Speciation In Drosophila Research Articles

A comprehensive evolutionary scenario for the origin and neofunctionalization of the Drosophila speciation gene Odysseus (OdsH).

Odysseus (OdsH) was the first speciation gene described in Drosophila related to hybrid sterility in offspring of mating between Drosophila mauritiana and Drosophila simulans. Its origin is attributed to the duplication of the gene unc-4 in the subgenus Sophophora. By using a much larger sample of Drosophilidae species, we showed that contrary to what has been previously proposed, OdsH origin occurred 62 MYA. Evolutionary rates, expression, and transcription factor-binding sites of OdsH evidence that it may have rapidly experienced neofunctionalization in male sexual functions. Furthermore, the analysis of the OdsH peptide allowed the identification of mutations of D. mauritiana that could result in incompatibility in hybrids. In order to find if OdsH could be related to hybrid sterility, beyond Sophophora, we explored the expression of OdsH in Drosophila arizonae and Drosophila mojavensis, a pair of sister species with incomplete reproductive isolation. Our data indicated that OdsH expression is not atypical in their male-sterile hybrids. In conclusion, we have proposed that the origin of OdsH occurred earlier than previously proposed, followed by neofunctionalization. Our results also suggested that its role as a speciation gene might be restricted to D. mauritiana and D. simulans.

Model-Based Species Delimitation: Are Coalescent Species Reproductively Isolated?

A large and growing fraction of systematists define species as independently evolving lineages that may be recognized by analyzing the population genetic history of alleles sampled from individuals belonging to those species. This has motivated the development of increasingly sophisticated statistical models rooted in the multispecies coalescent process. Specifically, these models allow for simultaneous estimation of the number of species present in a sample of individuals and the phylogenetic history of those species using only DNA sequence data from independent loci. These methods hold extraordinary promise for increasing the efficiency of species discovery but require extensive validation to ensure that they are accurate and precise. Whether the species identified by these methods correspond to the species that would be recognized by alternative species recognition criteria (such as measurements of reproductive isolation) is currently an open question and a subject of vigorous debate. Here, we perform an empirical test of these methods by making use of a classic model system in the history of speciation research, flies of the genus Drosophila. Specifically, we use the uniquely comprehensive data on reproductive isolation that is available for this system, along with DNA sequence data, to ask whether Drosophila species inferred under the multispecies coalescent model correspond to those recognized by many decades of speciation research. We found that coalescent based and reproductive isolation-based methods of inferring species boundaries are concordant for 77% of the species pairs. We explore and discuss potential explanations for these discrepancies. We also found that the amount of prezygotic isolation between two species is a strong predictor of the posterior probability of species boundaries based on DNA sequence data, regardless of whether the species pairs are sympatrically or allopatrically distributed. [BPP; Drosophila speciation; genetic distance; multispecies coalescent.].

Tissue-Specific cis-Regulatory Divergence Implicates eloF in Inhibiting Interspecies Mating in Drosophila

Reproductive isolation is a key component of speciation. In many insects, a major driver of this isolation is cuticular hydrocarbon pheromones, which help to identify potential intraspecific mates [1-3]. When the distributions of related species overlap, there may be strong selection on mate choice for intraspecific partners [4-9] because interspecific hybridization carries significant fitness costs [10]. Drosophila hasbeen a key model for the investigation of reproductive isolation; although both male and female mate choices have been extensively investigated [6,11-16], the genes underlying species recognition remain largely unknown. To explore the molecular mechanisms underlying Drosophila speciation, we measured tissue-specific cis-regulatory divergence using RNA sequencing (RNA-seq) in D.simulans × D.sechellia hybrids. By focusing on cis-regulatory changes specific to female oenocytes, the tissue that produces cuticular hydrocarbons, we rapidly identified a small number of candidate genes. We found that one of these, the fatty acid elongase eloF, broadly affects the hydrocarbons present on D.sechellia and D.melanogaster females, as well asthe propensity of D.simulans males to mate withthem. Therefore, cis-regulatory changes in eloF may be a major driver in the sexual isolation of D.simulans from multiple other species. Our RNA-seq approach proved to be far more efficient than quantitative trait locus (QTL) mapping in identifying candidate genes; the same framework can be used to pinpoint candidate drivers of cis-regulatory divergence in traits differing between any interfertile species.

The Drosophila speciation factor HMR localizes to genomic insulator sites.

