Fairbairn Daphne J
Department of Biology, University of California, Riverside, California 92521,USA.
Am Nat. 2005 Oct;166 Suppl 4:S69-84. doi: 10.1086/444600.
Within any given clade, male size and female size typically covary, but male size often varies more than female size. This generates a pattern of allometry for sexual size dimorphism (SSD) known as Rensch's rule. I use allometry for SSD among populations of the water strider Aquarius remigis (Hemiptera, Gerridae) to test the hypothesis that Rensch's rule evolves in response to sexual selection on male secondary sexual traits and an alternative hypothesis that it is caused by greater phenotypic plasticity of body size in males. Comparisons of three populations reared under two temperature regimes are combined with an analysis of allometry for genital and somatic components of body size among 25 field populations. Contrary to the sexual-selection hypothesis, genital length, the target of sexual selection, shows the lowest allometric slope of all the assayed traits. Instead, the results support a novel interpretation of the differential-plasticity hypothesis: that the traits most closely associated with reproductive fitness (abdomen length in females and genital length in males) are "adaptively canalized." While this hypothesis is unlikely to explain Rensch's rule among species or higher clades, it may explain widespread patterns of intraspecific variation in SSD recently documented for many insect species.
在任何给定的进化枝中，雄性体型和雌性体型通常会共同变化，但雄性体型的变化往往比雌性体型更大。这就产生了一种性大小二态性（SSD）的异速生长模式，即所谓的伦施法则。我利用水黾（Aquarius remigis，半翅目，黾蝽科）种群间SSD的异速生长来检验以下假设：伦施法则是在对雄性第二性征的性选择作用下进化而来的；以及另一种假设，即它是由雄性体型更大的表型可塑性导致的。将在两种温度条件下饲养的三个种群进行比较，并结合对25个野外种群中体型的生殖器和躯体部分的异速生长分析。与性选择假设相反，作为性选择目标的生殖器长度在所有被测性状中显示出最低的异速生长斜率。相反，结果支持了对差异可塑性假设的一种新解释：即与繁殖适应性最密切相关的性状（雌性的腹部长度和雄性的生殖器长度）是“适应性固定的”。虽然这一假设不太可能解释物种间或更高级进化枝中的伦施法则，但它可能解释了最近在许多昆虫物种中记录到的SSD种内变异的普遍模式。
