Instituto Multidisciplinario de Biología Vegetal, Universidad Nacional de Córdoba, CONICET, Córdoba, Argentina.
Departamento de Botánica y Zoología, CONACYT - Laboratorio Nacional de Identificación y Caracterización Vegetal, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, Zapopan, Mexico.
J Evol Biol. 2019 Aug;32(8):783-793. doi: 10.1111/jeb.13480. Epub 2019 May 8.
Covariation among traits can modify the evolutionary trajectory of complex structures. This process is thought to operate at a microevolutionary scale, but its long-term effects remain controversial because trait covariation can itself evolve. Flower morphology, and particularly floral trait (co)variation, has been envisioned as the product of pollinator-mediated selection. Available evidence suggests that major changes in pollinator assemblages may affect the joint expression of floral traits and their phenotypic integration. We expect species within a monophyletic lineage sharing the same pollinator type will show not only similarity in trait means but also similar phenotypic variance-covariance structures. Here, we tested this expectation using eighteen Salvia species pollinated either by bees or by hummingbirds. Our findings indicated a nonsignificant multivariate phylogenetic signal and a decoupling between means and variance-covariance phenotypic matrices of floral traits during the evolution to hummingbird pollination. Mean trait value analyses revealed significant differences between bee- and hummingbird-pollinated Salvia species although fewer differences were detected in the covariance structure between groups. Variance-covariance matrices were much more similar among bee- than hummingbird-pollinated species. This pattern is consistent with the expectation that, unlike hummingbirds, bees physically manipulate the flower, presumably exerting stronger selection pressures favouring morphological convergence among species. Overall, we conclude that the evolution of hummingbird pollination proceeded through different independent transitions. Thus, although the evolution of hummingbird pollination led to a new phenotypic optimum, the process involved the diversification of the covariance structure.
性状之间的共变可以改变复杂结构的进化轨迹。人们认为这个过程发生在微观进化尺度上，但由于性状共变本身可以进化，其长期影响仍存在争议。花形态，特别是花性状（协变），被认为是传粉媒介选择的产物。现有证据表明，传粉媒介组合的重大变化可能会影响花性状的共同表达及其表型整合。我们预计，在具有相同传粉类型的单系谱系内的物种，不仅在性状均值上表现出相似性，而且在表型方差-协方差结构上也表现出相似性。在这里，我们使用 18 种被蜜蜂或蜂鸟授粉的鼠尾草属植物来检验这一预期。我们的研究结果表明，在向蜂鸟授粉的进化过程中，花性状的多变量系统发育信号不显著，均值和方差-协方差表型矩阵之间存在解耦。尽管在组间协方差结构中检测到的差异较少，但均值性状值分析显示，被蜜蜂和蜂鸟授粉的鼠尾草属物种之间存在显著差异。方差-协方差矩阵在蜜蜂授粉的物种之间比在蜂鸟授粉的物种之间更为相似。这种模式与以下预期一致：与蜂鸟不同，蜜蜂会物理地操纵花朵，可能会对物种之间的形态趋同施加更强的选择压力。总体而言，我们得出结论，蜂鸟传粉的进化是通过不同的独立过渡进行的。因此，尽管蜂鸟传粉的进化导致了一个新的表型最优，但这个过程涉及到协方差结构的多样化。