Hybrid incompatibility between Drosophila melanogaster and D. simulans is caused by a lethal interaction of the proteins encoded by the Hmr and Lhr genes. In D. melanogaster the loss of HMR results in mitotic defects, an increase in transcription of transposable elements and a deregulation of heterochromatic genes. To better understand the molecular mechanisms that mediate HMR’s function, we measured genome-wide localization of HMR in D. melanogaster tissue culture cells by chromatin immunoprecipitation. Interestingly, we find HMR localizing to genomic insulator sites that can be classified into two groups. One group belongs to gypsy insulators and another one borders HP1a bound regions at active genes. The transcription of the latter group genes is strongly affected in larvae and ovaries of Hmr mutant flies. Our data suggest a novel link between HMR and insulator proteins, a finding that implicates a potential role for genome organization in the formation of species.

ON THE COYNE AND ORR-IGIN OF SPECIES: EFFECTS OF INTRINSIC POSTZYGOTIC ISOLATION, ECOLOGICAL DIFFERENTIATION, X CHROMOSOME SIZE, AND SYMPATRY ONDROSOPHILASPECIATION

Coyne and Orr found that mating discrimination (premating isolation) evolves much faster between sympatric than allopatric Drosophila species pairs. Their meta-analyses established that this pattern, expected under reinforcement, is common and that Haldane's rule is ubiquitous in Drosophila species divergence. We examine three possible contributors to the reinforcement pattern: intrinsic postzygotic isolation, dichotomized as to whether hybrid males show complete inviability/sterility; host-plant divergence, as a surrogate for extrinsic postzygotic isolation; and X chromosome size, whether roughly 20% or 40% of the genome is X-linked. We focus on "young" species pairs with overlapping ranges, contrasted with allopatric pairs. Using alternative criteria for "sympatry" and tests that compare either level of prezygotic isolation in sympatry or frequency of sympatry, we find no statistically significant effects associated with X chromosome size or our coarse quantifications of intrinsic postzygotic isolation or ecological differentiation. Although sympatric speciation seems very rare in animals, the pervasiveness of the reinforcement pattern and the commonness of range overlap for close relatives indicate that speciation in Drosophila is often not purely allopatric. It remains to determine whether increased premating isolation with sympatry results from secondary contact versus parapatric speciation and what drives this pattern.

Role of sexual selection in speciation in Drosophila

The power of sexual selection to drive changes in the mate recognition system through divergence in sexually selected traits gives it the potential to be a potent force in speciation. To know how sexual selection can bring such type of divergence in the genus Drosophila, comparative studies based on intra- and inter-sexual selection are documented in this review. The studies provide evidence that both mate choice and male-male competition can cause selection of trait and preference which thereby leads to divergence among species. In the case of intrasexual selection, various kinds of signals play significant role in affecting the species mate recognition system and hence causing divergence between the species. However, intrasexual selection can bring the intraspecific divergence at the level of pre- and post-copulatory stage. This has been better explained through Hawaiian Drosophila which has been suggested a wonderful model system in explaining the events of speciation via sexual selection. This is due to their elaborate mating displays and some kind of ethological isolation persisting among them. Similarly, the genetic basis of sexually selected variations can provide yet another path in understanding the speciation genetics via sexual selection more closely.

Behavioural reproductive isolation and speciation in Drosophila

The origin of premating reproductive isolation continues to help elucidate the process of speciation and is the central event in the evolution of biological species. Therefore, during the process of species formation the diverging populations must acquire some means of reproductive isolation so that the genes from one gene pool are prevented from dispersing freely into a foreign gene pool. In the genus Drosophila, the phenomenon of behavioural reproductive isolation, which is an important type of premating (prezygotic) reproductive isolating mechanisms, has been extensively studied and interesting data have been documented. In many cases incomplete sexual isolation has been observed and the pattern and degree of isolation within and between the species have often been used to elucidate the phylogenetic relationships. The present review documents an overview of speciation mediated through behavioural incompatibility in different species groups of Drosophila with particular reference to the models proposed on the basis of one-sided ethological isolation to predict the direction of evolution. This study is crucial for understanding the mechanism of speciation through behavioural incompatibility and also for an understanding of speciation genetics in future prospects.

