School of Biological and Chemical Sciences, Queen Mary University of London, London, UK.
Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, USA.
Mol Ecol. 2020 May;29(10):1839-1859. doi: 10.1111/mec.15445. Epub 2020 May 13.
Changes in behaviour may initiate shifts to new adaptive zones, with physical adaptations for novel environments evolving later. While new mutations are commonly considered engines of adaptive change, sensory evolution enabling access to new resources might also arise from standing genetic diversity, and even gene loss. We examine the relative contribution of molecular adaptations, measured by positive and relaxed selection, acting on eye-expressed genes associated with shifts to new adaptive zones in ecologically diverse bats from the superfamily Noctilionoidea. Collectively, noctilionoids display remarkable ecological breadth, from highly divergent echolocation to flight strategies linked to specialized insectivory, the parallel evolution of diverse plant-based diets (e.g., nectar, pollen and fruit) from ancestral insectivory, and-unusually for echolocating bats-often have large, well-developed eyes. We report contrasting levels of positive selection in genes associated with the development, maintenance and scope of visual function, tracing back to the origins of noctilionoids and Phyllostomidae (the bat family with most dietary diversity), instead of during shifts to novel diets. Generalized plant visiting was not associated with exceptional molecular adaptation, and exploration of these novel niches took place in an ancestral phyllostomid genetic background. In contrast, evidence for positive selection in vision genes was found at subsequent shifts to either nectarivory or frugivory. Thus, neotropical noctilionoids that use visual cues for identifying food and roosts, as well as for orientation, were effectively preadapted, with subsequent molecular adaptations in nectar-feeding lineages and the subfamily Stenodermatinae of fig-eating bats fine-tuning pre-existing visual adaptations for specialized purposes.
行为的变化可能引发向新的适应区的转变，而对新环境的生理适应则后来进化。虽然新的突变通常被认为是适应变化的引擎，但感官进化使能够获得新的资源也可能来自于现存的遗传多样性，甚至是基因丢失。我们研究了分子适应的相对贡献，这些适应通过正选择和放松选择来衡量，作用于与生态多样的夜翼目蝙蝠向新的适应区转变相关的眼表达基因。总的来说，夜翼目蝙蝠表现出了惊人的生态多样性，从高度分化的回声定位到与专门的食虫性相关的飞行策略，从食虫性到各种植物性饮食（如花蜜、花粉和水果）的平行进化，以及——对回声定位蝙蝠来说不寻常的是——通常有大而发达的眼睛。我们报告了与视觉功能的发育、维持和范围相关的基因中存在的正选择水平的差异，这些基因可以追溯到夜翼目和叶鼻蝠科（食虫性最丰富的蝙蝠科）的起源，而不是在向新的饮食转变期间。广义的植物访问与特殊的分子适应无关，这些新的生态位是在祖先的叶鼻蝠遗传背景下探索的。相比之下，在随后向花蜜或果实食性的转变中，发现了视觉基因的正选择证据。因此，新热带夜翼目蝙蝠利用视觉线索来识别食物和栖息地，以及进行定向，它们实际上已经预先适应了，随后在花蜜喂养的谱系和食无花果蝙蝠的 Stenodermatinae 亚科中出现了正选择，为专门的目的微调了预先存在的视觉适应。
