Data from: The evolution of alternative developmental pathways: footprints of selection on life-history traits in a butterfly

Developmental pathways may evolve to optimize alternative phenotypes across environments. However, the maintenance of such adaptive plasticity under relaxed selection has received little study. We compare expression of life history traits across two developmental pathways in two populations of the butterfly Pararge aegeria where both populations express a diapause pathway but one never expresses direct development in nature. In the population with ongoing selection on both pathways the difference between pathways in development time and growth rate was larger while the difference in body size was smaller compared with the population experiencing relaxed selection on one pathway. This indicates that relaxed selection on the direct pathway has allowed life history traits to drift towards values associated with lower fitness when following this pathway. Relaxed selection on direct development was also associated with a higher degree of genetic variation for protandry expressed as within-family sexual dimorphism in growth rate. Genetic correlations for larval growth rate across sexes and pathways were generally positive, with the notable exception of correlation estimates that involved directly developing males of the population that experienced relaxed selection on this pathway. We conclude that relaxed selection on one developmental pathway appears to have partly disrupted the developmental regulation life history trait expression. This in turn suggests that ongoing selection may be responsible for maintaining adaptive developmental regulation along alternative developmental pathways in these populations.

发育路径可演化以优化不同环境下的替代表型。然而，针对松弛选择下这类适应性表型可塑性的维持机制，相关研究仍较为匮乏。本研究以眼蝶（Pararge aegeria）的两个种群为对象，比较了二者两条发育路径间的生活史性状表达差异：两个种群均能表达滞育发育路径（diapause pathway），但其中一个种群在自然条件下从不表现出直接发育（direct development）。相较于仅对一条发育路径存在松弛选择的种群，在两条发育路径均持续受到选择的种群中，不同路径间的发育时长与生长速率差异更大，而体型大小的差异则更小。这表明，对直接发育路径的松弛选择，使得该路径下的生活史性状发生遗传漂变，趋近于与较低适合度（fitness）相关的表型值。此外，对直接发育路径的松弛选择还与更高水平的雄性先熟（protandry）遗传变异相关，该变异表现为生长速率在家系内的性别二型（sexual dimorphism）。不同性别与发育路径间的幼虫生长速率（larval growth rate）遗传相关总体为正，唯一显著例外的是涉及该路径松弛选择种群的直接发育雄虫的相关系数估计值。综上，对某一条发育路径的松弛选择似乎已部分破坏了生活史性状表达的发育调控机制。这进而表明，持续选择可能是维持这些种群中替代发育路径适应性发育调控的核心驱动力。