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David L. Stern - One of the best experts on this subject based on the ideXlab platform.
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The structure and evolution of cis-regulatory regions: the shavenbaby story.
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 2013Co-Authors: David L. Stern, Nicolás FrankelAbstract:In this paper, we provide a historical account of the contribution of a single line of research to our current understanding of the structure of cis-regulatory regions and the genetic basis for morphological evolution. We revisit the experiments that shed light on the evolution of larval cuticular patterns within the genus Drosophila and the evolution and structure of the shavenbaby gene. We describe the experiments that led to the discovery that multiple genetic changes in the cis-regulatory region of shavenbaby caused the loss of dorsal cuticular hairs (quaternary trichomes) in first instar larvae of Drosophila sechellia. We also discuss the experiments that showed that the convergent loss of quaternary trichomes in D. sechellia and Drosophila ezoana was generated by parallel genetic changes in orthologous enhancers of shavenbaby. We discuss the observation that multiple shavenbaby enhancers drive overlapping patterns of expression in the embryo and that these apparently redundant enhancers ensure robust shavenbaby expression and trichome morphogenesis under stressful conditions. All together, these data, collected over 13 years, provide a fundamental case study in the fields of gene regulation and morphological evolution, and highlight the importance of prolonged, detailed studies of single genes.
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Pupariation site preference within and between Drosophila sibling species.
Evolution; international journal of organic evolution, 2013Co-Authors: Deniz F. Erezyilmaz, David L. SternAbstract:Holometabolous insects pass through a sedentary pupal stage and often choose a location for pupation that is different from the site of larval feeding. We have characterized a difference in pupariation site choice within and between sibling species of Drosophila. We found that, in nature, Drosophila sechellia pupariate within their host fruit, Morinda citrifolia, and that they perform this behavior in laboratory assays. In contrast, in the laboratory, geographically diverse strains of Drosophila simulans vary in their pupariation site preference; D. simulans lines from the ancestral range in southeast Africa pupariate on fruit, or a fruit substitute, whereas populations from Europe or the New World select sites off of fruit. We explored the genetic basis for the evolved preference in puariation site preference by performing quantitative trait locus mapping within and between species. We found that the interspecific difference is controlled largely by loci on chromosomes X and II. In contrast, variation between two strains of D. simulans appears to be highly polygenic, with the majority of phenotypic effects due to loci on chromosome III. These data address the genetic basis of how new traits arise as species diverge and populations disperse.
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conserved regulatory architecture underlies parallel genetic changes and convergent phenotypic evolution
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Nicolás Frankel, Shu Wang, David L. SternAbstract:Similar morphological, physiological, and behavioral features have evolved independently in different species, a pattern known as convergence. It is known that morphological convergence can occur through changes in orthologous genes. In some cases of convergence, cis-regulatory changes generate parallel modifications in the expression patterns of orthologous genes. Our understanding of how changes in cis-regulatory regions contribute to convergence is hampered, usually, by a limited understanding of the global cis-regulatory structure of the evolving genes. Here we examine the genetic causes of a case of precise phenotypic convergence between Drosophila sechellia and Drosophila ezoana, species that diverged ∼40 Mya. Previous studies revealed that changes in multiple transcriptional enhancers of shavenbaby (svb, a transcript of the ovo locus) caused phenotypic evolution in the D. sechellia lineage. It has also been shown that the convergent phenotype of D. ezoana was likely caused by cis-regulatory evolution of svb. Here we show that the large-scale cis-regulatory architecture of svb is conserved between these Drosophila species. Furthermore, we show that the D. ezoana orthologs of the evolved D. sechellia enhancers have also evolved expression patterns that correlate precisely with the changes in the phenotype. Our results suggest that phenotypic convergence resulted from multiple noncoding changes that occurred in parallel in the D. sechellia and D. ezoana lineages.
