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J Anim Ecol

Title:		Elevated atmospheric concentrations of CO(2) increase endogenous immune function in a specialist herbivore
Author(s):		Decker LE; Jeffrey CS; Ochsenrider KM; Potts AS; de Roode JC; Smilanich AM; Hunter MD;
Address:		"Department of Biology, Stanford University, Stanford, CA, USA. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA. Chemistry Department, University of Nevada, Reno, NV, USA. Biology Department, Emory University, Atlanta, GA, USA. Department of Biology, University of Nevada, Reno, NV, USA"
Journal Title:		J Anim Ecol
Year:		2021
Volume:		20201206
Issue:		3
Page Number:		628 - 640
DOI:		10.1111/1365-2656.13395
ISSN/ISBN:		1365-2656 (Electronic) 0021-8790 (Linking)
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 CO(2) (eCO(2) ) 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 eCO(2) lose tolerance to the parasite, associated with changes in phytochemistry. Whether changes in milkweed phytochemistry induced by eCO(2) 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 CO(2) (aCO(2) ) or eCO(2) . 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 milkweed 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 aCO(2) plants and higher in larvae reared on foliage from eCO(2) plants. When grown under eCO(2) , 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 eCO(2) results in increased endogenous 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 underappreciated consequence of environmental change"
Keywords:		Animals *Asclepias *Butterflies Carbon Dioxide Herbivory Host-Parasite Interactions Immunity Asclepias Danaus plexippus Ophryocystis elektroscirrha cardenolides ecoimmunology haemocytes phenoloxidase;
Notes:		"MedlineDecker, Leslie E Jeffrey, Christopher S Ochsenrider, Kaitlin M Potts, Abigail S de Roode, Jacobus C Smilanich, Angela M Hunter, Mark D eng Research Support, U.S. Gov't, Non-P.H.S. England 2020/11/27 J Anim Ecol. 2021 Mar; 90(3):628-640. doi: 10.1111/1365-2656.13395. Epub 2020 Dec 6"