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- Sagvik, Jörgen, 1972, et al.
(author)
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A genetic component of resistance to fungal infection in frog embryos.
- 2008
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In: Proceedings. Biological sciences / The Royal Society. - : The Royal Society. - 0962-8452. ; 275:1641, s. 1393-6
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Journal article (peer-reviewed)abstract
- The embryo has traditionally been considered to completely rely upon parental strategies to prevent threats to survival posed by predators and pathogens, such as fungi. However, recent evidence suggests that embryos may have hitherto neglected abilities to counter pathogens. Using artificial fertilization, we show that among-family variation in the number of Saprolegnia-infected eggs and embryos in the moor frog, Rana arvalis, cannot be explained by maternal effects. However, analysed as a within-females effect, sire identity had an effect on the degree of infection. Furthermore, relatively more eggs and embryos were infected when eggs were fertilized by sperm from the same, compared with a different, population. These effects were independent of variation in fertilization success. Thus, there is likely to be a significant genetic component in embryonic resistance to fungal infection in frog embryos. Early developmental stages may show more diverse defences against pathogens than has previously been acknowledged.
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| 2. |
- Sagvik, Jörgen, 1972
(author)
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Ecological genetics of inbreeding, outbreeding and immunocompetence in Ranid frogs
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Using artificial fertilization, I crossed frogs from different populations to evaluate fitness consequences for the offspring from an inbreeding-outbreeding perspective, and to evaluate quantitative genetic effects on immunocompetence against a fungal pathogen (Saprolegnia). Crosses between closely situated populations of different sizes generated contrasting results for the effects of outbreeding on offspring traits between populations and life history stages, emphasizing the importance of epistatic effects and the difficulties of relying on generalizations when making conservation decisions (e.g., regarding translocations). Experimental infection of frog eggs from six populations with Saprolegnia fungus showed a significant family effect on the degree of infection of eggs and embryos, in particular at lower fertilization success and with a significant temperature ? population interaction effect. A paternal genetic effect on fungus resistance was found using a half-sib split design. Furthermore, relatively more eggs were infected when fertilized by sperm from the same, in contrast with a different population. However, there was no evidence for a stronger effect in isolated island populations. Although the mechanistic underpinnings remain unknown, these results suggest substantial levels of genetic variation in resistance to Saprolegnia in natural populations within and among populations. We also found that pre-hatching exposure to Saprolegnia dramatically reduced the size at metamorphosis in the absence of further exposure to the fungus, possible as a delayed effect of impaired embryonic development. However, in contrast to some other amphibians, induced hatching in response to Saprolegnia could not be confirmed. In conclusion, the results suggest that frog populations are genetically diverse even at small geographic scale with frequently strong and unpredictable consequences of in- and outbreeding for the response to stressors.
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| 3. |
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| 4. |
- Sagvik, Jörgen, 1972, et al.
(author)
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Intraspecific variation in resistance of frog eggs to fungal infection
- 2007
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In: Evolutionary Ecology. - : Springer Science and Business Media LLC. - 1573-8477 .- 0269-7653. ; Online
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Journal article (peer-reviewed)abstract
- Documenting sources of variation in host viability at pathogen exposure within and among populations is an important task in order to predict host-pathogen evolutionary dynamics. In the present study, we investigated family and population variation in the degree of embryonic infection of the pathogenic fungus Saprolegnia spp., by infecting moor frog (Rana arvalis) eggs from six populations and exposing them to two different temperatures. We found a significant family effect on the degree of Saprolegnia-infection of eggs and embryos, suggesting that there is genetic variation in resistance among embryos, or variation among females in some aspect of maternally induced resistance. Furthermore, infection level differed significantly between temperatures, with most families having more infected eggs in the relatively colder temperature. However, eggs and embryos from the different populations showed different degrees of Saprolegnia-infection in the two temperatures, i.e., there was a significant population × temperature interaction on the proportion of infected eggs. Thus, the degree of Saprolegnia-infection is sensitive to variation at the level of the family, population and environmental conditions, suggesting that responses to fungal outbreaks will vary geographically and will be difficult to predict.
