| 1. |
- Bererhi, Badreddine, et al.
(författare)
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Effect of MHC and inbreeding on disassortative reproduction: A data revisit, extension and inclusion of fertilization in sand lizards
- 2023
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- The harmful effects of close inbreeding have been recognized for centuries and, with the rise of Mendelian genetics, was realized to be an effect of homozygosis. This historical background led to great interest in ways to quantify inbreeding, its depression effects on the phenotype and flow-on effects on mate choice and other aspects of behavioral ecology. The mechanisms and cues used to avoid inbreeding are varied and include major histocompatibility complex (MHC) molecules and the peptides they transport as predictors of the degree of genetic relatedness. Here, we revisit and complement data from a Swedish population of sand lizards (Lacerta agilis) showing signs of inbreeding depression to assess the effects of genetic relatedness on pair formation in the wild. Parental pairs were less similar at the MHC than expected under random mating but mated at random with respect to microsatellite relatedness. MHC clustered in groups of RFLP bands but no partner preference was observed with respect to partner MHC cluster genotype. Male MHC band patterns were unrelated to their fertilization success in clutches selected for analysis on the basis of showing mixed paternity. Thus, our data suggest that MHC plays a role in pre-copulatory, but not post-copulatory partner association, suggesting that MHC is not the driver of fertilization bias and gamete recognition in sand lizards.
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| 2. |
- Bererhi, Badreddine
(författare)
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Evolutionary genetics and consequences of inbreeding in sand lizards (Lacerta agilis)
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inbreeding is a well-known phenomenon in evolutionary and conservation biology. In the 19th century, Charles Darwin demonstrated the detrimental effects of inbreeding in plants, followed by over a century of extensive research including various animal and plant taxa. The effects of consanguineous matings are particularly pronounced in fitness-determining traits, such as life-history and sexually selected traits. Accordingly, a large body of literature has developed on traits that are directly associated with fitness, such as survival and reproductive output. Sexually selected traits have however received less attention. Due to its detrimental effects on fitness, inbreeding is often associated with the evolution of inbreeding avoidance mechanisms. This logical expectation is, however, not always met, with a number of studies reporting an absence of inbreeding avoidance in populations affected by inbreeding depression. The inconsistency in reports of inbreeding avoidance among studies is likely due to a balance between the costs and benefits of inbreeding, rendering predictions exceedingly difficult. I used long-term data (collected over a decade) from a Swedish population of sand lizards (Lacerta agilis) to measure the effects of inbreeding on two key ontogenetic stages, embryonic development and first year post-hatching, survival, and a trait expressed in adult males, the intra-sexually selected green badge. The badge is developed laterally by males during the mating season, and varies in size and pigment saturation among individuals. This area of green nuptial coloration functions as a signal of fighting ability during male-male interactions, for access to females. I studied the mating pattern in the population, for signs of inbreeding avoidance. In addition, I evaluated the role of the major histocompatibility complex (MHC) as a cue of kinship. Inbreeding significantly affected hatching success, but not first year survival. Both structural and pigmentary components of the badge were affected by individual-level heterozygosity (size, pigment saturation, and brightness). Finally, no evidence of inbreeding avoidance was found, but parental pairs were more dissimilar at the MHC than expectations under random mating. Thus, parental pair similarity at the MHC does not appear to reliably reflect genome-wide similarity, in the Asketunnan population. The effects of inbreeding in natural populations are difficult to measure. Traditionally, survival and reproductive success have been used to measure inbreeding depression. However, the results of these approaches can be confounded by various factors, such as environmental heterogeneity and parental effects. Moreover, the magnitude of inbreeding depression may vary according to the considered ontogenic stage. Thus, an alternative would be to measure inbreeding depression using cellular function, which should reflect the accumulation of stress experienced by an individual over long periods of time. Telomeres offer this possibility, as their attrition rate is linked to somatic stress. Thus, one would expect inbred individuals to have short telomers, relative to less inbred conspecifics. Surprisingly, no such effect was found in the study population. The only significant effect of inbreeding on telomere length that was found is a deviation from the mean maternal heterozygosity that is associated with shorter hatchling telomeres, suggesting stabilizing selection. The final objective of the thesis was to estimate the additive genetic variance, and heritability, of badge size. The impetus for this work is the “lek paradox” theory, which predicts the erosion of additive genetic variance in fitness-determining traits, due to strong directional selection. In addition, the importance of genic capture for maintaining additive genetic variance in badge size was assessed by estimating additive genetic variance in body condition. The results of these analyses show a significant estimate of additive genetic variance in badge size, but not in body condition, which appears to be environmentally determined. This suggests that age and sex-dependent selection, combined with a complex genetic architecture that underlies multiple colour components, may explain the persistence of additive genetic variance in badge size in the sexually dichromatic sand lizard.
