Biology subjects

Meisel, R. P.

Publications and source records attributed to Meisel, R. P..

17 recordsLinked to original sources

bioRxiv2026

X-Y divergence of house fly (Musca domestica) proto-sex chromosomes follows distinct evolutionary trajectories despite residing in the same genome

Sex determination systems and sex chromosomes frequently differ between species. One cause of these differences is new sex determining genes that drive evolutionary turnover of sex chromosomes. At the earliest stages of this turnover, X and Y (or Z and W) chromosomes start out as nearly identical homologs, and they can diverge via chromosomal rearrangements (e.g., inversions) that suppress X-Y recombination. However, multiple examples from across animals and plants provide exceptions to this canonical model of sex chromosome evolution. For example, some X-Y pairs remain undifferentiated for long evolutionary time periods, while other sex chromosomes become differentiated without chromosomal rearrangements. How or why these non-canonical trajectories occur remains elusive, despite increasing evidence of their pervasiveness. The house fly, Musca domestica, is a well-suited system to address this gap because all six chromosomes can be a Y, providing multiple replicates of a natural experiment within a single genomic environment. To test for canonical and non-canonical evolutionary trajectories, we generated haplotype-resolved chromosome-level assemblies from five strains of the house fly, each of which carries a different Y chromosome (IM, IIM, IIIM, VM, and YM). We identified an inversion on only one of the sex chromosomes (IIM), which was associated with elevated X-Y divergence but did not capture the male-determining locus. In contrast, there was X-Y divergence across almost the entire length of the IM, IIIM, and VM sex chromosomes, despite no detectable inversions. YM was the only sex chromosome to contain substantial Y-specific sequences, which were limited to a segment on one end of the chromosome containing the male-determining gene. This YM chromosome, and its corresponding X, were highly diverged from the X chromosome found in many other flies (Muller element F), despite a strong cytological resemblance. This study highlights how multiple different canonical and non-canonical modes of sex chromosome evolution can co-exist within a single genome.

genomics↗

bioRxiv2026

House fly proto-Y chromosomes differentially affect courtship success regardless of social context and female type

Genetic variation exists for many male reproductive traits despite apparent strong sexual selection in favor of particular males. Understanding how that variation is maintained is an unresolved problem in evolutionary biology. One proposed solution to this problem is genotype-by-environment interactions (GEIs), where no male genotype is universally superior across environments. Another proposed answer is variation in female preference, such that different females prefer different male genotypes. Additionally, male genotypes may differ in their reproductive output as they age. The house fly Musca domestica is a well-suited system to evaluate these explanations for genetic variation in male reproductive traits because two male genotypes (YM and IIIM) differ in mating performance. Specifically, IIIM males outcompete YM males in mating assays because IIIM males have a shorter copulation latency. To determine the relative importance of GEIs, female variation, and male age on the maintenance of genetic variation in male reproductive behaviors, we performed non-competitive (one male to one female) and competitive (one IIIM male and one YM male to one female) mating assays while considering multiple ages and different female strains. IIIM males attempted more matings regardless of competition level, female genotype or age, but mated faster than YM males only with females of their own strain and only performed more matings in non-competitive trials. However, female strain did not improve the mating success of YM males. We also did not observe evidence for genotype-by-age interactions on male mating success. Importantly, we did not identify any conditions where YM males outcompeted IIIM males, and therefore there was no evidence for interactions or trade-offs that could explain the maintenance of genetic variation for male mating success. To explain the maintenance of IIIM and YM males, other factors such as additional social environments or varying temperature should be investigated, as the genotypes are found in natural environments with contrasting temperatures.

evolutionary biology↗

bioRxiv2026

Drosophila pseudoobscura third chromosome inversion arrangements have sex-specific effects on life history traits

