The price of defence : toxins, visual signals and oxidative state in an aposematic butterfly
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In a variety of aposematic species, the conspicuousness of an individual's warning signal and the quantity of its chemical defence are positively correlated. This apparent honest signalling is predicted by resource competition models which assume that the production and maintenance of aposematic defences compete for access to antioxidant molecules that have dual functions as pigments and in protecting against oxidative damage. To test for such trade-offs, we raised monarch butterflies (Danaus plexippus) on different species of their milkweed host plants (Apocynaceae) that vary in quantities of cardenolides to test whether (i) the sequestration of cardenolides as a secondary defence is associated with costs in the form of oxidative lipid damage and reduced antioxidant defences; and (ii) lower oxidative state is associated with a reduced capacity to produce aposematic displays. In male monarchs conspicuousness was explained by an interaction between oxidative damage and sequestration: males with high levels of oxidative damage became less conspicuous with increased sequestration of cardenolides, whereas those with low oxidative damage became more conspicuous with increased levels of cardenolides. There was no significant effect of oxidative damage or concentration of sequestered cardenolides on female conspicuousness. Our results demonstrate a physiological linkage between the production of coloration and oxidative state, and differential costs of sequestration and signalling in monarch butterflies.
Blount , J D , Rowland , H M , Mitchell , C , Speed , M P , Ruxton , G D , Endler , J A & Brower , L P 2023 , ' The price of defence : toxins, visual signals and oxidative state in an aposematic butterfly ' , Proceedings of the Royal Society B: Biological Sciences , vol. 290 , no. 1991 , 20222068 . https://doi.org/10.1098/rspb.2022.2068
Proceedings of the Royal Society B: Biological Sciences
Copyright © 2023 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.
DescriptionFunding: J.D.B. was supported by a Royal Society University Research Fellowship. H.M.R., G.D.R. and M.P.S. were supported by NERC (NE/D010 667/1) during data collection, and H.M.R. was supported by a Junior Research Fellowship from Churchill College, Cambridge and the Max Planck Society during data analysis and manuscript preparation.
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