| 1. |
- Ahnesjö, Ingrid, et al.
(författare)
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Considering gender‑biased assumptions in evolutionary biology
- 2020
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Ingår i: Evolutionary biology. - : Springer Nature. - 0071-3260 .- 1934-2845. ; 47, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- Many organisms studied by evolutionary biologists have different sexes, and the evolution of separate sexes and sexual dimorphisms in morphology and behaviour are central questions in evolutionary biology. Considering scientists to be embedded in a social and cultural context, we are also subjected to the risk of gender-biased assumptions and stereotypical thinking to appear when working on topics related to sexual reproduction and sexual dimorphism. Here we present, for continued discussion, a set of good-practice guidelines aimed at (1) helping to improve researchers’ awareness of gender-biased assumptions underlying language use, generalizations, and interpretation of observations; and (2) providing recommendations to increase transparency, avoid problematic terminology, and improve study designs.
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| 2. |
- Cortazar-Chinarro, Maria, et al.
(författare)
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Major Histocompatibility Complex Variation and Haplotype Associated Survival in Response to Experimental Infection of Two Bd-GPL Strains Along a Latitudinal Gradient
- 2022
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media S.A.. - 2296-701X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- While both innate and adaptive immune system mechanisms have been implicated in resistance against the chytrid fungus Batrachochytrium dendrobatidis (Bd), studies on the role of specific MHC haplotypes on Bd infection are rare. Here, we studied variation in MHC Class IIB loci in the common toad Bufo bufo along a latitudinal gradient across Sweden. In general, Swedish toad populations had few MHC Class IIB haplotypes and MHC diversity declined from south (13 haplotypes) to the north (four haplotypes). The low diversity may compromise the ability of northern populations to fight emerging disease, such as Bd. In a laboratory experiment, we infected newly metamorphosed toads with two strains of the Global Pandemic Lineage of the fungus (Bd-GPL) and compared survival with sham controls. Bd-infected toads had lower survival compared to controls. Moreover, survival was dependent on the Bd-strain and northern toads had lower Bd-mediated survival than southern individuals. MHC diversity was lower in northern toads. All northern experimental animals were monomorphic for a single MHC haplotype, whereas we found seven different haplotypes in southern experimental animals. In southern toads, survival was dependent on both Bd-strain and MHC haplotype suggesting differential infection dynamics depending on both Bd-strain and host immune system characteristics.
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| 3. |
- Meurling, Sara, et al.
(författare)
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Body size mediates latitudinal population differences in response to Bd infection in two amphibian species
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The chytrid fungus Batrachochytrium dendrobatidis (Bd), is a generalist pathogen which has caused amphibian population declines worldwide. In many species Bd infection causes the disease chytridiomycosis, leading to high mortality. However, infection may cause sub-lethal fitness effects even in species that are resistant or tolerant to Bd. Moreover, populations of the same species may differ in their sensitivity to Bd, but the factors behind this variation are poorly understood. Here we exposed two common North European amphibians (moor frog Rana arvalis, common toad Bufo bufo) from two latitudinally divergent regions to two different BdGPL strains in a laboratory experiment. We found that Bd exposure lowered survival in both species, but this effect was much stronger in B. bufo. Moreover, survival was lower in the northern region in both species, this difference again being much stronger in B. bufo. Northern individuals were smaller in both species and the survival difference between regions was size mediated with smaller individuals being more sensitive to Bd. We discuss potential additional factors contributing to this result. Bd exposure also led to sub-lethal effects in terms of reduced growth in both species suggesting that even individuals surviving the infection may have reduced fitness mediated by reduction if body size. However, we did not detect any differences in amphibian responses to the two Bd strains.
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| 4. |
- Meurling, Sara, et al.
(författare)
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Body size mediates latitudinal population differences in the response to chytrid fungus infection in two amphibians
- 2024
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Ingår i: Oecologia. - 0029-8549 .- 1432-1939. ; 204:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Siljestam, Mattias, 1989-, et al.