Chromosomal inversions can create polymorphic "supergenes" consisting of many alleles in linkage disequilibrium that affect constellations of traits. The coadaptation hypothesis supposes that many alleles within an inversion haplotype have synergistic epistatic interactions, which are maintained by suppressed recombination in inversion heterozygotes, heterozygote advantage, and context-dependent fitness effects. The fitness benefits of chromosomal inversions frequently arise from effects on life history syndromes, including ecotypes and reproductive strategies. Life history syndromes can also be caused by individual pleiotropic alleles in ways that resemble the effects of chromosomal inversions. It is therefore possible that the fitness effects of chromosomal inversions arise because of pleiotropic alleles and not coadaptation. These two hypotheses can be distinguished because pleiotropy predicts greater genetic correlations of traits than coadaptation. To test the coadaptation and pleiotropy hypotheses, we measured three life history traits (lifespan, development time, and body size) in Drosophila pseudoobscura with six different chromosomal inversion genotypes. We assayed males and females raised at multiple temperatures in order to expose phenotype variation. Temperature affected lifespan and development more than any other factor, but we also observed differences in mortality rates and development times that depended on chromosomal inversions and sex. Despite these context-dependent effects on life history traits, we failed to identify genetic correlations that would be evidence for pleiotropic alleles. Our results therefore suggest that the coadaptation hypothesis is better supported.

evolutionary biology↗

bioRxiv2026

Population genomics of Drosophila pseudoobscura

Drosophila pseudoobscura is an historically important organism in evolutionary genetics, serving as a model system in studies of chromosomal inversions, speciation, sex chromosome evolution, and sex-ratio drive. However, previous population genetics analysis of D. pseudoobscura focused on individual chromosomes or used fragmented genome assemblies as a reference. To address these shortcomings, we generated a D. pseudoobscura population genomics resource consisting of newly sequenced genomes from 60 inbred lines sampled across the species geographic range in North America. Using these data and a chromosome-scale reference genome, we examined patterns of nucleotide diversity and population structure across the chromosomes. We found no strong evidence of population structure on most chromosomes, consistent with prior results. In contrast, we identified population structure on the third chromosome, which we attributed to a well-characterized inversion polymorphism. We assigned individual third chromosome haplotypes to inversion arrangements, demonstrating how tests for population structure can be used to identify polymorphic chromosomal rearrangements. Tajimas D was negative across most of the genome, consistent with a recent population expansion. However, the distribution of genetic variation differed across third chromosome inversion arrangements in ways that were consistent with their hypothesized evolutionary histories, and we identified inter-arrangement genetic differentiation that could be attributed to the inversions suppressing genetic exchange. The population genomic data we have collected is publicly available and will support future research on evolutionary genetics. SummaryThe genomes of 60 isolates of Drosophila pseudoobscura were sequenced and analyzed. This species is a model organism for multiple areas in evolutionary genetics research, including chromosomal rearrangement, sex chromosomes, and speciation. This article presents the largest population genomic data set collected in this species. The analysis of the data demonstrates how population structure detection approaches can be used to identify polymorphic chromosomal inversions. The data presented will be valuable for future work on fundamental questions in population genetics.

genomics↗

bioRxiv2024

Frequencies of house fly proto-Y chromosomes across populations are predicted by temperature heterogeneity within populations

Sex chromosomes often differ between closely related species and can even be polymorphic within populations. Species with polygenic sex determination segregate for multiple different sex determining loci within populations, making them uniquely informative of the selection pressures that drive the evolution of sex chromosomes. The house fly (Musca domestica) is a model species for studying polygenic sex determination because male determining genes have been identified on all six of the chromosomes, which means that any chromosome can be a "proto-Y" chromosome. In addition, chromosome IV can carry a female-determining locus, making it a W chromosome. The different proto-Y chromosomes are distributed along latitudinal clines on multiple continents, their distributions can be explained by seasonality in temperature, and they have temperature-dependent effects on physiological and behavioral traits. It is not clear, however, how the clinal distributions interact with the effect of seasonality on the frequencies of house fly proto-Y chromosomes across populations. To address this question, we measured the frequencies of house fly Y and W chromosomes across nine populations in the United States of America. We confirmed the clinal distribution along the eastern coast of North America, but it is limited to the eastern coast. In contrast, annual mean daily temperature range is significantly correlated with proto-Y chromosome frequencies across the entire continent. Our results therefore suggest that temperature heterogeneity can explain the distributions of house fly proto-Y chromosomes in a way that does not depend on the cline. These results contribute to our understanding of how ecological factors affect sex chromosome evolution.

