Body size mediates latitudinal population differences in the response to chytrid fungus infection in two amphibians.

Factors behind intraspecific variation in sensitivity to pathogens remain poorly understood. We investigated how geographical origin in two North European amphibians affects tolerance to infection by the chytrid fungus Batrachochytrium dendrobatidis (Bd), a generalist pathogen which has caused amphibian population declines worldwide. We exposed newly metamorphosed individuals of moor frog Rana arvalis and common toad Bufo bufo from two latitudinal regions to two different BdGPL strains. We measured survival and growth as infections may cause sub-lethal effects in fitness components even in the absence of mortality. Infection loads were higher in B. bufo than in R. arvalis, and smaller individuals had generally higher infection loads. B. bufo had high mortality in response to Bd infection, whereas there was little mortality in R. arvalis. Bd-mediated mortality was size-dependent and high-latitude individuals were smaller leading to high mortality in the northern B. bufo. Bd exposure led to sub-lethal effects in terms of reduced growth suggesting that individuals surviving the infection may have reduced fitness mediated by smaller body size. In both host species, the Swedish Bd strain caused stronger sublethal effects than the British strain. We suggest that high-latitude populations can be more vulnerable to chytrids than those from lower latitudes and discuss the possible mechanisms how body size and host geographical origin contribute to the present results.

Wetland productivity determines trade-off between biodiversity support and greenhouse gas production.

Establishing wetlands for nutrient capture and biodiversity support may introduce trade-offs between environmentally beneficial functions and detrimental greenhouse gas emissions. Investigating the interaction of nutrient capture, primary production, greenhouse gas production and biodiversity support is imperative to understanding the overall function of wetlands and determining possible beneficial synergistic effects and trade-offs. Here, we present temporally replicated data from 17 wetlands in hemi-boreal Sweden. We explored the relationship between nutrient load, primary producing algae, production of methane and nitrous oxide, and emergence rates of chironomids to determine what factors affected each and how they related to each other. Chironomid emergence rates correlated positively with methane production and negatively with nitrous oxide production, where water temperature was the main driving factor. Increasing nutrient loads reduced methanogenesis through elevated nitrogen concentrations, while simultaneously enhancing nitrous oxide production. Nutrient loads only indirectly increased chironomid emergence rates through increased chlorophyll-a concentration, via increased phosphorus concentrations, with certain taxa and food preference functional groups benefitting from increased chlorophyll-a concentrations. However, water temperature seemed to be the main driving factor for chironomid emergence rates, community composition and diversity, as well as for greenhouse gas production. These findings increase our understanding of the governing relationships between biodiversity support and greenhouse gas production, and should inform future management when constructing wetlands.

Species composition of shoreline wolf spider communities vary with salinity, but their diets vary with wrack inflow.

Wolf spiders are typically the most common group of arthropod predators on both lake and marine shorelines because of the high prey availability in these habitats. However, shores are also harsh environments due to flooding and, in proximity to marine waters, to toxic salinity levels. Here, we describe the spider community, prey availabilities, and spider diets between shoreline sites with different salinities, albeit with comparatively small differences (5‰ vs. 7‰). Despite the small environmental differences, spider communities between lower and higher saline sites showed an almost complete species turnover. At the same time, differences in prey availability or spider gut contents did not match changes in spider species composition but rather changed with habitat characteristics within a region, where spiders collected at sites with thick wrack beds had a different diet than sites with little wrack. These data suggest that shifts in spider communities are due to habitat characteristics other than prey availabilities, and the most likely candidate restricting species in high salinity would be saline sensitivity. At the same time, species absence from low-saline habitats remains unresolved.

Occurrence of Batrachochytrium dendrobatidis in Sweden: higher infection prevalence in southern species.

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in amphibian populations. While Bd is widespread in southern and central Europe, its occurrence and distribution in northernmost Europe is mostly unknown. We surveyed for Bd in breeding anurans in Sweden by sampling 1917 amphibians from 101 localities and 3 regions in Sweden (southern, northern and central). We found that Bd was widespread in southern and central Sweden, occurring in all 9 investigated species and in 45.5% of the 101 localities with an overall prevalence of 13.8%. No infected individuals were found in the 4 northern sites sampled. The records from central Sweden represent the northernmost records of Bd in Europe. While the proportion of sites positive for Bd was similar between the southern and central regions, prevalence was much higher in the southern region. This was because southern species with a distribution mainly restricted to southernmost Sweden had a higher prevalence than widespread generalist species. The nationally red-listed green toad Bufotes variabilis and the fire-bellied toad Bombina bombina had the highest prevalence (61.4 and 48.9%, respectively). Across species, Bd prevalence was strongly positively, correlated with water temperature at the start of egg laying. However, no individuals showing visual signs of chytridiomycosis were found in the field. These results indicate that Bd is widespread and common in southern and central Sweden with southern species, breeding in higher temperatures and with longer breeding periods, having higher prevalence. However, the impact of Bd on amphibian populations in northernmost Europe remains unknown.