Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 38, 35392, Giessen, Germany.
Cell Tissue Res. 2021 Jan;383(1):301-325. doi: 10.1007/s00441-020-03377-5. Epub 2021 Jan 26.
Extant anuran amphibians originate from an evolutionary intersection eventually leading to fully terrestrial tetrapods. In many ways, they have to deal with exposure to both terrestrial and aquatic environments: (i) phylogenetically, as derivatives of the first tetrapod group that conquered the terrestrial environment in evolution; (ii) ontogenetically, with a development that includes aquatic and terrestrial stages connected via metamorphic remodeling; and (iii) individually, with common changes in habitat during the life cycle. Our knowledge about the structural organization and function of the amphibian olfactory system and its relevance still lags behind findings on mammals. It is a formidable challenge to reveal underlying general principles of circuity-related, cellular, and molecular properties that are beneficial for an optimized sense of smell in water and air. Recent findings in structural organization coupled with behavioral observations could help to understand the importance of the sense of smell in this evolutionarily important animal group. We describe the structure of the peripheral olfactory organ, the olfactory bulb, and higher olfactory centers on a tissue, cellular, and molecular levels. Differences and similarities between the olfactory systems of anurans and other vertebrates are reviewed. Special emphasis lies on adaptations that are connected to the distinct demands of olfaction in water and air environment. These particular adaptations are discussed in light of evolutionary trends, ontogenetic development, and ecological demands.
现存的无尾两栖动物起源于一个进化的交点，最终导致了完全的陆生四足动物。在很多方面，它们都必须应对陆地和水生环境的暴露：（i）从系统发生的角度来看，它们是第一批在进化中征服陆地环境的四足动物群体的衍生物；（ii）从个体发生的角度来看，它们的发育包括通过变态重塑连接的水生和陆生阶段；（iii）从个体的角度来看，在生命周期中栖息地会发生常见的变化。我们对两栖动物嗅觉系统的结构组织和功能及其相关性的了解仍然落后于对哺乳动物的发现。揭示与环路相关的、细胞的和分子特性的基本原理是一项艰巨的挑战，这些原理有利于在水和空气中优化嗅觉。最近在结构组织方面的发现结合行为观察，有助于理解嗅觉在这个在进化上重要的动物群体中的重要性。我们描述了外周嗅觉器官、嗅球和更高的嗅觉中枢在组织、细胞和分子水平上的结构。我们还回顾了无尾两栖动物和其他脊椎动物的嗅觉系统之间的差异和相似之处。特别强调了与水和空气环境中嗅觉的独特需求相关的适应。这些特殊的适应是根据进化趋势、个体发生发育和生态需求来讨论的。