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Morphological evolution caused by many subtle-effect substitutions in regulatory DNA
Nature, 2011Co-Authors: Nicolás Frankel, FranÇois Payre, Deniz F. Erezyilmaz, Alistair P Mcgregor, Shu Wang, David L. SternAbstract:Morphology evolves often through changes in developmental genes, but the causal mutations, and their effects, remain largely unknown. The evolution of naked cuticle on larvae of Drosophila sechellia resulted from changes in five transcriptional enhancers of shavenbaby ( svb ), a transcript of the ovo locus that encodes a transcription factor that governs morphogenesis of microtrichiae, hereafter called ‘trichomes’. Here we show that the function of one of these enhancers evolved through multiple single-nucleotide substitutions that altered both the timing and level of svb expression. The consequences of these nucleotide substitutions on larval morphology were quantified with a novel functional assay. We found that each substitution had a relatively small phenotypic effect, and that many nucleotide changes account for this large morphological difference. In addition, we observed that the substitutions had non-additive effects. These data provide unprecedented resolution of the phenotypic effects of substitutions and show how individual nucleotide changes in a transcriptional enhancer have caused morphological evolution. Morphological evolution often involves changes in developmental genes, but the number and effects of the causal mutations remain largely unknown. Frankel et al . use the gene shavenbaby in Drosophila sechellia as a model system for studying the genetics of this phenomenon. They show that evolutionary change in one of the five cis -regulatory enhancers of shavenbaby resulted from many nucleotide substitutions that altered both the timing and level of gene expression. Thus many mutations of small effect — not just one mutation of large effect — were needed for this fruitfly to evolve a hairless larva. The work provides quantitative support, at the single nucleotide substitution level, for Charles Darwin's favoured view of a 'gradualist' evolutionary process.
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Morphological evolution caused by many subtle-effect substitutions in regulatory DNA
Nature, 2011Co-Authors: Nicolás Frankel, FranÇois Payre, Deniz F. Erezyilmaz, Alistair P Mcgregor, Shu Wang, David L. SternAbstract:Morphology evolves often through changes in developmental genes, but the causal mutations, and their effects, remain largely unknown. The evolution of naked cuticle on larvae of Drosophila sechellia resulted from changes in five transcriptional enhancers of shavenbaby (svb), a transcript of the ovo locus that encodes a transcription factor that governs morphogenesis of microtrichiae, hereafter called ‘trichomes’. Here we show that the function of one of these enhancers evolved through multiple single-nucleotide substitutions that altered both the timing and level of svb expression. The consequences of these nucleotide substitutions on larval morphology were quantified with a novel functional assay. We found that each substitution had a relatively small phenotypic effect, and that many nucleotide changes account for this large morphological difference. In addition, we observed that the substitutions had non-additive effects. These data provide unprecedented resolution of the phenotypic effects of substitutions and show how individual nucleotide changes in a transcriptional enhancer have caused morphological evolution.
Nicolás Frankel - One of the best experts on this subject based on the ideXlab platform.
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The structure and evolution of cis-regulatory regions: the shavenbaby story.
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 2013Co-Authors: David L. Stern, Nicolás FrankelAbstract:In this paper, we provide a historical account of the contribution of a single line of research to our current understanding of the structure of cis-regulatory regions and the genetic basis for morphological evolution. We revisit the experiments that shed light on the evolution of larval cuticular patterns within the genus Drosophila and the evolution and structure of the shavenbaby gene. We describe the experiments that led to the discovery that multiple genetic changes in the cis-regulatory region of shavenbaby caused the loss of dorsal cuticular hairs (quaternary trichomes) in first instar larvae of Drosophila sechellia. We also discuss the experiments that showed that the convergent loss of quaternary trichomes in D. sechellia and Drosophila ezoana was generated by parallel genetic changes in orthologous enhancers of shavenbaby. We discuss the observation that multiple shavenbaby enhancers drive overlapping patterns of expression in the embryo and that these apparently redundant enhancers ensure robust shavenbaby expression and trichome morphogenesis under stressful conditions. All together, these data, collected over 13 years, provide a fundamental case study in the fields of gene regulation and morphological evolution, and highlight the importance of prolonged, detailed studies of single genes.
