Parasitoid resistance in Drosophila varies considerably, among and within species. An immune resp... more Parasitoid resistance in Drosophila varies considerably, among and within species. An immune response, lamellocyte-mediated encapsulation, evolved in a subclade of Drosophila and was subsequently lost in at least one species within this subclade. While the mechanisms of resistance are fairly well documented in D. melanogaster, much less is known for closely related species. Here, we studied the inter- and intra-species variation in gene expression after parasitoid attack in Drosophila. We used RNA-seq after parasitization of four closely related Drosophila species of the melanogaster subgroup and replicated lines of D. melanogaster experimentally selected for increased resistance to gain insights into short- and long-term evolutionary changes. We found a core set of genes that are consistently up-regulated after parasitoid attack in the species and lines tested, regardless of their level of resistance. Another set of genes showed no up-regulation or expression in D. sechellia, the s...
The mass rearing of insects as animal feed is a new and rapidly growing component of circular agr... more The mass rearing of insects as animal feed is a new and rapidly growing component of circular agriculture, which offers the opportunity to develop it in such a way that it promotes insect health and welfare. Behaviour is an important indicator of animal performance and welfare. In this review, we synthesise the current behavioural knowledge on two saprophytic dipteran species that are increasingly being used as mini-livestock, the black soldier fly (Hermetia illucens) and the housefly (Musca domestica). We evaluate which behaviours need to be considered to optimise insect production and welfare under mass-rearing conditions. We distinguish between the different life stages (adults and larvae), and describe their feeding behaviour, social interactions (adult mating, larval aggregation), oviposition behaviour and possible cannibalism. For each species, we review what is known about these behaviours in natural environments, and how this is affected by abiotic factors or interactions wi...
During the last decade the potential of insects for human nutritional protein is increasingly rec... more During the last decade the potential of insects for human nutritional protein is increasingly recognised. Direct consumption of insects contributes to a reduction of the ecological footprint of human food production and is claimed to have health benefits. An alternative is feeding poultry (broilers and layers) with insect-derived protein. This offers several additional advantages, e.g. a more extensive use of (new sources) of organic by-products of food industry for insect production. Implementation of a People-Planet-Profit (PPP) sustainable way of utilising these opportunities requires the development of sustainable business models. Such business models need to be based on the opportunities of insect-derived protein in feeding poultry but should also include the risks associated with insect-derived protein for feeding poultry. This article explores the insect-fed poultry production value chain through an interdisciplinary approach. First, the essential features of this value chain...
Background: Haplodiploidy, where females develop from diploid, fertilized eggs and males from hap... more Background: Haplodiploidy, where females develop from diploid, fertilized eggs and males from haploid, unfertilized eggs, is abundant in some insect lineages. Some species in these lineages reproduce by thelytoky that is caused by infection with endosymbionts: infected females lay haploid eggs that undergo diploidization and develop into females, while males are very rare or absent. It is generally assumed that in thelytokous wasps, endosymbionts merely diploidize the unfertilized eggs, which would then trigger female development. Results: We found that females in the parasitoid wasp Asobara japonica infected with thelytoky-inducing Wolbachia produce 0.7-1.2 % male offspring. Seven to 39 % of these males are diploid, indicating that diploidization and female development can be uncoupled in A. japonica. Wolbachia titer in adults was correlated with their ploidy and sex: diploids carried much higher Wolbachia titers than haploids, and diploid females carried more Wolbachia than diploid males. Data from introgression lines indicated that the development of diploid individuals into males instead of females is not caused by malfunction-mutations in the host genome but that diploid males are most likely produced when the endosymbiont fails to activate the female sex determination pathway. Our data therefore support a two-step mechanism by which endosymbionts induce thelytoky in A. japonica: diploidization of the unfertilized egg is followed by feminization, whereby each step correlates with a threshold of endosymbiont titer during wasp development. Conclusions: Our new model of endosymbiont-induced thelytoky overthrows the view that certain sex determination mechanisms constrain the evolution of endosymbiont-induced thelytoky in hymenopteran insects. Endosymbionts can cause parthenogenesis through feminization, even in groups in which endosymbiont-diploidized eggs would develop into males following the hosts' sex determination mechanism. In addition, our model broadens our understanding of the mechanisms by which endosymbionts induce thelytoky to enhance their transmission to the next generation. Importantly, it also provides a novel window to study the yet-poorly known haplodiploid sex determination mechanisms in haplodiploid insects.