ASYMMETRICAL PATTERNS OF SPECIATION UNIQUELY SUPPORT REINFORCEMENT INDROSOPHILA

Understanding how often natural selection directly favors speciation, a process known as reinforcement, has remained an outstanding problem for over 70 years. Although reinforcement has been strongly criticized in the past, it is once again seen as more realistic due to the seminal discovery of enhanced prezygotic isolation among sympatric species and to a handful of well-studied examples. Nevertheless, the pattern of enhanced isolation in sympatry has alternative explanations, highlighting the need to uncover unique signatures of reinforcement to determine its overall frequency in nature. Using a novel dataset on asymmetrical prezygotic and postzygotic isolation among Drosophila species, I uncover new patterns explicitly predicted by reinforcement. Broadly, I found that almost all sympatric species had concordant isolation asymmetries, where the more costly reciprocal mating has greater prezygotic isolation relative to the less costly mating. No such patterns exist in allopatry. Using simulations, I ruled out alternative explanations and showed that concordant isolation asymmetries in sympatry are likely unique signatures of reinforcement. These results allowed me to estimate that reinforcement may impact 60-83% of all sympatric Drosophila and enhance premating isolation by 18-26%. These findings suggest that reinforcement plays a key role in Drosophila speciation.

Sex Chromosome-Specific Regulation in the Drosophila Male Germline But Little Evidence for Chromosomal Dosage Compensation or Meiotic Inactivation

Author SummaryMany species have heteromorphic sex chromosomes (XY males or ZW females) where one sex chromosome (the Y or W) has degenerated. In the somatic cells of mammals, worms, and flies, the X-to-autosome ratio of expression is equalized between the sexes by dedicated sex chromosome-specific dosage compensation systems. In the germline cells of male mammals and worms, however, the X chromosome is transcriptionally silenced early in meiosis. Here we have analyzed gene expression in Drosophila testes and show that the X chromosome lacks both of these types of chromosomal regulation. We find that X chromosome-wide dosage compensation is absent from most cells in the Drosophila male germline, and there is little or no evidence for X chromosome-specific inactivation during meiosis. However, another kind of sex-chromosome-specific regulation occurs. Testes-specific transgene reporters show much weaker expression when inserted on the X chromosome versus the autosomes, suggesting that some other, uncharacterized mechanism limits their expression from the X during spermatogenesis. The strong suppression of X-linked transgenes—but not X-linked endogenous genes—suggests that endogenous X-linked testes-specific promoters might have adapted to a suppressive X chromosome environment in the Drosophila male germline.

Comparative genomics analysis of metallothioneins in twelve Drosophila species

Metallothioneins (MTs) are a superfamily of Cys-rich polypeptides that bind heavy metal ions, both for physiological and detoxification purposes. They are present in all organisms, but their origin is probably polyphyletic, so that MT evolutionary studies are rather scarce. We present a thorough search and analysis of the MT coding sequences in the 12 Drosophila genomes completely sequenced, taking as reference the features reported for D. melanogaster, where four isogenes ( MtnA to MtnD) are known and deeply characterized. We include a fifth isoform in this study, named MtnE, and recently annotated. The MTs polymorphism pattern is essentially the same for the 12 Drosophila species. Invariably, a MtnA form and an MtnB-cluster, comprising the MtnB-to-MtnE forms in tandem array, are observed. The whole set of genes are kept in the same synteny element (Muller E), but implicated in rearrangement events (mainly inversions), encompassing all or some of the isogenes. Gene exon/intron architecture, and cDNA and protein sequences appear highly conserved through Drosophila speciation, concordantly with an essential function for MT isoforms in flies, even for those previously considered as minor products. Data presented here will be comprehensively analyzed to provide a valuable guide for future MT evolutionary, structure and function studies.

Reinforcement can overcome gene flow during speciation in Drosophila.

Reinforcement, the strengthening of prezygotic reproductive isolation by natural selection in response to maladaptive hybridization [1-3], is one of the few processes in which natural selection directly favors the evolution of species as discrete groups (e.g., [4-7]). The evolution of reproductive barriers via reinforcement is expected to evolve in regions where the ranges of two species overlap and hybridize as an evolutionary solution to avoiding the costs of maladaptive hybridization [2,3,8]. The role of reinforcement in speciation has, however, been highly controversial because population-genetic theory suggests that the process is severely impeded by both hybridization [8-11] and migration of individuals from outside the contact zone [12,13]. To determine whether reinforcement could strengthen the reproductive barriers between two sister species of Drosophila in the face of these impediments, I initiated experimental populations of these two species that allowed different degrees of hybridization, as well as migration from outside populations. Surprisingly, even in the face of gene flow, reinforcement could promote the evolution of reproductive isolation within only five generations. As theory predicts, high levels of hybridization (and/or strong selection against hybrids) and migration impeded this evolution. These results suggest that reinforcement can help complete the process of speciation.

