Data from: The genetic covariance between life-cycle stages separated by metamorphosis.

Metamorphosis is common in animals, yet the genetic associations between life-cycle stages are poorly understood. Given the radical changes that occur at metamorphosis, selection may differ before and after metamorphosis, and the extent that genetic associations between pre-and post-metamorphic traits constrain evolutionary change is a subject of considerable interest. In some instances, metamorphosis may allow the genetic decoupling of life-cycle stages, whereas in others, metamorphosis could allow complementary responses to selection across the life-cycle. Using a diallel breeding design, we measured survival at four ontogenetic stages (embryo, larval, juvenile and adult survival), in the ascidian Ciona intestinalis and examined the orientation of additive genetic variation with respect to the metamorphic boundary. We found support for one eigenvector of G (〖g_obs〗_max), which contrasted larval survival against embryo survival and juvenile survival. Target matrix rotation confirmed that while the trait combination represented by 〖g_obs〗_max shows genetic associations can extend beyond metamorphosis, there is still considerable scope for decoupled phenotypic evolution. Therefore, although genetic associations across metamorphosis could limit that range of phenotypes that are attainable, traits on either side of the metamorphic boundary are capable of some independent evolutionary change in response to the divergent conditions encountered during each life-cycle stage.

变态发育在动物界中普遍存在，但学界对不同生命周期阶段间的遗传关联仍知之甚少。鉴于变态发育过程中发生的剧烈形态与生理转变，变态前后的选择压力可能存在差异，而变态前后性状间的遗传关联对演化改变的限制程度，一直是广受关注的核心研究议题。在部分情境中，变态发育可实现生命周期不同阶段的遗传解耦；而在另一些情况下，变态发育则能使整个生命周期内的性状对选择压力产生互补性演化响应。本研究采用双列杂交设计（diallel breeding design），以被囊动物（ascidian）玻璃海鞘（Ciona intestinalis）为研究对象，测定了其4个个体发育阶段（胚胎期、幼体期、稚虫期与成体期）的存活率，并围绕变态边界分析了加性遗传变异的分布取向。我们在遗传方差-协方差矩阵（G）中发现了一个特征向量〖g_obs〗_max，该向量对比了幼体存活率与胚胎期、稚虫期存活率的差异。目标矩阵旋转分析证实，尽管〖g_obs〗_max所表征的性状组合表明遗传关联可跨越变态边界延伸，但表型演化的解耦仍存在极大空间。因此，尽管变态发育前后的遗传关联可能会限制可获得的表型范围，但位于变态边界两侧的性状，仍可针对不同生命周期阶段所遭遇的差异化环境条件，发生一定程度的独立演化改变。