Palmer-Young, Evan
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Graduate Student
Last Name
Palmer-Young
First Name
Evan
Discipline
Life Sciences
Expertise
Introduction
Name
3 results
Search Results
Now showing 1 - 3 of 3
Publication Effects of the floral phytochemical eugenol on parasite evolution and bumble bee infection and preference(2018-01-01) Palmer-Young, Evan C.; Calhoun, Austin C.; Mirzayeva, Anastasiya; Sadd, Benn M.Ecological and evolutionary pressures on hosts and parasites jointly determine infection success. In pollinators, parasite exposure to floral phytochemicals may influence between-host transmission and within-host replication. In the bumble bee parasite Crithidia bombi, strains vary in phytochemical resistance, and resistance increases under in vitro selection, implying that resistance/infectivity trade-offs could maintain intraspecific variation in resistance. We assessed costs and benefits of in vitro selection for resistance to the floral phytochemical eugenol on C. bombi infection in Bombus impatiens fed eugenol-rich and eugenol-free diets. We also assessed infection-induced changes in host preferences for eugenol. In vitro, eugenol-exposed cells initially increased in size, but normalized during adaptation. Selection for eugenol resistance resulted in considerable (55%) but non-significant reductions in infection intensity; bee colony and body size were the strongest predictors of infection. Dietary eugenol did not alter infection, and infected bees preferred eugenol-free over eugenol-containing solutions. Although direct effects of eugenol exposure could influence between-host transmission at flowers, dietary eugenol did not ameliorate infection in bees. Limited within-host benefits of resistance, and possible trade-offs between resistance and infectivity, may relax selection for eugenol resistance and promote inter-strain variation in resistance. However, infection-induced dietary shifts could influence pollinator-mediated selection on floral traits.Publication Context-Dependent Medicinal Effects of Anabasine and Infection-Dependent Toxicity in Bumble Bees(2017-01) Palmer-Young, Evan C.; Hogeboom, Alison; Palmer-Young, Evan; Kaye, Alexander J.; Donnelly, Dash; Andicoechea, Jonathan; Connon, Sara June; Weston, Ian; Skyrm, Kimberly; Irwin, Rebecca E.; Adler, Lynn S.; Palmer-Young, Evan; Palmer-Young, EvanBackground Floral phytochemicals are ubiquitous in nature, and can function both as antimicrobials and as insecticides. Although many phytochemicals act as toxins and deterrents to consumers, the same chemicals may counteract disease and be preferred by infected individuals. The roles of nectar and pollen phytochemicals in pollinator ecology and conservation are complex, with evidence for both toxicity and medicinal effects against parasites. However, it remains unclear how consistent the effects of phytochemicals are across different parasite lineages and environmental conditions, and whether pollinators actively self-medicate with these compounds when infected. Approach Here, we test effects of the nectar alkaloid anabasine, found in Nicotiana, on infection intensity, dietary preference, and survival and performance of bumble bees (Bombus impatiens). We examined variation in the effects of anabasine on infection with different lineages of the intestinal parasite Crithidia under pollen-fed and pollen-starved conditions. Results We found that anabasine did not reduce infection intensity in individual bees infected with any of four Crithidia lineages that were tested in parallel, nor did anabasine reduce infection intensity in microcolonies of queenless workers. In addition, neither anabasine nor its isomer, nicotine, was preferred by infected bees in choice experiments, and infected bees consumed less anabasine than did uninfected bees under no-choice conditions. Furthermore, anabasine exacerbated the negative effects of infection on bee survival and microcolony performance. Anabasine reduced infection in only one experiment, in which bees were deprived of pollen and post-pupal contact with nestmates. In this experiment, anabasine had antiparasitic effects in bees from only two of four colonies, and infected bees exhibited reduced—rather than increased—phytochemical consumption relative to uninfected bees. Conclusions Variation in the effect of anabasine on infection suggests potential modulation of tritrophic interactions by both host genotype and environmental variables. Overall, our results demonstrate that Bombus