Bonine Kevin E, Gleeson Todd T, Garland Theodore
Department of Ecology and Evolutionary Biology, University of Arizona, P.O. Box 210088 Tucson, AZ 85721, USA.
J Exp Biol. 2005 Dec;208(Pt 23):4529-47. doi: 10.1242/jeb.01903.
Previously, we found that phrynosomatid lizards, a diverse group common in the southwestern USA, vary markedly in fiber-type composition of the iliofibularis (a hindlimb muscle important in locomotion). Phrynosomatidae comprises three subclades: the closely related sand and horned lizards, and their relatives the Sceloporus group. The variation in muscle fiber-type composition for 11 phrynosomatid species is attributable mainly to differences between the sand- and horned-lizard subclades. Here, we expand the phrynosomatid database with three additional species and compare these results with data collected for 10 outgroup (distantly related) species. Our goal was to determine if the patterns found in Phrynosomatidae hold across a broader phylogenetic range of the extant lizards and to elucidate the evolution of muscle fiber-type composition and related traits. To allow for meaningful comparisons, data were collected from species that are primarily terrestrial and relatively small in size (3.5-65 g body mass). Results indicate that the fiber-type variation observed within the Phrynosomatidae almost spans the range of variation observed in our sample of 24 species from eight families. However, one species of Acanthodactylus (Lacertidae) had a consistent region of large tonic fibers (that did not stain darkly for either succinic dehydrogenase or myosin ATPase activity), a fiber-type only occasionally seen in the other 23 species examined. Many species have a large proportion of either fast-twitch glycolytic (FG; e.g. sand lizards and Aspidoscelis) or fast-twitch oxidative-glycolytic (FOG) fibers (e.g. horned lizards), with the slow-oxidative proportion occupying only 1-17% of the iliofibularis. Importantly, the negative relationship between FG and FOG composition observed in Phrynosomatidae appears to be a characteristic of lizards in general, and could lead to functional trade-offs in aspects of locomotor performance, as has previously been reported for Lacertidae. Reconstruction of ancestral trait values by use of phylogenetically based statistical methods indicates especially large changes in fiber-type composition during the evolution of horned lizards.
此前，我们发现角蜥科蜥蜴是美国西南部常见的一个多样化群体，其髂腓肌（一种对运动很重要的后肢肌肉）的纤维类型组成差异显著。角蜥科包括三个亚分支：亲缘关系密切的沙蜥和角蜥，以及它们的近亲棱蜥类群。11种角蜥科蜥蜴肌肉纤维类型组成的差异主要归因于沙蜥亚分支和角蜥亚分支之间的差异。在此，我们将另外三个物种纳入角蜥科数据库，并将这些结果与为10个外类群（远缘相关）物种收集的数据进行比较。我们的目标是确定在角蜥科中发现的模式是否在现存蜥蜴更广泛的系统发育范围内成立，并阐明肌肉纤维类型组成和相关特征的进化。为了进行有意义的比较，数据收集自主要为陆生且体型相对较小（体重3.5 - 65克）的物种。结果表明，在角蜥科中观察到的纤维类型变异几乎涵盖了我们从八个科的24个物种样本中观察到的变异范围。然而，一种沙鱼蜥（蜥蜴科）有一个持续存在大量慢收缩纤维的区域（对琥珀酸脱氢酶或肌球蛋白ATP酶活性均不着深色），这种纤维类型在其他23个被检查的物种中只是偶尔出现。许多物种的快缩糖酵解型（FG；如沙蜥和侧斑鞭尾蜥）或快缩氧化糖酵解型（FOG）纤维（如角蜥）比例很大，慢氧化型比例仅占髂腓肌的1 - 17%。重要的是，在角蜥科中观察到的FG和FOG组成之间的负相关关系似乎是蜥蜴的普遍特征，并且可能导致运动性能方面的功能权衡，正如之前在蜥蜴科中所报道的那样。使用基于系统发育的统计方法重建祖先性状值表明，在角蜥的进化过程中，纤维类型组成发生了特别大的变化。
