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      The relationship between poison frog chemical defenses and age, body size, and sex

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          Abstract

          Introduction

          Amphibians secrete a wide diversity of chemicals from skin glands as defense against predators, parasites, and pathogens. Most defensive chemicals are produced endogenously through biosynthesis, but poison frogs sequester lipophilic alkaloids from dietary arthropods. Alkaloid composition varies greatly, even among conspecific individuals collected at the same time and place, with some individuals having only a few micrograms of one or a few alkaloids and others possessing >1 mg of >30 alkaloids. The paucity of alkaloids in juveniles and their abundance in adults suggests that alkaloids accumulate over time; however, alkaloid diversity is highly variable among adult poison frogs and has never been studied in relation to individual age. Using skeletochronology to infer individual ages and gas chromatography–mass spectrometry and vapor phase Fourier-transform infrared spectral analysis to identify the defensive chemicals of 63 individuals, we tested the relationship between defensive chemicals and age, size, and sex in the Brazilian red-belly toad, Melanophryniscus moreirae, a poison frog that possesses both sequestered alkaloids and the biosynthesized indolealkylamine bufotenine.

          Results

          Adult females were, on average, older and larger than adult males. Juveniles were smaller but not necessarily younger than adults and possessed bufotenine and 18 of the 37 alkaloids found in adults. Alkaloid richness was positively related to age, but not size, whereas the quantities of sequestered alkaloids and bufotenine were positively related to size, but not age. Defensive chemicals were unrelated to sex, independent of size.

          Conclusions

          The relationship between alkaloid richness and age appears to result from the gradual accumulation of alkaloids over a frog’s lifetime, whereas the relationship between the quantity of defensive chemicals and size appears to be due to the greater storage capacity of larger individuals. The decoupling of age and size effects increases the amount of individual variation that can occur within a population, thereby possibly enhancing anti-predator efficacy. Further, given that both richness and quantity contribute to the overall chemical defense of individual frogs, our results suggest that older, larger individuals are better defended than younger, smaller ones. These considerations underscore the importance of including age in studies of the causes and consequences of variation in poison frog chemical defenses.

          Electronic supplementary material

          The online version of this article (doi:10.1186/s12983-015-0120-2) contains supplementary material, which is available to authorized users.

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          Most cited references 63

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            Sequestration of defensive substances from plants by Lepidoptera.

            A number of aposematic butterfly and diurnal moth species sequester unpalatable or toxic substances from their host plants rather than manufacturing their own defensive substances. Despite a great diversity in their life histories, there are some general features in the selective utilization of plant secondary metabolites to achieve effective protection from predators. This review illustrates the biochemical, physiological, and ecological characteristics of phytochemical-based defense systems that can shed light on the evolution of the widely developed sequestering lifestyles among the Lepidoptera.
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                Author and article information

                Contributors
                amjeckel@gmail.com
                rsaporito@jcu.edu
                taran.grant@gmail.com
                Journal
                Front Zool
                Front. Zool
                Frontiers in Zoology
                BioMed Central (London )
                1742-9994
                1 October 2015
                1 October 2015
                2015
                : 12
                Affiliations
                [ ]Department of Zoology, Institute of Biosciences, University of São Paulo, 05508-090 São Paulo, São Paulo Brazil
                [ ]Department of Biology, John Carroll University, University Heights, OH 44118 USA
                Article
                120
                10.1186/s12983-015-0120-2
                4591705
                © Jeckel et al. 2015

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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                Research
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                © The Author(s) 2015

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