Simon Monique Nouailhetas, Marroig Gabriel
Departamento de Genética e Biologia Evolutiva Instituto de Biociências Universidade de São Paulo São Paulo Brasil.
Ecol Evol. 2017 Nov 7;7(24):10752-10769. doi: 10.1002/ece3.3592. eCollection 2017 Dec.
The theory of morphological integration and modularity predicts that if functional correlations among traits are relevant to mean population fitness, the genetic basis of development will be molded by stabilizing selection to match functional patterns. Yet, how much functional interactions actually shape the fitness landscape is still an open question. We used the anuran skull as a model of a complex phenotype for which we can separate developmental and functional modularity. We hypothesized that functional modularity associated to functional demands of the adult skull would overcome developmental modularity associated to bone origin at the larval phase because metamorphosis would erase the developmental signal. We tested this hypothesis in toad species of the complex using species phenotypic correlation pattern (P-matrices). Given that the toad species are distributed in very distinct habitats and the skull has important functions related to climatic conditions, we also hypothesized that differences in skull trait covariance pattern are associated to differences in climatic variables among species. Functional and hormonal-regulated modules are more conspicuous than developmental modules only when size variation is retained on species P-matrices. Without size variation, there is a clear modularity signal of developmental units, but most species have the functional model as the best supported by empirical data without allometric size variation. Closely related toad species have more similar climatic niches and P-matrices than distantly related species, suggesting phylogenetic niche conservatism. We infer that the modularity signal due to embryonic origin of bones, which happens early in ontogeny, is blurred by the process of growth that occurs later in ontogeny. We suggest that the species differing in the preferred modularity model have different demands on the orbital functional unit and that species contrasting in climate are subjected to divergent patterns of natural selection associated to neurocranial allometry and T3 hormone regulation.
形态整合与模块性理论预测，如果性状之间的功能相关性与种群平均适合度相关，那么发育的遗传基础将通过稳定选择来塑造，以匹配功能模式。然而，功能相互作用实际上在多大程度上塑造了适合度景观仍是一个悬而未决的问题。我们将无尾两栖动物的头骨作为一个复杂表型的模型，对于这个模型我们可以区分发育模块性和功能模块性。我们假设，与成年头骨功能需求相关的功能模块性将克服与幼体阶段骨骼起源相关的发育模块性，因为变态会消除发育信号。我们使用物种表型相关模式（P矩阵）在该复合体的蟾蜍物种中检验了这一假设。鉴于蟾蜍物种分布在非常不同的栖息地，且头骨具有与气候条件相关的重要功能，我们还假设头骨性状协方差模式的差异与物种间气候变量的差异有关。只有当物种P矩阵上保留了大小变化时，功能和激素调节的模块才比发育模块更明显。没有大小变化时，发育单元有明显的模块性信号，但大多数物种的功能模型在没有异速生长大小变化的情况下得到了实证数据的最佳支持。亲缘关系较近的蟾蜍物种比亲缘关系较远的物种具有更相似的气候生态位和P矩阵，这表明系统发育生态位保守性。我们推断，由于骨骼胚胎起源导致的模块性信号，在个体发育早期就已出现，但在个体发育后期发生的生长过程中被模糊了。我们认为，在首选模块性模型上存在差异的物种，对眼眶功能单元有不同的需求，并且在气候上形成对比的物种受到与神经颅异速生长和T3激素调节相关的不同自然选择模式的影响。
