Rhesus macaque cone ratio heritability

A defining feature of catarrhine primates is uniform trichromacy – the
ability to distinguish red (long; L), green (medium; M), and blue (short;
S) wavelengths of light. While the tuning of photoreceptors is conserved,
the ratio of L:M cones in the retina is variable within and between
species, with human cone ratios differing from other catarrhines. Yet, the
sources and structure of variation in cone ratios are poorly understood,
precluding a broader understanding of color vision variability. Here, we
report a large-scale study of a pedigreed population of macaques. We
collected foveal RNA and analysed opsin gene expression using cDNA. We
estimated the additive genetic variance of cone ratios. The average L:M
ratio and standard error was 1.03:1± 0.02. There was no age effect, and
genetic contribution to variation was negligible. We found marginal sex
effects with females having larger ratios than males. S cone ratios
(0.143: 1± 0.002) had significant genetic variance with a heritability
estimate of 43% but did not differ between sexes or age groups. Our
results contextualize the derived human condition of L-cone dominance and
provide new information about the heritability of cone ratios and
variation in primate color vision.

狭鼻猴类（catarrhine primates）的标志性特征之一是统一的三色视觉（trichromacy）——即能够分辨红光（长波；L）、绿光（中波；M）与蓝光（短波；S）波段的可见光。尽管光感受器（photoreceptors）的光谱调谐特性具有保守性，但不同物种乃至同一物种个体间，视网膜（retina）内L:M型视锥细胞（cones）的比例存在差异，人类的视锥细胞比例与其他狭鼻猴类存在显著区别。
然而，目前学界对视锥细胞比例变异的来源与结构仍知之甚少，这限制了我们对灵长类色觉变异的全面认知。本研究针对一个拥有完整谱系记录的猕猴（macaques）种群开展了大规模研究：我们采集了中央凹RNA（foveal RNA），并通过互补脱氧核糖核酸（cDNA）分析视蛋白基因（opsin gene）的表达情况，进而估算了视锥细胞比例的加性遗传方差（additive genetic variance）。
本次研究测得的平均L:M比例及其标准误（standard error）为1.03:1±0.02。研究未观测到年龄效应，且遗传因素对视锥比例变异的贡献可忽略不计；仅存在微弱的性别效应，雌性个体的L:M比例高于雄性。S型视锥细胞比例（0.143:1±0.002）则存在显著的遗传变异，其遗传力（heritability）估算值为43%，且该比例不存在性别或年龄差异。
本研究结果为人类所特有的L型视锥细胞占优（L-cone dominance）的演化状态提供了背景参照，同时为视锥细胞比例的遗传机制以及灵长类色觉变异的研究提供了全新的科学依据。