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Establishment and spread of invasive species can be facilitated by lack of natural enemies in the... more Establishment and spread of invasive species can be facilitated by lack of natural enemies in the invaded area. Host-range evolution of natural enemies augments their ability to reduce the impact of the invader and could enhance their value for biological control. We assessed the potential of the Drosophila parasitoid, Leptopilina heterotoma (Hymenoptera: Figitidae), to exploit the invasive pest Drosophila suzukii by focusing on three performance indices: (i) attack rate; (ii) host killing, consisting of killing rate and lethal attack rate (killing efficiency); and (iii) successful offspring How to cite this article: Kruitwagen A, Wertheim B, Beukeboom LW. Artificial selection for nonreproductive host killing in a native parasitoid on the invasive pest, Drosophila
Rearing insects for food and feed is a rapidly growing industry, because it provides excellent op... more Rearing insects for food and feed is a rapidly growing industry, because it provides excellent opportunities for a sustainable approach to animal protein production. Two fly species, the black soldier fly (BSF) and the house fly (HF), naturally live in decaying organic matter (e.g. compost), and can thus be effectively reared on organic rest streams from the food and agricultural industry. The adoption of these insects as mini-livestock on microbially rich substrates, however, requires us to address how we can safeguard insect health under mass-rearing conditions. In this review, we discuss what is known about the innate immunity of insects in general, especially focusing on a comparative approach to current knowledge for the two dipteran species BSF and HF. We also discuss environmental factors that may affect innate immunity in mass-rearing settings, including temperature, insect densities and diet composition. Furthermore, we address the role of the microbiome in insect health an...
Proceedings of the Royal Society B: Biological Sciences, 2012
Seminal fluid proteins (Sfps) alter female behaviour and physiology and can mediate sexual confli... more Seminal fluid proteins (Sfps) alter female behaviour and physiology and can mediate sexual conflict. In Drosophila melanogaster , a single Sfp, the sex peptide (SP), triggers remarkable post-mating responses in females, including altered fecundity, feeding, immunity and sexual receptivity. These effects can favour the evolutionary interests of males while generating costs in females. We tested the hypothesis that SP is an upstream master-regulator able to induce diverse phenotypes through efficient induction of widespread transcriptional changes in females. We profiled mRNA responses to SP in adult female abdomen (Abd) and head+thorax (HT) tissues using microarrays at 3 and 6 h following mating. SP elicited a rich, subtle signature of temporally and spatially controlled mRNAs. There were significant alterations to genes linked to egg development, early embryogenesis, immunity, nutrient sensing, behaviour and, unexpectedly, phototransduction. There was substantially more variation in...
Parasitoids are insect parasites whose larvae develop in the bodies of other insects. The main im... more Parasitoids are insect parasites whose larvae develop in the bodies of other insects. The main immune defense against parasitoids is encapsulation of the foreign body by blood cells, which subsequently often melanize. The capsule sequesters and kills the parasite. The molecular processes involved are still poorly understood, especially compared with insect humoral immunity. We explored the transcriptional response to parasitoid attack in Drosophila larvae at nine time points following parasitism, hybridizing five biologic replicates per time point to whole-genome microarrays for both parasitized and control larvae. We found significantly different expression profiles for 159 probe sets (representing genes), and we classified them into 16 clusters based on patterns of co-expression. A series of functional annotations were nonrandomly associated with different clusters, including several involving immunity and related functions. We also identified nonrandom associations of transcripti...
