Elevated atmospheric concentrations of CO ₂ increase endogenous immune function in a specialist herbivore

Terrestrial

Fauna

Climate

Atmospheric

asclepias

cardenolides

ecoimmunology

haemocytes

Danaus plexippus

Ophryocystis elektroscirrha

phenoloxidase

Title	Elevated atmospheric concentrations of CO 2 increase endogenous immune function in a specialist herbivore
Publication Type	Journal Article
Year of Publication	2021
Authors	Decker LE, Jeffrey CS, Ochsenrider KM, Potts AS, Roode JC, Smilanich AM, Hunter MD
Secondary Authors	Ardia D
Journal	Journal of Animal Ecology
Volume	907
Issue	3
Pagination	628 - 640
Date Published	Jan-03-2021
ISSN	0021-8790
Abstract	Animals rely on a balance of endogenous and exogenous sources of immunity to mitigate parasite attack. Understanding how environmental context affects that balance is increasingly urgent under rapid environmental change. In herbivores, immunity is determined, in part, by phytochemistry which is plastic in response to environmental conditions. Monarch butterflies Danaus plexippus, consistently experience infection by a virulent parasite Ophryocystis elektroscirrha, and some medicinal milkweed (Asclepias) species, with high concentrations of toxic steroids (cardenolides), provide a potent source of exogenous immunity. We investigated plant-mediated influences of elevated CO2 (eCO2) on endogenous immune responses of monarch larvae to infection by O. elektroscirrha. Recently, transcriptomics have revealed that infection by O. elektroscirrha does not alter monarch immune gene regulation in larvae, corroborating that monarchs rely more on exogenous than endogenous immunity. However, monarchs feeding on medicinal milkweed grown under eCO2 lose tolerance to the parasite, associated with changes in phytochemistry. Whether changes in milkweed phytochemistry induced by eCO2 alter the balance between exogenous and endogenous sources of immunity remains unknown. We fed monarchs two species of milkweed; A. curassavica (medicinal) and A. incarnata (non-medicinal) grown under ambient CO2 (aCO2) or eCO2. We then measured endogenous immune responses (phenoloxidase activity, haemocyte concentration and melanization strength), along with foliar chemistry, to assess mechanisms of monarch immunity under future atmospheric conditions. The melanization response of late-instar larvae was reduced on medicinal milk-weed in comparison to non-medicinal milkweed. Moreover, the endogenous immune responses of early-instar larvae to infection by O. elektroscirrha were generally lower in larvae reared on foliage from aCO2 plants and higher in larvae reared on foliage from eCO2 plants. When grown under eCO2, milkweed plants exhibited lower cardenolide concentrations, lower phytochemical diversity and lower nutritional quality (higher C:N ratios). Together, these results suggest that the loss of exogenous immunity from foliage under eCO2 results in increased en-dogenous immune function. Animal populations face multiple threats induced by anthropogenic environmental change. Our results suggest that shifts in the balance between exogenous and endogenous sources of immunity to parasite attack may represent an underap-preciated consequence of environmental change.
URL	https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2656.13395
DOI	10.1111/jane.v90.310.1111/1365-2656.13395
Short Title	J Anim Ecol

Related research sites: 

UMBS Elevated Carbon Dioxide Facility

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