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Mohamed A F Noor - One of the best experts on this subject based on the ideXlab platform.
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inversions shape the divergence of Drosophila pseudoobscura and Drosophila persimilis on multiple timescales
Evolution, 2021Co-Authors: Katharine L Korunes, Carlos A Machado, Mohamed A F NoorAbstract:By shaping meiotic recombination, chromosomal inversions can influence genetic exchange between hybridizing species. Despite the recognized importance of inversions in evolutionary processes such as divergence and speciation, teasing apart the effects of inversions over time remains challenging. For example, are their effects on sequence divergence primarily generated through creating blocks of linkage disequilibrium prespeciation or through preventing gene flux after speciation? We provide a comprehensive look into the influence of inversions on gene flow throughout the evolutionary history of a classic system: Drosophila pseudoobscura and Drosophila persimilis. We use extensive whole-genome sequence data to report patterns of introgression and divergence with respect to chromosomal arrangements. Overall, we find evidence that inversions have contributed to divergence patterns between D. pseudoobscura and D. persimilis over three distinct timescales: (1) segregation of ancestral polymorphism early in the speciation process, (2) gene flow after the split of D. pseudoobscura and D. persimilis, but prior to the split of D. pseudoobscura subspecies, and (3) recent gene flow between sympatric D. pseudoobscura and D. persimilis, after the split of D. pseudoobscura subspecies. We discuss these results in terms of our understanding of evolution in this classic system and provide cautions for interpreting divergence measures in other systems.
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pseudobase a genomic visualization and exploration resource for the Drosophila pseudoobscura subgroup
Fly, 2021Co-Authors: Katharine L Korunes, Russell B Myers, Ryan Hardy, Mohamed A F NoorAbstract:Drosophila pseudoobscura is a classic model system for the study of evolutionary genetics and genomics. Given this long-standing interest, many genome sequences have accumulated for D. pseudoobscura and closely related species D. persimilis, D. miranda, and D. lowei. To facilitate the exploration of genetic variation within species and comparative genomics across species, we present PseudoBase, a database that couples extensive publicly available genomic data with simple visualization and query tools via an intuitive graphical interface, amenable for use in both research and educational settings. All genetic variation (SNPs and indels) within the database is derived from the same workflow, so variants are easily comparable across data sets. Features include an embedded JBrowse interface, ability to pull out alignments of individual genes/regions, and batch access for gene lists. Here, we introduce PseudoBase, and we demonstrate how this resource facilitates use of extensive genomic data from flies of the Drosophila pseudoobscura subgroup.
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disentangling types of linked selection using patterns of nucleotide variation in Drosophila pseudoobscura
2021Co-Authors: Katharine L Korunes, Kieran Samuk, Mohamed A F NoorAbstract:A central goal in evolutionary genetics is to understand the forces that drive patterns of nucleotide variation within species. Recombination rate and nucleotide diversity are positively correlated across loci within many species. Selective sweeps and background selection both may contribute to this pattern by reducing nucleotide variation disproportionately in regions of low recombination. While there is unambiguous documentation of some forms of selective sweeps, it is less clear how much background selection and soft selective sweeps contribute. Here, we discuss the study of these different types of linked selection, paying particular attention to the large body of work devoted to linked selection in Drosophila. We discuss patterns of nucleotide variation in the classic model system Drosophila pseudoobscura, and we leverage this system to test for the effects of linked selection in the near absence of hard, complete selective sweeps. Our case study of variation in sets of loci shared between Drosophila pseudoobscura and D. miranda suggests that selection at linked sites may reduce nucleotide variation even in the absence of hard selective sweeps. We discuss how this work relates to recent approaches and challenges in the study of how selection at linked sites influences patterns of nucleotide variation.