Many organisms experience an Allee effect: their populations do not grow optimally at low densiti... more Many organisms experience an Allee effect: their populations do not grow optimally at low densities. In addition, individuals compete with one another at high densities. The Allee effect and competition thus create a lower and an upper bound to local population size. Local populations can, however, be connected through dispersal. By using a spatio-temporal integro-difference simulation model, parameterized for Drosophila melanogaster, we explore the consequences of the Allee effect, scramble competition and dispersal for different combinations of resource distributions, initial adult distributions and densities, modes of dispersal and boundary conditions. We found that the initial distribution and density of adults determines whether a population can establish, while resource availability, the ability to reach resources and heterogeneity are mainly responsible for subsequent population persistence. In our model heterogeneity was introduced by the distribution of resources, the initial adult distribution, and the boundary conditions. Although local population dynamics are inherently unstable, overall stability can be attained by (re)colonization processes. The averaged dynamics of the total population turned out to be reasonably smooth, so apparently upper and lower local population bounds, coupled with dispersal, created an effective stable mean population density for the system as a whole. This suggests that stable mean population densities for spatial populations can be emergent properties appearing at sufficiently large scales, as opposed to inherent properties occurring at all scales. We also found, in agreement with most literature but contrary to some recent literature, that population persistence can be facilitated by a leptokurtic dispersal mode, which has higher probabilities of traveling both short and long distances, but smaller probability of traveling intermediate distances than random dispersal.
Measurement of food intake in the fruit fly Drosophila melanogaster is often necessary for studie... more Measurement of food intake in the fruit fly Drosophila melanogaster is often necessary for studies of behaviour, nutrition and drug administration. There is no reliable and agreed method for measuring food intake of flies in undisturbed, steady state, and normal culture conditions. We report such a method, based on measurement of feeding frequency by proboscisextension, validated by short-term measurements of food dye intake. We used the method to demonstrate that (a) female flies feed more frequently than males, (b) flies feed more often when housed in larger groups and (c) fly feeding varies at different times of the day. We also show that alterations in food intake are not induced by dietary restriction or by a null mutation of the fly insulin receptor substrate chico. In contrast, mutation of takeout increases food intake by increasing feeding frequency while mutation of ovo D increases food intake by increasing the volume of food consumed per proboscisextension. This approach provides a practical and reliable method for quantification of food intake in Drosophila under normal, undisturbed culture conditions.
Proceedings of the Royal Society B: Biological Sciences, 2014
In this study, we characterize changes in the genome during a swift evolutionary adaptation, by c... more In this study, we characterize changes in the genome during a swift evolutionary adaptation, by combining experimental selection with high-throughput sequencing. We imposed strong experimental selection on an ecologically relevant trait, parasitoid resistance in Drosophila melanogaster against Asobara tabida. Replicated selection lines rapidly evolved towards enhanced immunity. Larval survival after parasitization increased twofold after just five generations of selection. Whole-genome sequencing revealed that the fast and strong selection response in innate immunity produced multiple, highly localized genomic changes. We identified narrow genomic regions carrying a significant signature of selection, which were present across all chromosomes and covered in total less than 5% of the whole D. melanogaster genome. We identified segregating sites with highly significant changes in frequency between control and selection lines that fell within these narrow 'selected regions'. These segregating sites were associated with 42 genes that constitute possible targets of selection. A region on chromosome 2R was highly enriched in significant segregating sites and may be of major effect on parasitoid defence. The high genetic variability and small linkage blocks in our base population are likely responsible for allowing this complex trait to evolve without causing widespread erosive effects in the genome, even under such a fast and strong selective regime.
Clinal variation in quantitative traits is widespread, but its genetic basis awaits identificatio... more Clinal variation in quantitative traits is widespread, but its genetic basis awaits identification. Drosophila melanogaster shows adaptive, clinal variation in traits such as body size along latitudinal gradients on multiple continents. To investigate genome wide transcription differentiation between North and South that might contribute to the clinal phenotypic variation, we compared RNA expression patterns during development of D. melanogaster from tropical northern and temperate southern populations using whole genome tiling arrays. We found that genes that were differentially expressed between the cline ends were generally associated with metabolism and growth, and experimental alteration of expression of a sample of them generally resulted in altered body size in the predicted direction, sometimes significantly so. We further identified the serpent (srp) transcription factor binding sites to be enriched near genes up-regulated in expression in the south. Analysis of clinal populations revealed a significant cline in the expression level of srp. Experimental over-expression of srp increased body size, as predicted from its clinal expression pattern, suggesting that it may be involved in regulating adaptive clinal variation in Drosophila. This study identified a handful of genes that contributed to clinal phenotypic variation through altered gene expression level, yet misexpression of individual gene led to modest body size change.
