Parallel functional changes in independent testis-specific duplicates of Aldehyde dehydrogenase in Drosophila

The roles of gene duplications in the dynamics of evolutionary conflicts

Evolutionary conflicts occur when there is antagonistic selection between different individuals of the same or different species, life stages or between levels of biological organization. Remarkably, conflicts can occur within species or within genomes. In the dynamics of evolutionary conflicts, gene duplications can play a major role because they can bring very specific changes to the genome: changes in protein dose, the generation of novel paralogues with different functions or expression patterns or the evolution of small antisense RNAs. As we describe here, by having those effects, gene duplication might spark evolutionary conflict or fuel arms race dynamics that takes place during conflicts. Interestingly, gene duplication can also contribute to the resolution of a within-locus evolutionary conflict by partitioning the functions of the gene that is under an evolutionary trade-off. In this review, we focus on intraspecific conflicts, including sexual conflict and illustrate the various roles of gene duplications with a compilation of examples. These examples reveal the level of complexity and the differences in the patterns of gene duplications within genomes under different conflicts. These examples also reveal the gene ontologies involved in conflict and the genomic location of the elements of the conflict. The examples provide a blueprint for the direct study of these conflicts or the exploration of the presence of similar conflicts in other lineages.

Recurrent Duplication and Diversification of a Vital DNA Repair Gene Family Across Drosophila

Maintaining genome integrity is vital for organismal survival and reproduction. Essential, broadly conserved DNA repair pathways actively preserve genome integrity. However, many DNA repair proteins evolve adaptively. Ecological forces like UV exposure are classically cited drivers of DNA repair evolution. Intrinsic forces like repetitive DNA, which also imperil genome integrity, have received less attention. We recently reported that a Drosophila melanogaster-specific DNA satellite array triggered species-specific, adaptive evolution of a DNA repair protein called Spartan/MH. The Spartan family of proteases cleave hazardous, covalent crosslinks that form between DNA and proteins ("DNA-protein crosslink repair"). Appreciating that DNA satellites are both ubiquitous and universally fast-evolving, we hypothesized that satellite DNA turnover spurs adaptive evolution of DNA-protein crosslink repair beyond a single gene and beyond the D. melanogaster lineage. This hypothesis predicts pervasive Spartan gene family diversification across Drosophila species. To study the evolutionary history of the Drosophila Spartan gene family, we conducted population genetic, molecular evolution, phylogenomic, and tissue-specific expression analyses. We uncovered widespread signals of positive selection across multiple Spartan family genes and across multiple evolutionary timescales. We also detected recurrent Spartan family gene duplication, divergence, and gene loss. Finally, we found that ovary-enriched parent genes consistently birthed functionally diverged, testis-enriched daughter genes. To account for Spartan family diversification, we introduce a novel mechanistic model of antagonistic coevolution that links DNA satellite evolution and adaptive regulation of Spartan protease activity. This framework promises to accelerate our understanding of how DNA repeats drive recurrent evolutionary innovation to preserve genome integrity.

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.

Sex-linked gene traffic underlies the acquisition of sexually dimorphic UV color vision in Heliconius butterflies

The acquisition of novel sexually dimorphic traits poses an evolutionary puzzle: How do new traits arise and become sex-limited? Recently acquired color vision, sexually dimorphic in animals like primates and butterflies, presents a compelling model for understanding how traits become sex-biased. For example, some Heliconius butterflies uniquely possess UV (ultraviolet) color vision, which correlates with the expression of two differentially tuned UV-sensitive rhodopsins, UVRh1 and UVRh2. To discover how such traits become sexually dimorphic, we studied Heliconius charithonia, which exhibits female-specific UVRh1 expression. We demonstrate that females, but not males, discriminate different UV wavelengths. Through whole-genome shotgun sequencing and assembly of the H. charithonia genome, we discovered that UVRh1 is present on the W chromosome, making it obligately female-specific. By knocking out UVRh1, we show that UVRh1 protein expression is absent in mutant female eye tissue, as in wild-type male eyes. A PCR survey of UVRh1 sex-linkage across the genus shows that species with female-specific UVRh1 expression lack UVRh1 gDNA in males. Thus, acquisition of sex linkage is sufficient to achieve female-specific expression of UVRh1, though this does not preclude other mechanisms, like cis-regulatory evolution from also contributing. Moreover, both this event, and mutations leading to differential UV opsin sensitivity, occurred early in the history of Heliconius. These results suggest a path for acquiring sexual dimorphism distinct from existing mechanistic models. We propose a model where gene traffic to heterosomes (the W or the Y) genetically partitions a trait by sex before a phenotype shifts (spectral tuning of UV sensitivity).

Evolution of genome structure in the Drosophila simulans species complex

The rapid evolution of repetitive DNA sequences, including satellite DNA, tandem duplications, and transposable elements, underlies phenotypic evolution and contributes to hybrid incompatibilities between species. However, repetitive genomic regions are fragmented and misassembled in most contemporary genome assemblies. We generated highly contiguous de novo reference genomes for the Drosophila simulans species complex (D. simulans, D. mauritiana, and D. sechellia), which speciated ∼250,000 yr ago. Our assemblies are comparable in contiguity and accuracy to the current D. melanogaster genome, allowing us to directly compare repetitive sequences between these four species. We find that at least 15% of the D. simulans complex species genomes fail to align uniquely to D. melanogaster owing to structural divergence-twice the number of single-nucleotide substitutions. We also find rapid turnover of satellite DNA and extensive structural divergence in heterochromatic regions, whereas the euchromatic gene content is mostly conserved. Despite the overall preservation of gene synteny, euchromatin in each species has been shaped by clade- and species-specific inversions, transposable elements, expansions and contractions of satellite and tRNA tandem arrays, and gene duplications. We also find rapid divergence among Y-linked genes, including copy number variation and recent gene duplications from autosomes. Our assemblies provide a valuable resource for studying genome evolution and its consequences for phenotypic evolution in these genetic model species.

