Biology subjects

Irwin, R. E.

Publications and source records attributed to Irwin, R. E..

6 recordsLinked to original sources

bioRxiv2025

Nectar yeast scent additions fail to impact overall bouquet composition and bumble bee visitation in a montane herb

Premise of researchThe factors that mediate how foragers locate food supplies are of vital importance in understanding their energy acquisition and survival. Microbes that inhabit floral nectar can play outsized roles in altering nectar chemistry and nutrition, thereby affecting floral visitors. MethodologyHere, we consider one such nectar microbe, the cosmopolitan, specialist nectar yeast, Metschnikowia reukaufii (Metschnikowiaceae), by inoculating a nectar analog of the subalpine wildflower, Corydalis caseana ssp. brandegeei (Fumariaceae), and then characterizing the yeasts impacts on floral scent composition and the foraging behavior of its main pollinator, Bombus appositus (Apidae). We assessed foraging behavior of B. appositus in a flower array near the Rocky Mountain Biological Laboratory (Colorado, USA) to test the hypothesis that foragers preferentially visit yeast-inoculated flowers over sterile controls. Additionally, we assessed whether bees spent more time at, and fed more quickly on, yeast-inoculated flowers. In a separate experiment, we tested whether Corydalis inflorescences inoculated with M. reukaufii had different scent bouquets than sterile inflorescences. Pivotal resultsWe found that bumble bee pollinators showed no preference for the focal yeast species, with inoculated nectar having no effect on number of flowers visited, time spent on individual flowers, or time spent accessing nectar. Further, the overall scent bouquet compositions of yeast-inoculated Corydalis inflorescences were not statistically significantly different than those of sterile inflorescences, despite increased emissions of several volatiles that are known to be produced by M. reukaufii. ConclusionsOur findings suggest that B. appositus does not respond to the presence of M. reukaufii in the nectar of Corydalis, and instead, yeast-associated volatile emissions may serve as a reliable cue of a nectar reward that is unused by these pollinators. These findings suggest a few avenues for future research, particularly how morphologically complex, highly scented flowers interact with VOCs produced by nectar-inhabiting microbes, and how floral visitors interpret these signals.

ecology↗

bioRxiv2025

Self-medicating behavior in bumble bees has cascading consequences for pollination and plant reproduction

The sublethal effects of parasites can profoundly influence host traits and propagate to other trophic levels via indirect effects. To date, research on such trait-mediated indirect effects of parasites has focused on non-adaptive changes to host behavior, but adaptive sickness behaviors, such as self-medication, could also indirectly affect community composition and even the evolution of medicinal traits in lower trophic levels. Here, we used interactions among the parasite Crithidia bombi, the bumble bee host Bombus impatiens, and Monarda fistulosa, a bee-pollinated plant with multiple chemotypes (genetically determined chemical phenotypes), to experimentally test whether parasite infection influences pollinator foraging, pollination success, and female plant reproduction differentially for medicinal vs. non-medicinal chemotypes. Compounds from three Monarda chemotypes reduced Crithidia infection intensity in bees (thymol, carvacrol, and 1,8-cineole; hereafter medicinal chemotypes), while two others did not ((R)-(-)-linalool and geraniol; hereafter non-medicinal chemotypes), compared to control sucrose solutions. We found evidence for self-medication in tent foraging choice assays: infected bees preferred medicinal chemotypes while uninfected bees foraged indiscriminately, leading to differences in pollen receipt. Crithidia infection had weak but compounding chemotype-specific effects on seed production, germination rate, and offspring chemotype, such that pollination by infected bees resulted in a 57% increase in the proportion of medicinal plants in the F1 generation compared to pollination by uninfected bees. Self-medicating behavior can have differential effects on the reproduction of medicinal vs. non-medicinal plants, suggesting that pollinator parasites may act as agents of selection on the phytochemistry of floral rewards. SIGNIFICANCE STATEMENTParasite infection can alter host behavior in multiple ways, including by inducing self-medication. Self-medication has been documented in diverse animal taxa, yet we know very little about the broader ecological or evolutionary consequences of this response to infection. Here, we demonstrate that bumble bees infected with a common parasite show a preference for plant genotypes whose nectar contains antiparasitic compounds, and that this results in differential pollination and reproductive success for medicinal vs. non-medicinal individuals of a chemically polymorphic plant species. Our findings highlight self-medication as a previously understudied mechanism by which parasite infection could initiate cascading effects across trophic levels, and suggest that parasites may indirectly influence the evolution of plant traits via pollinator self-medication behaviors.

