In insects, basal pathogen resistance and immune priming can evolve as mutually exclusive strategies, with distinct infection outcomes. However, the evolutionary drivers of such diverse immune functions remain poorly understood. Here, we addressed this key issue by systematically analyzing the differential fitness costs and benefits of priming vs resistance evolution in Tribolium beetle populations infected with Bacillus thuringiensis. Surprisingly, resistant beetles had increased post-infection reproduction and a longer lifespan under both starving as well as fed conditions, with no other measurable costs. In contrast, priming reduced offspring early survival, development rate and reproduction. Priming did improve post-infection survival of offspring, but this added trans-generational benefit of immune priming might not compensate for its pervasive costs. Resistance was thus consistently more beneficial. Overall, our work demonstrates the evolutionary change in trans-generational priming response, and provides a detailed comparison of the complex fitness consequences of evolved priming vs resistance.

在昆虫中，基础病原体抗性和免疫启动可以演变为相互排斥的策略，具有不同的感染结果。然而，这种多样化免疫功能的进化驱动因素仍然知之甚少。在这里，我们通过系统分析感染苏云金芽孢杆菌的Tribolium甲虫种群的启动与抗性进化的差异适应性成本和收益来解决这个关键问题. 令人惊讶的是，抗性甲虫在饥饿和进食条件下都增加了感染后的繁殖和更长的寿命，而没有其他可衡量的成本。相比之下，引发减少了后代的早期存活、发育速度和繁殖。启动确实提高了后代的感染后存活率，但免疫启动的这种增加的跨代利益可能无法弥补其普遍的成本。因此，抵抗总是更有益。总体而言，我们的工作展示了跨代启动反应的进化变化，并详细比较了进化启动与抗性的复杂适应性后果。