Data from: Strength of selection on Trpc2 gene predicts accessory olfactory bulb form in bat vomeronasal evolution

Vestigial characters are common across the tree of life, but the underlying evolutionary processes shaping phenotypic loss are poorly understood. The mammalian vomeronasal system, which detects social chemical cues important to fitness, is an impressive example of a sensory system lost multiple times. Three times more losses are inferred among bats than in other mammalian orders. We characterized the relationship between amino acid substitutions in a gene tightly linked to vomeronasal function (Trpc2) and the accessory olfactory bulb, a brain region that processes the detection of these vomeronasal chemical cues. By applying a phylogenetic logistic regression, we found a strong negative relationship between the branch lengths representing rates of codon changes in the Trpc2 gene tree and the presence or absence of an accessory olfactory bulb. Longer branch lengths predict loss of the accessory olfactory bulb, suggesting selection has relaxed on the system as a whole. Based on this relationship, we predicted the absence of an accessory olfactory bulb in 19 bat species with unknown morphology. Several species with predicted losses have specialized skull morphology, suggesting a potential tradeoff between adaptation in skull shape and maintenance of the vomeronasal system. This study offers a new approach to relate genetic mechanisms and phenotypes at a macroevolutionary scale.退化性状（vestigial characters）在生命之树中广泛存在，但塑造表型丢失的潜在进化过程仍未得到充分阐释。可检测对个体适合度至关重要的社会化学信号的哺乳动物犁鼻系统（vomeronasal system），是感觉系统多次独立丢失的典型范例。据推断，蝙蝠类群中的犁鼻系统丢失事件数量是其他哺乳纲类群的三倍。我们对与犁鼻功能紧密关联的基因Trpc2的氨基酸替换特征与副嗅球（accessory olfactory bulb）——负责处理犁鼻化学信号检测的脑区——之间的关联进行了表征分析。通过系统发育logistic回归（phylogenetic logistic regression）分析，我们发现Trpc2基因树中代表密码子替换速率的分支长度与副嗅球的存在与否呈显著负相关：更长的分支长度预示着副嗅球的丢失，这表明该感觉系统整体受到的选择压力已松弛。基于这一关联，我们预测了19种形态学数据未知的蝙蝠类群不存在副嗅球。其中部分被预测存在副嗅球丢失的蝙蝠类群具有特化的头骨形态，这提示头骨形态适应与犁鼻系统维持之间可能存在进化权衡。本研究为宏观进化尺度下关联遗传机制与表型特征提供了全新的研究路径。