impatiens prefer diets without nicotine and anabasine, and suggest that the medicinal effects and toxicity of anabasine may be context dependent. Future research should identify the specific environmental and genotypic factors that determine whether nectar phytochemicals have medicinal or deleterious effects on pollinators.Publication EFFECTS OF FLORAL PHYTOCHEMICALS ON GROWTH AND EVOLUTION OF A PARASITE OF BUMBLE BEES(2018-02) Palmer-Young, EvanBackground: Nectar and pollen are rich in phytochemicals, some of which can reduce disease in pollinators, including agriculturally important honey and bumble bees. Floral phytochemicals could influence the ecological and evolutionary relationships between plants, their pollinators, and parasites that cause pollinator disease. Antiparasitic effects of phytochemicals could be exploited to ameliorate pollinator disease and decline, and thereby sustain pollinator-dependent agricultural production. However, prior studies showed variable effects of phytochemicals on infection in live bees, where differences in bee genotype, abiotic conditions, and parasite strain could influence results. Approach: I used cell cultures of the intestinal trypanosome parasite of bumble bees, Crithidia bombi, to (1) describe how resistance to 9 floral phytochemicals varied among 4 parasite strains, (2) describe the antiparasitic effect of phytochemical combinations, and (3) test for evolution of resistance to individual phytochemicals and a two-phytochemical blend. Results: (1) Resistance to floral phytochemicals: C. bombi showed striking resistance to the phenolics gallic acid, caffeic acid, and chlorogenic acid at levels beyond those found in nectar and pollen; literature searches showed that C. bombi resistance to these compounds exceeded that of bloodstream trypanosomes by several orders of magnitude. Phytochemical resistance varied among C. bombi isolates, indicating that medicinal effects of phytochemicals are dependent on parasite strain. Thymol and eugenol inhibited growth at concentrations below the toxicity thresholds of bees. Inhibitory concentrations of thymol were similar to those found in Thymus vulgaris nectar, indicating that medicinal effects of phytochemicals on pollinator disease are ecologically relevant, and could be achieved through strategic planting of phytochemical-rich flowers. (2) Synergistic effects of combined phytochemicals: Thymol and eugenol had synergistic effects against 3 of 4 C. bombi strains—inhibition of parasites exposed to phytochemical combinations was stronger than predicted based on the activities of isolated phytochemicals. Synergy between phytochemicals suggests that phytochemical combinations may have greater antiparasitic potential in comparison to single phytochemicals. Synergistic phytochemical combinations in diverse floral landscapes could allow pollinators to self-medicate without toxicity, thereby ameliorating diseases that contribute to pollinator decline. (3) Evolution of resistance to phytochemicals: Resistance of C. bombi increased under single and combined phytochemical exposure, without any associated cost of reduced growth under phytochemical-free conditions. After six weeks’ exposure, phytochemical concentrations that initially inhibited growth by >50%, and exceeded concentrations in floral nectar, had minimal effects on evolved parasite lines. Unexpectedly, a two-phytochemical combination did not impede resistance evolution compared to single compounds. These results demonstrate that repeated phytochemical exposure, which could occur in homogeneous floral landscapes or with therapeutic phytochemical treatment of managed hives, can cause rapid evolution of resistance in a pollinator parasite. Evolved resistance could diminish the antiparasitic value of phytochemical ingestion, weakening an important natural defense against infection. Conclusion: These results show the potential of phytochemical-rich flowers to directly ameliorate pollinator infection, a recognized contributor to bee decline. Results also suggest benefits of diverse landscapes for pollinator health. Phytochemically complex mixtures in diverse floral landscapes could synergistically inhibit parasite growth and curtail the evolution of phytochemical resistance in parasites, thereby optimizing the medicinal effects of phytochemicals on bees. Deliberate planting of high-phytochemical crops and hedgerow species could reduce the effects of disease on bee populations, thereby benefitting agricultural production.