evolutionary biology↗

bioRxiv2024

Testis- and ovary-expressed polo transcripts and gene duplications affect male fertility when expressed in the germline

Polo-like kinases (Plks) are essential for spindle attachment to the kinetochore during prophase and the subsequent dissociation after anaphase in both mitosis and meiosis. There are structural differences in the spindle apparatus between mitosis, male meiosis, and female meiosis. It is therefore possible that alleles of Plk genes could improve kinetochore attachment or dissociation in spermatogenesis or oogenesis, but not both. These opposing effects could result in sexually antagonistic selection at Plk loci. In addition, Plk genes have been independently duplicated in many different evolutionary lineages within animals. This raises the possibility that Plk gene duplication may resolve sexual conflicts over mitotic and meiotic functions. We investigated this hypothesis by comparing the evolution, gene expression, and functional effects of the single Plk gene in Drosophila melanogaster (polo) and the duplicated Plks in Drosophila pseudoobscura (Dpse-polo and Dpse-polo-dup1). We found that the protein-coding sequence of Dpse-polo-dup1 is evolving significantly faster than a canonical polo gene across all functional domains, yet the essential structure of encoded protein appears to be retained. Dpse-polo-dup1 is expressed primarily in testis, while other polo genes have broader expression profiles. Furthermore, over or ectopic expression of polo or Dpse-polo in the D. melanogaster male germline results in greater male infertility than ectopic expression of Dpse-polo-dup1. Lastly, ectopic expression of Dpse-polo or an ovary-derived transcript of polo in the male germline causes males to sire female-biased broods. However, there is no sex-bias in the progeny when Dpse-polo-dup1 is ectopically expressed or a testis-derived transcript of polo is overexpressed in the D. melanogaster male germline. Our results therefore suggest that Dpse-polo-dup1 may have experienced positive selection to improve its regulation of the male meiotic spindle, resolving sexual conflict over meiotic Plk functions. Alternatively, Dpse-polo-dup1 may encode a hypomorphic Plk that has reduced deleterious effects when overexpressed in the male germline. Similarly, testis transcripts of D. melanogaster polo may be optimized for regulating the male meiotic spindle, and we provide evidence that the untranslated regions of the polo transcript may be involved in sex-specific germline functions.

genetics↗

bioRxiv2022

Uncertainty favors an induced immune response to infection

Organisms use constitutive or induced defenses against pathogens, parasites, and herbivores. Constitutive defenses are constantly on, whereas induced defenses are activated upon exposure to an enemy. Constitutive and induced defenses each have costs and benefits, which can affect the type of defense that evolves in response to pathogens. Previous models that compared the two lacked mechanistic details about host defense, did not consider pathogen proliferation rates, or lacked both features. To address this gap, we developed a detailed mechanistic model of the well-characterized Drosophila melanogaster immune signaling network. We evaluated the factors favoring the evolution of constitutive and induced defenses by comparing the fitness of each strategy under stochastic fly-bacteria interactions. We show that an induced defense is favored when bacteria are at low density, heterogeneously distributed, or have fluctuating distributions in ways that depend on the bacterial proliferation rate. Our model also predicts that the specific negative regulators that optimize the induced response depend on the bacterial proliferation rate. We therefore conclude that an induced immune defense is favored in environments where bacterial encounters are uncertain--because of heterogeneity in spatial or temporal distributions--but that benefit depends on the mechanism of induction and pathogen properties.

evolutionary biology↗

bioRxiv2021

Induction and inhibition of Drosophila X chromosome gene expression are both impeded by the dosage compensation complex