. Evolutionary ecology of communication signals that induce aggregative behaviour. Á/ Oikos 109: ... more . Evolutionary ecology of communication signals that induce aggregative behaviour. Á/ Oikos 109: 117 Á/124.
... The third and largest species, the bush rat Rattus fuscipes, differs in that it is not a mars... more ... The third and largest species, the bush rat Rattus fuscipes, differs in that it is not a marsupial, has territorial females (Woodside 1983) and small home-ranges and finally, in lacking an abrupt male annual die-off, thus having overlapping generations of both sexes (Robinson 1987 ...
Wertheim, B., Vet, L. E. M. and Dicke, M. 2003. Increased risk of parasitism as ecological costs ... more Wertheim, B., Vet, L. E. M. and Dicke, M. 2003. Increased risk of parasitism as ecological costs of using aggregation pheromones: laboratory and field study of Drosophila-Leptopilina interaction. -Oikos 100: 269-282.
Individual hosts normally respond to parasite attack by launching an acute immune response (a phe... more Individual hosts normally respond to parasite attack by launching an acute immune response (a phenotypic plastic response), while host populations can respond in the longer term by evolving higher level of defence against parasites. Little is known about the genetics of the evolved response: the identity and number of genes involved and whether it involves a pre-activation of the regulatory systems governing the plastic response. We explored these questions by surveying transcriptional changes in a Drosophila melanogaster strain artificially selected for resistance against the hymenopteran endoparasitoid Asobara tabida. Using micro-arrays, we profiled gene expression at seven time points during development (from the egg to the second instar larva) and found a large number of genes (almost 900) with altered expression levels. Bioinformatic analysis showed that some were involved in immunity or defence-associated functions but many were not. Previously, we had defined a set of genes whose level of expression changed after parasitoid attack and a comparison with the present set showed a significant though comparatively small overlap. This suggests that the evolutionary response to parasitism is not a simple pre-activation of the plastic, acute response. We also found overlap in the genes involved in the evolutionary response to parasitism and to other biotic and abiotic stressors, perhaps suggesting a 'module' of genes involved in a generalized stress response as has been found in other organisms.
Parasitoid resistance in Drosophila varies considerably, among and within species. An immune resp... more Parasitoid resistance in Drosophila varies considerably, among and within species. An immune response, lamellocyte-mediated encapsulation, evolved in a subclade of Drosophila and was subsequently lost in at least one species within this subclade. While the mechanisms of resistance are fairly well documented in D. melanogaster, much less is known for closely related species. Here, we studied the inter- and intra-species variation in gene expression after parasitoid attack in Drosophila. We used RNA-seq after parasitization of four closely related Drosophila species of the melanogaster subgroup and replicated lines of D. melanogaster experimentally selected for increased resistance to gain insights into short- and long-term evolutionary changes. We found a core set of genes that are consistently up-regulated after parasitoid attack in the species and lines tested, regardless of their level of resistance. Another set of genes showed no up-regulation or expression in D. sechellia, the s...
The mass rearing of insects as animal feed is a new and rapidly growing component of circular agr... more The mass rearing of insects as animal feed is a new and rapidly growing component of circular agriculture, which offers the opportunity to develop it in such a way that it promotes insect health and welfare. Behaviour is an important indicator of animal performance and welfare. In this review, we synthesise the current behavioural knowledge on two saprophytic dipteran species that are increasingly being used as mini-livestock, the black soldier fly (Hermetia illucens) and the housefly (Musca domestica). We evaluate which behaviours need to be considered to optimise insect production and welfare under mass-rearing conditions. We distinguish between the different life stages (adults and larvae), and describe their feeding behaviour, social interactions (adult mating, larval aggregation), oviposition behaviour and possible cannibalism. For each species, we review what is known about these behaviours in natural environments, and how this is affected by abiotic factors or interactions wi...
During the last decade the potential of insects for human nutritional protein is increasingly rec... more During the last decade the potential of insects for human nutritional protein is increasingly recognised. Direct consumption of insects contributes to a reduction of the ecological footprint of human food production and is claimed to have health benefits. An alternative is feeding poultry (broilers and layers) with insect-derived protein. This offers several additional advantages, e.g. a more extensive use of (new sources) of organic by-products of food industry for insect production. Implementation of a People-Planet-Profit (PPP) sustainable way of utilising these opportunities requires the development of sustainable business models. Such business models need to be based on the opportunities of insect-derived protein in feeding poultry but should also include the risks associated with insect-derived protein for feeding poultry. This article explores the insect-fed poultry production value chain through an interdisciplinary approach. First, the essential features of this value chain...