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conserved regulatory architecture underlies parallel genetic changes and convergent phenotypic evolution
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Nicolás Frankel, Shu Wang, David L. SternAbstract:Similar morphological, physiological, and behavioral features have evolved independently in different species, a pattern known as convergence. It is known that morphological convergence can occur through changes in orthologous genes. In some cases of convergence, cis-regulatory changes generate parallel modifications in the expression patterns of orthologous genes. Our understanding of how changes in cis-regulatory regions contribute to convergence is hampered, usually, by a limited understanding of the global cis-regulatory structure of the evolving genes. Here we examine the genetic causes of a case of precise phenotypic convergence between Drosophila sechellia and Drosophila ezoana, species that diverged ∼40 Mya. Previous studies revealed that changes in multiple transcriptional enhancers of shavenbaby (svb, a transcript of the ovo locus) caused phenotypic evolution in the D. sechellia lineage. It has also been shown that the convergent phenotype of D. ezoana was likely caused by cis-regulatory evolution of svb. Here we show that the large-scale cis-regulatory architecture of svb is conserved between these Drosophila species. Furthermore, we show that the D. ezoana orthologs of the evolved D. sechellia enhancers have also evolved expression patterns that correlate precisely with the changes in the phenotype. Our results suggest that phenotypic convergence resulted from multiple noncoding changes that occurred in parallel in the D. sechellia and D. ezoana lineages.
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Morphological evolution caused by many subtle-effect substitutions in regulatory DNA
Nature, 2011Co-Authors: Nicolás Frankel, FranÇois Payre, Deniz F. Erezyilmaz, Alistair P Mcgregor, Shu Wang, David L. SternAbstract:Morphology evolves often through changes in developmental genes, but the causal mutations, and their effects, remain largely unknown. The evolution of naked cuticle on larvae of Drosophila sechellia resulted from changes in five transcriptional enhancers of shavenbaby ( svb ), a transcript of the ovo locus that encodes a transcription factor that governs morphogenesis of microtrichiae, hereafter called ‘trichomes’. Here we show that the function of one of these enhancers evolved through multiple single-nucleotide substitutions that altered both the timing and level of svb expression. The consequences of these nucleotide substitutions on larval morphology were quantified with a novel functional assay. We found that each substitution had a relatively small phenotypic effect, and that many nucleotide changes account for this large morphological difference. In addition, we observed that the substitutions had non-additive effects. These data provide unprecedented resolution of the phenotypic effects of substitutions and show how individual nucleotide changes in a transcriptional enhancer have caused morphological evolution. Morphological evolution often involves changes in developmental genes, but the number and effects of the causal mutations remain largely unknown. Frankel et al . use the gene shavenbaby in Drosophila sechellia as a model system for studying the genetics of this phenomenon. They show that evolutionary change in one of the five cis -regulatory enhancers of shavenbaby resulted from many nucleotide substitutions that altered both the timing and level of gene expression. Thus many mutations of small effect — not just one mutation of large effect — were needed for this fruitfly to evolve a hairless larva. The work provides quantitative support, at the single nucleotide substitution level, for Charles Darwin's favoured view of a 'gradualist' evolutionary process.
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Morphological evolution caused by many subtle-effect substitutions in regulatory DNA
Nature, 2011Co-Authors: Nicolás Frankel, FranÇois Payre, Deniz F. Erezyilmaz, Alistair P Mcgregor, Shu Wang, David L. SternAbstract:Morphology evolves often through changes in developmental genes, but the causal mutations, and their effects, remain largely unknown. The evolution of naked cuticle on larvae of Drosophila sechellia resulted from changes in five transcriptional enhancers of shavenbaby (svb), a transcript of the ovo locus that encodes a transcription factor that governs morphogenesis of microtrichiae, hereafter called ‘trichomes’. Here we show that the function of one of these enhancers evolved through multiple single-nucleotide substitutions that altered both the timing and level of svb expression. The consequences of these nucleotide substitutions on larval morphology were quantified with a novel functional assay. We found that each substitution had a relatively small phenotypic effect, and that many nucleotide changes account for this large morphological difference. In addition, we observed that the substitutions had non-additive effects. These data provide unprecedented resolution of the phenotypic effects of substitutions and show how individual nucleotide changes in a transcriptional enhancer have caused morphological evolution.
Kathreen Bitner - One of the best experts on this subject based on the ideXlab platform.
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the evolution of ovoviviparity in a temporally varying environment
The American Naturalist, 2015Co-Authors: Laurence D. Mueller, Kathreen BitnerAbstract:Environments that vary within a generation of an organism provide opportunities for adaptation if the level of variation is severe and predictable. We describe a model of evolution in such environments with genotypes that show trade-offs in viability and fecundity. One genotype develops rapidly and has superior viability but reduced fertility relative to the alternative genotype. Conditions that allow the evolution of the rapidly developing genotypes are explored. We show how the evolution of ovoviviparity and resource specialization in Drosophila sechellia shares many important features of this model. We suggest that our model may capture many of the evolutionary forces responsible for the evolution of niche specialization and ovoviviparity seen in D. sechellia.
