Tomašević Kolarov Nataša, Cvijanović Milena, Denoël Mathieu, Ivanović Ana
University of Belgrade, Institute for Biological Research "Siniša Stanković", Belgrade, Serbia.
Laboratory of Fish and Amphibian Ethology, Behavioral Biology Unit, Freshwater and Oceanic Science Unit of Research (FOCUS), University of Liège, Liège, Belgium.
J Exp Zool B Mol Dev Evol. 2017 Dec;328(8):737-748. doi: 10.1002/jez.b.22758. Epub 2017 Jun 30.
Tetrapod limbs are serially homologous structures that represent a particularly interesting model for studies on morphological integration, i.e. the tendency of developmental systems to produce correlated variation. In newts, limbs develop at an early larval stage and grow continuously, including after the habitat transition from water to land following metamorphosis. However, aquatic and terrestrial environments impose different constraints and locomotor modes that could affect patterns of morphological integration and evolvability. We hypothesize that this would be the case for alternative heterochronic morphs in newts, i.e. aquatic paedomorphs that keep gills at the adult stage and adult metamorphs that are able to disperse on land. To this end, we analyzed patterns and strengths of correlations between homologous skeletal elements of the fore- and hindlimbs as well as among skeletal elements within limbs in both phenotypes in the alpine newt, Ichthyosaura alpestris. Our results showed that metamorphs and paedomorphs had similar, general patterns of limb integration. Partial correlations between homologous limb elements and within limb elements were higher in paedomorphs when compared to metamorphs. A decrease in partial correlation between homologous limb elements in metamorphs is accompanied with a higher evolvability of the terrestrial morph. All these results indicate that environmental demands shaped the patterns of morphological integration of alpine newt limbs and that the observed diversity in correlation structure could be related to a qualitative difference in the modes of locomotion between the morphs.
四足动物的四肢是系列同源结构，是研究形态整合（即发育系统产生相关变异的趋势）的一个特别有趣的模型。在蝾螈中，四肢在幼体早期发育并持续生长，包括在变态后从水生栖息地过渡到陆地之后。然而，水生和陆地环境施加了不同的限制和运动模式，这可能会影响形态整合模式和进化能力。我们假设蝾螈的替代异时形态也是如此，即成年期保留鳃的水生幼态持续型和能够在陆地上扩散的成年变态型。为此，我们分析了高山蝾螈（Ichthyosaura alpestris）两种表型中前肢和后肢同源骨骼元素之间以及四肢内骨骼元素之间的相关性模式和强度。我们的结果表明，变态型和幼态持续型具有相似的肢体整合总体模式。与变态型相比，幼态持续型中同源肢体元素之间以及肢体元素内部的偏相关性更高。变态型中同源肢体元素之间偏相关性的降低伴随着陆地形态更高的进化能力。所有这些结果表明，环境需求塑造了高山蝾螈四肢的形态整合模式，并且观察到的相关结构多样性可能与不同形态之间运动模式的质的差异有关。