Background: Haplodiploidy, where females develop from diploid, fertilized eggs and males from hap... more Background: Haplodiploidy, where females develop from diploid, fertilized eggs and males from haploid, unfertilized eggs, is abundant in some insect lineages. Some species in these lineages reproduce by thelytoky that is caused by infection with endosymbionts: infected females lay haploid eggs that undergo diploidization and develop into females, while males are very rare or absent. It is generally assumed that in thelytokous wasps, endosymbionts merely diploidize the unfertilized eggs, which would then trigger female development. Results: We found that females in the parasitoid wasp Asobara japonica infected with thelytoky-inducing Wolbachia produce 0.7-1.2 % male offspring. Seven to 39 % of these males are diploid, indicating that diploidization and female development can be uncoupled in A. japonica. Wolbachia titer in adults was correlated with their ploidy and sex: diploids carried much higher Wolbachia titers than haploids, and diploid females carried more Wolbachia than diploid males. Data from introgression lines indicated that the development of diploid individuals into males instead of females is not caused by malfunction-mutations in the host genome but that diploid males are most likely produced when the endosymbiont fails to activate the female sex determination pathway. Our data therefore support a two-step mechanism by which endosymbionts induce thelytoky in A. japonica: diploidization of the unfertilized egg is followed by feminization, whereby each step correlates with a threshold of endosymbiont titer during wasp development. Conclusions: Our new model of endosymbiont-induced thelytoky overthrows the view that certain sex determination mechanisms constrain the evolution of endosymbiont-induced thelytoky in hymenopteran insects. Endosymbionts can cause parthenogenesis through feminization, even in groups in which endosymbiont-diploidized eggs would develop into males following the hosts' sex determination mechanism. In addition, our model broadens our understanding of the mechanisms by which endosymbionts induce thelytoky to enhance their transmission to the next generation. Importantly, it also provides a novel window to study the yet-poorly known haplodiploid sex determination mechanisms in haplodiploid insects.
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Establishment and spread of invasive species can be facilitated by lack of natural enemies in the... more Establishment and spread of invasive species can be facilitated by lack of natural enemies in the invaded area. Host-range evolution of natural enemies augments their ability to reduce the impact of the invader and could enhance their value for biological control. We assessed the potential of the Drosophila parasitoid, Leptopilina heterotoma (Hymenoptera: Figitidae), to exploit the invasive pest Drosophila suzukii by focusing on three performance indices: (i) attack rate; (ii) host killing, consisting of killing rate and lethal attack rate (killing efficiency); and (iii) successful offspring How to cite this article: Kruitwagen A, Wertheim B, Beukeboom LW. Artificial selection for nonreproductive host killing in a native parasitoid on the invasive pest, Drosophila
Rearing insects for food and feed is a rapidly growing industry, because it provides excellent op... more Rearing insects for food and feed is a rapidly growing industry, because it provides excellent opportunities for a sustainable approach to animal protein production. Two fly species, the black soldier fly (BSF) and the house fly (HF), naturally live in decaying organic matter (e.g. compost), and can thus be effectively reared on organic rest streams from the food and agricultural industry. The adoption of these insects as mini-livestock on microbially rich substrates, however, requires us to address how we can safeguard insect health under mass-rearing conditions. In this review, we discuss what is known about the innate immunity of insects in general, especially focusing on a comparative approach to current knowledge for the two dipteran species BSF and HF. We also discuss environmental factors that may affect innate immunity in mass-rearing settings, including temperature, insect densities and diet composition. Furthermore, we address the role of the microbiome in insect health an...
