Data from: Constraint around quarter-power allometric scaling in wild tomatoes (Solanum sect. Lycopersicon; Solanaceae)

The West-Brown-Enquist (WBE) metabolic scaling theory posits that many organismal features scale predictably with body size because of selection to minimize transport costs in resource distribution networks. Many scaling exponents are quarter-powers, as predicted by WBE, but there are also biologically significant deviations that could reflect adaptation to different environments. A central but untested prediction of the WBE model is that wide deviation from optimal scaling is penalized, leading to a pattern of constraint on scaling exponents. Here, we demonstrate, using phylogenetic comparative methods, that variation in allometric scaling between mass and leaf area across 17 wild tomato taxa is constrained around a value indistinguishable from that predicted by WBE but significantly greater than 2/3 (geometric-similarity model). The allometric-scaling exponent was highly correlated with fecundity, water use, and drought response, suggesting that it is functionally significant and therefore could be under selective constraints. However, scaling was not strictly log–log linear but rather declined during ontogeny in all species, as has been observed in many plant species. We caution that although our results supported one prediction of the WBE model, it did not strongly test the model in other important respects. Nevertheless, phylogenetic comparative methods such as those used here are powerful but underutilized tools for metabolic ecology that complement existing methods to adjudicate between models.西-布朗-恩奎斯特（West-Brown-Enquist, WBE）代谢缩放理论（metabolic scaling theory）提出，诸多生物体特征会随体型大小呈现可预测的缩放关系，这是因为自然选择会最小化资源分配网络（resource distribution networks）中的运输成本。正如WBE理论所预测的那样，诸多缩放指数（scaling exponents）呈现四分之一幂次特征，但同时也存在具有生物学意义的偏差，这些偏差或可反映生物对不同环境的适应性。 WBE模型的一项核心且尚未得到验证的预测是，与最优缩放模式的大幅偏差会受到选择惩罚，进而形成缩放指数受到约束的格局。本研究借助系统发育比较方法（phylogenetic comparative methods），对17个野生番茄类群（wild tomato taxa）的质量与叶面积（leaf area）之间的异速缩放（allometric scaling）变异展开分析，结果表明其异速缩放指数被约束在与WBE理论预测值无显著差异的水平，但显著高于2/3（即几何相似模型（geometric-similarity model）的预测值）。 该异速缩放指数与繁殖力（fecundity）、水分利用（water use）以及干旱响应（drought response）均呈显著相关性，这表明其具备功能重要性，因此可能处于选择约束之下。不过，所有物种的缩放关系并非严格的双对数线性（log–log linear）模式，而是在个体发育（ontogeny）过程中逐渐降低，这一现象已在诸多植物类群中被观测到。 我们需要注意，尽管本研究结果支持了WBE模型的一项预测，但并未在其他重要方面对该模型开展充分检验。尽管如此，本研究使用的这类系统发育比较方法，是一类功能强大但尚未得到充分利用的代谢生态学（metabolic ecology）研究工具，可与现有方法互补，用于在不同模型之间做出判定。