ecology↗

bioRxiv2022

Skewness in bee and flower phenological distributions

Phenological distributions are characterized by their central tendency, breadth, and shape, and all three determine the extent to which interacting species overlap in time. Pollination mutualisms rely on temporal co-occurrence of pollinators and their floral resources, and while much work has been done to characterize the shapes of flower phenological distributions, similar studies including pollinators are lacking. Here, we provide the first broad assessment of skewness, a component of distribution shape, for a bee community. We compare skewness in bees to that in flowers, related bee and flower skewness to other properties of their phenology, and quantify the potential consequences of differences in skewness between bees and flowers. Both bee and flower phenologies tend to be right-skewed, with a more exaggerated asymmetry in bees. Early-season species tend to be the most skewed, and this relationship is also stronger in bees than in flowers. Based on a simulation experiment, differences in bee and flower skewness could account for up to 14% of pair-wise overlap differences. Given the potential for interaction loss, we argue that difference in skewness of interacting species is an under-appreciated property of phenological change.

ecology↗

bioRxiv2021

Mites alight! Sunflower crop area and pollen supplementation enhance honey bee resistance to Varroa destructor

Anthropogenic landscape changes can affect parasite epidemiology in wild and agricultural animals. Honey bees are agricultural animals whose services are threatened by loss of floral resources and by parasites, most notably the invasive mite Varroa destructor. Existing mite control strategies rely heavily on chemical treatments that can adversely affect bees. Alternative, pesticide-free control methods are urgently needed to maintain effective pollination services. Many flowering plants provide nectar and pollen that enhance resistance to parasites in animals. Enrichment of landscapes with antiparasitic floral resources could therefore provide a sustainable means of parasite control in pollinators. Floral rewards of Asteraceae plants have been shown to reduce parasitic infection in diverse bee species, including honey and bumble bees. Here, we tested the effects of sunflower (Helianthus annuus) cropland and pollen supplementation on honey bee resistance to macro- and microparasites. Our results show that each doubling of sunflower crop area is associated with a 28% reduction in mite infestation intensity. Late-summer supplementation of colonies with sunflower pollen reduced mite infestation by 2.75-fold relative to an artificial pollen. Our findings suggest the potential for sunflower plantings or pollen supplements to counteract a main driver of honey bee losses worldwide.

ecology↗

bioRxiv2020

UHRF1 suppresses viral mimicry through both DNA methylation-dependent and -independent mechanisms

Some chemotherapeutic agents which cause loss of DNA methylation have been recently shown to induce a state of "viral mimicry" involving upregulation of endogenous retroviruses (ERV) and a subsequent innate immune response. This approach may be useful in combination with immune checkpoint cancer therapies, but relatively little is known about normal cellular control of ERV suppression. The UHRF1 protein can interact with the maintenance methylation protein DNMT1 and is known to play an important role in epigenetic control in the cell. To examine potential roles of this protein in differentiated cells, we first established stable knockdowns in normal human lung fibroblasts. While these knockdown cells showed the expected loss of DNA methylation genome-wide, transcriptional changes were instead dominated by a single response, namely activation of innate immune signalling, consistent with viral mimicry. We confirmed using mechanistic approaches that activation of interferons and interferon-stimulated genes involved in double-stranded RNA detection was crucial to the response. ERVs were demethylated and transcriptionally activated in UHRF1 knockdown cells. As in these normal cell lines, ERV activation and interferon response also occurred following the transient loss of UHRF1 in both melanoma and colon cancer cell lines. Restoring UHRF1 in either transient- or stable knockdown systems abrogated ERV reactivation and interferon response, but without substantial restoration of DNA methylation. Rescued cell lines were hypersensitive to depletion of SETDB1, implicating H3K9me3 as crucial to UHRF1-mediated repression in the absence of DNA methylation. Confirming this, cells rescued with UHRF1 containing point mutations affecting H3K9me3 binding could not mediate silencing of ERV transcription or the innate immune response. Finally, by introducing similar point mutations in the mouse homologue, we could show that this pathway is conserved in mice. Our results therefore implicate UHRF1 as a key regulator of ERV suppression and strengthen the basis for cancer cell hypomethylation therapy.

genomics↗

bioRxiv2017

The bovine alveolar macrophage DNA methylome is resilient to infection with Mycobacterium bovis

DNA methylation is pivotal in orchestrating gene expression patterns in various mammalian biological processes. Perturbation of the bovine alveolar macrophage (bAM) transcriptome, due to Mycobacterium bovis (M. bovis) infection, has been well documented; however, the impact of this intracellular pathogen on the bAM epigenome has not been determined. Here, whole genome bisulfite sequencing (WGBS) was used to assess the effect of M. bovis infection on the bAM DNA methylome. The methylomes of bAM infected with M. bovis were compared to those of non-infected bAM 24 hours post-infection (hpi). No differences in DNA methylation (CpG or non-CpG) were observed. Analysis of DNA methylation at proximal promoter regions uncovered >250 genes harbouring intermediately methylated (IM) promoters (average methylation of 33-66%). Gene ontology analysis, focusing on genes with low, intermediate or highly methylated promoters, revealed that genes with IM promoters were enriched for immune-related GO categories; this enrichment was not observed for genes in the high or low methylation groups. Targeted analysis of genes in the IM category confirmed the WGBS observation. This study is the first in cattle examining genome-wide DNA methylation at single nucleotide resolution in an important bovine cellular host-pathogen interaction model, providing evidence for IM promoter methylation in bAM.

genomics↗