Proceedings of the Royal Society B: Biological Sciences, 2012
Seminal fluid proteins (Sfps) alter female behaviour and physiology and can mediate sexual confli... more Seminal fluid proteins (Sfps) alter female behaviour and physiology and can mediate sexual conflict. In Drosophila melanogaster , a single Sfp, the sex peptide (SP), triggers remarkable post-mating responses in females, including altered fecundity, feeding, immunity and sexual receptivity. These effects can favour the evolutionary interests of males while generating costs in females. We tested the hypothesis that SP is an upstream master-regulator able to induce diverse phenotypes through efficient induction of widespread transcriptional changes in females. We profiled mRNA responses to SP in adult female abdomen (Abd) and head+thorax (HT) tissues using microarrays at 3 and 6 h following mating. SP elicited a rich, subtle signature of temporally and spatially controlled mRNAs. There were significant alterations to genes linked to egg development, early embryogenesis, immunity, nutrient sensing, behaviour and, unexpectedly, phototransduction. There was substantially more variation in...
Parasitoids are insect parasites whose larvae develop in the bodies of other insects. The main im... more Parasitoids are insect parasites whose larvae develop in the bodies of other insects. The main immune defense against parasitoids is encapsulation of the foreign body by blood cells, which subsequently often melanize. The capsule sequesters and kills the parasite. The molecular processes involved are still poorly understood, especially compared with insect humoral immunity. We explored the transcriptional response to parasitoid attack in Drosophila larvae at nine time points following parasitism, hybridizing five biologic replicates per time point to whole-genome microarrays for both parasitized and control larvae. We found significantly different expression profiles for 159 probe sets (representing genes), and we classified them into 16 clusters based on patterns of co-expression. A series of functional annotations were nonrandomly associated with different clusters, including several involving immunity and related functions. We also identified nonrandom associations of transcripti...
Many organisms experience an Allee effect: their populations do not grow optimally at low densiti... more Many organisms experience an Allee effect: their populations do not grow optimally at low densities. In addition, individuals compete with one another at high densities. The Allee effect and competition thus create a lower and an upper bound to local population size. Local populations can, however, be connected through dispersal. By using a spatio-temporal integro-difference simulation model, parameterized for Drosophila melanogaster, we explore the consequences of the Allee effect, scramble competition and dispersal for different combinations of resource distributions, initial adult distributions and densities, modes of dispersal and boundary conditions. We found that the initial distribution and density of adults determines whether a population can establish, while resource availability, the ability to reach resources and heterogeneity are mainly responsible for subsequent population persistence. In our model heterogeneity was introduced by the distribution of resources, the initial adult distribution, and the boundary conditions. Although local population dynamics are inherently unstable, overall stability can be attained by (re)colonization processes. The averaged dynamics of the total population turned out to be reasonably smooth, so apparently upper and lower local population bounds, coupled with dispersal, created an effective stable mean population density for the system as a whole. This suggests that stable mean population densities for spatial populations can be emergent properties appearing at sufficiently large scales, as opposed to inherent properties occurring at all scales. We also found, in agreement with most literature but contrary to some recent literature, that population persistence can be facilitated by a leptokurtic dispersal mode, which has higher probabilities of traveling both short and long distances, but smaller probability of traveling intermediate distances than random dispersal.
Measurement of food intake in the fruit fly Drosophila melanogaster is often necessary for studie... more Measurement of food intake in the fruit fly Drosophila melanogaster is often necessary for studies of behaviour, nutrition and drug administration. There is no reliable and agreed method for measuring food intake of flies in undisturbed, steady state, and normal culture conditions. We report such a method, based on measurement of feeding frequency by proboscisextension, validated by short-term measurements of food dye intake. We used the method to demonstrate that (a) female flies feed more frequently than males, (b) flies feed more often when housed in larger groups and (c) fly feeding varies at different times of the day. We also show that alterations in food intake are not induced by dietary restriction or by a null mutation of the fly insulin receptor substrate chico. In contrast, mutation of takeout increases food intake by increasing feeding frequency while mutation of ovo D increases food intake by increasing the volume of food consumed per proboscisextension. This approach provides a practical and reliable method for quantification of food intake in Drosophila under normal, undisturbed culture conditions.
