Sandoval C P, Nosil P
Marine Science Institute, University of California, Santa Barbara 93106, USA.
Evolution. 2005 Nov;59(11):2405-13.
The evolution of ecological specialization has been a central topic in ecology because specialized adaptations to divergent environments can result in reproductive isolation and facilitate speciation. However, the order in which different aspects of habitat adaptation and habitat preference evolve is unclear. Timema walking-stick insects feed and mate on the host plants on which they rest. Previous studies of T. cristinae ecotypes have documented divergent, host-specific selection from visual predators and the evolution of divergent host and mate preferences between populations using different host-plant species (Ceanothus or Adenostoma). Here we present new data that show that T. podura, a nonsister species of T. cristinae, has also formed ecotypes on these host genera and that in both species these ecotypes exhibit adaptive divergence in color-pattern and host preference. Color-pattern morphs exhibit survival trade-offs on different hosts due to differential predation. In contrast, fecundity trade-offs on different hosts do not occur in either species. Thus, host preference in both species has evolved before divergent physiological adaptation but in concert with morphological adaptations. Our results shed light onto which traits are involved in the initial stages of ecological specialization and ecologically based reproductive isolation.
生态特化的演化一直是生态学的核心议题，因为对不同环境的特化适应可能导致生殖隔离并促进物种形成。然而，栖息地适应和栖息地偏好的不同方面演化的先后顺序尚不清楚。蒂梅马竹节虫在其栖息的寄主植物上取食和交配。先前对克氏蒂梅马竹节虫生态型的研究记录了来自视觉捕食者的不同的、寄主特异性的选择，以及使用不同寄主植物物种（加州鼠李或腺柳）的种群之间不同寄主和配偶偏好的演化。在此，我们展示了新的数据，表明蒂氏蒂梅马竹节虫（克氏蒂梅马竹节虫的非姐妹物种）在这些寄主属上也形成了生态型，并且在这两个物种中，这些生态型在体色模式和寄主偏好上都表现出适应性分化。由于捕食差异，体色模式变体在不同寄主上表现出生存权衡。相比之下，这两个物种在不同寄主上均未出现繁殖力权衡。因此，这两个物种的寄主偏好均在生理分化之前演化，但与形态适应协同演化。我们的结果揭示了哪些性状参与了生态特化和基于生态的生殖隔离的初始阶段。
