Biology subjects

Hawthorne, D. J.

Publications and source records attributed to Hawthorne, D. J..

8 recordsLinked to original sources

bioRxiv2025

The cys-loop ligand-gated ion channel gene superfamily of the Colorado potato beetle, Leptinotarsa decemlineata

BackgroundThe insect cys-loop ligand-gated ion channel (cysLGIC) superfamily includes nicotinic acetylcholine receptors (nAChRs), {gamma}-aminobutyric acid (GABA) receptors, glutamate- or histamine-gated chloride channels (GluCls and HisCls), pH-sensitive chloride channels (pHCls) and several other functionally uncharacterized receptors. Several of these receptors are target sites of neonicotinoids and other insecticides. Characterizing sequences of cysLGIC genes can facilitate the study of functional expression of subunits allowing insecticide/receptor interaction research, and can promote molecular resistance monitoring tools development. The Colorado potato beetle (CPB) is an agricultural pest that threatens the production of solanaceous crops. Although this insect shows frequent evolution of insecticide resistance, its cysLGIC superfamily is not well characterized. ResultsTwenty-two candidate CPB cysLGIC subunit genes were identified, and the functional regions of their protein sequences were annotated. CPB possesses 22 candidate cysLGIC subunit genes such as nAChR 4, nAChR 6, RDL, and GluCl subunits, with similar sequence, structure, and alternative exon use as that in other insects. RNA A-to-I editing was observed of nAChR 6. Two copies of the pHCl subunit gene were identified, the first duplication of this gene observed in insects. ConclusionThe number of cysLGIC superfamily genes is similar to that of other insect species. Alternative splicing and RNA editing conserved in insect species were also identified in expected subunits, potentially contributing to structural and functional diversity of the receptor. Evidence of naturally truncated nAChR 4 and duplicated pHCl was observed, which invites future validation.

genomics↗

bioRxiv2022

Oversharing by honey bees and the spread of viruses

Deformed wing virus (DWV) is an emerging insect pathogen efficiently transmitted through communicable and vector-borne routes with Apis mellifera. Continual transmission of DWV between hosts and vectors is required for maintenance of the pathogen within the population, and this vector-host-pathogen system offers unique disease transmission dynamics for pathogen maintenance between vector and a social host. In a series of experiments, we study how vector-vector, host-host and host-vector transmission routes maintain DWV in a honey bee population. We found co-infestations on shared hosts allowed for movement of DWV from mite to mite. Additionally, two social behaviors of the honeybee, trophallaxis and cannibalization of pupae, provide routes for communicable transmission from bee to bee. Communicable circulation of the virus solely amongst hosts was then shown to act as a reservoir of DWV for naive Varroa to acquire and subsequently vector the pathogen. Our findings illustrate communicable transmission between hosts can maintain and influence the future acquisition and vectoring of a pathogen by a vector. There are a handful of other infectious diseases, both zoonotic and which impact human health, that have potentially similar transmission dynamics.

pathology↗

bioRxiv2022

Promiscuous feeding across multiple honey bee hosts amplifies the vectorial capacity of Varroa destructor

Varroa destructor is a cosmopolitan pest and leading cause of colony loss of the European honey bee. Historically described as a competent vector of honey bee viruses, this arthropod vector is cause for the global pandemic of Deformed wing virus, now endemic in honeybee populations. Our work shows viral spread is driven by Varroa actively switching from one adult bee to another as they feed. Assays using fluorescent microspheres were used to show the movement of fluids in both directions between host and vector when Varroa feed. Therefore, Varroa could be in either an infectious or naive state dependent upon the disease status of their host. We tested this and confirm that the relative risk of a Varroa feeding was dependent on the infectiousness of their previous host. Varroa exhibit remarkable heterogeneity in their host switching behavior, with some Varroa switching infrequently while others switch at least daily. As a result, relatively few of the most active Varroa parasitize the majority of bees. This multiple feeding behavior has analogs in vectorial capacity models of other systems, where promiscuous feeding by individual vectors is a leading driver of vectorial capacity. We propose that the honeybee-Varroa relationship offers a unique opportunity to apply principles of vectorial capacity to a social organism, as virus transmission is both vectored and occurs through multiple host-to-host routes common to a crowded society.

animal behavior and cognition↗

bioRxiv2022

Culture and genomic analysis of Arsenophonus apicola sp. nov. isolated from the honeybee Apis mellifera

The genus Arsenophonus has been traditionally considered to be comprised of heritable bacterial symbionts of arthropods. Recent work has reported a microbe related to the type species A. nasoniae as infecting the honey bee, Apis mellifera. The association was unusual for members of the genus in that the microbe-host interaction arose through environmental and social exposure rather than vertical transmission. In this study, we describe the in vitro culture of ArsBeeUS, a strain of this microbe isolated from A. mellifera in the USA. The 16S rRNA sequence of the isolated strain clearly indicates it falls within the genus Arsenophonus. Biolog analysis indicates the bacterium has a restricted range of nutrients that support growth. In vivo experiments demonstrate the strain proliferates rapidly on injection into A. mellifera hosts. We further report the closed genome sequence for the strain. The genome is 3.3 MB and 37.6% GC, which is smaller than A. nasoniae but larger than the genomes reported for non-culturable Arsenophonus symbionts. The genome is complex, with 6 plasmids and 11 predicted intact phage elements, but notably less complex than A. nasoniae. With 92% average nucleotide identity (ANI) to the type strain A. nasoniae, the ArsBeeUS strain isolated is clearly distinct from the type species, and we propose the name Arsenophonus apicola sp. nov. (CECT 30499; LMG 32504).

microbiology↗

bioRxiv2020

Pupal cannibalism by worker honey bees contributes to the spread of Deformed wing virus.