Sex chromosomes frequently differ from the autosomes in the frequencies of genes with sexually dimorphic or tissue-specific expression. Multiple hypotheses have been put forth to explain the unique gene content of the X chromosome, including selection against male-beneficial X-linked alleles, expression limits imposed by the haploid dosage of the X in males, and interference by the dosage compensation complex (DCC) on expression in males. Here, we investigate these hypotheses by examining differential gene expression in Drosophila melanogaster following several treatments that have widespread transcriptomic effects: bacterial infection, viral infection, and abiotic stress. We found that genes that are induced (up-regulated) by these biotic and abiotic treatments are frequently under-represented on the X chromosome, but so are those that are repressed (down-regulated) following treatment. We further show that whether a gene is bound by the DCC in males can largely explain the paucity of both up- and down-regulated genes on the X chromosome. Specifically, genes that are bound by the DCC, or close to a DCC high-affinity site, are unlikely to be up- or down-regulated after treatment. This relationship, however, could partially be explained by a correlation between differential expression and breadth of expression across tissues. Nonetheless, our results suggest that DCC binding, or the associated chromatin modifications, inhibit both up- and down-regulation of X chromosome gene expression within specific contexts. We propose multiple possible mechanisms of action for the effect, including a role of Males absent on the first (Mof), a component of the DCC, as a dampener of gene expression variance in both males and females. This effect could explain why the Drosophila X chromosome is depauperate in genes with tissue-specific or induced expression, while the mammalian X has an excess of genes with tissue-specific expression.

genomics↗

bioRxiv2021

A conserved trans regulatory loop involving an odorant binding protein controls male mating behavior in flies

Y chromosomes have male-limited inheritance, which favors the fixation of alleles that affect spermatogenesis, courtship, and other male-specific traits. Y-linked male-beneficial alleles can also have female-deleterious (sexually antagonistic) effects because they never experience direct selection in females. However, determining the mechanisms underlying these male-beneficial effects is challenging because it can require studying Y-linked alleles while they still segregate as polymorphism. We used a Y chromosome polymorphism in the house fly, Musca domestica, to address this challenge. Two common male-determining Y chromosomes (YM and IIIM) segregate as stable polymorphisms in natural house fly populations, and they differentially affect multiple traits, including male courtship performance. We performed a meta-analysis of RNA-seq data and identified differentially expressed genes encoding odorant binding proteins (in the Obp56h family) as candidate causal agents in the courtship differences. The Obp56h genes are not found on either the YM or IIIM chromosomes, suggesting that they must be regulated in trans by one of the house fly sex chromosomes. Using a network analysis and allele-specific expression measurements, we identified multiple genes on the house fly IIIM chromosome that could serve as trans inhibitors of Obp56h gene expression. One of those genes is homologous to D. melanogaster CG2120, which encodes a transcription factor that binds both up- and down-stream of Obp56h. We found that up-regulation of CG2120 in D. melanogaster nervous tissues reduces copulation latency, consistent with this transcription factor acting as a negative regulator of Obp56h expression. We propose the name speed date (spdt) for CG2120, with the house fly homolog named Md-spdt. The expression of spdt across D. melanogaster development and tissues suggests that evolution of higher expression in neurons may be constrained by pleiotropic or sexual antagonistic effects. We hypothesize that a cis-regulatory allele that increases expression of Md-spdt on the IIIM chromosome exists because Y-linkage of this allele releases it from those constraints. This provides evidence for a molecular mechanism by which a Y-linked gene can evolve a male-beneficial function regardless of the negative effects on females.

evolutionary biology↗

bioRxiv2021

Gene expression in Lucilia sericata (Diptera: Calliphoridae) larvae exposed to Pseudomonas aeruginosa and Acinetobacter baumanii identifies shared and microbe-specific induction of immune genes

Antibiotic resistance is a continuing challenge in medicine. There are various strategies for expanding antibiotic therapeutic repertoires, including the use of blow flies. Their larvae exhibit strong antibiotic and antibiofilm properties that alter microbiome communities. One species, Lucilia sericata, is used to treat problematic wounds due to its debridement capabilities and its excretions and secretions that kill some pathogenic bacteria. There is much to be learned about how L. sericata interacts with microbiomes at the molecular level. To address this deficiency, gene expression was assessed after feeding exposure (1 hour or 4 hours) to two clinically problematic pathogens: Pseudomonas aeruginosa and Acinetobacter baumanii. The results identified immunity related genes that were differentially expressed when exposed to these pathogens, as well as non-immune genes possibly involved in gut responses to bacterial infection. There was a greater response to P. aeruginosa that increased over time, while few genes responded to A. baumanii exposure and expression was not time-dependent. The response to feeding on pathogens indicates a few common responses and features distinct to each pathogen, which is useful in improving wound debridement therapy and helps develop biomimetic alternatives.

