Populations respond to novel environmental challenges either through genetic changes, through ada... more Populations respond to novel environmental challenges either through genetic changes, through adaptive phenotypic plasticity for the traits in question, or by a combination of these factors. Here, we investigated the evolutionary potential of phenotypic plasticity for male mating success, locomotory ability, and heating rate (a physiological performance trait) in the fruitflyDrosophila melanogaster, using isogenic male lines from the Drosophila Reference Genome Panel (DGRP) and hemi-clonal males. We quantified thermal reaction norms of how male mating success changed in relation to a temperate gradient, ranging from cold (18 °C) via optimal (24 °C) to hot and stressful environments (either 30 °C or 36 °C). We found significant differences in male mating success and locomotory performance between different lines, as well as significant main effects of temperature, but no significant genotype-by-environment interactions (GEI:s). A statistical power analysis revealed that the variance ...
Organisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular... more Organisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular adaptations to thermoregulate during hot and cold conditions. However, our knowledge of selection for thermoregulation and the potential for evolutionary responses is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we use thermal imaging to quantify selection and genetic variation in thermoregulation in ostriches (Struthio camelus), the world’s largest bird species that is experiencing increasingly volatile temperatures. We found that females who are better at regulating their head temperatures (“thermoregulatory capacity”) had higher egg-laying rates under hotter conditions. Thermoregulatory capacity was both heritable and showed signatures of local adaptation: females originating from more unpredictable climates were better at regulating their head temperatures in response to temperature fluctuations. Together these results reveal that pas...
Assortative mating is of interest because of its role in speciation and the maintenance of specie... more Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within-species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male-male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.
The importance of genetic and environmental variation in condition in shaping evolutionary trade-... more The importance of genetic and environmental variation in condition in shaping evolutionary trade-offs have recently been subject to much theoretical discussion, but is very difficult to investigate empirically in most field-based systems. We present the results from mechanistic experimental manipulations of reproductive investment and condition in two female colour morphs ('orange' and 'yellow') of side-blotched lizards (Uta stansburiana). We investigated the interactions between throat colour morphs, condition, local social environment and female survival using path-analysis. Using folliceablation experiments, we show that large clutch size has a negative effect on field survival among yellow females, and that this effect is partly mediated by immunosuppressive effects of large clutches. In orange females these effects were less pronounced, and there was a negative survival effect of strong antibody responses. Hence, we experimentally confirmed our previous findings of correlational selection between female morphotype and immunocompetence, an important condition trait. Manipulation of corticosterone revealed multiple ('pleiotropic') direct and indirect effects of this hormone on both condition and reproductive traits. We argue that interaction effects (e.g. between local environments and genotypes) could explain a substantial fraction of variation in condition and reproduction in natural populations. Increased attention to such interaction effects and their fitness consequences will provide novel insights in field studies of selection and reproductive allocation.
Fifteen polymorphic markers were developed from a microsatellite-enriched library for the lizard ... more Fifteen polymorphic markers were developed from a microsatellite-enriched library for the lizard Podarcis gaigeae. The loci were checked for variability in 68 individuals from a population on the island of Skyros, Greece. The number of alleles ranged from 3 to 23 per locus and expected heterozygosity from 0.29 and 0.94. Most markers were also polymorphic in three closely related Podarcis species, namely P. erhardi, P. taurica and P. milensis. The markers will be used to examine gene flow and differentiation of island and mainland populations of P. gaigeae.
Proceedings of the National Academy of Sciences of the United States of America, Oct 9, 2001
Density-dependent territorial interactions have been suggested to cause immunosuppression and the... more Density-dependent territorial interactions have been suggested to cause immunosuppression and thereby decrease fitness, but empirical support from natural populations is lacking. Data from a natural lizard population (Uta stansburiana) showed that breeding females surrounded by many territorial neighbors had suppressed immune function. Furthermore, variation in immunological condition had different effects on the fitness of the two heritable female throat-color morphs in this population. These interactive fitness effects caused correlational selection between female throat color and immune responsiveness. Population genetic theory predicts that this should have lead to the buildup and preservation of a genetic correlation between female morphotype and immunological condition. Accordingly, the throat color of a female was genetically correlated (rA ؍ ؊1.36; SE ؍ 0.55) with her daughter's immune responsiveness.
Global temperatures are increasing rapidly affecting species globally. Understanding if and how d... more Global temperatures are increasing rapidly affecting species globally. Understanding if and how different species can adapt fast enough to keep up with increasing temperatures is of vital importance. One mechanism that can accelerate adaptation and promote evolutionary rescue is sexual selection. Two different mechanisms by which sexual selection can facilitate adaptation are pre- and postcopulatory sexual selection. However, the relative effects of these different forms of sexual selection in promoting adaptation are unknown. Here, we present the results from an experimental study in which we exposed fruit flies Drosophila melanogaster to either no mate choice or 1 of 2 different sexual selection regimes (pre- and postcopulatory sexual selection) for 6 generations, under different thermal regimes. Populations showed evidence of thermal adaptation under precopulatory sexual selection, but this effect was not detected in the postcopulatory sexual selection and the no choice mating re...