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| 3. |
- Bererhi, Badreddine, et al.
(författare)
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Inconsistent inbreeding effects during lizard ontogeny
- 2019
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Ingår i: Conservation Genetics. - : Springer Science and Business Media LLC. - 1566-0621 .- 1572-9737. ; 20:4, s. 865-874
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Tidskriftsartikel (refereegranskat)abstract
- Reported effects of inbreeding vary among taxa and may depend on a number of factors, including what trait is measured, temporal variability, parental effects, or life history stage. To understand the effects of inbreeding during early life history stages, we estimated the effects of individual-level heterozygosity on hatching success and first year survival in a Swedish population of sand lizards (Lacerta agilis) over a period of almost a decade, using over 4000 eggs, 400 clutches, and over 3000 juveniles. Heterozygosity had a positive effect on hatching success, in standardized laboratory conditions, but no effect on first year survival. Also, both of these measures of viability varied across the years of the study, demonstrating the importance of temporal heterogeneity in pre and post-hatching conditions. Finally, we identified both paternal and maternal identity effects on hatching success. Thus, we show that selection on heterozygosity was not consistent across developmental life stages, emphasizing the need of considering a number of ontogenic stages, as well as potential parental and environmental effects, when studying the effects of heterozygosity on viability in natural populations.
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| 4. |
- Bererhi, Badreddine, et al.
(författare)
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Limited effects of inbreeding on breeding coloration
- 2023
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Ingår i: Journal of Heredity. - : Oxford University Press (OUP). - 0022-1503 .- 1465-7333. ; 114:2, s. 143-151
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Tidskriftsartikel (refereegranskat)abstract
- Animal color signals may function as indicators of fighting ability when males compete for access to females. This allows opponents to settle aggressive interactions before they escalate into physical combat and injury. Thus, there may be strong directional selection on these traits, toward enhanced signal quality. This renders sexually selected traits particularly susceptible to inbreeding depression, due to relatively low ratios of additive genetic variance to dominance variance. We measured the effects of inbreeding on an intrasexually selected color signal (the badge) in a population of Swedish sand lizards (Lacerta agilis) using the Rhh software based on 17 to 21 microsatellites. Males of this sexually dichromatic species use the badge during aggressive interactions to display, and assess, fighting ability. We found negative effects of homozygosity on badge size, saturation, and brightness. However, no such effects were observed on color hue. Pairwise correlations between badge size, hue, and saturation were all statistically significant. Thus, the sand lizard "badge" is a multicomponent signal with variation explained by covariation in badge size, saturation, and color hue. Body mass corrected for skeletal size (body condition) positively predicted badge size and saturation, encouraging future research on the extent that sexual signals may convey information on multigene targets (i.e. "genic capture").
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| 5. |
- Lindsay, Willow, 1980, et al.
(författare)
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Endless forms of sexual selection
- 2019
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Ingår i: PeerJ. - : PeerJ. - 2167-8359. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a "stock-taking'' workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the 'aesthetic sense' proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate 'null model' of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress.
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| 6. |
- Lindsay, Willow, 1980, et al.
(författare)
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Quantitative genetics of breeding coloration in sand lizards; genic capture unlikely to maintain additive genetic variance
- 2023
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 0018-067X .- 1365-2540.
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Tidskriftsartikel (refereegranskat)abstract
- Sexual selection on fitness-determining traits should theoretically erode genetic variance and lead to low heritability. However, many sexually selected traits maintain significant phenotypic and additive genetic variance, with explanations for this "lek paradox" including genic capture due to condition-dependence, and breaks on directional selection due to environmental sources of variance including maternal effects. Here we investigate genetic and environmental sources of variance in the intrasexually selected green badge of the sand lizard (Lacerta agilis). The badge functions as a cue to male fighting ability in this species, and male-male interactions determine mate acquisition. Using animal models on a pedigree including three generations of males measured over an extensive 9-year field study, we partition phenotypic variance in both badge size and body condition into additive genetic, maternal, and permanent environmental effects experienced by an individual over its lifespan. Heritability of badge size was 0.33 with a significant estimate of underlying additive genetic variance. Body condition was strongly environmentally determined in this species and did not show either significant additive genetic variance or heritability. Neither badge size nor body condition was responsive to maternal effects. We propose that the lack of additive genetic variance and heritability of body condition makes it unlikely that genic capture mechanisms maintain additive genetic variance for badge size. That said, genic capture was originally proposed for male traits under female choice, not agonistic selection. If developmental pathways generating variance in body condition, and/or the covarying secondary sex trait, differ between inter- and intrasexual selection, or the rate at which their additive genetic variance or covariance is depleted, future work may show whether genic capture is largely restricted to intersexual selection processes.