Proceedings of the Royal Society B: Biological Sciences, 2014
In this study, we characterize changes in the genome during a swift evolutionary adaptation, by c... more In this study, we characterize changes in the genome during a swift evolutionary adaptation, by combining experimental selection with high-throughput sequencing. We imposed strong experimental selection on an ecologically relevant trait, parasitoid resistance in Drosophila melanogaster against Asobara tabida. Replicated selection lines rapidly evolved towards enhanced immunity. Larval survival after parasitization increased twofold after just five generations of selection. Whole-genome sequencing revealed that the fast and strong selection response in innate immunity produced multiple, highly localized genomic changes. We identified narrow genomic regions carrying a significant signature of selection, which were present across all chromosomes and covered in total less than 5% of the whole D. melanogaster genome. We identified segregating sites with highly significant changes in frequency between control and selection lines that fell within these narrow 'selected regions'. These segregating sites were associated with 42 genes that constitute possible targets of selection. A region on chromosome 2R was highly enriched in significant segregating sites and may be of major effect on parasitoid defence. The high genetic variability and small linkage blocks in our base population are likely responsible for allowing this complex trait to evolve without causing widespread erosive effects in the genome, even under such a fast and strong selective regime.
Clinal variation in quantitative traits is widespread, but its genetic basis awaits identificatio... more Clinal variation in quantitative traits is widespread, but its genetic basis awaits identification. Drosophila melanogaster shows adaptive, clinal variation in traits such as body size along latitudinal gradients on multiple continents. To investigate genome wide transcription differentiation between North and South that might contribute to the clinal phenotypic variation, we compared RNA expression patterns during development of D. melanogaster from tropical northern and temperate southern populations using whole genome tiling arrays. We found that genes that were differentially expressed between the cline ends were generally associated with metabolism and growth, and experimental alteration of expression of a sample of them generally resulted in altered body size in the predicted direction, sometimes significantly so. We further identified the serpent (srp) transcription factor binding sites to be enriched near genes up-regulated in expression in the south. Analysis of clinal populations revealed a significant cline in the expression level of srp. Experimental over-expression of srp increased body size, as predicted from its clinal expression pattern, suggesting that it may be involved in regulating adaptive clinal variation in Drosophila. This study identified a handful of genes that contributed to clinal phenotypic variation through altered gene expression level, yet misexpression of individual gene led to modest body size change.
. Evolutionary ecology of communication signals that induce aggregative behaviour. Á/ Oikos 109: ... more . Evolutionary ecology of communication signals that induce aggregative behaviour. Á/ Oikos 109: 117 Á/124.
... The third and largest species, the bush rat Rattus fuscipes, differs in that it is not a mars... more ... The third and largest species, the bush rat Rattus fuscipes, differs in that it is not a marsupial, has territorial females (Woodside 1983) and small home-ranges and finally, in lacking an abrupt male annual die-off, thus having overlapping generations of both sexes (Robinson 1987 ...
Wertheim, B., Vet, L. E. M. and Dicke, M. 2003. Increased risk of parasitism as ecological costs ... more Wertheim, B., Vet, L. E. M. and Dicke, M. 2003. Increased risk of parasitism as ecological costs of using aggregation pheromones: laboratory and field study of Drosophila-Leptopilina interaction. -Oikos 100: 269-282.
Individual hosts normally respond to parasite attack by launching an acute immune response (a phe... more Individual hosts normally respond to parasite attack by launching an acute immune response (a phenotypic plastic response), while host populations can respond in the longer term by evolving higher level of defence against parasites. Little is known about the genetics of the evolved response: the identity and number of genes involved and whether it involves a pre-activation of the regulatory systems governing the plastic response. We explored these questions by surveying transcriptional changes in a Drosophila melanogaster strain artificially selected for resistance against the hymenopteran endoparasitoid Asobara tabida. Using micro-arrays, we profiled gene expression at seven time points during development (from the egg to the second instar larva) and found a large number of genes (almost 900) with altered expression levels. Bioinformatic analysis showed that some were involved in immunity or defence-associated functions but many were not. Previously, we had defined a set of genes whose level of expression changed after parasitoid attack and a comparison with the present set showed a significant though comparatively small overlap. This suggests that the evolutionary response to parasitism is not a simple pre-activation of the plastic, acute response. We also found overlap in the genes involved in the evolutionary response to parasitism and to other biotic and abiotic stressors, perhaps suggesting a 'module' of genes involved in a generalized stress response as has been found in other organisms.
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