immunology↗

bioRxiv2021

Thermal tolerance and preference are both consistent with the clinal distribution of house fly proto-Y chromosomes

Selection pressures can vary within localized areas and across massive geographical scales. Temperature is one of the best studied ecologically variable abiotic factors that can affect selection pressures across multiple spatial scales. Organisms rely on physiological (thermal tolerance) and behavioral (thermal preference) mechanisms to thermoregulate in response to environmental temperature. In addition, spatial heterogeneity in temperatures can select for local adaptation in thermal tolerance, thermal preference, or both. However, the concordance between thermal tolerance and preference across genotypes and sexes within species and across populations is greatly understudied. The house fly, Musca domestica, is a well-suited system to examine how genotype and environment interact to affect thermal tolerance and preference. Across multiple continents, house fly males from higher latitudes tend to carry the male-determining gene on the Y chromosome, whereas those from lower latitudes usually have the male-determiner on the third chromosome. We tested whether these two male-determining chromosomes differentially affect thermal tolerance and preference as predicted by their geographical distributions. We identify effects of genotype and developmental temperature on male thermal tolerance and preference that are concordant with the natural distributions of the chromosomes, suggesting that temperature variation across the species range contributes to the maintenance of the polymorphism. In contrast, female thermal preference is bimodal and largely independent of congener male genotypes. These sexually dimorphic thermal preferences suggest that temperature-dependent mating dynamics within populations could further affect the distribution of the two chromosomes. Together, the differences in thermal tolerance and preference across sexes and male genotypes suggest that different selection pressures may affect the frequencies of the male-determining chromosomes across different spatial scales. Impact StatementGenetic variation within species can be maintained by environmental factors that vary across the species range, creating clinal distributions of alleles responsible for ecologically important traits. Some of the best examples of clinal distributions come from temperature-dependent phenotypes, such as thermal tolerance and preference. Although genotype and developmental temperature strongly affect physiological and behavioral traits in ectotherms, the correlation between these traits across genotypes and sexes within species is greatly understudied. We show that two different male-determining chromosomes found in natural populations of house flies affect both thermal tolerance and preference in a way that is concordant with their clinal distributions across latitudes. This provides strong evidence that temperature variation across the species range contributes to the maintenance of the polymorphism. Furthermore, we find evidence that thermal preference is sexually dimorphic, suggesting that temperature-dependent mating dynamics could further affect the distribution of genetic variation in this system. Therefore, at a macro-geographical scale, the differences in thermal tolerance and preference across male genotypes likely contributes to the maintenance of the cline. Within populations, differences in thermal preference likely affect sexual selection dynamics, which may further affect the frequencies of the chromosomes.

evolutionary biology↗

bioRxiv2020

Temperature-dependent effects of house fly proto-Y chromosomes on gene expression act independently of the sex determination pathway

Sex determination, the developmental process by which sexually dimorphic phenotypes are established, evolves fast. Species with polygenic sex determination, in which master regulatory genes are found on multiple different proto-sex chromosomes, are informative models to study the evolution of sex determination. House flies are such a model system, with male determining loci possible on all six chromosomes and a female-determiner on one of the chromosomes as well. The two most common male-determining proto-Y chromosomes form latitudinal clines on multiple continents, suggesting that temperature variation is an important selection pressure responsible for maintaining polygenic sex determination in this species. To identify candidate genes that may be under selection, we used RNA-seq to test for temperature-dependent effects of the proto-Y chromosomes on gene expression in adult house flies. We find no evidence for ecologically meaningful temperature-dependent expression of sex determining genes between male genotypes, but we were likely not sampling an appropriate developmental time-point to identify such effect. In contrast, we identified many other genes whose expression depends on the interaction between proto-Y chromosome genotype and temperature, including genes that encode proteins involved in reproduction, metabolism, lifespan, stress response, and immunity. Notably, genes with genotype-by-temperature interactions on expression are not enriched on the proto-sex chromosomes. Moreover, there is no evidence that temperature-dependent expression is driven by chromosome-wide expression divergence between the proto-Y and proto-X alleles. Therefore, if temperature-dependent gene expression is responsible for differences in phenotypes and fitness of proto-Y genotypes across house fly populations, these effects are driven by a small number of temperature-dependent alleles on the proto-Y chromosomes that may in turn affect the expression of genes on other chromosomes.

