Biology subjects

Webster, M. T.

Publications and source records attributed to Webster, M. T..

7 recordsLinked to original sources

bioRxiv2026

Genetic determinants of intraspecific variation in crossover frequencies in the honeybee, Apis mellifera

Meiotic recombination facilitates natural selection and is necessary for correct chromosomal segregation in most sexually reproducing species. Crossover rates vary greatly both within and among species, but the determinants of this variation are not fully understood. The honeybee Apis mellifera has extremely high recombination rates. Honeybee males (drones) are haploid, which enables the distribution of crossovers to be directly estimated from the progeny of a single reproductive female (queen). Here we map crossover events in the honeybee using whole genome sequencing of 1509 drone progeny of 184 queens. This allows us to assay intra-specific variation in recombination rate and its genetic and non-genetic determinants. We estimate the average crossover rate as 23 cM/Mb, with between 22 and 88 crossovers events detected in individual offspring. We estimate 28% of this variation is additive heritable variation among queens. There is no effect of queen age or genetic background on crossover rate. A genome-wide association study identifies variation in the gene mlh1 as associated with mean crossover rate. We estimate that variation in the gene is associated with a 10% difference in crossover rate between the two homozygous genotypes at the most significant SNP. This gene has a well-established role in recombination and variation in the gene could affect crossover rates by affecting resolution of Holliday junctions as crossovers. This is the first gene discovered to be associated with recombination rate variation in an insect. Adaptive evolution of this gene could potentially underlie the extremely high recombination rates in honeybees.

genomics↗

bioRxiv2025

Genetic mapping in the red mason bee Osmia bicornis implicates ANTSR as an ancient sex-determining locus in bees and ants

Haplodiploid inheritance, in which females are diploid and males are haploid, is found in all species of Hymenoptera. Sex in haplodiploids is commonly determined by the alleles present at a complementary sex determination (CSD) locus, with heterozygosity triggering the female developmental pathway. The identity of this locus differs among taxa and is only known in a few species. Here, we map a single CSD locus to a 2 kbp region in the genome of the red mason bee Osmia bicornis. It overlaps the long noncoding RNA ANTSR, which has been identified as the sex-determining gene in the invasive ant Linepithema humile. This locus is homozygous in diploid males and exhibits extremely high levels of haplotype diversity, consistent with the action of frequency-dependent selection. The elevated levels of heterozygosity in the CSD locus enable us to fine-map potentially functional genetic variation within it. We also identify elevated levels of genetic diversity in the ortholog of the CSD locus in five other bee and ant genera, suggesting that it may govern sex determination widely in Hymenoptera. Our data are consistent with the hypothesis that ANTSR evolved a role in sex determination over 150 million years ago and is the ancestral sex-determination locus of bees and ants.

evolutionary biology↗

bioRxiv2025

A novel supergene controls queen size and colony social organization in the ant Myrmica ruginodis

In some ant species, the size of queens is dimorphic, with larger queens dispersing to form single-queen colonies and smaller queens remaining in natal colonies as part of multiple-queen societies. These alternative reproductive strategies influence colony kin structure and worker behavior, and their many independent origins make them ideal systems to study parallel evolution of genome organization and adaptability. We investigate the genetic basis of alternative reproductive strategies in the queen-size dimorphic ant Myrmica ruginodis by sampling 95 queens from 31 colonies in southern Finland. Whole-genome sequencing revealed a novel 9 Mb supergene associated with both queen size and social organization. Queens homozygous for the AA haplotype were larger and found only in single-queen colonies, while queens in multiple-queen colonies were smaller and contained only AB and BB genotypes. This supergene is not homologous to previously identified supergenes in ants, suggesting it was formed by a unique evolutionary pathway.

evolutionary biology↗

bioRxiv2024

Unexpectedly low recombination rates and presence of hotspots in termite genomes

Meiotic recombination is a fundamental evolutionary process that facilitates adaptation and the removal of deleterious genetic variation. Social Hymenoptera exhibit some of the highest recombination rates among metazoans, whereas high recombination rates have not been found among non-social species from this insect order. It is unknown whether elevated recombination rates are a ubiquitous feature of all social insects. In many metazoan taxa, recombination is mainly restricted to hotspots a few kilobases in length. However, little is known about the prevalence of recombination hotspots in insect genomes. Here we infer recombination rate and its fine-scale variation across the genomes of two social species from the insect order Blattodea: the termites Macrotermes bellicosus and Cryptotermes secundus. We used linkage-disequilibrium-based methods to infer recombination rate. We infer that recombination rates are close to 1 cM/Mb in both species, similar to the average metazoan rate. We also observed a highly punctate distribution of recombination in both termite genomes, indicative of the presence of recombination hotspots. We infer the presence of full-length PRDM9 genes in the genomes of both species, which suggests recombination hotspots in termites might be determined by PRDM9, as they are in mammals. We also find that recombination rates in genes are correlated with inferred levels of germline DNA methylation. The finding of low recombination rates in termites indicates that eusociality is not universally connected to elevated recombination rate. We speculate that the elevated recombination rates in social Hymenoptera are instead promoted by intense selection among haploid males.