Sensory Components of Behavioral Isolation Between Zimbabwe and Cosmopolitan Drosophila Melanogaster

Successful reproduction requires males and females from the same species to recognize and prefer each other over individuals of other species. Mate recognition is mediated through the sensory systems, and one way speciation can occur is through behavioral isolation via sensory cues.Drosophila melanogasterfemales from central Africa (the "Zimbabwe" morph) prefer to mate with Zimbabwe males over males from otherDrosophilastrains ("Cosmopolitan" strains). Cosmopolitan females typically show little or no preference towards Cosmopolitan males. We hypothesize that alterations in one or more cues detected by the sensory system underlie the mating preferences of Zimbabwe females. Here, we investigate the relative contributions of three sensory factors (olfaction, vision, and hearing) to female mating preference using a number of Zimbabwe strains. Our findings suggest that auditory and visual cues are the most critical to this mate choice preference phenomenon. These results elucidate plausible mechanisms underlying incipient speciation inDrosophila.

The Genomics of Speciation in Drosophila: Diversity, Divergence, and Introgression Estimated Using Low-Coverage Genome Sequencing

In nature, closely related species may hybridize while still retaining their distinctive identities. Chromosomal regions that experience reduced recombination in hybrids, such as within inversions, have been hypothesized to contribute to the maintenance of species integrity. Here, we examine genomic sequences from closely related fruit fly taxa of the Drosophila pseudoobscura subgroup to reconstruct their evolutionary histories and past patterns of genic exchange. Partial genomic assemblies were generated from two subspecies of Drosophila pseudoobscura (D. ps.) and an outgroup species, D. miranda. These new assemblies were compared to available assemblies of D. ps. pseudoobscura and D. persimilis, two species with overlapping ranges in western North America. Within inverted regions, nucleotide divergence among each pair of the three species is comparable, whereas divergence between D. ps. pseudoobscura and D. persimilis in non-inverted regions is much lower and closer to levels of intraspecific variation. Using molecular markers flanking each of the major chromosomal inversions, we identify strong crossover suppression in F1 hybrids extending over 2 megabase pairs (Mbp) beyond the inversion breakpoints. These regions of crossover suppression also exhibit the high nucleotide divergence associated with inverted regions. Finally, by comparison to a geographically isolated subspecies, D. ps. bogotana, our results suggest that autosomal gene exchange between the North American species, D. ps. pseudoobscura and D. persimilis, occurred since the split of the subspecies, likely within the last 200,000 years. We conclude that chromosomal rearrangements have been vital to the ongoing persistence of these species despite recent hybridization. Our study serves as a proof-of-principle on how whole genome sequencing can be applied to formulate and test hypotheses about species formation in lesser-known non-model systems.