Transmission routes impact pathogen virulence and genetics, therefore comprehensive knowledge of these routes and their contribution to pathogen circulation is essential for understanding host-pathogen interactions and designing control strategies. Deformed wing virus (DWV), a principal viral pathogen of honey bees associated with increased honey bee mortality and colony losses, became highly virulent with the spread of its vector, the ectoparasitic mite Varroa destructor. Reproduction of Varroa mites occurs in capped brood cells and mite-infested pupae from these cells usually have high levels of DWV. The removal of mite-infested pupae by worker bees, Varroa Sensitive Hygiene (VSH), leads to cannibalization of pupae with high DWV loads, thereby offering an alternative route for virus transmission. We used genetically tagged DWV to investigate virus transmission to and between worker bees following pupal cannibalisation under experimental conditions. We demonstrated that cannibalization of DWV-infected pupae resulted in high levels of this virus in worker bees and that the acquired virus was then transmitted between bees via trophallaxis, allowing circulation of Varroa-vectored DWV variants without the mites. Despite the known benefits of hygienic behaviour, it is possible that higher levels of VSH activity may result in increased transmission of DWV via cannibalism and trophallaxis.

microbiology↗

bioRxiv2019

Elevated rates of positive selection drive the evolution of pestiferousness in the Colorado potato beetle (Leptinotarsa decemlineata, Say)

Insect pests are characterized by expansion, preference and performance on agricultural crops, high fecundity and rapid adaptation to control methods, which we collectively refer to as pestiferousness. Which organismal traits and evolutionary processes facilitate certain taxa becoming pests remains an outstanding question for evolutionary biologists. In order to understand these features, we set out to test the relative importance of genomic properties that underlie the rapid evolution of pestiferousness in the emerging pest model: the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say. Within the Leptinotarsa genus, only CPB has risen to pest status on cultivated Solanum. Using whole genomes from ten closely related Leptinotarsa species, we reconstructed a high-quality species tree of this genus. Within this phylogenetic framework, we tested the relative importance of four drivers of rapid adaptation: standing genetic variation, gene family expansion and contraction, transposable element variation, and protein evolution. Throughout approximately 20 million years of divergence, Leptinotarsa show little evidence of gene family turnover or transposable element variation contributing to pest evolution. However, there is a clear pattern of pest lineages experiencing greater rates of positive selection on protein coding genes, as well as retaining higher levels of standing genetic variation. We also identify a suite of positively selected genes unique to the Colorado potato beetle that are directly associated with pestiferousness. These genes are involved in xenobiotic detoxification, chemosensation, and hormones linked with pest behavior and physiology.

evolutionary biology↗

bioRxiv2019

Regional differences in gene regulation may underlie patterns of sensitivity to novel insecticides in Colorado potato beetle

Agricultural insect pests frequently exhibit geographic variation in levels of insecticide resistance, which are often presumed to be due to the intensity of insecticide use for pest management. However, regional differences in the evolution of resistance to novel insecticides suggests that other factors are influencing rates of adaptation. We examined LC50 bioassay data spanning 15 years and six insecticides (abamectin, imidacloprid, spinosad, cyantraniliprole, chlorantraniliprole, and metaflumizone) for evidence of regional differences in Colorado potato beetle (CPB) baseline sensitivity to insecticides as they became commercially available. We consistently found that CPB populations from the Western USA had the highest baseline sensitivity to novel insecticides, while populations from the Eastern USA had the lowest. Comparisons of gene expression between populations from these regions revealed constitutively elevated expression of an array of detoxification genes in the East, but no evidence of additional induction when exposed to imidacloprid. Our results suggest a mechanism for geographic variation in rates of adaptation to insecticides whereby baseline levels of gene expression determine a populations response to novel insecticides. These findings have implications for the regional development of insecticide resistance management strategies and for the fundamental question of what determines the rate of adaptation to insecticides.

evolutionary biology↗

bioRxiv2017

Origin of pest lineages of the Colorado potato beetle, Leptinotarsa decemlineata

Colorado potato beetle (Leptinotarsa decemlineata Say) is a pest of potato throughout the Northern Hemisphere, but little is known about the beetles origins as a pest. To determine the origins of pest populations of CPB, we sampled the beetle from uncultivated Solanum host plants in Mexico, and from pest and non-pest populations in the U.S. We used mtDNA and nuclear loci to examine three hypotheses on the origin of the pest lineages: 1) the pest beetles originated from Mexican populations, 2) the pest beetles descended from hybridization between previously divergent populations, or 3) the pest beetles descended from populations that are native to the Plains states in the United States. We examined patterns of genetic diversity among geographic regions in order to detect invasion-related genetic information. Mitochondrial haplotypes of non-pest populations from Mexico and southern Arizona differed substantially from beetles collected from the southern plains and potato fields in the U. S., indicating that beetles from Mexico and Arizona did not contribute to founding the pest lineages. Similar results were observed for AFLP and microsatellite data. In contrast, non-pest populations from the southern plains of Colorado, Kansas, Nebraska, New Mexico, and Texas were genetically similar to U. S. pest populations, clearly indicating that they contributed to the founding of the pest lineages. Although some pest populations are less genetically diverse (e.g., Washington, Idaho), most of the pest populations do not show a significant reduction in genetic diversity compared to the plains populations in the U. S. In contrast to the colonization patterns typical of exotic pests, our analyses suggests that a large genetically heterogeneous beetle populations expanded onto potato from native Solanum hosts. As an endemic colonization of a novel host plant, this host range expansion may have contributed to the relatively abundant genetic diversity of contemporary populations, perhaps contributing to the rapid evolution of host range and insecticide resistance in this widely successful insect pest.

evolutionary biology↗