Melanin-based color patterns are an emerging model for studying molecular and evolutionary mechanisms driving phenotypic correlations. Extensive literature exists on color patterns and their correlated traits in the family Poeciliidae, indicating that these fishes are tractable models. We review the biology of polymorphic melanic side-spotting patterns characterized by macromelanophores forming irregular spotted patterns across fishes’ flanks. These patterns are present in the genera Gambusia, Limia, Phalloceros, Poecilia, and Xiphophorus. Their presence is controlled by dominant genes on autosomes or sex chromosomes. Variation in expression is under polygenic control; however, these genes’ identities are still largely unknown. In some Gambusia holbrooki and Poecilia latipinna, expression is dependent on low temperature exposure, but underlying molecular mechanisms are unknown. Spotted fish develop melanoma in rare cases and are a well-developed model for melanoma research. Little is known about other physiological correlates except that spotted G. holbrooki males exhibit higher basal cortisol levels than unspotted males and that metabolic rate does not differ between morphs in some Xiphophorus species. Behavioral differences between morphs are widespread, but specific to population, species, and social context. Spotted G. holbrooki males appear to be more social and more dominant. Juvenile spotted G. holbrooki have lower behavioral flexibility, and spotted X. variatus exhibit greater stress resistance. Findings conflict on whether morphs differ in sexual behavior and in sexual selection by females. Melanic side-spotting patterns are uncommon (<30%) in populations, although extreme high-frequency populations exist. This low frequency is surprising for dominant genes, indicating that a variety of selective pressures influence both these patterns and their correlated traits. Little is known about reproductive life history traits. Spotted G. holbrooki are larger and have higher survival when uncommon, but underlying mechanisms remain unknown. Spotted morphs appear to have a strong selective advantage during predation. Predators prefer to attack and consume unspotted morphs; however, this preference disappears when spotted G. holbrooki males are common, indicating negative frequency-dependent selection. Spotted morphs are preferred socially under turbid conditions, but other environmental factors that shape phenotypic correlations and morph fitness have not been studied. Finally, we present questions for future studies on melanic side-spotting patterns.

中文翻译：

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Poeciliid鱼多态性黑色侧斑模式的生物学

基于黑色素的颜色模式是研究驱动表型相关性的分子和进化机制的新兴模型。关于 Poeciliidae 科的颜色模式及其相关特征的大量文献表明这些鱼是易于处理的模型。我们回顾了多态性黑色素侧斑模式的生物学特征，其特征是大黑素细胞在鱼的侧翼形成不规则的斑点图案。这些模式存在于 Gambusia、Limia、Phalloceros、Poecilia 和 Xiphophorus 属中。它们的存在是由常染色体或性染色体上的显性基因控制的。表达的变化受多基因控制；然而，这些基因的身份在很大程度上仍是未知的。在一些 Gambusia holbrooki 和 Poecilia latipinna 中，表达依赖于低温暴露，但潜在的分子机制尚不清楚。斑点鱼在极少数情况下会发展为黑色素瘤，并且是黑色素瘤研究的成熟模型。除了斑点的 G. holbrooki 雄性表现出比未斑点的雄性更高的基础皮质醇水平，并且代谢率在某些剑属物种的变体之间没有差异之外，对其他生理相关性知之甚少。变种之间的行为差​​异很普遍，但特定于人口、物种和社会背景。斑点 G. holbrooki 雄性似乎更具社交性和支配性。幼年斑点 G. holbrooki 具有较低的行为灵活性，斑点 X. variatus 表现出更强的抗逆性。关于变种是否在性行为和女性的性选择方面不同的研究结果存在冲突。黑色素侧斑模式在人群中并不常见（<30%），尽管存在极端高频种群。这种低频率对于显性基因来说是令人惊讶的，这表明各种选择压力会影响这些模式及其相关性状。关于生殖生活史特征知之甚少。斑点 G. holbrooki 在不常见时更大，存活率更高，但潜在机制仍然未知。斑点变种在捕食过程中似乎具有很强的选择优势。掠食者更喜欢攻击和消耗未发现的变种；然而，当发现 G. holbrooki 雄性很常见时，这种偏好就会消失，表明负频率依赖性选择。在混浊条件下，斑点变种在社会上是首选，但尚未研究影响表型相关性和变种适应性的其他环境因素。最后，