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the evolution of ovoviviparity in a temporally varying environment
The American Naturalist, 2015Co-Authors: Laurence D. Mueller, Kathreen BitnerAbstract:Environments that vary within a generation of an organism provide opportunities for adaptation if the level of variation is severe and predictable. We describe a model of evolution in such environments with genotypes that show trade-offs in viability and fecundity. One genotype develops rapidly and has superior viability but reduced fertility relative to the alternative genotype. Conditions that allow the evolution of the rapidly developing genotypes are explored. We show how the evolution of ovoviviparity and resource specialization in Drosophila sechellia shares many important features of this model. We suggest that our model may capture many of the evolutionary forces responsible for the evolution of niche specialization and ovoviviparity seen in D. sechellia.
Jean R David - One of the best experts on this subject based on the ideXlab platform.
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Larval Tolerance in the Drosophila Melanogaster Species Complex Toward the Two Toxic Acids of the D. sechellia Host Plant
Hereditas, 2004Co-Authors: Mohammed Amlou, Brigitte Moreteau, Jean R DavidAbstract:The toxicity of hexanoic (C6) and octanoic (C8) acids, the two major components of the host plant of Drosophila sechellia, was investigated upon larvae of the four species included in the D. melanogaster complex and on interspecific hybrids between D. sechellia and D. simulans. Specific methods had to be devised for obtaining reproducible toxicity results. The three generalist species (D. melanogaster, D. mauritiana and D. simulans) were found to be very sensitive, as indicated by low lethal concentrations and an increase in development duration. By contrast D. sechellia was much more tolerant, especially toward C8 which is the most abundant product in the natural resource. Interspecific hybrids (F1 and backcrosses) exhibited intermediate characteristic, but a dominance of D. simulans sensitivity was observed for both acids and especially for C8. Data on larvae are quite different from those previously obtained on adults, and are more likely to reflect the natural selective pressures existing in the wild.
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Genetic Analysis of Drosophila sechellia Specialization: Oviposition Behavior Toward the Major Aliphatic Acids of Its Host Plant
Behavior genetics, 1998Co-Authors: Mohammed Amlou, Brigitte Moreteau, Jean R DavidAbstract:Oviposition behavior of the four species in the Drosophila melanogastercomplex (D. melanogaster, D. simulans, D. mauritiana, D. sechellia) was investigated versus natural morinda fruit (the normal resource of D. sechellia) and the two major aliphatic acids of this fruit (hexanoic acid, C6, and octanoic acid, C8). Two different experimental techniques were compared. When control and experimental food were set on the same egg laying plate, three species (D. sechellia, D. mauritiana, D. melanogaster) exhibited a significant preference for morinda; with aliphatic acids, only D. sechelliamanifested a preference. With separate oviposition sites, a preference was found in D. sechelliafor morinda and acids, and a general avoidance behavior in the three other species. Genetic analysis of the behavioral response toward C6 and C8 was done with the two plates technique on D. sechellia, D. simulans, F1 hybrids and backcrosses. Significant behavioral differences were observed with major effects due to genotype, concentration and their interaction. Hybrid behaviors were intermediate between those of their parents. In several cases, a qualitative reversal from preference to avoidance was observed with increasing concentration. In F1 flies, a dominance reversal was observed with increasing C8 concentration. Different reaction thresholds in different receptors might explain such observations.
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EVOLUTION OF A LESSER FITNESS TRAIT : EGG PRODUCTION IN THE SPECIALIST Drosophila sechellia
Genetical research, 1997Co-Authors: Samia R'kha, Jerry A. Coyne, Brigitte Moreteau, Jean R DavidAbstract:In the evolutionary process during which Drosophila sechellia became specialized on a toxic fruit (morinda), a spectacular decrease in female reproductive capacity took place when compared with the species' generalist relatives D. mauritiana and D. simulans . Comparisons of species and interspecific crosses showed that two different traits were modified: number of ovarioles and rate of egg production. During the conservation of a D. sechellia strain on usual food, adaptation to laboratory conditions led to an increase in the rate of oogenesis but not in ovariole number. Comparison of F 1 and backcross progeny also suggests that the two traits are determined by different genes (ovariole number has already been shown to be polygenic). When morinda is available as a resource, the low rate of egg production in D. sechellia is partly compensated by a stimulating effect, while an inhibition occurs in D. simulans . It is assumed that D. sechellia progressively adapted itself from rotten, non-toxic morinda to a fresher and more toxic resource. During this process the rate of oogenesis evolved from an inhibition to a stimulation by morinda. Simultaneously a spectacular decrease in ovariole number took place, either as a consequence of stochastic events related to the small population size of D. sechellia and a metapopulation dynamics, or as an adaptive process favouring dispersal capacities of the female.
