Protein-poor diet reduces host-specific immune gene expression in Bombus terrestris

Abstract

Parasites infect hosts non-randomly as genotypes of hosts vary in susceptibility to the same genotypes of parasites, but this specificity may be modulated by environmental factors such as nutrition. Nutrition plays an important role for any physiological investment. As immune responses are costly, resource limitation should negatively affect immunity through trade-offs with other physiological requirements. Consequently, nutritional limitation should diminish immune capacity in general, but does it also dampen differences among hosts? We investigated the effect of short-term pollen deprivation on the immune responses of our model host Bombus terrestris when infected with the highly prevalent natural parasite Crithidia bombi. Bumblebees deprived of pollen, their protein source, show reduced immune responses to infection. They failed to upregulate a number of genes, including antimicrobial peptides, in response to infection. In particular, they also showed less specific immune expression patterns across individuals and colonies. These findings provide evidence for how immune responses on the individual-level vary with important elements of the environment and illustrate how nutrition can functionally alter not only general resistance, but also alter the pattern of specific host-parasite interactions.

Timing and size of daily pollen meals eaten by adult females of a solitary bee (Nomia melanderi) (Apiformes: Halictidae)

“…Such regular pollen feeding highlights the importance of pollen, not just nectar, in the diet of adult solitary bees. These results support Richard's (1994) assertion that dietary pollen underpins a female solitary bee's ability to reproduce and, extrapolating from honeybee studies (Mao et al 2013;Brunner et al 2014;Wang et al 2014), may generally extend bees' longevity and maintain a healthy immune system. Given the magnitude and regularity of pollen feeding by adult female N. melanderi , combined with Taniguchi's (1956) broad taxonomic survey, we expect similar ingestion patterns from nesting females of other solitary bee species.…”

“…The sugars of ingested nectar are the primary source of energy for both adults and larvae of all bees, whereas pollen provides all essential amino acids, some lipids (i.e., sterols), vitamins (Schmidt and Buchmann 1985;Roulston and Cane 2000), and other chemicals central to bee health (Mao et al 2013;Brunner et al 2014). The manner in which pollen is incorporated into the diet of adults contrasts among bees, especially between eusocial and solitary species.…”

Plant diversity and composition compensate for negative effects of urbanization on foraging bumble bees

“…A potential explanation for their importance may be that Fabaceae pollen is richer in protein compared to pollen of other plant families, as suggested by Goulson et al (2005) and Hanley et al (2008). The differential importance of different plant families/species can thus likely be explained by differences in the plants' nectar or pollen quality, as bumble bees appear to require pollen of high protein content (Leonhardt and Blüthgen 2012), which was found to increase their survival and immunocompetence (Genissel et al 2002;Tasei and Aupinel 2008;Brunner et al 2014). Interestingly, most of the plants visited by bumble bees in this study were native plants, such as T. repens , R. fruticosus , or L. corniculatus (Table SII).…”

Secondary metabolites in floral nectar reduce parasite infections in bumblebees

“…Survival of bees infected with Crithidia that consumed the control diet was 46%, whereas infected bees consuming anabasine had 70% survival (figure 2e); despite the substantial disparity between these proportions, the difference was not statistically significant. However, because Crithidia has its biggest fitness impacts on food-stressed bees [50], the consequences of anabasine consumption may be underestimated by laboratory studies with ad libitum food. Future research should investigate sources of the high variation in survival and potential relationship to diet in more natural settings.…”