DISSERTATION RESEARCH: Understanding the eco-epidemiology of Lyme disease in the eastern United States through investigations of Blacklegged ticks host-seeking behavior

被黑腿扁虱叮咬是美国东部大多数人类莱姆病的原因。这种扁虱在整个地区都有发现，而大多数莱姆病是从东北部和中西部上段报告的。在过去的三年里，实地研究表明，硬蜱的分布与疾病之间的这种不匹配，在一定程度上是幼虫行为的惊人差异的结果。在北方，寻找鲜血食物的仙女经常从落叶中出来，爬上一根方便的树枝，等待路过的老鼠或鸟。这会将路过的人类置于危险之中，因为若虫可能会附着在袜子、裙子或裸露的脚踝上，并从那里找到咬人的地方。相比之下，南方若虫很少表现出这种攀爬行为，因为它们停留在落叶层中，因此很少有机会依附于路过的人类。这种行为似乎是由基因决定的，即使南方的硬蜱是在北方饲养的，它们的行为仍然像南方的硬蜱一样。但是，如果北方和南方的扁虱相互繁殖(其他研究人员已经证明了这是可能的)，它们的后代会有什么表现呢？这项研究旨在通过从父母的不同组合中饲养若虫来回答这个问题，这些组合在寻找宿主的行为上既有共同的，也有不同的。这些杂交后代的行为将被观察，以了解如果北方和南方的壁虱开始混杂在野外会出现什么样的后果。这一研究问题很重要，因为北极熊目前正在几个州向南扩散，包括俄亥俄州、弗吉尼亚州、伊利诺伊州和印第安纳州。这项研究的结果将对卫生保健提供者和公众有价值。在以前的工作中，PIS利用田间相互易位实验发现，来自其活动范围的北部和南部的若虫寻找寄主的不同行为有显着的遗传基础。总体而言，行为差异如此明显，似乎足以解释美国北部和东南部莱姆病发病率两个数量级的差异。这一奖项现在让研究人员解决了他们之前工作中提出的一个关键问题：一旦北方和南方的壁虱种群汇聚并杂交，会表现出什么样的探索行为？而且，这些寻找宿主的特征将以什么方式进化？PI将在两个北方和两个南方种群之间进行杂交实验，测量杂交的繁殖力，并量化产生的后代在密歇根州和田纳西州的田间竞技场寻找宿主的行为。这项研究旨在预测莱姆病风险将如何变化，在北部森林种群入侵目前由南方人口占据的州后，南方将如何变化莱姆病风险。此外，这个项目解决了关于遗传和环境在表型地理变异中的作用以及这些性状的进化能力的经典问题。

Bites from blacklegged ticks are the cause of most human Lyme disease in the eastern United States. This tick is found throughout the region, whereas most Lyme disease is reported from the Northeast and upper Midwest. Over the past three years, field studies have revealed that this mis-match between the distribution of ticks and disease is the result, in part, of a surprising difference in the behavior of juvenile nymphal ticks. In the North, nymphs looking for a blood meal often emerge from the leaf litter and climb a convenient twig to wait for a passing mouse or bird. This puts a passing human at risk because the nymph can attach to a sock or skirt or exposed ankle and from there find a place to bite. In contrast, Southern nymphs rarely exhibit this climbing behavior because they stay in the leaf litter, and so rarely have an opportunity to attach to a passing human. This behavior appears to be genetically determined, southern ticks continue to behave like southern ticks, even if they have been raised in the North. But what if northern and southern ticks breed with each other (which other researchers have shown is possible) and how will their offspring behave? This study aims to answer that question by raising nymphs from various combinations of parents that either share or differ in their host-seeking behavior. The behavior of these hybrid offspring will be observed in order to learn about the outcomes to be expected if northern and southern ticks begin to mingle in the wild. This research question is important because northern ticks are presently expanding southwards in several states, including Ohio, Virginia, Illinois, and Indiana. Results from this research will be of value to health care providers and the public. In prior work the PIs utilized a field reciprocal translocation experiment and found that there is a significant genetic basis to the differential host-seeking behavior of nymphs from the northern and southern parts of their range. Overall, the behavioral differences were so pronounced that they appear sufficient to explain the two-orders-of-magnitude difference in Lyme disease incidence between the northern and southeastern US. This award now allows the researchers to address a key question raised by their prior work: what questing behavior will be exhibited once northern and southern tick populations converge and hybridize? And, in what way will these host-seeking traits evolve? The PIs will conduct hybridization experiments between two northern and two southern populations, measure the fecundity of the crosses, and quantify host-seeking behavior of the resulting offspring in field arenas in both Michigan and Tennessee. The research aims to predict how Lyme disease risk will change in the South subsequent to invasion of northern tick populations into states currently occupied by southern populations. Furthermore, this project addresses classic questions regarding the role of genetics and environment on geographic variation of phenotypes and the ability of such traits to evolve.