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Toxicity and attraction effects produced byMorinda citrifolia fruits on theDrosophila melanogaster complex of species
CHEMOECOLOGY, 1992Co-Authors: Luc Legal, Jean R David, Jean-marc JallonAbstract:The ripe fruit of the Indian mulberry, Morinda citrifolia , is the host plant for Drosophila sechellia but is highly toxic for three closely related species ( D. melanogaster, D. simulans, D. mauritiana ). A simple bioassay is described with which a clear dose response to the fruit was found for these species. Significant differences in reactivity to the ripe fruit were found among species. Tested strains of D. simulans and D. mauritiana adults were more sensitive to the toxic properties of the fruit than D. melanogaster. A marked intraspecific variability was shown in D. melanogaster. Reciprocal interspecific hybridizations between D. sechellia and D. mauritiana suggested an autosomal dominant control of resistance. Moreover D. melanogaster intraspecific crossings suggested the influence of an additional X-linked factor. Responses of flies to Morinda fruit in different states were tested in a T olfactometer. The less resistant strains of Drosophila generally showed less preference for the ripe fruit.
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Sequence analysis of active mariner elements in natural populations of Drosophila simulans
Genetics, 1992Co-Authors: Pierre Capy, Jean R David, Akihiko Koga, Daniel L. HartlAbstract:Active and inactive mariner elements from natural and laboratory populations of Drosophila simulans were isolated and sequenced in order to assess their nucleotide variability and to compare them with previously isolated mariner elements from the sibling species Drosophila mauritiana and Drosophila sechellia. The active elements of D. simulans are very similar among themselves (average 99.7% nucleotide identity), suggesting that the level of mariner expression in different natural populations is largely determined by position effects, dosage effects and perhaps other factors. Furthermore, the D. simulans elements exhibit nucleotide identities of 98% or greater when compared with mariner elements from the sibling species. Parsimony analysis of mariner elements places active elements from the three species into separate groups and suggests that D. simulans is the species from which mariner elements in D. mauritiana and D. sechellia are most likely derived. This result strongly suggests that the ancestral form of mariner among these species was an active element. The two inactive mariner elements sequenced from D. simulans are very similar to the inactive peach element from D. mauritiana. The similarity may result from introgression between D. simulans and D. mauritiana or from selective constraints imposed by regulatory effects of inactive elements.
Corbin D. Jones - One of the best experts on this subject based on the ideXlab platform.
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Evolutionary Genetics: You Are What You Evolve to Eat
Current biology : CB, 2015Co-Authors: Ian Dworkin, Corbin D. JonesAbstract:The evolution of host specialization can potentially limit future evolutionary opportunities. A new study now shows how Drosophila sechellia, specialized on the toxic Morinda fruit, has evolved new nutritional needs influencing its reproduction.
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A Locus in Drosophila sechellia Affecting Tolerance of a Host Plant Toxin
Genetics, 2013Co-Authors: Eric A. Hungate, Eric Earley, Ian A. Boussy, David A. Turissini, Chau-ti Ting, Jennifer R. Moran, Corbin D. JonesAbstract:Many insects feed on only one or a few types of host. These host specialists often evolve a preference for chemical cues emanating from their host and develop mechanisms for circumventing their host’s defenses. Adaptations like these are central to evolutionary biology, yet our understanding of their genetics remains incomplete. Drosophila sechellia, an emerging model for the genetics of host specialization, is an island endemic that has adapted to chemical toxins present in the fruit of its host plant, Morinda citrifolia. Its sibling species, D. simulans, and many other Drosophila species do not tolerate these toxins and avoid the fruit. Earlier work found a region with a strong effect on tolerance to the major toxin, octanoic acid, on chromosome arm 3R. Using a novel assay, we narrowed this region to a small span near the centromere containing 18 genes, including three odorant binding proteins. It has been hypothesized that the evolution of host specialization is facilitated by genetic linkage between alleles contributing to host preference and alleles contributing to host usage, such as tolerance to secondary compounds. We tested this hypothesis by measuring the effect of this tolerance locus on host preference behavior. Our data were inconsistent with the linkage hypothesis, as flies bearing this tolerance region showed no increase in preference for media containing M. citrifolia toxins, which D. sechellia prefers. Thus, in contrast to some models for host preference, preference and tolerance are not tightly linked at this locus nor is increased tolerance per se sufficient to change preference. Our data are consistent with the previously proposed model that the evolution of D. sechellia as a M. citrifolia specialist occurred through a stepwise loss of aversion and gain of tolerance to M. citrifolia’s toxins.
