College of Veterinary Medicine, University of Illinois, 2001 South Lincoln Avenue, Urbana, Illinois 61802, USA.
Ecol Appl. 2011 Jun;21(4):1257-71. doi: 10.1890/10-0374.1.
The emergence of several diseases affecting amphibian populations worldwide has prompted investigations into determinants of the occurrence and abundance of parasites in frogs. To understand the spatial scales and identify specific environmental factors that determine risks of parasitism in frogs, helminth communities in metamorphic frogs of the northern leopard frog (Rana pipiens) were examined in relation to wetland and landscape factors at local (1 km) and regional (10 km) spatial extents in an agricultural region of Minnesota (USA) using regression analyses, ordination, and variance partitioning techniques. Greater amounts of forested and woody wetland habitats, shorter distances between woody wetlands, and smaller-sized open water patches in surrounding landscapes were the most consistently positive correlates with the abundances, richness, and diversity of helminths found in the frogs. Wetland and local landscape variables were suggested as most important for larval trematode abundances, whereas local and regional landscape variables appeared most important for adult helminths. As previously reported, the sum concentration of atrazine and its metabolite desethylatrazine, was the strongest predictor of larval trematode communities. In this report, we highlight the additional influences of landscape factors. In particular, our data suggest that anthropogenic activities that have resulted in the loss of the availability and connectivity of suitable habitats in the surrounding landscapes of wetlands are associated with declines in helminth richness and abundance, but that alteration of wetland water quality through eutrophication or pesticide contamination may facilitate the transmission of certain parasite taxa when they are present at wetlands. Although additional research is needed to quantify the negative effects of parasitism on frog populations, efforts to reduce inputs of agrochemicals into wetlands to limit larval trematode infections may be warranted, given the current high rates of amphibian declines and extinction events.
几种影响全球两栖动物种群的疾病的出现促使人们调查寄生虫在青蛙中发生和丰度的决定因素。为了了解寄生虫感染风险的空间尺度，并确定决定青蛙寄生虫风险的特定环境因素，在美国明尼苏达州（美国）的一个农业地区，利用回归分析、排序和方差分解技术，在局部（1 公里）和区域（10 公里）空间范围内，检查了北方豹蛙（Rana pipiens）变态期青蛙的寄生蠕虫群落与湿地和景观因素之间的关系。森林和木质湿地栖息地的数量增加、木质湿地之间的距离缩短以及周围景观中较小的开阔水面斑块与在青蛙中发现的寄生虫的丰度、丰富度和多样性呈最一致的正相关。湿地和局部景观变量被认为对幼虫吸虫的丰度最重要，而局部和区域景观变量对成年寄生虫似乎最重要。如前所述，莠去津及其代谢物去乙基莠去津的总和浓度是幼虫吸虫群落的最强预测因子。在本报告中，我们强调了景观因素的额外影响。特别是，我们的数据表明，由于周围湿地景观中适宜栖息地的可用性和连通性丧失而导致的人为活动与寄生虫丰富度和丰度的下降有关，但湿地水质通过富营养化或农药污染的改变可能会促进某些寄生虫类群的传播，当它们存在于湿地时。尽管需要进一步研究来量化寄生虫感染对青蛙种群的负面影响，但鉴于当前两栖动物下降和灭绝事件的高发率，减少农业化学物质进入湿地以限制幼虫吸虫感染的努力可能是合理的。