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natural selection shapes variation in genome wide recombination rate in Drosophila pseudoobscura
Current Biology, 2020Co-Authors: Kieran Samuk, Brenda Manzanowinkler, Kathryn R Ritz, Mohamed A F NoorAbstract:While recombination is widely recognized to be a key modulator of numerous evolutionary phenomena, we have a poor understanding of how recombination rate itself varies and evolves within a species. Here, we performed a comprehensive study of recombination rate (rate of meiotic crossing over) in two natural populations of Drosophila pseudoobscura from Utah and Arizona, USA. We used an amplicon sequencing approach to obtain high-quality genotypes in approximately 8,000 individual backcrossed offspring (17 mapping populations with roughly 530 individuals each), for which we then quantified crossovers. Interestingly, variation in recombination rate within and between populations largely manifested as differences in genome-wide recombination rate rather than remodeling of the local recombination landscape. Comparing populations, we discovered individuals from the Utah population displayed on average 8% higher crossover rates than the Arizona population, a statistically significant difference. Using a QST-FST analysis, we found that this difference in crossover rate was dramatically higher than expected under neutrality, indicating that this difference may have been driven by natural selection. Finally, using a combination of short- and long-read whole-genome sequencing, we found no significant association between crossover rate and structural variation at the 200-400 kb scale. Our results demonstrate that (1) there is abundant variation in genome-wide crossover rate in natural populations, (2) at the 200-400 kb scale, recombination rate appears to vary largely genome-wide, rather than in specific intervals, and (3) interpopulation differences in recombination rate may be the result of local adaptation.
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inversions shape the divergence of Drosophila pseudoobscura and d persimilis on multiple timescales
bioRxiv, 2019Co-Authors: Katharine L Korunes, Carlos A Machado, Mohamed A F NoorAbstract:By shaping meiotic recombination, chromosomal inversions can influence genetic exchange between hybridizing species. Despite the recognized importance of inversions in evolutionary processes such as divergence and speciation, teasing apart the effects of inversions over time remains challenging. Many recent studies have examined gene exchange between hybridizing species and observed higher divergence associated with inversion polymorphisms in hybrids. Studies have attributed such patterns either to interspecies gene flow homogenizing collinear regions or to pre-speciation segregation of inversion polymorphisms in the ancestral population. We provide a comprehensive look into the influence of chromosomal inversions on gene flow throughout the evolutionary history of a classic system: Drosophila pseudoobscura and D. persimilis. We acquired extensive whole-genome sequence data to report patterns of introgression and divergence with respect to chromosomal arrangement. Curiously, divergence measures to D. persimilis are higher for allopatric than sympatric D. pseudoobscura populations in both inverted and collinear regions, which could indicate recent gene exchange that affects even inverted regions. However, consideration of ancestral inversion polymorphisms and different evolutionary rates in these populations reveals that recent gene exchange is a major but not the sole driver of variation in overall sequence divergence. Overall, we show that inversions have contributed to divergence patterns between Drosophila pseudoobscura and D. persimilis over three distinct timescales: 1) pre-speciation segregation of ancestral polymorphism, 2) post-speciation ancient gene flow, and 3) recent introgression. We discuss these results in terms of our understanding of evolution in this classic system and provide cautions for interpreting divergence measures in similar datasets in other systems.
Stephen W Schaeffer - One of the best experts on this subject based on the ideXlab platform.
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how chromosomal rearrangements shape adaptation and speciation case studies in Drosophila pseudoobscura and its sibling species Drosophila persimilis
Molecular Ecology, 2019Co-Authors: Zachary L Fuller, Nitin Phadnis, Spencer A Koury, Stephen W SchaefferAbstract:The gene arrangements of Drosophila have played a prominent role in the history of evolutionary biology from the original quantification of genetic diversity to current studies of the mechanisms for the origin and establishment of new inversion mutations within populations and their subsequent fixation between species supporting reproductive barriers. This review examines the genetic causes and consequences of inversions as recombination suppressors and the role that recombination suppression plays in establishing inversions in populations as they are involved in adaptation within heterogeneous environments. This often results in the formation of clines of gene arrangement frequencies among populations. Recombination suppression leads to the differentiation of the gene arrangements which may accelerate the accumulation of fixed genetic differences among populations. If these fixed mutations cause incompatibilities, then inversions pose important reproductive barriers between species. This review uses the evolution of inversions in Drosophila pseudoobscura and D. persimilis as a case study for how inversions originate, establish and contribute to the evolution of reproductive isolation.