Happy Birthday, Mr. Darwin

![Figure][1] CREDITS (TOP TO BOTTOM): A. KONINGS; M. LOSOS The diversification and speciation of living organisms are the broad theme for this special section, continuing our celebration of Charles Darwin's 200th birthday. The five Reviews in this section present multiple views on research on diversification at scales ranging from the macroevolutionary to the molecular. Benton (p. [728][2]) examines the extents to which biotic and abiotic factors have shaped species diversity in the fossil record. Gavrilets and Losos (p. 732) use theoretical predictions and empirical data to identify general patterns in the temporal, spatial, and genetic/morphological properties of adaptive radiation. Schluter (p. [737][3]) reviews how research on ecological speciation has shifted in focus from morphological evolution to reproductive isolation, tracing the links between Darwin's ideas and current thinking. Fraser et al. (p. [741][4]) discuss the contentious area of microbial species formation. Finally, using examples from studies of genes and mutations involved in evolutionary change, Stern and Orgogozo (p. 746) illustrate how developmental biology and evolutionary theory might combine to reveal new predictive principles of genetic evolution. The special section is accompanied by evolutionary coverage in all other sections of the magazine. The News section features the second in our series of monthly “origins” essays, on the origins of art and symbolic behavior. The Commentary section includes reviews of new evolutionary books. Science Careers carries a feature on researchers in the museum world, who play a vital role in evolutionary research. In Reports, Krug et al. (p. [767][5]) reveal the legacy of the end-Cretaceous mass extinction for the subsequent diversification of bivalves [see the accompanying Perspective by Crame (p. [720][6])]. With a focus on conservation, Carnaval et al. (p. [785][7]) model spatially explicit evolutionary processes in endemic tree-frog species in the Brazilian Atlantic Forest (the biodiversity hotspot that inspired Darwin during his South American landfall). Forbes et al. (p. 776) reveal how a recent host shift of the fly Rhagoletis pomonella , a model for sympatric speciation, has led to incipient speciation in a parasitoid wasp that attacks the fly. Rowland and Emlen (p. 773) show facultative male trimorphism in dung beetles, a hitherto unsuspected level of intraspecific variation. Tang and Presgraves (p. [779][8]) report a cellular and molecular mechanism of hybrid sterility, which has a key role in speciation in Drosophila . And in Science Express, there is an echo of another of Darwin's central interests: Anderson et al. show that a melanism mutation has been selected for in gray wolves, most likely after a hybridization event with domestic dogs. This is a sample, not a survey. Research on speciation and diversification is itself expanding and diversifying. Evolutionary topics have been covered more frequently in Science in the first decade of the 21st century than in any previous one (and an order of magnitude more than in the years of the Modern Synthesis in the mid-20th century). This reflects not only the continuing efforts to understand and document the selective forces leading to speciation, but also how genetic research is homing in on the molecular and cellular mechanisms that enable diversification to occur. Darwin, we hope, would be thrilled. [1]: pending:yes [2]: /lookup/doi/10.1126/science.1157719 [3]: /lookup/doi/10.1126/science.1160006 [4]: /lookup/doi/10.1126/science.1159388 [5]: /lookup/doi/10.1126/science.1164905 [6]: /lookup/doi/10.1126/science.1169410 [7]: /lookup/doi/10.1126/science.1166955 [8]: /lookup/doi/10.1126/science.1169123

High-Resolution Genome-Wide Dissection of the Two Rules of Speciation in Drosophila

Postzygotic reproductive isolation is characterized by two striking empirical patterns. The first is Haldane's rule—the preferential inviability or sterility of species hybrids of the heterogametic (XY) sex. The second is the so-called large X effect—substitution of one species's X chromosome for another's has a disproportionately large effect on hybrid fitness compared to similar substitution of an autosome. Although the first rule has been well-established, the second rule remains controversial. Here, we dissect the genetic causes of these two rules using a genome-wide introgression analysis of Drosophila mauritiana chromosome segments in an otherwise D. sechellia genetic background. We find that recessive hybrid incompatibilities outnumber dominant ones and that hybrid male steriles outnumber all other types of incompatibility, consistent with the dominance and faster-male theories of Haldane's rule, respectively. We also find that, although X-linked and autosomal introgressions are of similar size, most X-linked introgressions cause hybrid male sterility (60%) whereas few autosomal introgressions do (18%). Our results thus confirm the large X effect and identify its proximate cause: incompatibilities causing hybrid male sterility have a higher density on the X chromosome than on the autosomes. We evaluate several hypotheses for the evolutionary cause of this excess of X-linked hybrid male sterility.

