Data from: The costs of being dark: the genetic basis of melanism and its association with fitness-related traits in the sand cricket

Melanism is an important component of insect cuticle and serves numerous functions that enhance fitness. Despite its importance, there is little information on its genetic basis or its phenotypic and genetic correlation with fitness-related traits. Here, we examine the heritability of melanism in the wing dimorphic sand cricket and determine its phenotypic and genetic correlation with wing morphology, gonad mass and size of the dorso-longitudinal muscles (the principle flight muscles). Previously demonstrated trade-offs among these traits are significant factors in the evolution of life history variation. Using path analysis, we show that melanization is causally related to gonad mass, but not flight muscle mass. Averaged over the sexes, the heritability of melanism was 0.61, the genetic correlation with gonad mass was −0.36 and with wing morph was 0.51. The path model correctly predicted the ranking of melanization score in lines selected for increased ovary mass, increased flight muscle mass, an index that increased both traits and an unselected control. Our results support the general hypothesis that melanization is costly for insects and negatively impacts investment in early reproduction.黑化（melanism）是昆虫表皮的重要组成部分，具备诸多提升个体适合度的功能。尽管其生物学意义重大，但目前关于其遗传基础，以及其与适合度相关性状的表型相关与遗传相关的研究仍较为匮乏。本研究以翅二态性沙蟋为研究材料，分析了黑化的遗传力，并明确了其与翅型、性腺质量以及背纵肌（主要飞行肌）大小的表型相关与遗传相关。此前已被证实的这些性状间的权衡关系，是生活史变异演化过程中的关键驱动因素。通过通径分析，我们发现黑化与性腺质量存在因果关联，但与飞行肌质量并无此类关联。按雌雄个体平均计算，黑化的遗传力为0.61；其与性腺质量的遗传相关系数为-0.36，与翅型的遗传相关系数为0.51。该通径模型可准确预测以下各组的黑化评分排名：卵巢质量提升选育系、飞行肌质量提升选育系、同时提升上述两性状的综合指数选育系，以及未选育对照组。本研究结果支持通用假说：黑化对昆虫存在适应性成本，且会对早期繁殖的资源投入产生负面影响。