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

在美国东部，被黑腿蜱叮咬是导致大多数人类莱姆病的原因。 这种蜱虫在整个地区都有发现，而大多数莱姆病的报告来自东北部和上中西部。 在过去的三年里，实地研究表明，蜱虫分布和疾病之间的这种不匹配部分是由于幼年若虫蜱虫行为的惊人差异。 在北方，寻找血餐的蝗虫经常从落叶中爬出来，爬上一根方便的树枝，等待一只路过的老鼠或鸟。 这使一个路过的人处于危险之中，因为若虫可以附着在袜子或裙子或暴露的脚踝上，并从那里找到一个地方咬人。 相比之下，南方古猿很少表现出这种攀爬行为，因为它们呆在落叶中，所以很少有机会附着在路过的人身上。这种行为似乎是由基因决定的，南方蜱继续表现得像南方蜱，即使它们在北方长大。但是，如果北方和南方的蜱虫相互繁殖（其他研究人员已经证明这是可能的），它们的后代会有什么行为呢？ 这项研究的目的是回答这个问题，从不同的父母组合，无论是共享或不同的主机寻求行为提高的负担。将观察这些杂交后代的行为，以了解如果北方和南方蜱开始在野外混合的预期结果。这个研究问题很重要，因为北方蜱目前正在几个州向南扩张，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。在先前的工作中，PI利用了田间相互易位实验，发现来自其分布区北方和南方的蝗虫的不同寄主寻找行为有显著的遗传基础。总体而言，行为差异如此明显，似乎足以解释美国北方和东南部莱姆病发病率的两个数量级差异。这个奖项现在允许研究人员解决他们先前工作中提出的一个关键问题：一旦北方和南方蜱虫种群聚集并杂交，会表现出什么样的探索行为？那么，这些寻找宿主的特征将以何种方式进化？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，并量化在密歇根州和田纳西州的田间竞技场中产生的后代的宿主寻找行为。该研究旨在预测在北方蜱虫种群入侵目前由南方种群占据的州后，莱姆病风险将如何在南方发生变化。此外，该项目还解决了关于遗传和环境对表型地理变异的作用以及这些性状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.