Genetics of Speciation

The American Genetics Association (AGA) is a nonprofit membership society whose mission is to promote the study of genetics. To meet this obligation, the AGA publishes the Journal of Heredity and promotes research in all fields of genetics. The latter is accomplished through an annual meeting and symposium, as well as by sponsorship of special events, such as workshops and symposia in areas of interest to the AGA. In 2006, the annual meeting and symposium of the AGA was held from 21–24 July in Vancouver, British Columbia. The symposium, cosponsored with Molecular Ecology, was titled ‘‘Genetics of Speciation’’ and attracted close to 300 participants. Allen Orr was the recipient of the 2006 Wilhelmine Key Lectureship and gave the keynote lecture on ‘‘Speciation in Drosophila: from Phenotypes to Molecules.’’ Six articles from the symposium, which focus mostly on the genetics of postzygotic isolation, are published in this issue; another six more ecologically orientated papers will appear in Molecular Ecology. The lead article was authored by Allen Orr, J. P. Masly, and Nitin Phadnis, who review what we know about the genetics of intrinsic postzygotic reproductive isolation, at least with respect to genes underlying hybrid incompatibilities. Based on the 4 such genes that had been published by the symposium date (July 2006), Orr et al. note several striking patterns. In particular, most of these genes are evolving rapidly due to natural selection, a finding that supports the neo-Darwinian contention that reproductive isolation typically evolves as a by-product of adaptation. Given the seeming unity of these results, Orr et al. ask the provocative question ‘‘is the genetics of postzygotic isolation wrapped up?’’ That is, will more work in this area likely yield any truly novel results? Fortunately, new results discussed by Orr et al. suggest, in fact, that we are in for some real surprises. Most startling is the discovery that genetic conflict may frequently be the cause of rapid evolution of genes underlying intrinsic postzygotic barriers rather than adaptation to a new environment. Second, there is now evidence that microchromosomal rearrangements may sometimes be the cause of hybrid incompatibilities rather than the traditional Dobzhansky–Muller model. Another of the symposium speakers, Mohamed Noor, has been a leader in exploring nontraditional mechanisms for the evolution of intrinsic postzygotic barriers. In particular, he has developed and empirically tested a model in which genomic regions with low recombination (such as chromosomal inversions) allow Dobzhansky–Muller incompatibilities to accumulate despite ongoing gene flow. In this issue, Cirulli and Noor localize the break points of an inversion between two Drosophila species. Contrary to most other studies, there were no shared repetitive sequences between the 2 break point regions. Thus, the cause of the inversion remains a mystery. Most attempts to localize hybrid incompatibilities have employed experimental crosses, in which associations between molecular markers and sterility or inviability are used to identify chromosomal segments or genes that contribute to hybrid disorders. Although this approach has been highly successful, it is difficult to apply to nonmodel organisms, which can be challenging to rear in the laboratory or greenhouse. Thus, a number of authors have explored the possibility of using patterns of introgression in natural hybrid zones to localize genes or chromosomal rearrangements that contribute to isolation. In ‘‘Searching the Genomes of Inbred Mouse Strains for Incompatibilities that Reproductively Isolate Their Wild Relatives,’’ Payseur and Place successfully employ this strategy to identify pairs of loci that may contribute to reproductive isolation between 2 mice species. One of the early conclusions (above) from studies of the genes causing hybrid incompatibilities is that postzygotic isolation often appears to be a by-product of adaptation. Thus, Leonie Moyle asks whether quantitative trait loci (QTLs) underlying putative prezygotic isolating traits in tomatoes, which presumably have been shaped by natural selection, colocalize with QTLs for hybrid sterility. Unfortunately, there is little evidence for a causal association between prezygotic and postzygotic isolation. Intrinsic postzygotic isolation may also arise through genome doubling or polyploidy. However, polyploidy has other genetic and phenotypic consequences beyond reproductive isolation. One of themost interesting of these (and potentially most important) is the observation that large shifts in gene expression may accompany polyploidization. Because polyploidy may involve both interspecific hybridization and genome doubling, the effects of these two processes on gene expression often are confounded. In ‘‘Evolution of Duplicate Gene Expression in Polyploid and Hybrid Plants,’’ Journal of Heredity doi:10.1093/jhered/esl066 a The American Genetic Association. 2007. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Speciation in Drosophila: From Phenotypes to Molecules

Study of the genetics of speciation--and especially of the genetics of intrinsic postzygotic isolation-has enjoyed remarkable progress over the last 2 decades. Indeed progress has been so rapid that one might be tempted to ask if the genetics of postzygotic isolation is now wrapped up. Here we argue that the genetics of speciation is far from complete. In particular, we review 2 topics where recent work has revealed major surprises: 1) the role of meiotic drive in hybrid sterility and 2) the role of gene transposition in speciation. These surprises, and others like them, suggest that evolutionary biologists may understand less about the genetic basis of speciation than seemed likely a few years ago.

What does Drosophila genetics tell us about speciation?

Studies of hybrid inviability, sterility and 'speciation genes' in Drosophila have given insight into the genetic changes that result in reproductive isolation. Here, I survey some extraordinary and important advances in Drosophila speciation research. However, 'reproductive isolation' is not the same as 'speciation', and this Drosophila work has resulted in a lopsided view of speciation. In particular, Drosophila are not always well-suited to investigating ecological and other selection-driven primary causes of speciation in nature. Recent advances have made use of far less tractable, but more charismatic organisms, such as flowering plants, vertebrates and larger insects. Work with these organisms has complemented Drosophila studies of hybrid unfitness to provide a more complete understanding of speciation.

