Data from: Unlinked Mendelian inheritance of red and black pigmentation in snakes: implications for Batesian mimicry

Identifying the genetic basis of mimetic signals is critical to understanding both the origin and dynamics of mimicry over time. For species not amenable to large laboratory breeding studies, widespread color polymorphism across natural populations offers a powerful way to assess the relative likelihood of different genetic systems given observed phenotypic frequencies. We classified color phenotype for 2,175 ground snakes (Sonora semiannulata) across the continental United States to analyze morph ratios and test among competing hypotheses about the genetic architecture underlying red and black coloration in coral snake mimics. We found strong support for a two-locus model under simple Mendelian inheritance, with red and black pigmentation being controlled by separate loci. We found no evidence of either linkage disequilibrium between loci or sex linkage. In contrast to Batesian mimicry systems like butterflies in which all color signal components are linked into a single “supergene,” our results suggest that the mimetic signal in colubrid snakes can be disrupted through simple recombination and that color evolution is likely to involve discrete gains and losses of each signal component. Both outcomes are likely to contribute to the exponential increase in rates of color evolution seen in snake mimicry systems over insect systems.

阐明拟态信号的遗传基础，对于解析拟态的起源及其随时间推移的动态变化至关重要。对于无法开展大规模实验室繁育研究的物种而言，自然种群中广泛存在的颜色多态性，为基于观测到的表型频率评估不同遗传系统的相对可能性提供了有力手段。我们对美国大陆范围内的2175条环纹地蛇（Sonora semiannulata）进行了颜色表型分型，以分析色型比例，并检验关于珊瑚蛇拟态类群红黑着色遗传架构的多种竞争性假说。我们发现，在简单孟德尔遗传模式下的双位点模型得到了强有力的支持：红、黑两种色素分别由不同的位点调控。未检测到位点间存在连锁不平衡，亦未发现性连锁现象。与蝴蝶这类贝茨拟态系统（其所有颜色信号组分均整合为单个"超基因"）不同，我们的研究结果表明，游蛇科蛇类的拟态信号可通过简单的重组被打破，且颜色演化大概率涉及各信号组分的独立获得与丢失。这两种结果均可能促成蛇类拟态系统中颜色演化速率较昆虫拟态系统出现指数级提升的现象。