Personality, immune response and reproductive success: an appraisal of the pace-of-life syndrome hypothesis

The pace-of-life syndrome (POLS) hypothesis is an extended concept of the life-history theory that includes behavioural traits. The studies challenging the POLS hypothesis often focus on the relationships between a single personality trait and a physiological and/or life-history trait. While pathogens represent a major selective pressure, few studies have been interested in testing relationships between behavioural syndrome, and several fitness components including immunity.
The aim of this study was to address this question in the mealworm beetle, Tenebrio molitor, a model species in immunity studies. The personality score was estimated from a multidimensional syndrome based of four repeatable behavioural traits.
In a first experiment, we investigated its relationship with two measures of fitness (reproduction and survival) and three components of the innate immunity (haemocyte concentration, and levels of activity of the phenoloxidase including the total proenzyme and the naturally activated one) to challenge the POLS hypothesis in T. molitor. Overall, we found a relationship between behavioural syndrome and reproductive success in this species, thus supporting the POLS hypothesis. We also showed a sex-specific relationship between behavioural syndrome and basal immune parameters.
In a second experiment, we tested whether this observed relationship with innate immunity could be confirmed in term of differential survival after challenging by entomopathogenic bacteria, Bacillus thuringiensis. In this case, no significant relationship was evidenced.
We recommend that future researchers on the POLS should control for differences in evolutionary trajectory between sexes and to pay attention to the choice of the proxy used, especially when looking at immune traits.

生活节奏综合征（pace-of-life syndrome, POLS）假说是涵盖行为性状（behavioural traits）的生命史理论（life-history theory）延伸概念。过往挑战该POLS假说的研究，多聚焦于单一人格性状与生理及/或生命史性状间的关联。尽管病原体是主要的选择压力（selective pressure），但鲜有研究检验行为综合征与包括免疫在内的多项适合度组分（fitness components）之间的关联。
本研究以免疫研究中的模式物种黄粉虫（Tenebrio molitor）为研究对象，旨在解答这一研究空白。本研究的人格得分基于四项可重复行为性状构成的多维综合征进行估算。
在第一项实验中，我们探究了行为综合征与两项适合度指标（繁殖与存活）以及三项先天免疫（innate immunity）组分（血细胞浓度、酚氧化酶活性水平——包含总酶原与天然活化型酶）之间的关联，以此检验黄粉虫中的POLS假说。整体而言，我们在该物种中发现了行为综合征与繁殖成功之间的关联，从而支持了POLS假说；此外，我们还揭示了行为综合征与基础免疫参数间存在性别特异性关联。
在第二项实验中，我们通过昆虫病原细菌（entomopathogenic bacteria）苏云金芽孢杆菌（Bacillus thuringiensis）侵染处理，检验了此前观察到的先天免疫关联是否可通过差异存活得到验证。本实验未发现显著关联。
我们建议未来开展POLS相关研究的学者，应控制不同性别间的演化轨迹差异，并关注所选替代指标的合理性，尤其是在研究免疫性状时。