Biology subjects

Allan, C. W.

Publications and source records attributed to Allan, C. W..

7 recordsLinked to original sources

bioRxiv2025

Evolution of the reproductive interactome: proteomic divergence and the origins of postmating-prezygotic reproductive incompatibilities

Reproductive proteins evolve rapidly, making them strong candidates for driving postmating-prezygotic (PMPZ) reproductive incompatibilities between populations. While most previous studies have focused on protein sequence divergence as a likely driver of PMPZ incompatibilities, reproductive proteomes may also diverge compositionally and/or quantitatively. Here, we combine quantitative proteomics, molecular evolutionary analyses, and protein-protein interaction (PPI) modeling to predict the molecular basis of reproductive incompatibilities between Drosophila mojavensis and D. arizonae. We demonstrate multidimensional divergence in reproductive proteomes including changes at the sequence, compositional, and quantitative levels. We further demonstrate that three divergent male seminal fluid proteins affect the size of the insemination reaction mass and/or fertilization success in D. arizonae. Despite high sequence divergence, predicted protein-protein interactions involving a conserved set of proteases and/or protease inhibitors were predicted to be maintained in heterospecific crosses. In contrast, predicted interspecies protein incompatibilities arose from proteome compositional divergence, suggesting that such changes may play a disproportionate role in PMPZ incompatibilities, at least for the subset of the interactome that we tested. Furthermore, extensive quantitative divergence, particularly for proteases and inhibitors, suggests pervasive stoichiometric mismatches in heterospecific matings. Altogether, our findings indicate that reproductive proteins are evolutionarily labile at multiple levels, and that compositional and quantitative divergence, rather than sequence changes alone, may be central to the early evolution of reproductive isolation.

evolutionary biology↗

bioRxiv2023

A pooled-sample draft genome assembly provides insights into host plant-specific transcriptional responses of a Solanaceae-specializing pest, Tupiocoris notatus (Hemiptera: Miridae)

The assembly of genomes from pooled samples of genetically heterogenous samples of conspecifics remains challenging. In this study we show that high-quality genome assemblies can be produced from samples of multiple wild-caught individuals. We sequenced DNA extracted from a pooled sample of conspecific herbivorous insects (Hemiptera: Miridae: Tupiocoris notatus) acquired from a greenhouse infestation in Tucson, Arizona (in the range of 30-100 individuals; 0.5 mL tissue by volume) using PacBio highly accurate long reads (HiFi). The initial assembly contained multiple haplotigs (>85% BUSCOs duplicated), but duplicate contigs could be easily purged to reveal a highly complete assembly (95.6% BUSCO, 4.4% duplicated) that is highly contiguous by short-read assembly standards (N50 = 675 kb; Largest contig = 4.3 Mb). We then used our assembly as the basis for a genome-guided differential expression study of host-plant specific transcriptional responses. We found thousands of genes (N = 4982) to be differentially expressed between our new data from individuals feeding on Datura wrightii (Solanaceae) and existing RNA-seq data from Nicotiana attenuata (Solanaceae) fed individuals. We identified many of these genes as previously documented detoxification genes such as glutathione-S-transferases, cytochrome P450s, UDP-glucosyltransferases. Together our results show that long-read sequencing of pooled samples can provide a cost-effective genome assembly option for small insects and provide insights into the genetic mechanisms underlying interactions between plants and herbivorous pests.

genomics↗

bioRxiv2023

Females translate male mRNA transferred during mating

Although RNA is found in the seminal fluid of diverse organisms, it is unknown whether this RNA is functional within females. Here, we develop an experimental proteomic method called VESPA (Variant Enabled SILAC Proteomic Analysis) to test the hypothesis that Drosophila male seminal fluid RNA is translated by females. We find strong evidence for 67 male-derived, female-translated proteins (mdFTPs) in female lower reproductive tracts at six hours postmating, many with predicted functions relevant to reproduction. Gene knockout experiments indicate that genes coding for mdFTPs play diverse roles in postmating interactions, with effects on fertilization efficiency, and the formation and persistence of the insemination reaction mass, a trait hypothesized to be involved in sexual conflict. These findings advance our understanding of reproduction by revealing a novel mechanism of postmating molecular interactions between the sexes that strengthens and extends male influences on reproductive outcomes in previously unrecognized ways. Given the diverse species known to carry RNA in seminal fluid, this discovery has broad significance for understanding molecular mechanisms of cooperation and conflict during reproduction.

evolutionary biology↗

bioRxiv2022

Chromosome-length genome assemblies of cactophilic Drosophila illuminate links between structural and sequence evolution.

