More Hosts, More Problems: Factors Related to the Distribution and Abundance of the Four-Host Trematode Parasite Alaria spp. in Amphibians in the San Francisco Bay Area of California, USA

摘要

A flatworm genus, Alaria spp., is a poorly understood parasite found in an aquatic system well suited to study the distribution, effects, and implications of infectious diseases. This North American parasite infects multiple hosts, including snails, amphibians, and mammals, to complete its life cycle. Using a survey of 67 ponds in Northern California, four aspects of Alaria spp. infection in amphibian hosts were studied: (1) natural occurrence, (2) effects of host biology, (3) spatial distribution, and (4) environmental determinants of occurrence. A thorough review of past reports of Alaria spp. as well as analysis involving t-tests, linear models, generalized linear models, and Moran’s I were carried out. The present study identifies Anaxyrus boreas, the Western toad, as a novel host of Alaria spp. As for frequency, Alaria spp. was only found at 27% of sites and only in 25.5% amphibians (range: 5% to 72% hosts per site) and the average abundance across hosts was 1.21 parasites per frog (0.02 to 5.33). There was no significant difference in Alaria spp. infection between Pseudacris regilla and A. boreas as well as between sexes of hosts. Host body size was significantly correlated with Alaria spp. infection. Alaria spp. infection in amphibian hosts was randomly spatially distributed in the study system. Finally, no variable was significantly correlated for presence of Alaria spp., but vegetated surface area, pond surface area, and pH were significant predictors of average Alaria spp. abundance. The negative correlation of vegetated surface area and pH with abundance is not well supported or understood. Experimental investigation of mechanisms and further surveys of Alaria spp. across years and geographical regions are necessary to fully understand the ecology of Alaria spp.