evolutionary biology↗

bioRxiv2020

Gene-level, but not chromosome-wide, divergence between a very young house fly Y chromosome and its homologous X chromosome

X and Y chromosomes are usually derived from a pair of homologous autosomes, which then diverge from each other over time. Although Y-specific features have been characterized in sex chromosomes of various ages, the earliest stages of Y chromosome evolution remain elusive. In particular, we do not know whether early stages of Y chromosome evolution consist of changes to individual genes or happen via chromosome-scale divergence from the X. To address this question, we quantified divergence between young proto-X and proto-Y chromosomes in the house fly, Musca domestica. We compared proto-sex chromosome sequence and gene expression between genotypic (XY) and sex-reversed (XX) males. We find evidence for sequence divergence between genes on the proto-X and proto-Y, including five genes with mitochondrial functions. There is also an excess of genes with divergent expression between the proto-X and proto-Y, but the number of genes is small. This suggests that individual proto-Y genes, but not the entire proto-Y chromosome, have diverged from the proto-X. We identified one gene, encoding an axonemal dynein assembly factor (which functions in sperm motility), that has higher expression in XY males than XX males because of a disproportionate contribution of the proto-Y allele to gene expression. The up-regulation of the proto-Y allele may be favored in males because of this genes function in spermatogenesis. The evolutionary divergence between proto-X and proto-Y copies of this gene, as well as the mitochondrial genes, is consistent with selection in males affecting the evolution of individual genes during early Y chromosome evolution.

evolutionary biology↗

bioRxiv2019

Functional genomics of the stable fly, Stomoxys calcitrans, reveals mechanisms underlying reproduction, host interactions, and novel targets for pest control

BackgroundThe stable fly, Stomoxys calcitrans, is a major blood-feeding pest of livestock that has near worldwide distribution, causing an annual cost of over $2 billion for control and product loss in the United States alone. Control of these flies has been limited to increased sanitary management practices and insecticide application for suppressing larval stages. Few genetic and molecular resources are available to help in developing novel methods for controlling stable flies.\n\nResultsThis study examines stable fly biology by utilizing a combination of high-quality genome sequencing, microbiome analyses, and RNA-seq analyses targeting multiple developmental stages and tissues. In conjunction, manual curation of over 1600 genes was used to examine gene content related to stable fly reproduction, interactions with their host, host-microbe dynamics, and putative routes for control. Most notable was establishment of reproduction-associated genes and identification of expanded vision, chemosensation, immune repertoire, and metabolic detoxification pathway gene families.\n\nConclusionsThe combined sequencing, assembly, and curation of the male stable fly genome followed by RNA-seq and downstream analyses provide insights necessary to understand the biology of this important pest. These resources and knowledge will provide the groundwork for expanding the tools available to control stable fly infestations. The close relationship of Stomoxys to other blood-feeding (Glossina) and non-blood-feeding flies (medflies, Drosophila, house flies) will allow for understanding the evolution of blood feeding among Cyclorrhapha flies.

genomics↗

bioRxiv2019

Minimal effects of proto-Y chromosomes on house fly gene expression in spite of evidence that selection maintains stable polygenic sex determination