A thorough understanding of adaptation and speciation requires model organisms with both a history of ecological and phenotypic study as well as a robust set of genomic resources. For decades, the cactophilic Drosophila species of the southwestern US and northern Mexico have fit this profile, serving as a crucial model system for understanding ecological adaptation, particularly in xeric environments, as well as the evolution of reproductive incompatibilities and speciation. Here, we take a major step towards gaining a complete molecular description of this system by assembling and annotating seven chromosome-length de novo genomes across the three species D. mojavensis, D. arizonae, and D. navojoa. Using this data, we present the most accurate reconstruction of the phylogenetic history of this clade to date. We further demonstrate a relationship between structural evolution and coding evolution both within and between species in this clade, and use this relationship to generate novel hypotheses for adaptation genes. All of our data are presented in a new public database (cactusflybase.arizona.edu), providing one of the most in-depth resources for the analysis of inter- and intraspecific evolutionary genomic data.

genomics↗

bioRxiv2021

Novel genetic basis of resistance to Bt toxin Cry1Ac in Helicoverpa zea

Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have advanced pest management, but their benefits are diminished when pests evolve resistance. Elucidating the genetic basis of pest resistance to Bt toxins can improve resistance monitoring, resistance management, and design of new insecticides. Here, we investigated the genetic basis of resistance to Bt toxin Cry1Ac in the lepidopteran Helicoverpa zea, one of the most damaging crop pests in the United States. To facilitate this research, we built the first chromosome-level genome assembly for this species, which has 31 chromosomes containing 375 Mb and 15,482 predicted proteins. Using a genome-wide association study, fine-scale mapping, and RNA-seq, we identified a 250-kb quantitative trait locus (QTL) on chromosome 13 that was strongly associated with resistance in a strain of H. zea that had been selected for resistance in the field and lab. The mutation in this QTL contributed to but was not sufficient for resistance, which implies alleles in more than one gene contributed to resistance. This QTL contains no genes with a previously reported role in resistance or susceptibility to Bt toxins. However, in resistant insects, this QTL has a premature stop codon in a kinesin gene which is a primary candidate as a mutation contributing to resistance. We found no changes in gene sequence or expression consistently associated with resistance for 11 genes previously implicated in lepidopteran resistance to Cry1Ac. Thus, the results reveal a novel and polygenic basis of resistance.

genetics↗

bioRxiv2019

Chromosome-level hybrid de novo genome assemblies as an attainable option for non-model organisms

The emergence of third generation sequencing (3GS; long-reads) is making closer the goal of chromosome-size fragments in de novo genome assemblies. This allows the exploration of new and broader questions on genome evolution for a number of non-model organisms. However, long-read technologies result in higher sequencing error rates and therefore impose an elevated cost of sufficient coverage to achieve high enough quality. In this context, hybrid assemblies, combining short-reads and long-reads provide an alternative efficient and cost-effective approach to generate de novo, chromosome-level genome assemblies. The array of available software programs for hybrid genome assembly, sequence correction and manipulation is constantly being expanded and improved. This makes it difficult for non-experts to find efficient, fast and tractable computational solutions for genome assembly, especially in the case of non-model organisms lacking a reference genome or one from a closely related species. In this study, we review and test the most recent pipelines for hybrid assemblies, comparing the model organism Drosophila melanogaster to a non-model cactophilic Drosophila, D. mojavensis. We show that it is possible to achieve excellent contiguity on this non-model organism using the DBG2OLC pipeline.

genomics↗

bioRxiv2019

Genomic analysis of the four ecologically distinct cactus host populations of Drosophila mojavensis

BackgroundRelationships between an organism and its environment can be fundamental in the understanding how populations change over time and species arise. Local ecological conditions can shape variation at multiple levels, among these are the evolutionary history and trajectories of coding genes. This study examines the rate of molecular evolution at protein-coding genes throughout the genome in response to host adaptation in the cactophilic Drosophila mojavensis. These insects are intimately associated with cactus necroses, developing as larvae and feeding as adults in these necrotic tissues. Drosophila mojavensis is composed of four isolated populations across the deserts of western North America and each population has adapted to utilize different cacti that are chemically, nutritionally, and structurally distinct. ResultsHigh coverage Illumina sequencing was performed on three previously unsequenced populations of D. mojavensis. Genomes were assembled using the previously sequenced genome of D. mojavensis from Santa Catalina Island (USA) as a template. Protein coding genes were aligned across all four populations and rates of protein evolution were determined for all loci using a several approaches. ConclusionsLoci that exhibited elevated rates of molecular evolution tended to be shorter, have fewer exons, low expression, be transcriptionally responsive to cactus host use and have fixed expression differences across the four cactus host populations. Fast evolving genes were involved with metabolism, detoxification, chemosensory reception, reproduction and behavior. Results of this study gives insight into the process and the genomic consequences of local ecological adaptation.

genomics↗