Olfactory receptors (ORs), encoded by the largest vertebrate multigene family, enable the detection of thousands of unique odorants in the environment and consequently play a critical role in species survival. Here, we advance our knowledge of OR gene evolution in procellariiform seabirds, an avian group which relies on the sense of olfaction for critical ecological functions. We built a cosmid library of Cory's Shearwater (Calonectris borealis) genomic DNA, a model species for the study of olfaction-based navigation, and sequence OR gene-positive cosmid clones with a combination of sequencing technologies. We identified 220 OR open reading frames, 20 of which are full length, intact OR genes, and found a large ratio of partial and pseudogenes to intact OR genes (2:1), suggestive of a dynamic mode of evolution. Phylogenetic analyses revealed that while a few genes cluster with those of other sauropsid species in a γ (gamma) clade that predates the divergence of different avian lineages, most genes belong to an avian-specific γ-c clade, within which sequences cluster by species, suggesting frequent duplication and/or gene conversion events. We identified evidence of positive selection on full length γ-c clade genes. These patterns are consistent with a key role of adaptation in the functional diversification of olfactory receptor genes in a bird lineage that relies extensively on olfaction.

中文翻译：

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Cory's Shearwater嗅觉受体基因的适应性进化特征为分子状海鸟嗅觉提供了分子基础。

由最大的脊椎动物多基因家族编码的嗅觉受体（OR）能够检测环境中成千上万种独特的气味，因此在物种生存中起着至关重要的作用。在这里，我们进一步介绍了在procellariiform海鸟中的OR基因进化的知识，这是一个禽类，依靠嗅觉实现关键的生态功能。我们构建了Cory的Shearwater（Calonectrisboalis）基因组DNA粘粒文库，该模型种用于研究基于嗅觉的导航，并结合测序技术对OR基因阳性粘粒克隆进行测序。我们鉴定了220个OR开放阅读框，其中20个是完整的OR基因全长，发现部分和假基因与完整OR基因的比例很高（2：1），这提示了动态进化模式。系统发育分析表明，尽管在一个γ（γ）进化枝中一些基因与其他蜥脚类物种的基因聚簇，但早于不同禽类谱系的分化，但大多数基因属于禽类特异性γ-c进化枝，其中的序列按物种聚类，表明存在频繁的重复和/或基因转换事件。我们确定了对全长γ-c进化枝基因进行阳性选择的证据。这些模式与广泛依赖嗅觉的鸟类谱系中嗅觉受体基因的功能多样化的适应性关键作用相一致。提示频繁的重复和/或基因转换事件。我们确定了对全长γ-c进化枝基因进行阳性选择的证据。这些模式与适应在鸟类谱系中嗅觉受体基因功能多样化中的关键作用相一致，而鸟类谱系广泛依赖嗅觉。提示频繁的重复和/或基因转换事件。我们确定了对全长γ-c进化枝基因进行阳性选择的证据。这些模式与适应在鸟类谱系中嗅觉受体基因功能多样化中的关键作用相一致，而鸟类谱系广泛依赖嗅觉。