Data from: Transcriptomic analysis of skin pigmentation variation in the Virginia opossum (Didelphis virginiana).

Skin and coat pigmentation are two of the best-studied examples of traits under natural selection given their quantifiable fitness interactions with the environment (e.g. camouflage) and signaling with other organisms (e.g. warning coloration). Previous morphological studies have found that skin pigmentation variation in the Virginia opossum (Didelphis virginiana) is associated with variation in precipitation and temperatures across its distribution range following Gloger’s rule (lighter pigmentation in temperate environments). To investigate the molecular mechanism associated with skin pigmentation variation, we used RNA-Seq and quantified gene expression of wild opossums from tropical and temperate populations. Using differential expression analysis and a coexpression network approach, we found that expression variation in genes with melanocytic and immune functions are significantly associated with the degree of skin pigmentation variation and may be underlying this phenotypic difference. We also found evidence suggesting that the Wnt/β-catenin signaling pathway might be regulating the depigmentation observed in temperate populations. Based on our study results, we present several alternative hypotheses that may explain Gloger’s rule pattern of skin pigmentation variation in opossum, including changes in pathogen diversity supporting a pathogen resistant hypothesis, thermal stress associated with temperate environments, pleiotropic and epistatic interactions between melanocytic and immune genes.皮肤与被毛色素沉着是自然选择作用下研究最为充分的性状范例之一，因其与环境存在可量化的适合度关联（如伪装作用），且可与其他生物进行信号交流（如警戒色）。此前的形态学研究发现，北美负鼠（Didelphis virginiana）的皮肤色素沉着变异与其分布范围内的降水与温度变化相关，符合格洛杰法则（Gloger’s rule）——即温带环境中个体色素沉着更浅。为探究与皮肤色素沉着变异相关的分子机制，本研究采用RNA测序（RNA-Seq）技术，对来自热带与温带种群的野生负鼠开展了基因表达定量分析。通过差异表达分析与共表达网络分析方法，本研究发现，携带黑素细胞相关功能与免疫功能的基因，其表达变异与皮肤色素沉着程度显著相关，或为该表型差异的分子基础。本研究还发现证据表明，Wnt/β-连环蛋白（Wnt/β-catenin）信号通路可能参与调控温带种群中观察到的色素减退现象。基于本研究结果，我们提出了若干可解释负鼠皮肤色素沉着变异符合格洛杰法则模式的备选假说，包括支持病原体抗性假说的病原体多样性变化、温带环境相关的热应激，以及黑素细胞功能基因与免疫基因之间的多效性与上位性互作。