Garrido Mario, Adler Valeria Hochman, Pnini Meital, Abramsky Zvika, Krasnov Boris R, Gutman Roee, Kronfeld-Schor Noga, Hawlena Hadas
Mitrani Department of Desert Ecology, Swiss Institute for Dryland Environmental and Energy Research, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel.
Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Parasit Vectors. 2016 Mar 1;9:120. doi: 10.1186/s13071-016-1407-7.
The study of changes in a host's energy allocation in response to parasites is crucial for understanding parasite impact on both individual- and population-level processes. Experimental studies have explored such responses mainly in a single subsample of hosts per study, primarily adult males, and have only assessed either the overall energy acquisition or expenditure, rather than their different components simultaneously, or the behavioral responses. Accordingly, two fundamental questions arise: why have multiple host strategies evolved to cope with increased energy expenditure? and, which factors determine this variation (e.g. host species, identity, age)? This study provides an important step towards addressing both questions by experimentally disentangling the short-term physiological and behavioral responses of juvenile and non-reproductive adult rodents to natural levels of flea infestation. These two cohorts represent extreme cases of the energy demand continuum, as the former, in contrast to the latter, is involved in growth--a highly energy-demanding process--and may not be able to operate far below its upper limit of energy expenditure, and thus should reduce its energy expenses upon the occurrence of extra demands (e.g. due to parasitic pressure). Accordingly, we hypothesized that the response to fleas is age-dependent and varies according to the age-specific energy requirements and constraints.
We monitored the behavior and physiology of juvenile and non-reproductive adult rodents before and after experimental flea infestation. First, we used a model selection approach to search for the factors that best explained the variability in the time budget, oxygen consumption, and body mass change in response to fleas. Then, using a path analysis approach, we quantified the different pathways connecting the important associations revealed at stage 1.
Compared to their flea-free counterparts, flea-infested adults groomed longer and had a higher oxygen consumption rate, but did not lose body mass. Infested juveniles also groomed longer but grew slower and had a similar rate of oxygen consumption.
Results suggest that both juvenile and adult rodents suffer from natural flea infestation levels. However, the comparison between the responses of juveniles and adults to experimental infestation, also suggests that juveniles may reallocate their energy expenditure from growth to maintenance, while non-reproductive adults increase their energy acquisition. Such age-dependent responses suggest that juveniles may be constrained by their higher need to rest for full functioning or by an upper limit in energy expenditure. Taken together, our study provides experimental evidence that hosts can compensate for the costs incurred by parasitism through physiological and behavioral plasticity, depending on their age, which probably determines their requirements and constraints. These compensatory responses may have important implications for the population dynamics of hosts and their parasites.
研究宿主能量分配如何响应寄生虫对于理解寄生虫对个体和种群水平过程的影响至关重要。实验研究主要在每项研究的单个宿主子样本中探索这种响应，主要是成年雄性，并且仅评估了整体能量获取或消耗，而不是同时评估其不同组成部分，也没有评估行为响应。因此，出现了两个基本问题：为什么会进化出多种宿主策略来应对增加的能量消耗？以及，哪些因素决定了这种变化（例如宿主物种、个体、年龄）？本研究朝着解决这两个问题迈出了重要一步，通过实验性地解开幼年和非繁殖成年啮齿动物对自然跳蚤感染水平的短期生理和行为响应。这两个群体代表了能量需求连续体的极端情况，因为前者与后者不同，参与生长——一个高度耗能的过程——并且可能无法在远低于其能量消耗上限的水平下运作，因此在出现额外需求（例如由于寄生虫压力）时应该减少其能量消耗。因此，我们假设对跳蚤的反应是年龄依赖性的，并且根据特定年龄的能量需求和限制而变化。
我们监测了实验性跳蚤感染前后幼年和非繁殖成年啮齿动物的行为和生理。首先，我们使用模型选择方法来寻找最能解释时间分配、氧气消耗和体重变化对跳蚤响应变异性的因素。然后，使用路径分析方法，我们量化了连接在第一阶段揭示的重要关联的不同途径。
与未感染跳蚤的同类相比，感染跳蚤的成年动物梳理毛发的时间更长，氧气消耗率更高，但体重没有减轻。感染跳蚤的幼年动物梳理毛发的时间也更长，但生长较慢，氧气消耗率相似。
结果表明，幼年和成年啮齿动物都会受到自然跳蚤感染水平的影响。然而，幼年和成年动物对实验性感染的反应比较也表明，幼年动物可能会将其能量消耗从生长重新分配到维持，而非繁殖成年动物则会增加其能量获取。这种年龄依赖性反应表明，幼年动物可能受到其为充分发挥功能而对休息的更高需求或能量消耗上限的限制。总之，我们的研究提供了实验证据，表明宿主可以根据年龄通过生理和行为可塑性来补偿寄生所产生的成本，这可能决定了它们的需求和限制。这些补偿反应可能对宿主及其寄生虫的种群动态产生重要影响。