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genomics of natural populations evolutionary forces that establish and maintain gene arrangements in Drosophila pseudoobscura
Molecular Ecology, 2017Co-Authors: Zachary L Fuller, Stephen Richards, Gwilym D Haynes, Stephen W SchaefferAbstract:The evolution of complex traits in heterogeneous environments may shape the order of genes within chromosomes. Drosophila pseudoobscura has a rich gene arrangement polymorphism that allows one to test evolutionary genetic hypotheses about how chromosomal inversions are established in populations. D. pseudoobscura has >30 gene arrangements on a single chromosome that were generated through a series of overlapping inversion mutations with >10 inversions with appreciable frequencies and wide geographic distributions. This study analyses the genomic sequences of 54 strains of Drosophila pseudoobscura that carry one of six different chromosomal arrangements to test whether (i) genetic drift, (ii) hitchhiking with an adaptive allele, (iii) direct effects of inversions to create gene disruptions caused by breakpoints, or (iv) indirect effects of inversions in limiting the formation of recombinant gametes are responsible for the establishment of new gene arrangements. We found that the inversion events do not disrupt the structure of protein coding genes at the breakpoints. Population genetic analyses of 2,669 protein coding genes identified 277 outlier loci harbouring elevated frequencies of arrangement-specific derived alleles. Significant linkage disequilibrium occurs among distant loci interspersed between regions with low levels of association indicating that distant allelic combinations are held together despite shared polymorphism among arrangements. Outlier genes showing evidence of genetic differentiation between arrangements are enriched for sensory perception and detoxification genes. The data presented here support the indirect effect of inversion hypothesis where chromosomal inversions are favoured because they maintain linked associations among multilocus allelic combinations among different arrangements.
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genomics of natural populations how differentially expressed genes shape the evolution of chromosomal inversions in Drosophila pseudoobscura
Genetics, 2016Co-Authors: Zachary L Fuller, Stephen Richards, Gwilym D Haynes, Stephen W SchaefferAbstract:Chromosomal rearrangements can shape the structure of genetic variation in the genome directly through alteration of genes at breakpoints or indirectly by holding combinations of genetic variants together due to reduced recombination. The third chromosome of Drosophila pseudoobscura is a model system to test hypotheses about how rearrangements are established in populations because its third chromosome is polymorphic for >30 gene arrangements that were generated by a series of overlapping inversion mutations. Circumstantial evidence has suggested that these gene arrangements are selected. Despite the expected homogenizing effects of extensive gene flow, the frequencies of arrangements form gradients or clines in nature, which have been stable since the system was first described >80 years ago. Furthermore, multiple arrangements exist at appreciable frequencies across several ecological niches providing the opportunity for heterokaryotypes to form. In this study, we tested whether genes are differentially expressed among chromosome arrangements in first instar larvae, adult females and males. In addition, we asked whether transcriptional patterns in heterokaryotypes are dominant, semidominant, overdominant, or underdominant. We find evidence for a significant abundance of differentially expressed genes across the inverted regions of the third chromosome, including an enrichment of genes involved in sensory perception for males. We find the majority of loci show additivity in heterokaryotypes. Our results suggest that multiple genes have expression differences among arrangements that were either captured by the original inversion mutation or accumulated after it reached polymorphic frequencies, providing a potential source of genetic variation for selection to act upon. These data suggest that the inversions are favored because of their indirect effect of recombination suppression that has held different combinations of differentially expressed genes together in the various gene arrangement backgrounds.
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molecular population genetics of inversion breakpoint regions in Drosophila pseudoobscura
G3: Genes Genomes Genetics, 2013Co-Authors: Andre G Wallace, Don Detweiler, Stephen W SchaefferAbstract:Paracentric inversions in populations can have a profound effect on the pattern and organization of nucleotide variability along a chromosome. Regions near inversion breakpoints are expected to have greater levels of differentiation because of reduced genetic exchange between different gene arrangements whereas central regions in the inverted segments are predicted to have lower levels of nucleotide differentiation due to greater levels of genetic flux among different karyotypes. We used the inversion polymorphism on the third chromosome of Drosophila pseudoobscura to test these predictions with an analysis of nucleotide diversity of 18 genetic markers near and away from inversion breakpoints. We tested hypotheses about how the presence of different chromosomal arrangements affects the pattern and organization of nucleotide variation. Overall, markers in the distal segment of the chromosome had greater levels of nucleotide heterozygosity than markers within the proximal segment of the chromosome. In addition, our results rejected the hypothesis that the breakpoints of derived inversions will have lower levels of nucleotide variability than breakpoints of ancestral inversions, even when strains with gene conversion events were removed. High levels of linkage disequilibrium were observed within all 11 breakpoint regions as well as between the ends of most proximal and distal breakpoints. The central region of the chromosome had the greatest levels of linkage disequilibrium compared with the proximal and distal regions because this is the region that experiences the highest level of recombination suppression. These data do not fully support the idea that genetic exchange is the sole force that influences genetic variation on inverted chromosomes.