(författare)
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Anisogamy Does Not Always Promote the Evolution of Mating Competition Traits in Males
- 2024
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 203:2, s. 230-253
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Tidskriftsartikel (refereegranskat)abstract
- Anisogamy has evolved in most sexually reproducing multicellular organisms allowing the definition of the male and female sexes, producing small and large gametes. Anisogamy, as the initial sexual dimorphism, is a good starting point to understand the evolution of further sexual dimorphisms. For instance, it is generally accepted that anisogamy sets the stage for more intense mating competition in males than in females. We argue that this idea stems from a restrictive assumption on the conditions under which anisogamy evolved in the first place: the absence of sperm limitation (assuming that all female gametes are fertilized). Here, we relax this assumption and present a model that considers the coevolution of gamete size with a mating competition trait, starting in a population without dimorphism. We vary gamete density to produce different scenarios of gamete limitation. We show that, while at high gamete density the evolution of anisogamy always results in male investment in competition, gamete limitation at intermediate gamete densities allows for either females or males to invest more into mating competition. Our results thus suggest that anisogamy does not always promote mating competition among males. The conditions under which anisogamy evolves matter, as well as the competition trait.
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| 6. |
- Siljestam, Mattias, 1989-, et al.
(författare)
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Genetic Polymorphism – A Result of LocalAdaptation or Heterozygote Advantage?
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Stable coexistence of different self-reproducing entities requires negative frequency dependence, such that each type has an advantage when rare. In community ecology, the entities of interest are species or morphs, and negative frequency dependence arises from competition for limiting factors. In this scenario, coexistence is generally interpreted as a result of local adaptation or niche differentiation. In diploid organisms, different alleles in a specific locus can coexist if heterozygote individuals have an advantage over homozygotes. Here, at the allelic level, negative frequency dependence arises because rare alleles tend to occur in a coalition with alleles different from themselves. A classical example are MHC genes where a heterozygote advantage arises if different alleles offer protection against different sets of pathogens. Coexistence of this type can be interpreted as facilitation or division of labour. Here, we study evolution of MHC alleles in a species occurring in two habitats with different pathogen communities. Our aim is to illustrate that both types of frequency-dependent selection can drive the evolution and maintenance of allelic polymorphism, with local adaptation dominating when migration between habitats is rare and MHC alleles have close to additive effects on survival, and facilitation dominating when migration occurs frequently and alleles that offer better protection against a given pathogen community have a more than additive effect on survival.
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| 7. |
- Siljestam, Mattias, 1989-, et al.
(författare)
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Heterozygote Advantage Can Explain the Extraordinary Diversity of Immune Genes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The majority of highly polymorphic genes are related to immune functions and with over 100 alleles within a population, genes of the major histocompatibility complex (MHC) are the most polymorphic loci in vertebrates. How such extraordinary polymorphism arose and is maintained is controversial. One possibility is heterozygote advantage (HA), which can in principle maintain any number of alleles, but biologically explicit models based on this mechanism have so far failed to reliably predict the coexistence of significantly more than ten alleles. We here present an eco-evolutionary model showing that under HA evolution can result in the emergence and maintenance of more than 100 alleles if the following two assumptions are fulfilled: first, pathogens are lethal in the absence of an appropriate immune defence; second, the combined effect of multiple pathogens on host survival exceeds the sum of the effects of each pathogen alone. Thus, our results show that HA can be a more potent force in explaining the extraordinary polymorphism found at MHC loci than currently recognized.
