzzling phenomenon in nature. How such traits evolve has fascinated evolutionary biologists since Darwin, whose ponderings about elaborate ornaments in males prompted him to develop the theory of sexual selection ([ 1 ][1]), and numerous studies have sought to explain the evolution of these traits ([ 2 ][2]). Less is known about the genetic and molecular mechanisms that allow species to generate divergent morphologies from nearly identical genomes ([ 3 ][3]). On page 1270 of this issue, Gazda et al. ([ 4 ][4]) show that sex-specific plumage coloration in hybrid canaries is controlled by a single genomic region containing the gene encoding β-carotene oxygenase 2 ( BCO2 ). Differences in coloration between the sexes are due to the up-regulation of BCO2 expression and consequent degradation of pigments in females, demonstrating that color differences between males and females can evolve through a simple molecular mechanism. One of the most prominent forms of sexual dimorphism is different coloration between males and females, or sexual dichromatism. Indeed, in some species, sex-specific coloration is so divergent that males and females were once considered different species ([ 1 ][1]). Sexual dichromatism is typically thought to arise from sexual selection for increased ornamentation in males ([ 1 ][1]) and, accordingly, is often used as a proxy for the strength of sexual selection in comparative studies ([ 5 ][5]). Alternatively, sexual dichromatism could also arise from natural selection for cryptic coloration in females ([ 6 ][6]). Recent studies indicate that sexual dichromatism is driven by sexual and natural selection operating in both sexes ([ 7 ][7], [ 8 ][8]). A better understanding of the genetic basis of sexual dichromatism is crucial for fully elucidating the underlying evolutionary processes. In birds, sexual dichromatism has evolved rapidly, with multiple gains and losses of dichromatism among closely related species ([ 7 ][7]), and is primarily driven by differences in carotenoid-based coloration ([ 9 ][9]). Carotenoids are the pigments responsible for most red, orange, and yellow colors observed in nature ([ 10 ][10]). These pigments are primarily synthesized by plants, bacteria, and fungi; most animals have to acquire carotenoids through their diet ([ 10 ][10]). Carotenoid-based coloration is widely considered to be a signal of individual quality or condition, although the exact physiological mechanisms of carotenoid signaling remain contentious ([ 11 ][11]). How carotenoids are processed and deposited in peripheral tissues and how sex-specific differences in carotenoid-based coloration arise are largely unclear. Gazda et al. studied the genetic basis of sexual dichromatism in domesticated canaries. They focused on mosaic canaries, which are generated by crossing the sexually dimorphic red siskin ( Spinus cucullatus ) with the sexually monomorphic common canary ( Serinus canaria ), followed by repeatedly crossing hybrid progeny with S. canaria (backcrossing). Mosaic canaries can be yellow or red, and males exhibit more carotenoid pigmentation than females (see the figure). On the basis of the breeding design, mosaic canaries should be genetically similar to the common canary throughout their genome except at the regions responsible for sexual dichromatism (the mosaic phenotype), which should be derived from the red siskin genome. By analyzing canary genome sequences, Gazda et al. identified a single 32-kb region of the genome associated with sexual dichromatism. To further narrow down their search, Gadza et al. studied gene expression patterns. All sexually dimorphic traits are generated by sex differences in gene expression during development, and most are controlled by the sex hormones estrogen and testosterone ([ 3 ][3]). The authors identified a single gene in the genomic region of interest that was differentially expressed in the feather follicles of males and females: BCO2 . The encoded enzyme degrades carotenoid molecules and is associated with variation in carotenoid concentrations in sheep, cows, and birds ([ 10 ][10]). Concordant with previous studies, Gazda et al. show that BCO2 is selectively expressed in developing white feather follicles, concluding that the reduced carotenoid pigmentation in mosaic females is caused by sex-specific upregulation of BCO2 . These results provide evidence that sex differences in carotenoid pigmentation arise not from differential deposition of pigments but from differential local degradation of pigments caused by