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Meiotic Transmission of Drosophila pseudoobscura Chromosomal Arrangements
2013Co-Authors: Richard P Meisel, Stephen W SchaefferAbstract:Drosophila pseudoobscura harbors a rich gene arrangement polymorphism on the third chromosome generated by a series of overlapping paracentric inversions. The arrangements suppress recombination in heterokaryotypic individuals, which allows for the selective maintenance of coadapted gene complexes. Previous mapping experiments used to determine the degree to which recombination is suppressed in gene arrangement heterozygotes produced non-recombinant progeny in non-Mendelian ratios. The deviations from Mendelian expectations could be the result of viability differences between wild and mutant chromosomes, meiotic drive because of achiasmate pairing of homologues in heterokaryotypic females during meiosis, or a combination of both mechanisms. The possibility that the frequencies of the chromosomal arrangements in natural populations are affected by mechanisms other than adaptive selection led us to consider these hypotheses. We performed reciprocal crosses involving both heterozygous males and females to determine if the frequency of the non-recombinant progeny deviates significantly from Mendelian expectations and if the frequencies deviate between reciprocal crosses. We failed to observe non-Mendelian ratios in multiple crosses, and the frequency of the non-recombinant classes differed in only one of five pairs of reciprocal crosses despite sufficient power to detect these differences in all crosses. Our results indicate that deviations from Mendelian expectations in recombination experiments involving the D. pseudoobscura inversion system are most likely due to fitness differences of gene arrangement karyotypes in different environments
Nina Wedell - One of the best experts on this subject based on the ideXlab platform.
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an x linked meiotic drive allele has strong recessive fitness costs in female Drosophila pseudoobscura
Proceedings of The Royal Society B: Biological Sciences, 2019Co-Authors: William Larner, Tom A R Price, Luke Holman, Nina WedellAbstract:Selfish 'meiotic drive' alleles are transmitted to more than 50% of offspring, allowing them to rapidly invade populations even if they reduce the fitness of individuals carrying them. Theory predicts that drivers should either fix or go extinct, yet some drivers defy these predictions by persisting at low, stable frequencies for decades. One possible explanation for this discrepancy is that drivers are especially costly when homozygous, although empirical tests of this idea are rare and equivocal. Here, we measure the fitness of female Drosophila pseudoobscura carrying zero, one or two copies of the X-linked driver sex ratio (SR). SR had strong negative effects on female offspring production and the probability of reproductive failure, and these effects were largely similar across four genetic backgrounds. SR was especially costly when homozygous. We used our fitness measurements to parametrize a population genetic model, and found that the female fitness costs observed here can explain the puzzlingly low allele frequency of SR in nature. We also use the model to show how spatial variation in female mating behaviour, fitness costs of SR and the reduced siring success of SR males can jointly explain the north-south cline in SR frequencies across North America.
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opposite environmental and genetic influences on body size in north american Drosophila pseudoobscura
BMC Evolutionary Biology, 2015Co-Authors: Michelle L Taylor, Alison Skeats, Tom A R Price, Alastair J Wilson, Nina WedellAbstract:Populations of a species often differ in key traits. However, it is rarely known whether these differences are associated with genetic variation and evolved differences between populations, or are instead simply a plastic response to environmental differences experienced by the populations. Here we examine the interplay of plasticity and direct genetic control by investigating temperature-size relationships in populations of Drosophila pseudoobscura from North America. We used 27 isolines from three populations and exposed them to four temperature regimes (16°C, 20°C, 23°C, 26°C) to examine environmental, genetic and genotype-by-environment sources of variance in wing size. By far the largest contribution to variation in wing size came from rearing temperature, with the largest flies emerging from the coolest temperatures. However, we also found a genetic signature that was counter to this pattern as flies originating from the northern, cooler population were consistently smaller than conspecifics from more southern, warmer populations when reared under the same laboratory conditions. We conclude that local selection on body size appears to be acting counter to the environmental effect of temperature. We find no evidence that local adaptation in phenotypic plasticity can explain this result, and suggest indirect selection on traits closely linked with body size, or patterns of chromosome inversion may instead be driving this relationship.
