Data from: Evolution of static allometries: adaptive change in allometric slopes of eye span in stalk-eyed flies

Julian Huxley showed that within-species (static) allometric (power-law) relations can arise from proportional growth regulation with the exponent in the power law equaling the factor of proportionality. Allometric exponents may therefore be hard to change and act as constraints on the independent evolution of traits. In apparent contradiction to this, many empirical studies have concluded that static allometries are evolvable. Many of these studies have been based, however, on a broad definition of allometry that includes any monotonic shape change with size, and do not falsify the hypothesis of constrained narrow-sense allometry. Here, we present the first phylogenetic comparative study of narrow-sense allometric exponents based on a reanalysis of data on eye span and body size in stalk-eyed flies (Diopsidae). Consistent with a role in sexual selection, we found strong evidence that male slopes were tracking "optima" based on sexual dimorphism and relative male trait size. This tracking was slow, however, with estimated times of 2-3 million years for adaptation to exceed ancestral influence on the trait. Our results are therefore consistent with adaptive evolution on million-year time scales, but cannot rule out that static allometry may act as a constraint on eye-span adaptation at shorter time scales.

朱利安·赫胥黎（Julian Huxley）曾证实，种内静态异速生长（allometric）关系可由比例生长调控过程产生，此时幂律（power-law）中的指数恰好等于比例系数。由此，异速生长指数往往难以发生改变，并可作为性状独立演化的约束条件。然而，诸多实证研究却得出静态异速生长具有可演化性的结论，这与前述观点看似矛盾。但这类研究中的多数采用了广义的异速生长定义——即囊括所有随体型产生的单调形状变化——并未证伪“狭义异速生长受约束”这一假说。本研究通过重新分析柄眼蝇（Diopsidae）的眼距与体型数据，开展了首个针对狭义异速生长指数的系统发育比较研究。与性选择的作用机制相符，我们发现有力证据表明雄性异速斜率正追踪基于性二态性与雄性相对性状大小的“最优值”。但该演化追踪进程较为缓慢，经估算，当适应效应超过祖先因素对性状的影响时，所需时长约为200万至300万年。因此，本研究结果支持百万年级别尺度下的适应性演化，但无法排除静态异速生长在更短时间尺度上对眼距适应性演化构成约束的可能性。