Biology subjects

Holmes, C. J.

Publications and source records attributed to Holmes, C. J..

10 recordsLinked to original sources

bioRxiv2026

Stage-specific and tomato-spotted wilt virus infection-induced changes in the salivary gland transcriptome of western flower thrips

Western flower thrips (WFTs) are critical vectors of tomato spotted wilt virus (TSWV), transmitting it via a circulative-propagative cycle. The insect-virus relationship is unusual in that only larvae can acquire the virus for transmission to plants to occur. During the larval stage, the virus circulates and replicates within many organs, reaching the salivary glands before the insect pupates, and remaining in infected organs when the insect becomes an adult. The virus continues to replicate in the salivary glands of adult insects, after which it is inoculated into plants via saliva during feeding. Understanding the interactions between TSWV and the WFT salivary glands is critical to furthering investigations of TSWV inoculation and efforts to block the spread of this devastating plant virus. Here, we document transcriptomic changes associated with TSWV infection of the salivary glands of adults (males and females) and second instar larvae. Gene sets enriched in adult male, female, and larval genes revealed a core set of genes associated with WFT salivary glands, as well as genes that differed between sexes and between adults and larvae. The transcriptome response to TSWV infection was higher in larvae (second instar in this study) than in adults, with nearly a 10x increase in differentially expressed genes. We hypothesize this occurred because larvae efficiently acquire the virus and the virus first enters the SGs at the L2 stage, whereas adult SGs are infected only if acquisition occurred in the larval stage. Thus, assessment of larvae detects responses to the early stages of infection, while assessment of adults detects responses to the later stages of infection. Similarly, functional changes in larval salivary glands were more diverse, with significant transcriptome differences associated with growth and development in this tissue during infection. Lastly, a comparative analysis of changes in a published SG proteome revealed a correlation between transcript and protein levels during infection, but little overlap between significant TSWV-responsive transcripts and proteins. These studies provide critical insight into the molecular changes associated with the first breach of the SGs in larvae by TSWV, revealing a markedly different transcriptomic response compared to that in adults.

molecular biology↗

bioRxiv2024

Impaired humidity sensing reduces tick survival by preventing water homeostasis

Off-host periods are critical for ticks, representing a time when environmental stress, particularly dehydration, can impact tick survival. To prevent dehydration, ticks must be able to detect and move into high humidity areas to allow for water vapor uptake. Ionotropic receptor 93a (Ir93a), which is highly expressed in the front forelegs (location of Hallers organ), increases expression following dehydration, suggesting a role for the forelegs in humidity detection. Although the Hallers organ is suggested as the site of humidity detection in ticks, humidity detection has not been extensively examined for ticks. Here, we assessed the ability of ticks to sense humidity and how altered humidity detection impacts tick survival by manipulating the Hallers organ. Permanent (cutting or heat ablation) or temporary blocking (silicone covering) of the Hallers organ impairs the ability of the American dog tick, Dermacentor variabilis, to rest in areas necessary to maintain hydration. Impaired detection of humidity did not impact tick survival when individuals were held under stable optimal conditions. Still, variable conditions (low and high humidity gradient) reduced survival through dehydration stress and decreased energy reserves, as chronic water vapor uptake is energetically expensive. Field validation of these studies in D. variabilis confirmed that humidity detection is critical to tick survival. Lastly, modeling indicates impaired humidity detection will reduce questing tick populations, specifically in the adult stages. These studies confirm that the Hallers organ is critical for humidity sensing in ticks. Without this ability, tick survival will be impaired by potential dehydration or more rapid depletion of energy reserves.

physiology↗

bioRxiv2024

The impact of sugar diet on humidity preference, survival, and host landing in mosquitoes

Mosquito-borne diseases have caused more than one million deaths each year. There is an urgent need to develop an effective way to reduce mosquito-host interaction to mitigate disease transmission. Sugar diets have long been linked to abnormal physiology in animals, making them potential candidates for mosquito control. Here, we show the impact of sugar diets on humidity preference and survival in Aedes aegypti and Culex pipiens. With two-choice assays between 100% and 75% relative humidity (RH), we demonstrate that the effect of sugar diets on humidity preference is species-specific where Ae. aegypti showed significant differences and the reduced effects were noted in Cx. pipiens. Among the sugar diets, arabinose significantly reduced the survival rate of mosquitoes even at low concentrations. Moreover, we found that host landing was not impacted by feeding on different sugar types. Our study suggests that specific sugar treatments could be applied to mosquito control by dampening their humidity preference and reducing their lifespan, thus reducing mosquito-borne disease transmission.

