Stathopoulos Sofia, Bishop Jacqueline M, O'Ryan Colleen
Department of Molecular and Cell Biology, University of Cape Town, Cape Town, Western Cape, South Africa.
Department of Biological Sciences, University of Cape Town, Cape Town, Western Cape, South Africa.
PLoS One. 2014 Apr 3;9(4):e93336. doi: 10.1371/journal.pone.0093336. eCollection 2014.
The Olfactory Receptor (OR) superfamily, the largest in the vertebrate genome, is responsible for vertebrate olfaction and is traditionally subdivided into 17 OR families. Recent studies characterising whole-OR subgenomes revealed a 'birth and death' model of evolution for a range of species, however little is known about fine-scale evolutionary dynamics within single-OR families. This study reports the first assessment of fine-scale OR evolution and variation in African mole-rats (Bathyergidae), a family of subterranean rodents endemic to sub-Saharan Africa. Because of the selective pressures of life underground, enhanced olfaction is proposed to be fundamental to the evolutionary success of the Bathyergidae, resulting in a highly diversified OR gene-repertoire. Using a PCR-sequencing approach, we analysed variation in the OR7 family across 14 extant bathyergid species, which revealed enhanced levels of functional polymorphisms concentrated across the receptors' ligand-binding region. We propose that mole-rats are able to recognise a broad range of odorants and that this diversity is reflected throughout their OR7 gene repertoire. Using both classic tests and tree-based methods to test for signals of selection, we investigate evolutionary forces across the mole-rat OR7 gene tree. Four well-supported clades emerged in the OR phylogeny, with varying signals of selection; from neutrality to positive and purifying selection. Bathyergid life-history traits and environmental niche-specialisation are explored as possible drivers of adaptive OR evolution, emerging as non-exclusive contributors to the positive selection observed at OR7 genes. Our results reveal unexpected complexity of evolutionary mechanisms acting within a single OR family, providing insightful perspectives into OR evolutionary dynamics.
嗅觉受体（OR）超家族是脊椎动物基因组中最大的超家族，负责脊椎动物的嗅觉，传统上分为17个OR家族。最近对整个OR亚基因组进行表征的研究揭示了一系列物种的“出生与死亡”进化模型，然而对于单个OR家族内的精细进化动态却知之甚少。本研究报告了对非洲鼹形鼠（滨鼠科）精细尺度的OR进化和变异的首次评估，滨鼠科是撒哈拉以南非洲特有的一类地下啮齿动物。由于地下生活的选择压力，增强的嗅觉被认为是滨鼠科进化成功的基础，这导致了高度多样化的OR基因库。我们采用聚合酶链反应测序方法，分析了14种现存滨鼠科物种的OR7家族变异，结果显示功能多态性水平增强，集中在受体的配体结合区域。我们认为鼹形鼠能够识别多种气味剂，这种多样性反映在它们整个OR7基因库中。我们使用经典测试和基于树的方法来测试选择信号，研究了鼹形鼠OR7基因树的进化力量。在OR系统发育中出现了四个得到充分支持的进化枝，具有不同的选择信号；从中性选择到正选择和纯化选择。我们探讨了滨鼠科的生活史特征和环境生态位特化，将其作为适应性OR进化的可能驱动因素，结果表明它们是OR7基因正选择的非排他性促成因素。我们的研究结果揭示了单个OR家族内进化机制的意外复杂性，为OR进化动态提供了有见地的观点。