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Genetic Changes Accompanying the Evolution of Host Specialization in Drosophila sechellia
Genetics, 2008Co-Authors: Ian Dworkin, Corbin D. JonesAbstract:Changes in host specialization contribute to the diversification of phytophagous insects. When shifting to a new host, insects evolve new physiological, morphological, and behavioral adaptations. Our understanding of the genetic changes responsible for these adaptations is limited. For instance, we do not know how often host shifts involve gain-of-function vs. loss-of-function alleles. Recent work suggests that some genes involved in odor recognition are lost in specialists. Here we show that genes involved in detoxification and metabolism, as well as those affecting olfaction, have reduced gene expression in Drosophila sechellia—a specialist on the fruit of Morinda citrifolia. We screened for genes that differ in expression between D. sechellia and its generalist sister species, D. simulans. We also screened for genes that are differentially expressed in D. sechellia when these flies chose their preferred host vs. when they were forced onto other food. D. sechellia increases expression of genes involved with oogenesis and fatty acid metabolism when on its host. The majority of differentially expressed genes, however, appear downregulated in D. sechellia. For several functionally related genes, this decrease in expression is associated with apparent loss-of-function alleles. For example, the D. sechellia allele of Odorant binding protein 56e (Obp56e) harbors a premature stop codon. We show that knockdown of Obp56e activity significantly reduces the avoidance response of D. melanogaster toward M. citrifolia. We argue that apparent loss-of-function alleles like Obp56e potentially contributed to the initial adaptation of D. sechellia to its host. Our results suggest that a subset of genes reduce or lose function as a consequence of host specialization, which may explain why, in general, specialist insects tend to shift to chemically similar hosts.
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The genetics of adaptation in Drosophila sechellia
Genetica, 2005Co-Authors: Corbin D. JonesAbstract:Drosophila sechellia is an island endemic of the Seychelles. After its geographic isolation on these islands, D. sechellia evolved into a host specialist on the fruit of Morinda citrifolia – a fruit often noxious and repulsive to Drosophila. Specialization on M. citrifolia required the evolution of a suite of adaptations, including resistance to and preference for some of the toxins found in this fruit. Several of these adaptive traits have been studied genetically. Here, I summarize what is known about the genetics of these traits and briefly describe the ecological and geographical context that shaped the evolution of these characters. The data from D. sechellia suggest that adaptations are not as genetically complex as historically thought, although almost all of the adaptations of D. sechellia involve several genes.
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Genetics of egg production in Drosophila sechellia.
Heredity, 2004Co-Authors: Corbin D. JonesAbstract:Drosophila sechellia, an island endemic that specializes on a single host plant, has a lower rate of egg production than its generalist sister species D. melanogaster, D. simulans, and D. mauritiana. Earlier work showed that part of this difference in egg production was due to a reduction in the number of ovarioles in D. sechellia relative to its sister species. Here, I extend this earlier work by genetically analyzing the difference in egg production between D. sechellia and D. simulans. In all, 10 genetic markers were used in several interspecific backcrosses to identify chromosome regions that affected the rate of egg production. While previously mapped factors affecting ovariole number appear to impact the rate of egg production, new, non-ovariole factors were also identified. Overall, the difference in egg production between D. sechellia and D. simulans appears to be a polygenic trait. The relationship between these factors and genes involved the adaptation of D. sechellia to its host plant is not yet clear. The data are consistent with the hypothesis that decline in egg production is, in part, a negative pleiotropic effect of genetic changes required for host specialization in D. sechellia, although finer-scale genetic analysis of both traits is needed to truly test this hypothesis.
