Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic.
Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.
BMC Biol. 2023 Jul 31;21(1):163. doi: 10.1186/s12915-023-01661-8.
Smell abilities differ greatly among vertebrate species due to distinct sensory needs, with exceptional variability reported in the number of olfactory genes and the size of the odour-processing regions of the brain. However, key environmental factors shaping genomic and phenotypic changes linked to the olfactory system remain difficult to identify at macroevolutionary scales. Here, we investigate the association between diverse ecological traits and the number of olfactory chemoreceptors in approximately two hundred ray-finned fishes.
We found independent expansions producing large gene repertoires in several lineages of nocturnal amphibious fishes, generally able to perform active terrestrial exploration. We reinforced this finding with on-purpose genomic and transcriptomic analysis of Channallabes apus, a catfish species from a clade with chemosensory-based aerial orientation. Furthermore, we also detected an augmented information-processing capacity in the olfactory bulb of nocturnal amphibious fishes by estimating the number of cells contained in this brain region in twenty-four actinopterygian species.
Overall, we report a convergent genomic and phenotypic magnification of the olfactory system in nocturnal amphibious fishes. This finding suggests the possibility of an analogous evolutionary event in fish-like tetrapod ancestors during the first steps of the water-to-land transition, favouring terrestrial adaptation through enhanced aerial orientation.
由于不同的感官需求，脊椎动物物种的嗅觉能力差异很大，报道称嗅觉基因的数量和大脑嗅觉处理区域的大小存在极大的可变性。然而，在宏观进化尺度上，仍难以确定塑造与嗅觉系统相关的基因组和表型变化的关键环境因素。在这里，我们研究了大约两百种硬骨鱼类的多种生态特征与嗅觉化学感受器数量之间的关系。
我们发现，在几种夜间两栖鱼类的谱系中，存在独立的扩张，产生了大量的基因库，这些鱼类通常能够进行主动的陆地探索。我们通过对 Channallabes apus 的专门基因组和转录组分析，加强了这一发现，Channallabes apus 是一个具有基于化学感觉的空气导向的分类群中的鲶鱼物种。此外，我们还通过估计 24 种硬骨鱼的嗅球中包含的细胞数量，检测到夜间两栖鱼类的嗅觉信息处理能力增强。
总的来说，我们报告了夜间两栖鱼类的嗅觉系统在基因组和表型上的趋同放大。这一发现表明，在鱼类四足动物祖先向陆地过渡的早期步骤中，可能发生了类似的进化事件，通过增强空气导向，有利于陆地适应。
