Temperament is a construct whose manifestations are quantifiable from an early age, and whose origins have been proposed as “biological.” Our goal was to determine whether maternal rank and infant genotype are associated with five measures of temperament in 3- to 4-month old rhesus monkeys (Macaca mulatta), all of whom were born and reared by their mothers in large, outdoor, half-acre cages. Maternal rank was defined as the proportion of animals outranked by each female, and the two genes of interest to us were monoamine oxidase and serotonin transporter, both of which are polymorphic in their promoter regions (MAOA-LPR and 5-HTTLPR, respectively), with one allele of each gene considered a “plasticity” allele, conferring increased sensitivity to environmental events. Our large sample size (n = 2014–3140) enabled us to examine the effects of individual genotypes rather than combining genotypes as is often done. Rank was positively associated with Confident temperament, but only for animals with the 5-repeat allele for MAOA-LPR. Rank had no other effect on temperament. In contrast, genotype had many different effects, with 5-HTTLPR associated with behavioral inhibition, and MAOA-LPR associated with ratings-based measures of temperament. We also examined the joint effect of the two genotypes and found some evidence for a dose-response: animals with the plasticity alleles for both genes were more likely to be behaviorally inhibited. Our results suggest phenotypic differences between animals possessing alleles for MAOA-LPR that show functional equivalence based on in vitro tests, and our data for 5-HTTLPR revealed differences between short/short homozygotes and long/short heterozygotes, strongly suggesting that combining genotypes for statistical analysis should be avoided if possible. Our analysis also provides evidence of sex differences in temperament, and, to our knowledge, the only evidence of differences in temperament based on specific pathogen-free status. We suggest several directions for future research.

中文翻译：

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母系等级、5-HTTLPR 基因型和 MAOA-LPR 基因型与幼年恒河猴气质的关系

气质是一种结构，其表现从很小的时候就可以量化，并且其起源被认为是“生物学的”。我们的目标是确定母亲等级和婴儿基因型是否与 3 至 4 个月大的恒河猴（ Macaca mulatta ）的五种气质测量相关，所有这些恒河猴都是由母亲在大型、户外、半封闭环境中出生和抚养的。英亩的笼子。母性等级被定义为每个雌性动物等级高于的动物比例，我们感兴趣的两个基因是单胺氧化酶和血清素转运蛋白，这两个基因的启动子区域都是多态性的（分别为 MAOA-LPR 和 5 - HTTLPR ），每个基因的一个等位基因被认为是“可塑性”等位基因，赋予对环境事件更高的敏感性。我们的大样本量（n  = 2014-3140）使我们能够检查单个基因型的影响，而不是像通常那样组合基因型。排名与自信气质呈正相关，但仅限于具有MAOA-LPR 5 重复等位基因的动物。等级对气质没有其他影响。相比之下，基因型有许多不同的影响，其中5-HTTLPR与行为抑制相关，MAOA-LPR与基于评级的气质测量相关。我们还检查了两种基因型的联合效应，并发现了一些剂量反应的证据：具有两种基因可塑性等位基因的动物更有可能受到行为抑制。我们的结果表明，拥有MAOA-LPR等位基因的动物之间存在表型差异，这些等位基因显示出基于体外测试的功能等效性，并且我们的5-HTTLPR数据揭示了短/短纯合子和长/短杂合子之间的差异，强烈表明结合基因型进行统计如果可能的话应避免分析。我们的分析还提供了性情性别差异的证据，据我们所知，这是基于特定无病原体状态的性情差异的唯一证据。我们为未来的研究提出了几个方向。