Ontogeny and phylogeny in the northern swordtail clade of Xiphophorus

It has been hypothesized than morphological diversity within clades can be generated by simple alterations of shared developmental programs. However, few studies have examined changes in heterochrony, the rate and timing of developmental events, in an explicitly phylogenetic context. We studied how developmental patterns have changed phylogenetically in the northern swordtail clade of Xiphophorus. We reared individuals of an outgroup and seven of nine species in the clade and followed their development for ~300 days. For each individual, we used nonlinear regression to estimate three growth parameters: growth rate, adult body size, and age of cessation of growth. We estimated sword growth rates in males by linear regression. We then used the means of these growth parameters to construct standard growth curves for each species and to study growth patterns in a phylogenetic context. A combined phylogeny was constructed from both phenotypic and DNA sequence data. The phenotypic data set, c...

已有假说提出，类群内的形态多样性可通过共享发育程序的简单改变得以产生。然而，鲜有研究在明确的系统发育框架下探讨异时性（heterochrony）——即发育事件的速率与时序——的变化。我们针对剑尾鱼属（Xiphophorus）北部剑尾鱼种系类群，研究了发育模式的系统发育演化规律。我们饲养了1个外类群（outgroup）个体以及该类群9个物种中的7个物种的个体，并对其发育过程进行了约300天的跟踪观测。针对每一个体，我们采用非线性回归（nonlinear regression）估算了3项生长参数：生长速率、成体体型以及生长停止年龄。我们通过线性回归（linear regression）估算了雄性个体的剑突生长速率。随后，我们利用这些生长参数的均值，为每个物种构建了标准化生长曲线，并在系统发育框架下分析其生长模式。我们结合表型数据与DNA序列数据构建了综合系统发育树。本次的表型数据集，c...