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| 7. |
- Lindsay, Willow R, et al.
(författare)
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Endless forms of sexual selection
- 2024
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The field of sexual selection has burgeoned with research into trait evolution in the context of ecology, sociality, phylogeny, natural selection, and sexual conflict. This paper is the product of a “stock-taking” workshop; our aim is to stimulate discussion, not to provide an exhaustive review. We identify outstanding questions organized into four thematic sections.1) Evolution of mate choice and mating systems. Variation in mate quality can generate mating competition and choice in either sex with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems. Specifically, polyandry evolves in response to the strength of pre- vs. post-copulatory selection. The evolution of polyandry may be related to diversity of pathogens and Major Histocompatibility Complex (MHC) genes. MHC genes are also potential cues of kinship in avoidance of inbreeding. The balance between inbreeding avoidance and inclusive fitness in mating decisions deserves greater attention.2) Sender and receiver mechanisms shaping signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are a challenge to measure. The neuroethology of sensory and cognitive receiver biases is the main key to signal form and the ‘aesthetic sense’ proposed by Darwin. Since a receiver bias is sufficient to both start and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate ‘null model’ of sexual selection.3) Genetic architecture of sexual selection. Despite advances in modern molecular techniques, the number and identity of genes underlying performance remain largely unknown. A combination of genomic techniques and long-term field studies that reveal ecological correlates of reproductive success is warranted. In-depth investigations into the genetic basis of sexual dimorphism will reveal constraints and trajectories of sexually selected trait evolution.4) Sexual selection and conflict as drivers of speciation. Population divergence and speciation is often driven by an interplay between sexual and natural selection. To what extent sexual selection promotes or counteracts population divergence may differ depending on the genetic architecture of traits as well as covariance between mating competition and local adaptation, if traits have multiple functions and if sensory systems used in mate choice are locally adapted. Also, post-copulatory processes, e.g. selection against heterospecific sperm, may influence the importance of sexual selection. Sexual conflict can shape speciation processes, since mate choice selection on females can restrict gene flow whereas selection on males is permissive.We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection.
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| 8. |
- Näslund, Joacim, 1985, et al.
(författare)
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Design of Emergence Test Arenas Can Affect the Results of Boldness Assays
- 2015
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Ingår i: Ethology. - : Wiley. - 0179-1613. ; 121:6, s. 556-565
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate whether and how arena design of emergence tests (a commonly used boldness assay where the latency to emerge from a start box is measured) can affect the behaviour of the subject animals. We used two populations of wild brown trout fry, captured on their hatching grounds, and measured emergence latency in arenas with two different sizes of start-box gates and two different environments into which the fish emerges from the start box (barren and complex), in a factorial design. We found that arena design affected the behaviour of the fish, but only in one of the populations. In the affected population, a large start-box gate in combination with a barren environment reduced emergence latency. Furthermore, the time from leaving the box until entering another compartment on the opposite side of the arena was shorter in a barren environment as compared to a more complex environment. We also found that smaller brown trout fry generally showed lower tendency for emerging from the start box at all. The results of this study suggest that direct comparisons among results from experiments using different arena designs may be problematic and highlight the importance of reporting details of arena design in publications. BOTT JC, 1989, BEHAVIOUR, V108, P104
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| 9. |
- Olsson, Mats, 1960, et al.
(författare)
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Inbreeding effects on telomeres in hatchling sand lizards (Lacerta agilis): An optimal family affair?
- 2022
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 31:24, s. 6605-16
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Tidskriftsartikel (refereegranskat)abstract
- Telomeres are nucleotide-protein caps, predominantly at the ends of Metazoan linear chromosomes, showing complex dynamics with regard to their lengthening and shortening through life. Their complexity has entertained the idea that net telomere length and attrition could be valuable biomarkers of phenotypic and genetic quality of their bearer. Intuitively, those individuals could be more heterozygous and, hence, less inbred. However, some inbred taxa have longer, not shorter, telomeres. To understand the role of inbreeding in this complex scenario we need large samples across a range of genotypes with known maternity and paternity in telomere-screened organisms under natural conditions. We assessed the effects of parental and hatchling inbreeding on telomere length in >1300 offspring from >500 sires and dams in a population of sand lizards (Lacerta agilis). Maternal and paternal ID and their interactions predict hatchling telomere length at substantial effect sizes (R-2 > .50). Deviation from mean maternal heterozygosity statistically predicts shorter offspring telomeres but this only when sibship is controlled for by paternal ID, and then is still limited (R-2 = .06). Raw maternal heterozygosity scores, ignoring absolute deviation from the mean, explained 0.07% of the variance in hatchling telomere length. In conclusion, inbreeding is not a driver of telomere dynamics in the sand lizard (Lacerta agilis) study system.
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