The evolution of sex chromosomes, and patterns of sex-biased gene expression and dosage compensat... more The evolution of sex chromosomes, and patterns of sex-biased gene expression and dosage compensation, are poorly known among early winged insects such as odonates. We assembled and annotated the genome of Ischnura elegans (blue-tailed damselfly), which, like other odonates, has a male-hemigametic sex-determining system (X0 males, XX females). By identifying X-linked genes in I. elegans and their orthologs in other insect genomes, we found homologies between the X chromosome in odonates and chromosomes of other orders, including the X chromosome in Coleoptera. Next, we showed balanced expression of X-linked genes between sexes in adult I. elegans, i.e. evidence of dosage compensation. Finally, among the genes in the sex-determining pathway only fruitless was found to be X-linked, while only doublesex showed sex-biased expression. This study reveals partly conserved sex chromosome synteny and independent evolution of dosage compensation among insect orders separated by several hundred million years of evolutionary history.
Temperature has a crucial influence on the places where species can survive and reproduce. Past r... more Temperature has a crucial influence on the places where species can survive and reproduce. Past research has primarily focused on survival, making it unclear if temperature fluctuations constrain reproductive success, and if so whether populations harbour the potential to respond to climatic shifts. Here, using two decades of data from a large experimental breeding programme of the iconic ostrich (Struthio camelus) in South Africa, we show that the number of eggs females laid and the number of sperm males produced were highly sensitive to natural temperature extremes (ranging from −5 °C to 45 °C). This resulted in reductions in reproductive success of up to 44% with 5 °C deviations from their thermal optimum. In contrast, gamete quality was largely unaffected by temperature. Extreme temperatures also did not expose trade-offs between gametic traits. Instead, some females appeared to invest more in reproducing at high temperatures, which may facilitate responses to climate change. Th...
The comment by Myers-Smith and Myers focuses on three main points: (i) the lack of a mechanistic ... more The comment by Myers-Smith and Myers focuses on three main points: (i) the lack of a mechanistic explanation for climate-selection relationships, (ii) the appropriateness of the climate data used in our analysis, and (iii) our focus on estimating climate-selection relationships across (rather than within) taxonomic groups. We address these critiques in our response.
Populations respond to novel environmental challenges either through genetic changes, through ada... more Populations respond to novel environmental challenges either through genetic changes, through adaptive phenotypic plasticity for the traits in question, or by a combination of these factors. Here, we investigated the evolutionary potential of phenotypic plasticity for male mating success, locomotory ability, and heating rate (a physiological performance trait) in the fruitflyDrosophila melanogaster, using isogenic male lines from the Drosophila Reference Genome Panel (DGRP) and hemi-clonal males. We quantified thermal reaction norms of how male mating success changed in relation to a temperate gradient, ranging from cold (18 °C) via optimal (24 °C) to hot and stressful environments (either 30 °C or 36 °C). We found significant differences in male mating success and locomotory performance between different lines, as well as significant main effects of temperature, but no significant genotype-by-environment interactions (GEI:s). A statistical power analysis revealed that the variance ...
Organisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular... more Organisms inhabiting extreme thermal environments, such as desert birds, have evolved spectacular adaptations to thermoregulate during hot and cold conditions. However, our knowledge of selection for thermoregulation and the potential for evolutionary responses is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we use thermal imaging to quantify selection and genetic variation in thermoregulation in ostriches (Struthio camelus), the world’s largest bird species that is experiencing increasingly volatile temperatures. We found that females who are better at regulating their head temperatures (“thermoregulatory capacity”) had higher egg-laying rates under hotter conditions. Thermoregulatory capacity was both heritable and showed signatures of local adaptation: females originating from more unpredictable climates were better at regulating their head temperatures in response to temperature fluctuations. Together these results reveal that pas...
Assortative mating is of interest because of its role in speciation and the maintenance of specie... more Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within-species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male-male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.
The importance of genetic and environmental variation in condition in shaping evolutionary trade-... more The importance of genetic and environmental variation in condition in shaping evolutionary trade-offs have recently been subject to much theoretical discussion, but is very difficult to investigate empirically in most field-based systems. We present the results from mechanistic experimental manipulations of reproductive investment and condition in two female colour morphs ('orange' and 'yellow') of side-blotched lizards (Uta stansburiana). We investigated the interactions between throat colour morphs, condition, local social environment and female survival using path-analysis. Using folliceablation experiments, we show that large clutch size has a negative effect on field survival among yellow females, and that this effect is partly mediated by immunosuppressive effects of large clutches. In orange females these effects were less pronounced, and there was a negative survival effect of strong antibody responses. Hence, we experimentally confirmed our previous findings of correlational selection between female morphotype and immunocompetence, an important condition trait. Manipulation of corticosterone revealed multiple ('pleiotropic') direct and indirect effects of this hormone on both condition and reproductive traits. We argue that interaction effects (e.g. between local environments and genotypes) could explain a substantial fraction of variation in condition and reproduction in natural populations. Increased attention to such interaction effects and their fitness consequences will provide novel insights in field studies of selection and reproductive allocation.
