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，黑腿蜱的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，而大多数莱姆病报告来自东北部和中西部北部。在过去的三年里，实地研究表明，蜱虫的分布和疾病之间的不匹配，部分是由于幼年蜱虫的行为存在令人惊讶的差异。在北方，寻找血餐的仙女经常从落叶堆中出现，爬上一根方便的树枝，等待路过的老鼠或鸟。这让路过的人处于危险之中，因为若虫可以附着在袜子、裙子或暴露的脚踝上，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，因为它们呆在落叶堆里，所以很少有机会附着在路过的人类身上。这种行为似乎是由基因决定的，南方蜱虫继续表现得像南方蜱虫，即使它们是在北方长大的。但是，如果南北蜱相互繁殖（其他研究人员已经证明这是可能的），它们的后代会如何表现呢？这项研究的目的是通过从不同的父母组合中抚养若虫来回答这个问题，这些父母的寻找宿主行为要么相同，要么不同。这些杂交后代的行为将被观察，以了解如果南北蜱虫开始在野外混合将会产生的预期结果。这个研究问题很重要，因为北方蜱虫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。在之前的研究中，研究人员利用了田间反向易位实验，发现来自其活动范围北部和南部的若虫寻找寄主行为的差异有重要的遗传基础。总的来说，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的两个数量级差异。这个奖项现在允许研究人员解决他们之前工作提出的一个关键问题：一旦南北蜱虫种群聚集和杂交，将会表现出什么样的探索行为？这些寻找寄主的特征将以何种方式进化？pi将在两个北方种群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场地产生的后代的寻主行为。这项研究的目的是预测在北方蜱虫种群入侵到目前由南方种群占据的州后，南方的莱姆病风险将如何变化。此外，该项目解决了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等经典问题。

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.