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can patterns of chromosome inversions in Drosophila pseudoobscura predict polyandry across a geographical cline
Ecology and Evolution, 2014Co-Authors: Paul Herrera, Michelle L Taylor, Alison Skeats, Tom A R Price, Nina WedellAbstract:Female multiple mating, known as polyandry, is ubiquitous and occurs in a wide variety of taxa. Polyandry varies greatly from species in which females mate with one or two males in their lifetime to species in which females may mate with several different males on the same day. As multiple mating by females is associated with costs, numerous hypotheses attempt to explain this phenomenon. One hypothesis not extensively explored is the possibility that polyandrous behavior is captured and “fixed” in populations via genetic processes that preserve the behavior independently of any adaptive benefit of polyandry. Here, we use female isolines derived from populations of Drosophila pseudoobscura from three locations in North America to examine whether different female remating levels are associated with patterns of chromosome inversions, which may explain patterns of polyandry across the geographic range. Populations differed with respect to the frequency of polyandry and the presence of inversion polymorphisms on the third chromosome. The population with the lowest level of female remating was the only one that was entirely comprised of homokaryotypic lines, but the small number of populations prevented us investigating this relationship further at a population level. However, we found no strong relationship between female remating levels and specific karyotypes of the various isolines.
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no evidence of mate discrimination against males carrying a sex ratio distorter in Drosophila pseudoobscura
Behavioral Ecology and Sociobiology, 2012Co-Authors: Tom A R Price, Zenobia Lewis, Damian T Smith, Gregory D D Hurst, Nina WedellAbstract:Selfish genetic elements (SGEs) that spread by manipulating spermatogenesis often have highly deleterious effects on males that carry them. Females that mate with male carriers of SGEs can also suffer significant costs: they receive fewer and poorer-quality sperm, their offspring will inherit the deleterious allele, and the sex ratio of their offspring will be biased towards the more common sex. To counter these costs, females are therefore expected to prefer to mate with males that do not carry sex ratio distorters or other deleterious selfish genetic elements. However, despite the potential costs, there are few examples of female choice against males carrying SGEs. We searched for evidence of a female preference in fruit fly Drosophila pseudoobscura against males carrying a costly meiotic driving X-chromosome Sex Ratio (SR). In a series of five non-competitive mate preference experiments, we find no evidence that females prefer to mate with non-SR males. Our use of five separate experiments, involving more than 800 females, makes it unlikely that this lack of a difference was due to low power or simple chance. We suggest that the lack of female choice against SGE-carrying males may be due to strong selection on SGEs to be indistinguishable from alternative alleles. Furthermore, polyandry, either in direct response to receiving an ejaculate from an SGE-carrying male or carried out indiscriminately when at risk of mating with carriers, may be an alternative response by females to limit the exposure of their offspring to SGEs.
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sex ratio drive promotes sexual conflict and sexual coevolution in the fly Drosophila pseudoobscura
Evolution, 2009Co-Authors: Tom A R Price, Zenobia Lewis, Damian T Smith, Gregory D D Hurst, Nina WedellAbstract:Selfish genetic elements occur in all living organisms and often cause reduced fertility and sperm competitive ability in males. In the fruit fly Drosophila pseudoobscura, the presence of a sex-ratio distorting X-chromosome meiotic driver Sex Ratio (SR) has been shown to promote the evolution of increased female remating rates in laboratory populations. This is favored because it promotes sperm competition, which decreases the risk to females of producing highly female-biased broods and to their offspring of inheriting the selfish gene. Here, we show that non-SR males in these SR populations evolved an increased ability to suppress female remating in response to the higher female remating rates, indicating male-female coevolution. This occurred even though SR was rare in the populations. This was further supported by a correlation between females' remating propensity and males' ability to suppress female remating across populations. Thus SR can generate sexual conflict over female remating rate between females and the noncarrier males that make up the majority of the males, promoting evolution of increased ability of males to suppress female remating.
Wyatt W Anderson - One of the best experts on this subject based on the ideXlab platform.
