Civitello David J, Penczykowski Rachel M, Smith Aimee N, Shocket Marta S, Duffy Meghan A, Hall Spencer R
Department of Biology, Indiana University, Bloomington, IN, 47405, USA.
School of Biology, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
J Anim Ecol. 2015 Jul;84(4):1010-7. doi: 10.1111/1365-2656.12363. Epub 2015 Mar 21.
Parasites can profoundly affect host populations and ecological communities. Thus, it remains critical to identify mechanisms that drive variation in epidemics. Resource availability can drive epidemics via traits of hosts and parasites that govern disease spread. Here, we map resource-trait-epidemic connections to explain variation in fungal outbreaks (Metschnikowia bicuspidata) in a zooplankton host (Daphnia dentifera) among lakes. We predicted epidemics would grow larger in lakes with more phytoplankton via three energetic mechanisms. First, resources should stimulate Daphnia reproduction, potentially elevating host density. Secondly, resources should boost body size of hosts, enhancing exposure to environmentally distributed propagules through size-dependent feeding. Thirdly, resources should fuel parasite reproduction within hosts. To test these predictions, we sampled 12 natural epidemics and tracked edible algae, fungal infection prevalence, body size, fecundity and density of hosts, as well as within-host parasite loads. Epidemics grew larger in lakes with more algal resources. Structural equation modelling revealed that resource availability stimulated all three traits (host fecundity, host size and parasite load). However, only parasite load connected resources to epidemic size. Epidemics grew larger in more dense Daphnia populations, but host density was unrelated to host fecundity (thus breaking its link to resources). Thus, via energetic mechanisms, resource availability can stimulate key trait(s) governing epidemics in nature. A synthetic focus on resources and resource-trait links could yield powerful insights into epidemics.
寄生虫会对宿主种群和生态群落产生深远影响。因此，识别驱动流行病变异的机制仍然至关重要。资源可用性可通过控制疾病传播的宿主和寄生虫特征来驱动流行病。在这里，我们绘制资源-特征-流行病的联系，以解释浮游动物宿主（齿状水蚤）中真菌爆发（双尖梅奇酵母）在不同湖泊间的变异。我们预测，通过三种能量机制，在浮游植物较多的湖泊中流行病会更严重。首先，资源应刺激水蚤繁殖，可能提高宿主密度。其次，资源应增加宿主的体型，通过依赖体型的摄食增加对环境中传播体的接触。第三，资源应为宿主体内的寄生虫繁殖提供能量。为了验证这些预测，我们对12次自然流行病进行了采样，并追踪了可食用藻类、真菌感染率、宿主的体型、繁殖力和密度，以及宿主体内寄生虫负荷。在藻类资源较多的湖泊中，流行病更为严重。结构方程模型显示，资源可用性刺激了所有三个特征（宿主繁殖力、宿主体型和寄生虫负荷）。然而，只有寄生虫负荷将资源与流行病规模联系起来。在水蚤种群密度更高的情况下，流行病更为严重，但宿主密度与宿主繁殖力无关（因此打破了其与资源的联系）。因此，通过能量机制，资源可用性可以刺激自然界中控制流行病的关键特征。对资源和资源-特征联系的综合关注可以为流行病提供有力的见解。
