Cox Robert M, Skelly Stephanie L, John-Alder Henry B
Program in Ecology and Evolution, Rutgers University, New Brunswick, New Jersey 08901, USA.
Evolution. 2003 Jul;57(7):1653-69. doi: 10.1111/j.0014-3820.2003.tb00371.x.
It is commonly argued that sexual size dimorphism (SSD) in lizards has evolved in response to two primary, nonexclusive processes: (1) sexual selection for large male size, which confers an advantage in intrasexual mate competition (intrasexual selection hypothesis), and (2) natural selection for large female size, which confers a fecundity advantage (fecundity advantage hypothesis). However, outside of several well-studied lizard genera, the empirical support for these hypotheses has not been examined with appropriate phylogenetic control. We conducted a comparative phylogenetic analysis to test these hypotheses using literature data from 497 lizard populations representing 302 species and 18 families. As predicted by the intrasexual selection hypothesis, male aggression and territoriality are correlated with SSD, but evolutionary shifts in these categorical variables each explain less than 2% of the inferred evolutionary change in SSD. We found stronger correlations between SSD and continuous estimates of intrasexual selection such as male to female home range ratio and female home range size. These results are consistent with the criticism that categorical variables may obscure much of the actual variation in intrasexual selection intensity needed to explain patterns in SSD. In accordance with the fecundity advantage hypothesis, SSD is correlated with clutch size, reproductive frequency, and reproductive mode (but not fecundity slope, reduced major axis estimator of fecundity slope, length of reproductive season, or latitude). However, evolutionary shifts in clutch size explain less than 8% of the associated change in SSD, which also varies significantly in the absence of evolutionary shifts in reproductive frequency and mode. A multiple regression model retained territoriality and clutch size as significant predictors of SSD, but only 16% of the variation in SSD is explained using these variables. Intrasexual selection for large male size and fecundity selection for large female size have undoubtedly helped to shape patterns of SSD across lizards, but the comparative data at present provide only weak support for these hypotheses as general explanations for SSD in this group. Future work would benefit from the consideration of alternatives to these traditional evolutionary hypotheses, and the elucidation of proximate mechanisms influencing growth and SSD within populations.
通常认为，蜥蜴的两性异形（SSD）是为应对两个主要的、并非相互排斥的过程而进化的：（1）对大型雄性体型的性选择，这在同性配偶竞争中具有优势（同性选择假说）；（2）对大型雌性体型的自然选择，这具有繁殖力优势（繁殖力优势假说）。然而，在几个经过充分研究的蜥蜴属之外，这些假说的实证支持尚未在适当的系统发育控制下进行检验。我们进行了一项比较系统发育分析，以使用来自代表302个物种和18个科的497个蜥蜴种群的文献数据来检验这些假说。正如同性选择假说所预测的，雄性攻击性和领地性与SSD相关，但这些分类变量的进化变化各自解释的SSD推断进化变化不到2%。我们发现SSD与同性选择的连续估计值之间存在更强的相关性，例如雄性与雌性的活动范围比率以及雌性活动范围大小。这些结果与这样的批评一致，即分类变量可能掩盖了解释SSD模式所需的同性选择强度的许多实际变化。根据繁殖力优势假说，SSD与窝卵数、繁殖频率和繁殖模式相关（但与繁殖力斜率、繁殖力斜率的简约主轴估计值、繁殖季节长度或纬度无关）。然而，窝卵数的进化变化解释的SSD相关变化不到8%，在繁殖频率和模式没有进化变化的情况下，SSD也有显著变化。一个多元回归模型保留领地性和窝卵数作为SSD的显著预测因子，但使用这些变量仅解释了SSD变化的16%。对大型雄性体型的同性选择和对大型雌性体型的繁殖力选择无疑有助于塑造蜥蜴的SSD模式，但目前的比较数据仅为这些假说作为该群体SSD的一般解释提供了微弱支持。未来的工作将受益于考虑这些传统进化假说的替代方案，以及阐明影响种群内生长和SSD的近端机制。