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| 8. |
- Siljestam, Mattias, 1989-
(författare)
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Mathematical Solutions to Divergent Evolution
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diversity is ubiquitous in nature and manifests through various forms of divergent evolution. Using mathematical models that consider the interplay between ecology and evolution, I explore mechanisms driving two types of such divergence: the emergence of genetic diversity in diploid organisms, and the initial sexual dimorphism of anisogamy.Genetic diversity is typically studied as a consequence of competition or local adaptation. However, diploidy introduces an alternative mechanism: heterozygote advantage (HA), where alleles provide complementary functionalities. A classical example is the immune genes of the Major Histocompatibility Complex (MHC), where alleles can protect against complementary sets of pathogens. HA can emerge if individuals encounter multiple pathogens. When pathogens are distributed over habitats, divergence can be driven by local adaptation, or an emerging HA if migration is high. Alternatively, if MHC alleles provide full defence as a single copy (adaptive context-specific dominance), HA can also emerge under low migration. I challenge the view that HA alone cannot explain the high polymorphism observed at MHC loci by demonstrating that over 100 alleles can be maintained based on two critical assumptions: pathogens can be lethal if not properly countered by an immune response, and the combined effect of multiple pathogens can exceed the sum of their individual impacts.For loci under sexually antagonistic selection, divergent evolution can facilitate the coexistence of alleles, each producing a homozygote genotype with an optimal phenotype in one sex while the heterozygote exhibits an intermediate maladapted phenotype. However, I show that sex-specific dominance is expected to evolve, resulting in a marginal HA across the sexes: a heterozygote carrying alleles optimal for each sex exhibits an optimal phenotype in both sexes, whereas the corresponding homozygotes are maladapted in one sex. This leads to further divergence and the coexistence of many alleles, for wide parameter ranges.Additionally, I challenge the traditional view that male-biased competition for mating is an inevitable consequence of anisogamy---the evolutionary differentiation in gamete size between the sexes. I present the first theoretical description of the coevolution of anisogamy and mating competition, demonstrating that anisogamy does not inherently favour male competition. Instead, the specific evolutionary conditions and the nature of the competition trait significantly influence which sex invests more in mating competition.This thesis not only enhances our understanding of the underlying drivers of genetic and phenotypic diversity but also challenges longstanding evolutionary paradigms, shedding light on the complex dynamics that shape life’s vast diversity.
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| 9. |
- Siljestam, Mattias, 1989-, et al.
(författare)
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Sex-specific Dominance and Its Effects on Allelic Diversity in Sexually Antagonistic Loci
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Sexually antagonistic (SA) selection, favouring different alleles in males and females, can contribute to the maintenance of genetic diversity. While current theory predicts that biallelic polymorphism can be maintained in SA loci, particularly with strong selection or sex-specific dominance, some candidate SA loci harbour more than two segregating alleles. This highlights a gap in our understanding of the origin and maintenance of SA genetic variation. We present a mathematical model to explore the evolution of alleles at either an autosomal or an X-linked locus under SA selection, affecting a quantitative trait with distinct female and male optima. We find that polyallelic polymorphism can evolve under conditions of sex-specific or X-linked dominance for the trait, particularly under weak selection, such that several alleles coexist in a single population through balancing selection. We show that additive allelic effects predict only biallelic polymorphism, and only under symmetric and relatively strong selection. However, our analysis also shows that sex-specific dominance (and X-linked dominance) evolves when permitted, which promotes the evolution of polyallelic polymorphism and reduces the gender load. We conclude that SA selection can drive the co-evolution of sex-specific dominance and polyallelic polymorphism, particularly under weak selection. To assess these findings, we analyse segregating variation in three populations of a seed beetle model system and find support for our predictions: (i) candidate SA loci show a relatively strong signal of polyallelic polymorphism and (ii) loci with the strongest signal of polyallelic polymorphism are enriched with genes associated with known SA phenotypes.
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| 10. |
- Siljestam, Mattias, et al.
(författare)
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The combined effects of temporal autocorrelation and the costs of plasticity on the evolution of plasticity
- 2017
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 30:7, s. 1361-1371
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Tidskriftsartikel (refereegranskat)abstract
- Adaptive phenotypic plasticity is an important source of intraspecific variation, and for many plastic traits, the costs or factors limiting plasticity seem cryptic. However, there are several different factors that may constrain the evolution of plasticity, but few models have considered costs and limiting factors simultaneously. Here we use a simulation model to investigate how the optimal level of plasticity in a population depends on a fixed maintenance fitness cost for plasticity or an incremental fitness cost for producing a plastic response in combination with environmental unpredictability (environmental fluctuation speed) limiting plasticity. Our model identifies two mechanisms that act, almost separately, to constrain the evolution of plasticity: (i) the fitness cost of plasticity scaled by the nonplastic environmental tolerance, and (ii) the environmental fluctuation speed scaled by the rate of phenotypic change. That is, the evolution of plasticity is constrained by the high cost of plasticity in combination with high tolerance for environmental variation, or fast environmental changes in combination with slow plastic response. Qualitatively similar results are found when maintenance and incremental fitness costs of plasticity are incorporated, although a larger degree of plasticity is selected for with an incremental cost. Our model highlights that it is important to consider direct fitness costs and phenotypic limitations in relation to nonplastic environmental tolerance and environmental fluctuations, respectively, to understand what constrains the evolution of phenotypic plasticity.
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