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sexual isolation between north american and bogota strains of Drosophila pseudoobscura
Behavior Genetics, 2012Co-Authors: Yongkyu Kim, Manuel Ruizgarcia, Diana Alvarez, Dennis Phillips, Wyatt W AndersonAbstract:Sexual isolation, the reduced ability of organisms of different species to successfully mate, is one of the reproductive barriers that prevent gene flow between different taxa. Various species-specific signals during courtship are attributed to the sexual isolation between them. Drosophila pseudoobscura has been widely used to study the behavioral and genetic mechanisms underlying selection for sexual isolation, as a model system for speciation. D. pseudoobscura and its sibling species, D. persmilis, live together in many locations but are reproductively isolated from one another. North American geographic strains of D. pseudoobscura from the American West mate at random. Several decades ago, D. pseudoobscura was collected in the vicinity of Bogota, Colombia, and later named the subspecies D. pseudoobscura bogotana. Nearly 5,000 matings were observed in this study. We analyzed mating behavior and cuticular hydrocarbon profiles as well as courtship within and between North American and Bogota strains of D. pseudoobscura. Here we report for the first time that Bogota strains of D. pseudoobscura do show statistically significant sexual isolation from North American strains. In addition, there are quantitative variations in cuticular hydrocarbons as well as in courtship behavior between Bogota and North American strains, and females of both North American and Bogota strains show strong preference for North American strain males having high mating propensities, suggesting that the Bogota strains are at an early stage that could lead to a separate species.
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preference status does not indicate intrinsic quality differences in Drosophila pseudoobscura
Integrative Zoology, 2010Co-Authors: Yongkyu Kim, Wyatt W Anderson, Patricia Adair Gowaty, Mary Beth WeberAbstract:The good genes hypothesis states that choosers prefer individuals of high intrinsic quality to individuals of lower intrinsic quality. Variation in longevity is thought to reflect, in part, intrinsic quality differences of individuals in addition to the costs of mating and reproduction. Here we report longevity variation of Drosophila pseudoobscura, a species in which previous experiments have demonstrated that individual mate preferences (pre-touching mate assessments) of females and males are associated with enhanced numbers of eclosed (adult) offspring and higher egg-to-adult survival (offspring viability). Using mate assessment arenas and protocols similar to those in a previous experiment that demonstrated fitness benefits to breeders and their offspring of mating with individuals they preferred, we tested the following predictions: (i) preferred discriminatees live longer than non-preferred discriminatees; (ii) males live longer than females; and (iii) virgins live longer than mated individuals. The experiment yielded 938 individuals for longevity analysis. Sex and mating status affected longevity: males lived longer than females, virgin females lived longer than mated females, but there were no differences in longevity for mated and virgin males. Non-preferred discriminatees of both sexes survived as long as preferred discriminatees, a result inconsistent with the prediction of the good genes hypothesis for mate preferences. To our knowledge, this is the first demonstration of the cost of reproduction for females in D. pseudoobscura and of longevity variation of preferred and non-preferred discriminatees.
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polyandry increases offspring viability and mother productivity but does not decrease mother survival in Drosophila pseudoobscura
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Patricia Adair Gowaty, Jessica Rawlings, Wyatt W AndersonAbstract:Polyandrous mating is common, but the benefits for females of polyandry remain controversial. To test whether mating with multiple males affects female fitness, we compared lifetime components of fitness of three experimental sets of Drosophila pseudoobscura females: monogamous females allowed to copulate one time (MOC); monogamous females held with a male over her entire life and experiencing many copulations (MMC); and polyandrous females with a different male over each day of their lives and also experiencing many copulations (PMC). Consistent with previous studies in this species, females in treatments in which multiple copulations occurred, MMC and PMC, had offspring with significantly higher egg-to-adult survival (i.e., offspring viability) and higher numbers of adult offspring (i.e., productivity) than MOC females, showing that multiple inseminations enhance offspring and mother fitness. In addition, although MMC females laid significantly more eggs than polyandrous (PMC) females, percent egg-to-adult survival and number of adult offspring were higher for PMC than MMC females, showing that polyandrous mating enhances the fitness of females more than multiply mating with only one male. Inconsistent with the cost of reproduction, lifespan was not significantly longer for MOC females than for MMC or PMC females. To our knowledge, this is the first study to examine simultaneously in outbred WT Drosophila pseudoobscura the lifetime costs and benefits to females of polyandry, monogamy with a single copulation, and monogamy with repeat copulations.
