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Habitat attributes are known to influence infectious diseases such as those caused by parasites, but most studies have only considered single host and (or) parasite taxa, making it difficult to assess which features may be of general importance and to predict how alterations could affect disease dynamics. We examined infection with trematode (flatworm) parasites in two commonly co-occurring host taxa (larval amphibians and larval odonates (dragonflies and damselflies)) to investigate links with landscape-level features, including agricultural activity. We also assessed pond community composition with respect to the abundance and richness of aquatic arthropods known to prey upon tadpoles and (or) free-swimming trematode infectious stages. Larval amphibians from agricultural sites were most likely to be parasitized but had lower infection intensities, and infected hosts were positively associated with increasing distance to the nearest forest habitat, but negatively with road distance. The opposite was observed for larval odonate infection status; however, probability and intensity of parasitism in both host taxa was negatively associated with greater predatory arthropod abundance, consistent with the 'dilution effect' of biodiversity on infectious diseases. Our approach demonstrates the importance of considering multiple host taxa when studying habitat links to diseases, and future studies incorporating even greater diversity will be needed. [ABSTRACT FROM AUTHOR]

Climate warming affects ectotherms globally, yet we know little regarding the variability in species' responses to warming, particularly in early life stages. Additionally, intraspecific variation in response to warming is understudied but may determine species' resilience to warming. To assess how temperature affects egg development rate in co-occurring dragonfly species, we manipulated temperature (range: 22-31 °C) and measured time to hatching. Warming decreased egg development time across all species, indicating that while climate warming will advance hatching phenology, maintained synchrony in hatching order will likely not affect species interactions. Our second experiment examined early life-history responses to warming in the dot-tailed whiteface ( Leucorrhinia intacta (Hagen, 1861)) dragonfly. We measured time to hatching, hatchling size, growth rate, and survival at four temperatures (23-30 °C), including a treatment with increased thermal variation. Warming resulted in smaller hatchlings with increased growth and mortality rates, whereas higher thermal variation did not have effects different from those of warming alone. We observed significant intraspecific variation in the responses to warming in both egg development time and hatchling size and this variation was correlated with date of oviposition. High levels of intraspecific variation may be important in buffering populations from the effects of climate warming. [ABSTRACT FROM AUTHOR]

Theoretical models predict that parasites reduce reproductive success of their hosts, but very few empirical studies have given support to this. Using the spearhead bluet ( Coenagrion hastulatum (Charpentier, 1825)) damselfly, we tested how immune response, wing length, and the number of both endo- and ecto-parasites affect egg production of host damselflies. The study was conducted with four different populations in southwest Finland. We found a negative association between endoparasitic gregarines and number of host eggs. Furthermore, immune response increased with the number of water mites, but decreased with the number of eggs. Contrary to previous studies with other damselfly species, the number of ectoparasitic water mites did not affect the number of eggs. Moreover, wing length, used as an indicator of individual size, was not associated with egg numbers. The negative effect of gregarine parasites on egg numbers is likely to affect the composition of host populations, i.e., damselflies that show higher resistance to these endoparasites will have more of their offspring represented in subsequent generations. In future, more experimental research on the varying effects of different parasite species on the number of eggs is needed. [ABSTRACT FROM AUTHOR]

Increasing evidence indicates that parasites play an important role within many systems as prey for higher trophic levels. Predation on parasites can decrease their numbers and may affect host infection rates. Cercariae, a free-living infectious stage of trematode parasites, are abundant in freshwater systems and are directly consumed by a number of freshwater predators. However, few studies have tested whether predators exhibit a preference for cercariae when alternative prey are available or how these preferences vary across predator body sizes. We assessed whether dragonfly larvae (dot-tailed whiteface, Leucorrhinia intacta (Hagen, 1861)), top predators in freshwater systems without fish, foraged preferentially when presented with two prey types, cercariae and zooplankton, and whether foraging preferences changed across predator body size. Body size of larval dragonfly predators was found to be significantly, and negatively, related to the fraction of cercariae in the diet. Larger bodied dragonfly larvae shifted their diet choice from cercariae to zooplankton. Changes in foraging selectivity as body size increases across a predator's ontogeny can alter the strength of predator-prey interactions. Further investigation into size-selective foraging on parasites may provide new insights into the effects of predation on parasite abundance and transmission in natural systems. [ABSTRACT FROM AUTHOR]

Certain parasite species have free-living stages, so habitat range may influence host-species range. We tested whether regional occurrence and habitat use of parasitic water mites were related to their host-species range. We collected 7445 Arrenurus Dugès, 1834 mites from 7107 coenagrionid damselflies, representing 11 host species from 13 sites in southeastern Ontario and southwestern Quebec. Because larval water mites are difficult to identify morphologically to species, we chose to amplify the barcode fragment of cytochrome oxidase subunit I to explore host-species ranges. Fifteen operational taxonomic units or clades were identified based on the amplification from 217 larval mites. The Arrenurus clades that were present in both bog and marsh habitats had a broader host-species range than clades found only in marshes (the comparison with one clade found only in bogs lacked statistical power). As predicted, host-species range increased with the regional occurrence of an Arrenurus clade. Additionally, the most commonly barcoded species also have high host-species ranges. This result could be because species with broader host-species ranges are more common and were more likely to be sampled and barcoded (an explanation we favor), or due to sampling bias. Although this is the first study exploring whether habitat range affects host-species range, further investigation is needed to tease apart which habitat factors influence host-species ranges the most. [ABSTRACT FROM AUTHOR]