Phenotypic integration is an important metric that describes the degree of covariation among traits in a population, and is hypothesized to arise due to selection for shared functional processes. Our ability to identify the genetic and/or developmental underpinnings of integration is marred by temporally overlapping cell‐, tissue‐ and structure‐level processes that serve to continually 'overwrite' the structure of covariation among traits through ontogeny. Here, we examine whether traits that are integrated at the phenotypic level also exhibit a shared genetic basis (e.g. pleiotropy). We micro‐CT scanned two hard tissue traits, and two soft tissue traits (mandible, pectoral girdle, atrium and ventricle, respectively) from an F₅ hybrid population of Lake Malawi cichlids, and used geometric morphometrics to extract 3D shape information from each trait. Given the large degree of asymmetric variation that may reflect developmental instability, we separated symmetric from asymmetric components of shape variation. We then performed quantitative trait loci (QTL) analysis to determine the degree of genetic overlap between shapes. While we found ubiquitous associations among traits at the phenotypic level, except for a handful of notable exceptions, our QTL analysis revealed few overlapping genetic regions. Taken together, this indicates developmental interactions can play a large role in determining the degree of phenotypic integration among traits, and likely obfuscate the genotype to phenotype map, limiting our ability to gain a comprehensive picture of the genetic contributors responsible for phenotypic divergence.

中文翻译：

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表型整合的弱遗传信号暗示发育过程是性状共变的主要调节因子

表型整合是描述群体中性状之间的共变程度的重要指标，并且假设是由于共享功能过程的选择而产生的。我们识别整合的遗传和/或发育基础的能力受到时间上重叠的细胞、组织和结构水平过程的损害，这些过程通过个体发育不断“覆盖”性状之间的共变结构。在这里，我们检查在表型水平上整合的性状是否也表现出共同的遗传基础（例如多效性）。我们扫描了马拉维湖慈鲷F ₅杂交群体的两个硬组织特征和两个软组织特征（分别是下颌骨、胸带、心房和心室），并使用几何形态测量学从每个特征中提取 3D 形状信息。考虑到很大程度的不对称变异可能反映了发育的不稳定性，我们将形状变异的对称成分与不对称成分分开。然后，我们进行了数量性状基因座（QTL）分析，以确定形状之间的遗传重叠程度。虽然我们在表型水平上发现性状之间普遍存在关联，但除了少数值得注意的例外之外，我们的 QTL 分析显示很少有重叠的遗传区域。总而言之，这表明发育相互作用在确定性状之间表型整合程度方面可以发挥重要作用，并且可能混淆基因型与表型图谱，限制我们全面了解导致表型分歧的遗传因素的能力。