How Important Is Sexual Conflict?

Next article No AccessHow Important Is Sexual Conflict?David Hosken and Rhonda SnookDavid Hosken Search for more articles by this author and Rhonda Snook Search for more articles by this author 1. Centre for Ecology and Conservation, University of Exeter in Cornwall, Tremough, Penryn, Cornwall TR10 9EZ, United Kingdom;2. Department of Animal and Plant Sciences, Alfred Denny Building, University of Sheffield, Western Bank, Sheffield S10 2TN, United KingdomPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 165, Number S5May 2005HOW IMPORTANT IS SEXUAL CONFLICT?A Special Issue Edited by David Hosken and Rhonda Snook Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/429355 Views: 112Total views on this site Citations: 25Citations are reported from Crossref © 2005 by The University of Chicago.PDF download Crossref reports the following articles citing this article:Marcus Lee, Carlota Solano Udina, Lars-Anders Hansson Fear of sex: sexual conflict exposed as avoidance in a parthenogenetic invertebrate, Behavioral Ecology and Sociobiology 75, no.88 (Jul 2021).https://doi.org/10.1007/s00265-021-03054-9David J. Hosken, C. 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Chapman Timing is everything: expanding the cost of sexual attraction hypothesis, Animal Behaviour 88 (Feb 2014): 219–224.https://doi.org/10.1016/j.anbehav.2013.11.029Ryne A. Palombit Sexual Conflict in Nonhuman Primates, (Jan 2014): 191–280.https://doi.org/10.1016/B978-0-12-800286-5.00005-5Abderrahman Khila, Ehab Abouheif, Locke Rowe Function, Developmental Genetics, and Fitness Consequences of a Sexually Antagonistic Trait, Science 336, no.60816081 (May 2012): 585–589.https://doi.org/10.1126/science.1217258Adrian L. O'Loghlen, Stephen I. Rothstein, Jane M. Waterman When Less Is Best: Female Brown-Headed Cowbirds Prefer Less Intense Male Displays, PLoS ONE 7, no.55 (May 2012): e36130.https://doi.org/10.1371/journal.pone.0036130Rebecca M. Stumpf, Rodolfo Martinez-Mota, Krista M. Milich, Nicoletta Righini, Milena R. Shattuck Sexual conflict in primates, Evolutionary Anthropology: Issues, News, and Reviews 20, no.22 (Apr 2011): 62–75.https://doi.org/10.1002/evan.20297Adrian L. O’Loghlen, Stephen I. Rothstein Multimodal signalling in a songbird: male audiovisual displays vary significantly by social context in brown-headed cowbirds, Animal Behaviour 79, no.66 (Jun 2010): 1285–1292.https://doi.org/10.1016/j.anbehav.2010.03.001Matthew D. Hall, Simon P. Lailvaux, Mark W. Blows, Robert C. Brooks SEXUAL CONFLICT AND THE MAINTENANCE OF MULTIVARIATE GENETIC VARIATION, Evolution 64, no.66 (Dec 2009): 1697–1703.https://doi.org/10.1111/j.1558-5646.2009.00932.xRyne A. Palombit Conflict and Bonding Between the Sexes, (Sep 2009): 53–83.https://doi.org/10.1007/978-3-642-02725-3_3John Archer Does sexual selection explain human sex differences in aggression?, Behavioral and Brain Sciences 32, no.3-43-4 (Aug 2009): 249.https://doi.org/10.1017/S0140525X09990951KRISTA K. 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The genetic basis of reproductive isolation: insights from Drosophila.

Recent studies of the genetics of speciation in Drosophila have focused on two problems: (i) identifying and characterizing the genes that cause reproductive isolation, and (ii) determining the evolutionary forces that drove the divergence of these "speciation genes." Here, I review this work. I conclude that speciation genes correspond to ordinary loci having normal functions within species. These genes fall into several functional classes, although a role in transcriptional regulation could prove particularly common. More important, speciation genes are typically very rapidly evolving, and this divergence is often driven by positive Darwinian selection. Finally, I review recent work in Drosophila pseudoobscura on the possible role of meiotic drive in the evolution of the genes that cause postzygotic isolation.