physiology↗

bioRxiv2024

Multiple bouts of blood feeding in mosquitoes allow prolonged survival and are predicted to increase viral transmission during drought

Survival through periods of drought is critical for mosquitoes to reside in semi-arid regions with humans. Dry conditions increase blood feeding propensity in mosquitoes, but it is unknown if dehydration-induced bloodmeals increase feeding beyond what is necessary for reproduction. Following a bloodmeal, prolonged exposure to dry conditions increased secondary blood feeding in mosquitoes by nearly two-fold, and chronic blood feeding allowed mosquitoes to survive up to twenty days without access to water sources. This refeeding did not alter the number of eggs generated, suggesting this refeeding is for hydration and nutrient replenishment. Exposure to desiccating conditions following a bloodmeal resulted in increased activity, decreased sleep levels, and prompted a return of CO2 sensing before egg deposition. Increased blood feeding during the vitellogenic stage and higher survival during dry periods are predicted to increase pathogen transmission, allowing for a rapid rebound in mosquito populations when more favorable conditions return. This explains the elevated levels of specific arbovirus cases in association with periodic dry conditions and warrants further consideration as climate change progresses. Overall, these results solidify our understanding of the role of dry periods on mosquito blood feeding and how mosquito dehydration contributes to vectorial capacity and disease transmission dynamics Significance statementBouts of dehydration yield substantial changes to insects physiology and behavior. Mosquitoes are exceptionally prone to dehydration due to high water loss rates, but few integrative studies have examined the comprehensive impact of drought conditions on mosquitoes. Here, we demonstrate that dry conditions lead to multiple blood feeding events, allowing mosquitoes to survive dry periods. This repeated blood feeding is associated with higher activity and an early return of attraction to vertebrate hosts. Increased dry season survival and more frequent blood feeding are predicted to yield higher transmission of mosquito-borne viruses. This suggests that a higher prevalence of drought associated with climate change will have varying impacts on mosquito-borne diseases.

physiology↗

bioRxiv2023

Tyrosine transfer RNA levels and modifications during blood-feeding and vitellogenesis in the mosquito, Aedes aegypti

Mosquitoes such as Aedes aegypti must consume a blood meal for the nutrients necessary for egg production. Several transcriptome and proteome changes occur post blood meal that likely corresponds with codon usage alterations. Transfer RNA (tRNA) is the adapter molecule that reads messenger RNA (mRNA) codons to add the appropriate amino acid during protein synthesis. Chemical modifications to tRNA enhance codons decoding, improving the accuracy and efficiency of protein synthesis. Here, we examined tRNA modifications and transcripts associated with the blood meal and subsequent periods of vitellogenesis in A. aegypti. More specifically, we assessed tRNA transcript abundance and modification levels in the fat body at critical times post blood-feeding. Based on a combination of alternative codon usage and identification of particular modifications, we identified that increased transcription of tyrosine tRNAs is likely critical during the synthesis of egg yolk proteins in the fat body following a blood meal. Altogether, changes in both the abundance and modification of tRNA are essential factors in the process of vitellogenin production after blood-feeding in mosquitoes.

biochemistry↗

bioRxiv2023

Dehydration stress and Mayaro virus vector competence in Aedes aegypti

The mosquito Aedes aegypti is a competent vector of multiple pathogens including dengue, Zika, yellow fever, chikungunya, and Mayaro viruses. Ae. aegypti is highly invasive and is currently present in the Americas, Oceania, Asia, and Europe, but its distribution and the pathogens it transmits are expected to change due to climate change. Relative humidity is an environmental variable that affects mosquito biology and distribution and can differ between location, habitat, and season, with mosquitoes facing significant variation in relative humidity during their lifespan. Low relative humidity can induce dehydration in mosquitoes, leading to alterations in physiological and behavioral responses relevant for pathogen transmission such as bloodfeeding and host-seeking behavior. In this study, we evaluated the short and long-term effects of dehydration stress on mortality and Mayaro virus vector competence in Ae. aegypti. Our results show that exposure to dehydration does not impact viral titers, nor infection, dissemination and transmission rates, in mosquitoes infected with Mayaro virus. However, we detected a significant effect of dehydration on mosquito mortality and blood feeding frequency regardless of infection status. The previously observed effects of higher feeding during dehydration and the current observation of altered survival along with no impact on vector competence suggest that the impact of dehydration on viral transmission in mosquitoes will likely be complex.

microbiology↗

bioRxiv2022

Dehydration alters transcript levels in the midgut, likely facilitating rapid rehydration

