The water hyacinth grasshopper Cornops aquaticum (Bruner 1906) constitutes an appropriate model to assess phenotypic and karyotypic variability in the context of differentiation and adaptation of insect populations because it occurs over a wide latitudinal range. This study represents a general analysis of phenotype, karyotype and molecular variation in native populations of C. aquaticum in South America. This is also relevant because this insect is considered a promising biological control agent of water hyacinth, a native South American aquatic plant but a pest in South Africa. Along Paraná and Uruguay River Basins, body size correlated negatively with latitude, and positively so with temperature and rainfall in both sexes. To test whether the chromosomal and phenotypic patterns were adaptive, we compared them with neutral microsatellite loci variation in populations from the medium and lower course of the Paraná River. Firstly, the lack of pairwise association between karyotype and phenotype distance matrixes with that of neutral loci suggested non-neutrality. Secondly, phenotypic differentiation for all morphometric traits (PST) was significantly larger than molecular differentiation (FST), indicating a prevailing divergence selection effect on the observed phenotypic patterns. Finally, the phenotypic and genotypic spatial structures – inferred from Bayesian approaches – were discordant: neutral genetic structure clustered together most populations except for the two southernmost, downstream ones, whereas phenotypic spatial structure groups together all the deltaic populations and singles out the two northernmost ones. The results suggest directional selection leading to higher centric fusion frequencies in the downstream populations and favouring morphometric optimal differences in relation to the environment.

中文翻译：

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空间种群结构：水葫芦蚱蜢Cornopsaquaticum种群的适应模式（Bruner 1906）

水葫芦蚱蜢水生玉米(Bruner 1906) 构成了一个合适的模型来评估昆虫种群分化和适应背景下的表型和核型变异性，因为它发生在广泛的纬度范围内。这项研究代表了对本地种群的表型、核型和分子变异的一般分析。C. 水生在南美洲。这也是相关的，因为这种昆虫被认为是水葫芦的一种有前途的生物防治剂，水葫芦是一种南美本土水生植物，但在南非是一种害虫。沿着巴拉那和乌拉圭河流域，体型与纬度呈负相关，与两性的温度和降雨量呈正相关。为了测试染色体和表型模式是否具有适应性，我们将它们与巴拉那河中下游人群中的中性微卫星基因座变异进行了比较。首先，核型和表型距离矩阵与中性基因座之间缺乏成对关联表明非中性。其次，所有形态特征的表型分化（磷英石) 明显大于分子分化 (F英石），表明对观察到的表型模式存在普遍的分歧选择效应。最后，从贝叶斯方法推断的表型和基因型空间结构不一致：中性遗传结构将大多数种群聚集在一起，除了两个最南端的下游种群，而表型空间结构将所有三角洲种群组合在一起，并挑选出两个最北端的种群. 结果表明定向选择导致下游种群中更高的中心融合频率，并有利于与环境相关的形态学最佳差异。