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- Meurling, Sara, 1977-
(författare)
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The response in native wildlife to an invading pathogen: Swedish amphibians and Batrachochytrium dendrobatidis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Reimer, Olof, 1959-
(författare)
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Predator-induced phenotypic plasticity in the marine mussel Mytilus edulis
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I investigated whether the risk of predation can induce development of defensive traits in the blue mussel Mytilus edulis, a common species of the temperate seashores. I performed a series of field and laboratory experiments in which I exposed blue mussels to waterborne scents from its main predators, the starfish Asterias rubens, and the shore crab Carcinus maenas.I found that predator scents can elicit a variety of responses in the mussels. In the short term the exposure caused activity reduction (decreased respiration, excretion, and shell-gaping rate). This behaviour probably serves to reduce the risk of detection by predators. Predator scents affected other behaviours as well, such that the exposed mussels aggregated more and strengthened their byssal attachment. To be aggregated and firmly attached is likely beneficial when attacked by predators. Furthermore, I found that the growth pattern changed in starfish-exposed mussels, within a few weeks. They grew less in outer size, but became more compact and strong, with relatively larger adductor muscle and thicker shell. In practical tests I found that the induced mussels survived significantly better, when attacked by starfish. I also discovered that predator-exposed mussels increased their gonad ratio, which suggests that they increased the reproductive output. To put more effort on reproduction and try to "escape as gametes" may serve as an "ultimate defence", that is effective even when mussels have small chances to survive the predator attacks.All these inducible changes seem to be beneficial in situations when the predation risk increases. Inducible defences are not unique for blue mussels. In the recent decades, the evidence has grown, that predator-inducible plasticity is geographically and taxonomically widespread, both in freshwater and marine habitats. Inducible defences may evolve in environments with variable predation pressure. The prey benefits by developing the defences only when the predation risk is large, and disabling the defences and avoiding the costs when predators are absent, thereby increasing the competitive ability. In a comparative experiment with the related tropical mussel Perna viridis I did not detect any inducible morphological defences. In contrast to tropical environments, the temperate seashores are typically very dynamic, with harsh and variable conditions, leading to continuous changes in the biotic assemblages, and variable predation pressure. The organisms living here will likely benefit by being phenotypically plastic and adaptable.
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| 3. |
- Råberg, Sonja, 1972-
(författare)
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Trophic effects on the maintenance of biodiversity in the Fucus zone
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ecologically important macroalgae with large thalli and complex structures are threatened worldwide due to anthropogenic activities such as pollution. In the northern Baltic Sea the salinity is very low; the only large algae producing complex structural habitats found there are the fucoid species Fucus radicans and F. vesiculosus. This thesis investigates the importance of these two species for the diversity of the faunal communities living in algal vegetation. The trophic effects of high nutrient supply and grazers on the survival, facilitation, and diversity of F. vesiculosus were also studied. Fucoid vegetation generally harboured a higher biomass and different composition of associated fauna m–2 than did vegetation types without fucoids. Through the occurrence of Pilayella littoralis, high nutrient supply had indirect negative effects on early stages of F. vesiculosus survival; these effects were exerted by both the presence of and exudates from P. littoralis. Another indirect effect of high nutrient supply was higher epiphytic load, but this did not have any impact on the growth of F. vesiculosus. Instead, grazers had a positive effect by reducing the biomass of fouling epiphytes, though the identity of the grazer species was crucial in this. Furthermore, when investigating the effect of grazers on the epiphyte biomass it became evident that only the presence of two species with complementary feeding habits effectively prevented overgrowth. The biodiversity of the epiphytes was affected by both nutrient level and grazing pressure, which indicates that the effect of grazers on algal diversity depends on resource supply. This thesis demonstrates that fucoids are important for hard bottom fauna, and that F. vesiculosus (particularly at early life stages, and to a lesser extent as adults) is sensitive to high nutrient loads. Furthermore, it was evident that specific species of grazers, i.e., Theodoxus fluviatilis, were able to facilitate the growth of this alga.
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