Data from: Scaling of morphological characters across trait type, sex and environment: a meta-analysis of static allometries

Biological diversity is to a large extent a matter of variation in size. Proportional (isometric) scaling where large and small individuals are magnified versions of each other is often assumed the most common way morphological traits scale relative to overall size within species. However, the many traits showing non-proportional (allometric) scaling have motivated some of the most discussed hypotheses on scaling relationships in biology, like the positive allometry hypothesis for secondary sexual traits and the negative allometry hypothesis for genitals. I evaluate more than 3200 allometric parameters from the literature and find that negative allometry, not isometry, is the expected scaling relationship of morphological traits within species. Slopes of secondary sexual traits are more often steeper compared to other traits, but slopes larger than unity is also common for traits not under sexual selection. The steepness of the allometric slope is accordingly a weak predictor of past and present patterns of selection. Scaling of genitals varies across taxonomic groups, but negative allometry of genitals in insects and spiders is a consistent pattern. Lastly, I find indications that terrestrial organisms have an overall different scaling of morphological traits compared to aquatic species.

生物多样性在很大程度上体现为体型大小的变异。通常认为，等比例（isometric）缩放——即大小个体互为彼此的放大/缩小版本——是物种种内形态性状随整体体型缩放的最普遍模式。然而，大量呈现非等比例（allometric）缩放的性状，催生了生物学领域关于缩放关系的诸多热门假说，例如次级性征（secondary sexual traits）的正异速生长假说，以及生殖器的负异速生长假说。本研究梳理了已发表文献中的3200余个异速生长参数，结果显示，物种种内形态性状的预期缩放模式并非等比例缩放，而是负异速生长。相较于其他性状，次级性征的异速斜率往往更陡，但非性选择作用下的性状，其斜率大于1的情况也并不少见。因此，异速斜率的陡峭程度仅能微弱预测过往及当前的选择模式。生殖器的缩放模式随分类群而异，但昆虫与蜘蛛类群的生殖器负异速生长是一致的普遍模式。最后，本研究发现陆生生物与水生生物的形态性状整体缩放模式存在显著差异。