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experimental constraints on mate preferences in Drosophila pseudoobscura decrease offspring viability and fitness of mated pairs
Proceedings of the National Academy of Sciences of the United States of America, 2007Co-Authors: Wyatt W Anderson, Yongkyu Kim, Patricia Adair GowatyAbstract:Using Drosophila pseudoobscura, we tested the hypothesis that social constraints on the free expression of mate preferences, by both females and males, decrease offspring viability and reproductive success of mating pairs. Mate preference arenas eliminated intrasexual combat and intersexual coercion. The time female and male choosers spent in arena tests near either of two opposite-sex individuals measured the preferences of choosers. We placed choosers in breeding trials with their preferred or nonpreferred discriminatee when they met the minimum criteria for showing the same preference in two consecutive tests. There was no statistically significant difference in the frequency of female and male choosers meeting minimal preference criteria. There was a significant difference between female and male choosers for offspring viability, with female choice having the greater effect, but there was not a significant difference in the overall reproductive success of male and female choosers. There were significant differences in fitness between matings to preferred and nonpreferred partners. Female and male choosers paired with their nonpreferred discriminatees had offspring of significantly lower viability, as predicted by the constraints hypothesis. Reproductive success, our measure of overall fitness, was greater when males or females mated with the partner they preferred rather than the one they did not prefer.
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mechanisms of genetic exchange within the chromosomal inversions of Drosophila pseudoobscura
Genetics, 2005Co-Authors: Stephen W Schaeffer, Wyatt W AndersonAbstract:We have used the inversion system of Drosophila pseudoobscura to investigate how genetic flux occurs among the gene arrangements. The patterns of nucleotide polymorphism at seven loci were used to infer gene conversion events between pairs of different gene arrangements. We estimate that the average gene conversion tract length is 205 bp and that the average conversion rate is 3.4 × 10−6, which is 2 orders of magnitude greater than the mutation rate. We did not detect gene conversion events between all combinations of gene arrangements even though there was sufficient nucleotide variation for detection and sufficient opportunity for exchanges to occur. Genetic flux across the inverted chromosome resulted in higher levels of differentiation within 0.1 Mb of inversion breakpoints, but a slightly lower level of differentiation in central inverted regions. No gene conversion events were detected within 17 kb of an inversion breakpoint suggesting that the formation of double-strand breaks is reduced near rearrangement breakpoints in heterozygotes. At least one case where selection rather than proximity to an inversion breakpoint is responsible for reduction in polymorphism was identified.
Rhonda R. Snook - One of the best experts on this subject based on the ideXlab platform.
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mating system variation drives rapid evolution of the female transcriptome in Drosophila pseudoobscura
Ecology and Evolution, 2014Co-Authors: Rhonda R. Snook, Elina Immonen, Michael G RitchieAbstract:Interactions between the sexes are believed to be a potent source of selection on sex-specific evolution. The way in which sexual interactions influence male investment is much studied, but effects on females are more poorly understood. To address this deficiency, we examined gene expression in virgin female Drosophila pseudoobscura following 100 generations of mating system manipulations in which we either elevated polyandry or enforced monandry. Gene expression evolution following mating system manipulation resulted in 14% of the transcriptome of virgin females being altered. Polyandrous females elevated expression of a greater number of genes normally enriched in ovaries and associated with mitosis and meiosis, which might reflect female investment into reproductive functions. Monandrous females showed a greater number of genes normally enriched for expression in somatic tissues, including the head and gut and associated with visual perception and metabolism, respectively. By comparing our data with a previous study of sex differences in gene expression in this species, we found that the majority of the genes that are differentially expressed between females of the selection treatments show female-biased expression in the wild-type population. A striking exception is genes associated with male-specific reproductive tissues (in D. melanogaster), which are upregulated in polyandrous females. Our results provide experimental evidence for a role of sex-specific selection arising from differing sexual interactions with males in promoting rapid evolution of the female transcriptome.
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Sexual selection and experimental evolution of chemical signals in Drosophila pseudoobscura
Journal of Evolutionary Biology, 2012Co-Authors: J. Hunt, C. Mitchell, Helen S. Crudgington, Rhonda R. Snook, A. J. MooreAbstract:Our expectations for the evolution of chemical signals in response to sexual selection are uncertain. How are chemical signals elaborated? Does sexual selection result in complexity of the composition or in altered quantities of expression? We addressed this in Drosophila pseudoobscura by examining male and female cuticular hydrocarbons (CHs) after 82 generations of elevated (E) sexual selection or relaxed sexual selection through monogamy (M). The CH profile consisted of 18 different components. We extracted three eigenvectors using principal component analysis that explained 72% of the variation. principal component (PC)1 described the amount of CHs produced, PC2 the trade-off between short- and long-chain CHs and PC3 the trade-off between apparently arbitrary CHs. In both sexes, the amount of CHs produced was greater in flies from the E treatment. PC3 was also higher, indicating that sexual selection also influenced the evolution of CH composition. The sexes differed in all three PCs, indicating substantial sexual dimorphism in this species, although the magnitude of this dimorphism was not increased as a result of our experimental evolution. Collectively, our work provides direct evidence that sexual selection plays an important role in the evolution of CHs in D. pseudoobscura and that both increased quantity and overall composition are targeted.