genomics↗

bioRxiv2021

Genome sequencing and morphometric analysis of alpine bumblebees experiencing climate change reveal ongoing phenotypic shifts and a lack of population structure

Over the last six decades, populations of the bumblebees Bombus sylvicola and Bombus balteatus in Colorado have experienced decreases in tongue length, a trait important for plant-pollinator mutualisms. It has been hypothesized that this observation reflects selection resulting from shifts in floral composition under climate change. Here we used morphometrics and population genomics to determine whether morphological change is ongoing, investigate the genetic basis of morphological variation, and analyze population structure in these populations. We generated a genome assembly of B. balteatus. We then analyzed whole-genome sequencing data and morphometric measurements of 580 samples of both species from seven high-altitude localities. Out of 281 samples originally identified as B. sylvicola, 67 formed a separate genetic cluster comprising a newly-discovered cryptic species ("incognitus"). However, an absence of genetic structure within species suggests that gene flow is common between mountains. We found a significant decrease in tongue length between bees collected between 2012-2014 and in 2017, indicating that morphological shifts are ongoing. We did not discover any genetic associations with tongue length, but a SNP related to production of a proteolytic digestive enzyme was implicated in body size variation. We identified evidence of covariance between kinship and both tongue length and body size, which is suggestive of a genetic component of these traits, although it is possible that shared environmental effects between colonies are responsible. Our results provide evidence for ongoing modification of a morphological trait important for pollination and indicate that this trait likely has a complex genetic and environmental basis.

evolutionary biology↗

bioRxiv2018

A hybrid de novo genome assembly of the honeybee, Apis mellifera, with chromosome-length scaffolds

BackgroundThe ability to generate long sequencing reads and access long-range linkage information is revolutionizing the quality and completeness of genome assemblies. Here we use a hybrid approach that combines data from four genome sequencing and mapping technologies to generate a new genome assembly of the honeybee Apis mellifera. We first generated contigs based on PacBio sequencing libraries, which were then merged with linked-read 10x Chromium data followed by scaffolding using a BioNano optical genome map and a Hi-C chromatin interaction map, complemented by a genetic linkage map.\n\nResultsEach of the assembly steps reduced the number of gaps and incorporated a substantial amount of additional sequence into scaffolds. The new assembly (Amel_HAv3) is significantly more contiguous and complete than the previous one (Amel_4.5), based mainly on Sanger sequencing reads. N50 of contigs is 120-fold higher (5.381 Mbp compared to 0.053 Mbp) and we anchor >98% of the sequence to chromosomes. All of the 16 chromosomes are represented as single scaffolds with an average of three sequence gaps per chromosome. The improvements are largely due to the inclusion of repetitive sequence that was unplaced in previous assemblies. In particular, our assembly is highly contiguous across centromeres and telomeres and includes hundreds of AvaI and AluI repeats associated with these features.\n\nConclusionsThe improved assembly will be of utility for refining gene models, studying genome function, mapping functional genetic variation, identification of structural variants, and comparative genomics.

genomics↗

bioRxiv2016

Whole genome resequencing of a laboratory-adapted Drosophila melanogaster population sample

As part of a study into the molecular genetics of sexually dimorphic complex traits, we used next-generation sequencing to obtain data on genomic variation in an outbred laboratory-adapted fruit fly (Drosophila melanogaster) population. We successfully resequenced the whole genome of 2 females from the Berkeley reference line (BDGP6/dm6), and 220 hemiclonal females that were heterozygous for the same reference line genome, and a unique haplotype from the outbred base population (LHM). The use of a static and known genetic background enabled us to obtain sequences from whole-genome phased haplotypes. We used a BWA-Picard-GATK pipeline for mapping sequence reads to the dm6 reference genome assembly, at a median depth-of coverage of 31X, and have made the resulting data publicly-available in the NCBI Short Read Archive (BioProject PRJNA282591). Haplotype Caller discovered and genotyped 1,726,931 genetic variants (SNPs and indels, <200bp). Additionally, we used GenomeStrip/2.0 to discover and genotype 167 large structural variants (1-100Kb in size). Sequence data and quality-filtered genotype data are publicly-available at NCBI (Short Read Archive, dbSNP and dbVar). We have also released the unfiltered genotype data, and the code and logs for data processing, summary statistics, and graphs, via the research data repository, Zenodo, (https://zenodo.org/, Sussex Drosophila Sequencing community).

genomics↗