Evolution of Social Immunity and Disease Transfer in Honey Bees

蜜蜂的一个独特的社会行为是一个群体如何在没有人类干预的情况下减轻幼虫的感染。这些行为，包括梳理和消灭受感染的幼虫，被统称为蜜蜂的卫生行为，更通常被称为社会免疫。在管理或养殖蜂群的背景下，这是一个理想的特性，可以帮助减少蜂群损失，并有可能帮助种群反弹。在拟议的工作中，我将开发群体水平和遗传模型，可以通过菌落网络跟踪卫生等位基因的传播。由于蜜蜂交配是单倍体-二倍体的特性，以及一个蜂群中唯一能繁殖的雌蜂可以与多达20只雄蜂受精的事实，确定最佳的卫生行为繁殖计划可能是复杂的。通过这样的建模，将有可能确定条件，在这些条件下，我们可以实现蜂群中卫生蜜蜂的一致比例，然后将自我可持续发展。这种分析可以用来帮助和告知表型或基因型育种计划的最佳实践。此外，所建立的模型可用于探索社会免疫与个体免疫之间关系的两种主要假设。第一个是社会群体假说，它认为群居昆虫的拥挤生活条件会增加对病原体的脆弱性，从而选择个体免疫，尽管代谢成本很高。群体回归假说认为，社会免疫会放松对个体免疫功能的选择，并在群体中维持在较低的水平。通过开发两个种群之间的竞争模型，一个表现出社会免疫力的突变体和一个由于选择压力而保持高度个体免疫力的野生型，我将能够深入了解每种假设可能更有益的条件，以及在当前条件下哪种假设可能更常见。这个模型将能够回答关于膜翅目昆虫在疾病背景下的社会性后果的基本问题。这项研究计划的长期目标是建立一个数学框架，用于研究宽松选择对物种进化的影响。培养具有较强跨学科技能的本科生是本课程不可或缺的一部分。

One unique social behaviour of honey bees is how a colony can mitigate infection of larvae without human interventions. These behaviours, which include grooming and destroying infected larvae, are collectively known as hygienic behaviours in honey bees and more generally referred to as social immunity. In the context of managed or farmed honey bee colonies, this is a desirable trait which could help minimize colony losses and potentially help populations rebound. In the proposed work, I will develop population-level and genetic models which can track the spread of hygienic alleles through a network of colonies. Due to the haploid-diploid nature of honey bee mating, as well as the fact that a queen (the only reproductive female within a colony) can be fertilized by up to 20 males, determining the best practices for breeding programs for hygienic behavior can be complex. Through such modeling it will be possible to determine the conditions in which we can realize a consistent proportion of hygienic bees within colonies that will then be self-sustainable. This analysis can then be used to aid and inform best practices for phenotypic or genotypic breeding programs. Moreover, the developed models can be used to explore the two leading hypotheses on the relationship between social immunity and individual immunity. The first is the Social Group Hypothesis which states that the crowded living conditions of social insects can increase vulnerability to pathogens and thus select for individual immunity, despite high metabolic cost. The Regressive Group Hypothesis states that social immunity will relax selection on individual immune function, and it will be maintained at much lower levels in a population. By developing a competition model between two populations, a mutant which exhibits social immunity and a wild type which maintains high individual immunity due to selection pressure, I will be able to provide insights into the conditions under which each hypothesis may be more beneficial, and which may be more common given present conditions. This model will be able to answer fundamental questions about the consequences of sociability in the Hymenoptera in the context of disease. The long-term objective of this research program is to develop a mathematical framework which can be used to study the effects of relaxed selection on the evolution of a species. The training of undergraduate students with strong interdisciplinary skills is integral to this program.