Sex determination is the developmental process by which organismal sex is established. Sex determination evolves fast, often due to changes in the master regulators at the top of the pathway. In addition, some species are polymorphic for multiple different master regulators within natural populations. Understanding the forces that maintain this polygenic sex determination can be informative of the factors that drive the evolution of sex determination. The house fly, Musca domestica, is a well-suited model to those ends because natural populations harbor male-determining loci on each of the six chromosomes and a bi-allelic female-determiner. Multiple lines of evidence suggest that natural selection maintains polygenic sex determination in house fly. However, previous work found that there are very few sequence differences between proto-Y chromosomes and their homologous X chromosomes. This suggests that there is not much genetic variation upon which natural selection could act to maintain polygenic sex determination in house fly. To address this paradox, we performed RNA-seq experiments that examine the effects of the two most common proto-Y chromosomes on gene expression. We find that the proto-Y chromosomes do indeed have a relatively minor effect on gene expression, as expected based on the minimal X-Y sequence differences. Despite these minimal gene expression differences, we identify some patterns that are consistent with sex-specific selection acting on phenotypic effects of proto-Y chromosomes. Our results suggest that, if natural selection maintains polygenic sex determination in house fly, the phenotypic differences under selection are minor and possibly depend on ecological contexts that were not tested in our experimental design.

genomics↗

bioRxiv2019

The Glossina Genome Cluster: Comparative Genomic Analysis of the Vectors of African Trypanosomes

BackgroundTsetse flies (Glossina sp.) are the sole vectors of human and animal trypanosomiasis throughout sub-Saharan Africa. Tsetse are distinguished from other Diptera by unique adaptations, including lactation and the birthing of live young (obligate viviparity), a vertebrate blood specific diet by both sexes and obligate bacterial symbiosis. This work describes comparative analysis of six Glossina genomes representing three sub-genera: Morsitans (G. morsitans morsitans (G.m. morsitans), G. pallidipes, G. austeni), Palpalis (G. palpalis, G. fuscipes) and Fusca (G. brevipalpis) which represent different habitats, host preferences and vectorial capacity. ResultsGenomic analyses validate established evolutionary relationships and sub-genera. Syntenic analysis of Glossina relative to Drosophila melanogaster shows reduced structural conservation across the sex-linked X chromosome. Sex linked scaffolds show increased rates of female specific gene expression and lower evolutionary rates relative to autosome associated genes. Tsetse specific genes are enriched in protease, odorant binding and helicase activities. Lactation associated genes are conserved across all Glossina species while male seminal proteins are rapidly evolving. Olfactory and gustatory genes are reduced across the genus relative to other characterized insects. Vision associated Rhodopsin genes show conservation of motion detection/tracking functions and significant variance in the Rhodopsin detecting colors in the blue wavelength ranges. ConclusionsExpanded genomic discoveries reveal the genetics underlying Glossina biology and provide a rich body of knowledge for basic science and disease control. They also provide insight into the evolutionary biology underlying novel adaptations and are relevant to applied aspects of vector control such as trap design and discovery of novel pest and disease control strategies.

genomics↗

bioRxiv2018

The X chromosome of the German cockroach, Blattella germanica, is homologous to a fly X chromosome despite 400 million years divergence

BackgroundSex chromosome evolution is a dynamic process that can proceed at varying rates across lineages. For example, different chromosomes can be sex-linked between closely related species, whereas other sex chromosomes have been conserved for >100 million years. Cases of long-term sex chromosome conservation could be informative of factors that constrain sex chromosome evolution. Cytological similarities between the X chromosomes of the German cockroach (Blattella germanica) and most flies suggest that they may be homologous--possibly representing an extreme case of long-term conservation.\n\nResultsTo test the hypothesis that the cockroach and fly X chromosomes are homologous, we analyzed whole genome sequence data from cockroach. We found evidence in both sequencing coverage and heterozygosity that a significant excess of the same genes are on both the cockroach and fly X chromosomes. We also present evidence that the candidate X-linked cockroach genes may be dosage compensated in hemizygous males. Consistent with this hypothesis, three regulators of transcription and chromatin on the fly X chromosome are conserved in the cockroach genome.\n\nConclusionsOur results support our hypothesis that the German cockroach shares the same X chromosome as most flies. This may represent convergent evolution of the X chromosome in the lineages leading to cockroaches and flies. Alternatively, the common ancestor of most insects may have had an X chromosome that resembled the extant cockroach and fly X. Cockroaches and flies diverged [~]400 million years ago, which would be the longest documented conservation of a sex chromosome. Cockroaches and flies have different mechanisms of sex determination, raising the possibility that the X chromosome was conserved despite evolution of the sex determination pathway.

genomics↗