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| 5. |
- Sagvik, Jörgen, 1972, et al.
(author)
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Outbreeding depression in the common frog, Rana temporaria
- 2005
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In: Conservation Genetics. - : Springer Science and Business Media LLC. - 1566-0621 .- 1572-9737. ; 6:2, s. 205-211
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Journal article (peer-reviewed)abstract
- Theory suggests that parental relatedness is a continuous variable with a fitness optimum that we heretoforth will refer to as 'optimal outbreeding. In the present paper, we test this proposition from a conservation (translocation) perspective. Amphibians are facing a global decline and many amphibian populations are today small and threatened by extinction. Because genetic differentiation is often high between amphibian populations, they could be particularly sensitive to outbreeding depression, e.g. due to breakdown of locally adapted gene complexes. We tested if outbreeding would reduce fitness in common frogs, Rana temporaria, crossed from a large and an isolated, small population, separated by 130 km, using artificial fertilization. For females from the large population, tadpoles were significantly smaller and more malformed in crosses with males from the small population, than with males from the large population. For the small population, however, no significant paternal genetic effects could be found. The difference in response to outbreeding between populations was accompanied with significant differences in the importance of maternal effects. We conclude that care should be taken when translocating frogs between distantly related populations to avoid outbreeding depression.
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| 6. |
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| 7. |
- Sherman, Craig D. H., et al.
(author)
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Female Choice for Males with Greater Fertilization Success in the Swedish Moor Frog, Rana arvalis
- 2010
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In: PLOS ONE. - 1932-6203. ; 5:10
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Journal article (peer-reviewed)abstract
- Background Studies of mate choice in anuran amphibians have shown female preference for a wide range of male traits despite females gaining no direct resources from males (i.e. non-resource based mating system). Nevertheless, theoretical and empirical studies have shown that females may still gain indirect genetic benefits from choosing males of higher genetic quality and thereby increase their reproductive success. Methodology/Principal Findings We investigated two components of sexual selection in the Moor frog (Rana arvalis), pre-copulatory female choice between two males of different size (‘large’ vs. ‘small’), and their fertilization success in sperm competition and in isolation. Females' showed no significant preference for male size (13 small and six large male preferences) but associated preferentially with the male that subsequently was the most successful at fertilizing her eggs in isolation. Siring success of males in competitive fertilizations was unrelated to genetic similarity with the female and we detected no effect of sperm viability on fertilization success. There was, however, a strong positive association between a male's innate fertilization ability with a female and his siring success in sperm competition. We also detected a strong negative effect of a male's thumb length on his competitive siring success. Conclusions/Significance Our results show that females show no preference for male size but are still able to choose males which have greater fertilization success. Genetic similarity and differences in the proportion of viable sperm within a males ejaculate do not appear to affect siring success. These results could be explained through pre- and/or postcopulatory choice for genetic benefits and suggest that females are able to perceive the genetic quality of males, possibly basing their choice on multiple phenotypic male traits.
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| 8. |
- Uller, Tobias, 1977, et al.
(author)
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Crosses between frog populations reveal genetic divergence in larval life history at short geographic distance
- 2006
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In: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066. ; 89:1, s. 189-195
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Journal article (peer-reviewed)abstract
- A number of studies have documented interpopulation divergence in amphibian larval life-history traits across latitudes. Because many frogs are philopatric and have a patchy habitat distribution, genetic divergence could also exist on a much smaller geographical scale, revealed by recent estimates of population divergence using molecular markers. Whether this divergence is reflected in phenotypic traits is virtually unknown. Using artificial fertilization, individuals of the common frog, Rana temporaria, were crossed from two populations situated 130 km apart and differing in population size. The pattern of size at metamorphosis showed evidence of non-additive effects, as demonstrated by a significant interaction between male and female population of origin. Outbreeding resulted in an increase in metamorph size when eggs from the small population were fertilized with sperm from the large population. In the reciprocal cross, however, the pattern was in the opposite direction, with no significant effect of male population of origin. Genetic divergence of populations separated by a relatively short geographical distance may be more common in frogs than previously acknowledged, with potential implications for conservation of declining amphibian species.
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