The switch to parasitism on an ecological and evolutionary scale

在生态和进化层面上向寄生的转变

• 批准号: 435245-2013
• 负责人: Luong, Lien
• 金额: $ 1.89万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2013
• 资助国家: 加拿大
• 起止时间: 2013-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=533165
• 关键词: switch; parasitism; ecological; evolutionary; scale

Pathogenic organisms that are harmless under certain conditions can suddenly become extremely harmful under different circumstances. Indeed levels of parasitism vary continuously in nature, with some species shifting along a continuum from benign to pathogenic over ecological and evolutionary time. But even more fundamental to this issue is the process by which parasitism per se evolved. Understanding the ecological and evolutionary factors that facilitate the acquisition of parasitism is important because it allows epidemiologists to more accurately predict when and where infectious diseases will emerge, and develop effective control measures. I will investigate the life-history evolution of parasites that express variation in host exploitation strategies, and identify the selective pressures that lead to the transition to a parasitic lifestyle. Facultative parasites present a unique and interesting opportunity for addressing these questions because they regularly shift from free-living to parasitic lifestyles. The facultative ectoparasitic mite, Macrocheles subbadius feeds and reproduces on highly ephemeral habitats - rotting cacti. However, mites become parasitic under certain circumstances by attaching to and feeding on cactophilic drosophilid hosts. Therefore, it appears the mites are capable of context-dependent expression of infectivity (ability to parasitize a host). The flies and mites co-occur naturally in the wild and are highly amendable to laboratory microcosm experiments. I plan to manipulate environmental conditions to test the ecological consequences of environmental heterogeneity on mite behaviour and infection (aim 1). To determine the heritability of the infectivity trait, I will perform experimental evolution by artificially selecting for mites with divergent levels of infectivity; the selected lines will be used to measure the evolutionary trade-offs between the evolution of parasitism and other key parasite life history traits (aim 2). Additionally, I will identify the ecological factors that select for increased reliance on hosts over a long period of time, i.e., the evolutionary transition to parasitism (aim 3).

在某些条件下无害的病原生物在不同情况下可能突然变得极其有害。事实上，自然界中的寄生水平不断变化，一些物种在生态和进化过程中沿着从良性到致病的连续体转变。但这个问题更根本的是寄生本身的进化过程。了解促进获得寄生性的生态和进化因素非常重要，因为它使流行病学家能够更准确地预测传染病何时何地出现，并制定有效的控制措施。我将研究表达宿主利用策略变化的寄生虫的生活史进化，并确定导致向寄生生活方式转变的选择压力。兼性寄生虫为解决这些问题提供了一个独特而有趣的机会，因为它们经常从自由生活转变为寄生生活方式。兼性外寄生螨Macrocheles subbadius以高度短暂的栖息地——腐烂的仙人掌为食并繁殖。然而，螨虫在某些情况下会通过附着在嗜果蝇宿主上并以其为食而成为寄生动物。因此，看来螨虫能够根据环境表达感染性（寄生宿主的能力）。苍蝇和螨虫在野外自然共存，并且非常适合实验室微观实验。我计划操纵环境条件来测试环境异质性对螨虫行为和感染的生态影响（目标 1）。为了确定传染性特征的遗传力，我将通过人工选择具有不同传染性水平的螨虫来进行实验进化；选定的品系将用于衡量寄生进化与其他关键寄生虫生活史特征之间的进化权衡（目标2）。此外，我将确定在很长一段时间内选择增加对宿主依赖的生态因素，即向寄生的进化过渡（目标 3）。