Fifteen polymorphic markers were developed from a microsatellite-enriched library for the lizard ... more Fifteen polymorphic markers were developed from a microsatellite-enriched library for the lizard Podarcis gaigeae. The loci were checked for variability in 68 individuals from a population on the island of Skyros, Greece. The number of alleles ranged from 3 to 23 per locus and expected heterozygosity from 0.29 and 0.94. Most markers were also polymorphic in three closely related Podarcis species, namely P. erhardi, P. taurica and P. milensis. The markers will be used to examine gene flow and differentiation of island and mainland populations of P. gaigeae.
Proceedings of the National Academy of Sciences of the United States of America, Oct 9, 2001
Density-dependent territorial interactions have been suggested to cause immunosuppression and the... more Density-dependent territorial interactions have been suggested to cause immunosuppression and thereby decrease fitness, but empirical support from natural populations is lacking. Data from a natural lizard population (Uta stansburiana) showed that breeding females surrounded by many territorial neighbors had suppressed immune function. Furthermore, variation in immunological condition had different effects on the fitness of the two heritable female throat-color morphs in this population. These interactive fitness effects caused correlational selection between female throat color and immune responsiveness. Population genetic theory predicts that this should have lead to the buildup and preservation of a genetic correlation between female morphotype and immunological condition. Accordingly, the throat color of a female was genetically correlated (rA ؍ ؊1.36; SE ؍ 0.55) with her daughter's immune responsiveness.
Global temperatures are increasing rapidly affecting species globally. Understanding if and how d... more Global temperatures are increasing rapidly affecting species globally. Understanding if and how different species can adapt fast enough to keep up with increasing temperatures is of vital importance. One mechanism that can accelerate adaptation and promote evolutionary rescue is sexual selection. Two different mechanisms by which sexual selection can facilitate adaptation are pre- and postcopulatory sexual selection. However, the relative effects of these different forms of sexual selection in promoting adaptation are unknown. Here, we present the results from an experimental study in which we exposed fruit flies Drosophila melanogaster to either no mate choice or 1 of 2 different sexual selection regimes (pre- and postcopulatory sexual selection) for 6 generations, under different thermal regimes. Populations showed evidence of thermal adaptation under precopulatory sexual selection, but this effect was not detected in the postcopulatory sexual selection and the no choice mating re...
The evolution of sex chromosomes, and patterns of sex-biased gene expression and dosage compensat... more The evolution of sex chromosomes, and patterns of sex-biased gene expression and dosage compensation, are poorly known among early winged insects such as odonates. We assembled and annotated the genome of Ischnura elegans (blue-tailed damselfly), which, like other odonates, has a male-hemigametic sex-determining system (X0 males, XX females). By identifying X-linked genes in I. elegans and their orthologs in other insect genomes, we found homologies between the X chromosome in odonates and chromosomes of other orders, including the X chromosome in Coleoptera. Next, we showed balanced expression of X-linked genes between sexes in adult I. elegans, i.e. evidence of dosage compensation. Finally, among the genes in the sex-determining pathway only fruitless was found to be X-linked, while only doublesex showed sex-biased expression. This study reveals partly conserved sex chromosome synteny and independent evolution of dosage compensation among insect orders separated by several hundred million years of evolutionary history.
Temperature has a crucial influence on the places where species can survive and reproduce. Past r... more Temperature has a crucial influence on the places where species can survive and reproduce. Past research has primarily focused on survival, making it unclear if temperature fluctuations constrain reproductive success, and if so whether populations harbour the potential to respond to climatic shifts. Here, using two decades of data from a large experimental breeding programme of the iconic ostrich (Struthio camelus) in South Africa, we show that the number of eggs females laid and the number of sperm males produced were highly sensitive to natural temperature extremes (ranging from −5 °C to 45 °C). This resulted in reductions in reproductive success of up to 44% with 5 °C deviations from their thermal optimum. In contrast, gamete quality was largely unaffected by temperature. Extreme temperatures also did not expose trade-offs between gametic traits. Instead, some females appeared to invest more in reproducing at high temperatures, which may facilitate responses to climate change. Th...
The comment by Myers-Smith and Myers focuses on three main points: (i) the lack of a mechanistic ... more The comment by Myers-Smith and Myers focuses on three main points: (i) the lack of a mechanistic explanation for climate-selection relationships, (ii) the appropriateness of the climate data used in our analysis, and (iii) our focus on estimating climate-selection relationships across (rather than within) taxonomic groups. We address these critiques in our response.
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Papers by Erik Svensson