sex-biased expression of BCO2 . This observation is intriguing because recent avian phylogenetic studies show that variation in sexual dichromatism is often driven by the loss of bright colors in females, contrary to the common assumption that dichromatism evolves through the gain of bright, elaborate plumage in males ([ 8 ][8]). ![Figure][12] Canary coloration Sex-specific colors (sexual dichromatism) in hybrid canaries are controlled by a single gene encoding β-carotene oxygenase 2 ( BCO2 ) that is inherited from the red siskin. They arise by crossing and backcrossing red siskins and common canaries and selecting for sexual dichromatism. GRAPHIC: MELISSA THOMAS BAUM/ SCIENCE Does BCO2 also explain sexual dichromatism in other species? To test the generality of their mechanism, Gazda et al. examined gene expression in developing feathers of three species with varying degrees of sexual dichromatism in carotenoid-based pigmentation: the common canary ( S. canaria ), the European serin ( Serinus serinus ), and the house finch ( Haemorhous mexicanus ). Patterns of BCO2 expression in the European serin are consistent with patterns observed in the mosaic canaries: Females and feather patches with less carotenoid pigmentation have higher expression of BCO2 . By contrast, BCO2 expression was not associated with carotenoid pigmentation in house finches, suggesting that multiple mechanisms for sexual dichromatism exist even within finches. The findings of Gazda et al. provide an important contribution to the understanding of the genetic basis of sexual dichromatism and reveal several exciting avenues for future research. The authors provide evidence that suggests that the regulation of BCO2 expression may be complex, with multiple modifiers of expression located both near the gene (cis-regulatory elements) and in more distant regions of the genome (trans-regulatory elements). Further, sexual dichromatism is known to be linked to estrogen concentrations in mosaic canaries, because reproductively senescent and ovariectomized females develop the same plumage as males ([ 4 ][4]). Exactly how estrogen affects BCO2 expression remains an open question. The regulatory pathway of BCO2 , as well as those of other genes involved in depositing or degrading carotenoids, is a prime candidate in understanding the mechanisms for sexual dimorphism in other taxa. The simple genetic and molecular basis of carotenoid-based sexual dichromatism illustrated in the study of Gazda et al. may help explain why sexual dichromatism evolves so rapidly. Further studies of this locus may help disentangle the relative importance of natural and sexual selection, and the role of sex chromosomes, in the evolution of sexual dichromatism. Researchers are now poised to deepen the understanding of the evolutionary origin and maintenance of sexually divergent traits. 1. [↵][13]1. C. Darwin , The Descent of Man, and Selection in Relation to Sex (John Murray, 1871). 2. [↵][14]1. M. Andersson , Sexual Selection (Princeton Univ. Press, 1994). 3. [↵][15]1. T. M. Williams, 2. S. B. Carroll , Nat. Rev. Genet. 10, 797 (2009). [OpenUrl][16][CrossRef][17][PubMed][18][Web of Science][19] 4. [↵][20]1. M. A. Gazda et al ., Science 368, 1270 (2020). [OpenUrl][21][Abstract/FREE Full Text][22] 5. [↵][23]1. K. Kraaijeveld et al ., Biol. Rev. Camb. Philos. Soc. 86, 367 (2011). [OpenUrl][24][CrossRef][25][PubMed][26][Web of Science][27] 6. [↵][28]1. A. R. Wallace , Darwinism: An Exposition of the Theory of Natural Selection with Some of Its Applications (Macmillan, 1889). 7. [↵][29]1. A. V. Badyaev, 2. G. E. Hill , Annu. Rev. Ecol. Evol. Syst. 34, 27 (2003). [OpenUrl][30][CrossRef][31] 8. [↵][32]1. J. J. Price , J. Ornithol. 160, 1213 (2019). [OpenUrl][33] 9. [↵][34]1. A. V. Badyaev, 2. G. Hill , Biol. J. Linn. Soc. Lond. 69, 153 (2000). [OpenUrl][35][CrossRef][36][Web of Science][37] 10. [↵][38]1. D. P. L. Toews et al ., Trends Genet. 33, 171 (2017). [OpenUrl][39][CrossRef][40][PubMed][41] 11. [↵][42]1. P. A. Svensson et al ., Behaviour 148, 131 (2011). [OpenUrl][43][CrossRef][44] Acknowledgments: N.C. is supported by NIH grant R35GM133412. 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领域	气候变化 ; 资源环境
URL	查看原文
引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/274459
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Nancy Chen. A gene for color differences between sexes[J]. Science,2020.
APA	Nancy Chen.(2020).A gene for color differences between sexes.Science.
MLA	Nancy Chen."A gene for color differences between sexes".Science (2020).