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sexual selection and interacting phenotypes in experimental evolution a study of Drosophila pseudoobscura mating behavior
Evolution, 2008Co-Authors: Leonardo D. Bacigalupe, A. J. Moore, Helen S. Crudgington, Jon Slate, Rhonda R. SnookAbstract:Sexual selection requires social interactions, particularly between the sexes. When trait expression is influenced by social interactions, such traits are called interacting phenotypes and only recently have the evolutionary consequences of interacting phenotypes been considered. Here we investigated how variation in relative fitness, or the opportunity for sexual selection, affected the evolutionary trajectories of interacting phenotypes. We used experimentally evolved populations of the naturally promiscuous Drosophila pseudoobscura, in which the numbers of potential interactions between the sexes, and therefore relative fitness, were manipulated by altering natural levels of female promiscuity. We considered two different mating interactions between the sexes: mating speed and copulation duration. We investigated the evolutionary trajectories of means and (co)variances (P) and also the influence of genetic drift on the evolutionary response of these interactions. Our sexual selection treatments did not affect the means of either mating speed or copulation duration, but they did affect P. We found that the means of both traits differed among replicates within each selection treatment whereas the Ps did not. Changes as a consequence of genetic drift were excluded. Our results show that although variable potential strengths of sexual interactions influence the evolution of interacting phenotypes, the influence may be nonlinear.
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Sexual conflict does not drive reproductive isolation in experimental populations of Drosophila pseudoobscura
Journal of Evolutionary Biology, 2007Co-Authors: Leonardo D. Bacigalupe, A. J. Moore, Helen S. Crudgington, F. Hunter, Rhonda R. SnookAbstract:Sexual conflict has been predicted to drive reproductive isolation by generating arbitrary but rapid coevolutionary changes in reproductive traits among allopatric populations. A testable prediction of this proposal is that allopatric populations experiencing different levels of sexual conflict should exhibit different levels of reproductive isolation. We tested this prediction using experimentally evolved populations of the promiscuous Drosophila pseudoobscura. We manipulated sexual conflict by enforcing either monogamy, maintaining natural levels of promiscuity, or elevating promiscuity. Within each treatment, we carried out sympatric and allopatric crosses using replicated populations and examined pre-zygotic (number of mating pairs, mating speed and copulation duration) and post-zygotic (hybrid inviability and sterility) indicators of reproductive isolation. After 50 generations of selection, none of the measures conformed to predictions of sexual conflict driving reproductive isolation. Our results cannot be explained by lack of genetic variation or weak selection and suggest that sexual conflict may not be a widespread engine of speciation.
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Experimental Manipulation of Sexual Selection and the Evolution of Courtship Song in Drosophila pseudoobscura
Behavior Genetics, 2005Co-Authors: Rhonda R. Snook, Helen S. Crudgington, A. Robertson, M. G. RitchieAbstract:Courtship song serves as a sexual signal and may contribute to reproductive isolation between closely related species. Using lines of Drosophila pseudoobscura experimentally selected under different sexual selection regimes, we tested whether increased promiscuity and enforced monogamy led to evolutionary changes in courtship song elements. In D. pseudoobscura , males produce both a low and high rate repetition song. We found that both song types diverged after selection and that the direction of changes was consistent with ordered hypotheses of predicted directions of change under the different mating system structures. In particular, latency to the initiation of song and duration of the interpulse interval (IPI) decreased in highly promiscuous lines and increased in monogamous lines. These results suggest that courtship song may rapidly evolve under different mating system structures, representing either functional evolution of more stimulatory song under conditions of strong sexual selection, or might result from increased courtship vigor, or represent correlated evolution. Some speciation theory predicts that increased sexual selection should result in increased variance of traits between allopatric populations, facilitating reproductive isolation. We also found that courtship song elements were not equally variable between replicate lines.
