Inverse of Rensch’s rule of allometry for sexual size dimorphism in Bufo andrewsi

Difference in body size between males and females (sexual size dimorphism: SSD) and its variation are a common phenomenon in animal kingdom. Rensch’s rule predicts that the degree of SSD variation increases with the enlarged mean body size when males are larger than females and decreases when females are larger than males. Here, whether the patterns of variations in SSD in the Andrew’s toad (<em>Bufo andrewsi</em>) follow Rensch’s rule was tested using unpublished data from 14 populations and published data from 17 populations. Results show the reduced major axis regression of log₁₀ (male size) on log₁₀ (female size) across all populations displayed a significant hyperallometric relationship, which was consistent with inverse Rensch’s rule (the degree of SSD increased with enlarged mean body size). SSD could also be explained by sexual age difference (SAD) due to a positive SSD–SAD relationship among all populations. The findings suggest that the occurrence of inverse Rensch’s rule in <em>B. andrewsi</em> is likely to be a result of fecundity selection on increased reproductive investments in larger females. This table is descriptive information about the study sites of Andrew’s toad (<em>B. andrewsi</em>), together with mean (± SD) body size and age of males and females.

雌雄个体间的体型差异（即两性体型二态性，sexual size dimorphism, SSD）及其变异是动物界广泛存在的现象。伦施法则（Rensch’s rule）预测：当雄性体型大于雌性时，SSD的变异程度会随种群平均体型的增大而升高；当雌性体型大于雄性时，该变异程度则会降低。
本研究依托14个种群的未发表数据与17个种群的已发表数据，检验了安德鲁蟾蜍（Bufo andrewsi）的SSD变异模式是否符合伦施法则。
对所有种群的雄性体型以10为底的对数值与雌性体型以10为底的对数值开展约化主轴回归分析，结果显示二者呈现显著的超异速生长关系，这与逆伦施法则的结论一致——即SSD程度随平均体型增大而升高。
此外，由于所有种群间均存在SSD与两性年龄差（sexual age difference, SAD）的正相关关系，因此SSD亦可通过SAD得到合理解释。
研究结果表明，安德鲁蟾蜍（Bufo andrewsi）中逆伦施法则的出现，大概率是针对体型更大雌性的繁殖投入提升所带来的繁殖力选择（fecundity selection）作用的结果。
本附表收录了安德鲁蟾蜍（Bufo andrewsi）的研究样地相关描述性信息，同时包含雌雄个体的平均（±标准差）体型与年龄数据。