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Occurrence of Batrachochytrium dendrobatidis in Sweden: higher infection prevalence in southern species
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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 three regions in Sweden (Southern, Northern and Central). We found that Bd was widespread in southern and central Sweden, occurring in all nine investigated species and in 45.5 % of the 101 localities with an overall prevalence of 13.8%. No infected individuals were found in the four 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 areas, prevalence was much higher in the southern area. This was due to southern species with a distribution mainly restricted to southernmost Sweden having higher prevalence than widespread generalist species. The nationally red-listed green toad Bufotes variabilis and 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.

Keywords [en]
chytrid, emerging diseases, amphibian
National Category
Ecology
Research subject
Biology with specialization in Animal Conservation
Identifiers
URN: urn:nbn:se:uu:diva-396761OAI: oai:DiVA.org:uu-396761DiVA, id: diva2:1368889
Funder
Swedish Research Council FormasAvailable from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-12
In thesis
1. The response in native wildlife to an invading pathogen: Swedish amphibians and Batrachochytrium dendrobatidis
Open this publication in new window or tab >>The response in native wildlife to an invading pathogen: Swedish amphibians and Batrachochytrium dendrobatidis
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Emerging infectious diseases are causing mortality and declines in wildlife populations globally. My thesis aims to get as clear a picture as possible of the effect the invasive chytrid fungus Batrachochytrium dendrobatidis has on the Swedish amphibian community.

In Paper I I performed a large-scale survey testing for the presence of Bd in three regions in Sweden (Southern, Central and Northern). I sampled 1917 amphibians from 101 localities and found that Bd was widespread in southern and central Sweden, occurring in all nine investigated species and in 45.5 % of the sampled sites with an overall prevalence of 13.8%. I found a positive correlation between the temperature at spawning for each species and species prevalence. Species that require higher temperatures for egg-laying are distributed in the southern parts of the country, which led to a higher prevalence in the southern region.

In Paper II, I investigated which local environmental factors in breeding habitats, landscape structure and amphibian community affect the occurrence and prevalence of Bd among breeding sites in southern Sweden. Bd prevalence in the four species with the highest prevalence (Bombina bombina, Bufotes variabilis, Epidalea calamita and Rana arvalis) was higher in ponds surrounded by less mature forest, few wetlands, and higher pH.

In Papers III and IV, I looked at species and population differences in responses to Bd infection. I performed an infection experiment described in Paper III, where I exposed individuals from two common Swedish species (moor frog R. arvalis and common toad Bufo bufo) originating from two regions (north and south) with two different strains of Bd (from Sweden and the UK). I found that infection led to lower survival and growth in both species, more so in B. bufo than in R. arvalis. Small size proved to be a strong determinant of survival. As individuals from the northern population were significantly smaller than the southern ones, this may have led to the northern populations being more affected by Bd infection. In Paper IV, I studied variation in MHC Class IIB loci in B. bufo along a latitudinal gradient across Sweden. Variation in MCH genes decreased from south to north. Also, differences in survival from the experiment in Paper III could be explained by MHC haplotypes. I found that survival in the southern region was dependent on both Bd-strain and MHC haplotype.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 44
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1879
Keywords
Emerging diseases, chytrid, amphibians, wildlife
National Category
Ecology
Research subject
Biology with specialization in Animal Conservation
Identifiers
urn:nbn:se:uu:diva-396987 (URN)978-91-513-0812-8 (ISBN)
Public defence
2019-12-13, Ekmansalen, EBC, Norbyvägen 14, Uppsala, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Available from: 2019-11-15 Created: 2019-11-12 Last updated: 2019-11-18

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Kärvemo, SimonCortazar-Chinarro, MariaHöglund, JacobLaurila, Anssi

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