The mosquito midgut is an important site for bloodmeal regulation while also acting as a primary site for pathogen exposure within the mosquito. Recent studies show that exposure to dehydrating conditions alters mosquito bloodfeeding behaviors as well as post-feeding regulation, likely altering how pathogens interact with the mosquito. Unfortunately, few studies have explored the underlying dynamics between dehydration and bloodmeal utilization, and the overall impact on disease transmission dynamics remains veiled. In this study, we find that dehydration-based feeding in the yellow fever mosquito, Aedes aegypti, prompts alterations to midgut gene expression, as well as subsequent physiological factors involving water control and post-bloodfeeding (pbf) regulation. Altered expression of ion transporter genes in the midgut of dehydrated mosquitoes and rapid reequilibration of hemolymph osmolality after a bloodmeal indicate an ability to expedite fluid and ion processing. These alterations ultimately indicate that female A. aegypti employ mechanisms to ameliorate the detriments of dehydration by imbibing a bloodmeal, providing an effective avenue for rehydration. Continued research into bloodmeal utilization and the resulting effects on arthropod-borne transmission dynamics becomes increasingly important as drought prevalence is increased by climate change.

physiology↗

bioRxiv2020

Genome-enabled insights into the biology of thrips as crop pests

BackgroundThe western flower thrips, Frankliniella occidentalis (Pergande), is a globally invasive pest and plant virus vector on a wide array of food, fiber and ornamental crops. While there are numerous studies centered on thrips pest and vector biology, feeding behaviors, ecology, and insecticide resistance, the underlying genetic mechanisms of the processes governing these areas of research are largely unknown. To address this gap, we present the F. occidentalis draft genome assembly and official gene set. ResultsWe report on the first genome sequence for any member of the insect order Thysanoptera. Benchmarking Universal Single-Copy Ortholog (BUSCO) assessments of the genome assembly (size = 415.8 Mb, scaffold N50 = 948.9 Kb) revealed a relatively complete and well-annotated assembly in comparison to other insect genomes. The genome is unusually GC-rich (50%) compared to other insect genomes to date. The official gene set (OGS v1.0) contains 16,859 genes, of which [~]10% were manually verified and corrected by our consortium. We focused on manual annotation, phylogenetic and expression evidence analyses for gene sets centered on primary themes in the life histories and activities of plant-colonizing insects. Highlights include: 1) divergent clades and large expansions in genes associated with environmental sensing (chemosensory receptors) and detoxification (CYP4, CYP6 and CCE enzymes) of substances encountered in agricultural environments; 2) a comprehensive set of salivary gland-associated genes supported by enriched expression; 3) apparent absence of members of the IMD innate immune defense pathway; and 4) developmental- and sex-specific expression analyses of genes associated with progression from larvae to adulthood through neometaboly, a distinct form of maturation compared to complete metamorphosis in the Holometabola. ConclusionsAnalysis of the F. occidentalis genome offers insights into the polyphagous behavior of this insect pest to find, colonize and survive on a widely diverse array of plants. The genomic resources presented here enable a more complete analysis of insect evolution and biology, providing a missing taxon for contemporary insect genomics-based analyses. Our study also offers a genomic benchmark for molecular and evolutionary investigations of other thysanopteran species.

genomics↗

bioRxiv2019

Multi-level analysis of reproduction in an Antarctic midge identifies female and male accessory gland products that are altered by larval stress and impact progeny viability

The Antarctic midge, Belgica antarctica, is a wingless, non-biting midge endemic to Antarctica. Larval development requires at least two years, but adult life lasts only two weeks. The nonfeeding adults mate in swarms and females die shortly after oviposition. Eggs are suspended in a gel of unknown composition that is expressed from the female accessory gland. This project characterizes molecular mechanisms underlying reproduction in this midge by examining differential gene expression in whole males, females, and larvae, as well as in male and female accessory glands. Functional studies were used to assess the role of the gel encasing the eggs, as well as the impact of stress on reproductive biology. RNA-seq analyses revealed sex- and development-specific gene sets along with those associated with the accessory glands. Proteomic analyses were used to define the composition of the egg-containing gel, which is generated during multiple developmental stages and derived from both the accessory gland and other female organs. Functional studies indicate the gel provides a larval food source and thermal and dehydration buffer, all of which are critical for viability. Larval dehydration stress directly reduces production of storage proteins and key accessory gland components, a feature that impacts adult reproductive success. Modeling reveals that bouts of dehydration may significantly impact population growth. This work lays a foundation for further examination of reproduction in midges and provides new information related to general reproduction in dipterans. A key aspect is that reproduction and stress dynamics, currently understudied in polar organisms, are likely to prove critical for determining how climate change will alter survivability.

genomics↗

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↗