Leaché A D, Sites J W
Genome Center, Department of Evolution and Ecology, University of California, Davis, Davis, CA 95616, USA.
Cytogenet Genome Res. 2009;127(2-4):166-81. doi: 10.1159/000293285. Epub 2010 Mar 4.
The genus Sceloporus is a diverse clade of lizards that exhibits substantial variation in chromosome numbers and sex chromosome heteromorphisms, 2 features of the genome that are static among most other pleurodont iguanian lizards. Evolutionary changes to the fundamental number of chromosomes are hypothesized to be a primary factor responsible for driving the diversification of Sceloporus. We explore the patterns of chromosome evolution in Sceloporus using a combination of ancestral state estimations and species diversification tests. Phylogenetic relationships and divergence times within Sceloporus (53 species representing all 19 species groups) are estimated using 4 nuclear genes (>3.3 kb) and relaxed-clock analyses that incorporate a fossil calibration on the root of the tree. We test the hypothesis that chromosome evolution is correlated with shifts in species diversification using cross-validation predictive densities, a new Bayesian approach for modeling the number of species that are predicted to have evolved in the absence of a certain historical event (e.g., a change in chromosome numbers). Results of the cross-validation predictive densities approach indicate that chromosomal evolution is correlated with significantly higher species diversity than predicted under the background rate of diversification in Sceloporus. We conclude by discussing the future of comparative cytogenetic investigations in Sceloporus.
强棱蜥属是一个多样化的蜥蜴类群，其染色体数目和性染色体异形性存在显著差异，而在大多数其他侧生齿鬣蜥科蜥蜴中，基因组的这两个特征是稳定的。染色体基数的进化变化被认为是推动强棱蜥多样化的主要因素。我们结合祖先状态估计和物种多样化测试，探索强棱蜥的染色体进化模式。利用4个核基因（>3.3 kb）和宽松分子钟分析（在树的根部纳入化石校准），估计了强棱蜥属内的系统发育关系和分歧时间（代表所有19个物种组的53个物种）。我们使用交叉验证预测密度检验染色体进化与物种多样化转变相关的假设，交叉验证预测密度是一种新的贝叶斯方法，用于模拟在没有特定历史事件（如染色体数目变化）的情况下预计进化出的物种数量。交叉验证预测密度方法的结果表明，与在强棱蜥多样化背景速率下预测的情况相比，染色体进化与显著更高的物种多样性相关。我们通过讨论强棱蜥比较细胞遗传学研究的未来得出结论。
