Hollander Johan, Adams Dean C, Johannesson Kerstin
Department of Marine Ecology, Göteborg University, Tjärnö Marine Biological Laboratory, S-452 96 Strimstad, Sweden.
Evolution. 2006 Dec;60(12):2490-7.
Variation in ontogenetic development among individuals may be a major contributor to morphological variation within species. Evolution of different growth trajectories might, for example, evolve as a response to varying ecological contexts of individuals living in different environments, or by life-stage or gender differences. The intertidal periwinkle Littorina saxatilis is strongly polymorphic in shell shape. We compared ontogenetic trajectories between life stages, local populations, and sexes to understand how different morphological end points are reached during ontogeny and what might cause these differences. Applying landmark-based geometric morphometrics, we captured shell shape variation for four Swedish populations of this species. We also derived a method to visualize ontogenetic trajectories described by the relationship of size to the multivariate shape space. We found that growth trajectories differed between individuals living in different habitats, as well as between sexes and maturity stages. Males living on rocky cliffs grew isometrically throughout life, whereas females from the same habitat switched from isometric growth as juveniles to allometric growth as adults. In contrast, males and females living on boulders grew allometrically as juveniles but changed to isometric growth at sexual maturity. Thus, in this species, ontogenetic growth seems influenced by habitat-associated selection as well as by gender and age-specific selection. These differing selection regimes result in ontogenetic shifts in allometry in three of the four groups examined.
个体间个体发育的差异可能是物种内形态变异的主要原因。例如，不同生长轨迹的进化可能是对生活在不同环境中的个体所面临的不同生态环境的反应，或者是由于生命阶段或性别的差异。潮间带滨螺Littorina saxatilis的壳形具有很强的多态性。我们比较了不同生命阶段、当地种群和性别之间的个体发育轨迹，以了解在个体发育过程中如何达到不同的形态终点以及可能导致这些差异的原因。应用基于地标点的几何形态测量学，我们获取了该物种四个瑞典种群的壳形变异。我们还推导了一种方法来可视化由大小与多变量形状空间的关系所描述的个体发育轨迹。我们发现，生活在不同栖息地的个体之间、性别之间以及成熟阶段之间的生长轨迹存在差异。生活在岩石峭壁上的雄性在整个生命过程中呈等速生长，而来自同一栖息地的雌性则从幼年时的等速生长转变为成年时的异速生长。相比之下，生活在巨石上的雄性和雌性在幼年时呈异速生长，但在性成熟时转变为等速生长。因此，在这个物种中，个体发育生长似乎受到与栖息地相关的选择以及性别和年龄特异性选择的影响。这些不同的选择机制导致了所研究的四组中的三组在异速生长方面发生个体发育转变。