Genomic signatures of globally enhanced gene duplicate accumulation in the megadiverse higher Diptera fueling intralocus sexual conflict resolution

Gene duplication is an important source of evolutionary innovation. To explore the relative impact of gene duplication during the diversification of major insect model system lineages, we performed a comparative analysis of lineage-specific gene duplications in the fruit fly Drosophila melanogaster (Diptera: Brachycera), the mosquito Anopheles gambiae (Diptera: Culicomorpha), the red flour beetle Tribolium castaneum (Coleoptera), and the honeybee Apis mellifera (Hymenoptera). Focusing on close to 6,000 insect core gene families containing maximally six paralogs, we detected a conspicuously higher number of lineage-specific duplications in Drosophila (689) compared to Anopheles (315), Tribolium (386), and Apis (223). Based on analyses of sequence divergence, phylogenetic distribution, and gene ontology information, we present evidence that an increased background rate of gene duplicate accumulation played an exceptional role during the diversification of the higher Diptera (Brachycera), in part by providing enriched opportunities for intralocus sexual conflict resolution, which may have boosted speciation rates during the early radiation of the megadiverse brachyceran subclade Schizophora.

Genomic and biochemical evidence of dietary adaptation in a marine herbivorous fish

Adopting a new diet is a significant evolutionary change, and can profoundly affect an animal's physiology, biochemistry, ecology and genome. To study this evolutionary transition, we investigated the physiology and genomics of digestion of a derived herbivorous fish, Cebidichthys violaceus. We sequenced and assembled its genome (N50 = 6.7 Mb) and digestive transcriptome, and revealed the molecular changes related to digestive enzymes (carbohydrases, proteases and lipases), finding abundant evidence of molecular adaptation. Specifically, two gene families experienced expansion in copy number and adaptive amino acid substitutions: amylase and carboxyl ester lipase (cel), which are involved in the digestion of carbohydrates and lipids, respectively. Both show elevated levels of gene expression and increased enzyme activity. Because carbohydrates are abundant in the prickleback's diet and lipids are rare, these findings suggest that such dietary specialization involves both exploiting abundant resources and scavenging rare ones, especially essential nutrients, like essential fatty acids.

Parallel Evolution of Two dmrt1-Derived Genes, dmy and dm-W, for Vertebrate Sex Determination

Animal sex-determining genes, which bifurcate for female and male development, are diversified even among closely related species. Most of these genes emerged independently from various sex-related genes during species diversity as neofunctionalization-type genes. However, the common mechanisms of this divergent evolution remain poorly understood. Here, we compared the molecular evolution of two sex-determining genes, the medaka dmy and the clawed frog dm-W, which independently evolved from the duplication of the transcription factor-encoding masculinization gene dmrt1. Interestingly, we detected parallel amino acid substitutions, from serine (S) to threonine (T), on the DNA-binding domains of both ancestral DMY and DM-W, resulting from positive selection. Two types of DNA-protein binding experiments and a luciferase reporter assay demonstrated that these S-T substitutions could strengthen the DNA-binding abilities and enhance the transcriptional regulation function. These findings suggest that the parallel S-T substitutions may have contributed to the establishment of dmy and dm-W as sex-determining genes.

•

We detected parallel amino acid substitutions in two sex-determining genes, dmy and dm-W

•

Both the substitutions from dmrt1 duplication are under positive selection

•

These substitutions enhanced their DNA-binding activity as transcription factors

•

These substitutions might have contributed to the establishment of dmy and dm-W

Active Sites of Reduced Epidermal Fluorescence1 (REF1) Isoforms Contain Amino Acid Substitutions That Are Different between Monocots and Dicots

Plant aldehyde dehydrogenases (ALDHs) play important roles in cell wall biosynthesis, growth, development, and tolerance to biotic and abiotic stresses. The Reduced Epidermal Fluorescence1 is encoded by the subfamily 2C of ALDHs and was shown to oxidise coniferaldehyde and sinapaldehyde to ferulic acid and sinapic acid in the phenylpropanoid pathway, respectively. This knowledge has been gained from works in the dicotyledon model species Arabidopsis thaliana then used to functionally annotate ALDH2C isoforms in other species, based on the orthology principle. However, the extent to which the ALDH isoforms differ between monocotyledons and dicotyledons has rarely been accessed side-by-side. In this study, we used a phylogenetic approach to address this question. We have analysed the ALDH genes in Brachypodium distachyon, alongside those of other sequenced monocotyledon and dicotyledon species to examine traits supporting either a convergent or divergent evolution of the ALDH2C/REF1-type proteins. We found that B. distachyon, like other grasses, contains more ALDH2C/REF1 isoforms than A. thaliana and other dicotyledon species. Some amino acid residues in ALDH2C/REF1 isoforms were found as being conserved in dicotyledons but substituted by non-equivalent residues in monocotyledons. One example of those substitutions concerns a conserved phenylalanine and a conserved tyrosine in monocotyledons and dicotyledons, respectively. Protein structure modelling suggests that the presence of tyrosine would widen the substrate-binding pocket in the dicotyledons, and thereby influence substrate specificity. We discussed the importance of these findings as new hints to investigate why ferulic acid contents and cell wall digestibility differ between the dicotyledon and monocotyledon species.