Variable Alkaloid Defenses in the Dendrobatid Poison Frog

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by John Carroll University John Carroll University Carroll Collected 2017 Faculty Bibliography Faculty Bibliographies Community Homepage 3-2017 Variable Alkaloid Defenses in the Dendrobatid Poison Frog Oophaga pumilio are Perceived as Differences in Palatability to Arthropods Sarah Bolton John Carroll University, [email protected] Kelsey Dickerson University of California - Berkeley Ralph Saporito John Carroll University, [email protected] Follow this and additional works at: https://collected.jcu.edu/fac_bib_2017 Part of the Biology Commons, and the Ecology and Evolutionary Biology Commons Recommended Citation Bolton, Sarah; Dickerson, Kelsey; and Saporito, Ralph, "Variable Alkaloid Defenses in the Dendrobatid Poison Frog Oophaga pumilio are Perceived as Differences in Palatability to Arthropods" (2017). 2017 Faculty Bibliography. 62. https://collected.jcu.edu/fac_bib_2017/62 This Article is brought to you for free and open access by the Faculty Bibliographies Community Homepage at Carroll Collected. It has been accepted for inclusion in 2017 Faculty Bibliography by an authorized administrator of Carroll Collected. For more information, please contact [email protected]. Variable Alkaloid Defenses in the Dendrobatid Poison Frog Oophaga pumilio are Perceived as Differences in Palatability to Arthropods 1 2 1 Sarah K. Bolton & Kelsie Dickerson & Ralph A. Saporito Abstract Conspicuously colored dendrobatid frogs sequester palatability spectrum suggests that variable alkaloid defenses alkaloid defenses from dietary arthropods, resulting in consid- in O. pumilio are ecologically relevant and play an important erable alkaloid variation among populations; however, little is role in natural predator-prey interactions, particularly with re- known about how variation is perceived as a defense against spect to arthropod predators. predators. Previous studies have found variable alkaloids in the dendrobatid Oophaga pumilio to be associated with dif- Keywords Ant . Chemical defense . Ectatomma ruidum . ferences in toxicity to laboratory mice, suggesting variable Vinegar fly . Palatability assay . Palatability spectrum defenses are important. Arthropods are natural predators that use chemoreception to detect prey, including frogs, and may therefore perceive variation in alkaloid profiles as differences Introduction in palatability. The goal of the present study is to determine how arthropods respond to variable alkaloid defenses in Chemical defenses are present in a variety of organisms and O. pumilio. Frog alkaloids were sampled from individual represent unique protective adaptations aimed at deterring mi- O. pumilio from ten geographic locations throughout the crobial pathogens, parasites, and natural predators (Savitzky Bocas del Toro region of Panama and the Caribbean coast of et al. 2012; Speed et al. 2012). Chemically defended organ- Costa Rica. Alkaloid extracts were used in feeding bioassays isms have a widespread distribution across many taxa, giving with the vinegar fly Drosophila melanogaster and the ant rise to several different classes of defensive chemicals such as Ectatomma ruidum. Both species of arthropods fed signifi- terpenoids, phenolics, steroids, biogenic amines, peptides, cantly less on frog alkaloid extracts when compared to con- proteins, and alkaloids (Hancock and Scott 2000; Mithöfer trols, and differences in alkaloid palatability were observed and Boland 2012). Most chemically defended organisms can among frog populations, as well as between sexes and life synthesize their own defensive compounds, but others seques- stages within a population. Differences in alkaloid quantity, ter defenses and are entirely dependent on external sources richness, and type were the main predictors of arthropod pal- such as diet or symbionts for their chemical protection atability. Our findings also represent the first direct evidence (Hartmann et al. 2001;Termoniaetal.2001; Williams of a palatability spectrum in a vertebrate that sequesters chem- 2010). Numerous phytophagous arthropods have evolved spe- ical defenses from dietary sources. Further, the presence of a cialized adaptations to circumvent plant defenses and sequester them for use in their own defense (Opitz and Müller 2009; Wittstock and Gershenzon 2002), and several vertebrates are * Ralph A. Saporito [email protected] also adapted to sequester defenses from their diet (for reviews, see Saporito et al. 2012; Savitzky et al. 2012). Among verte- 1 Department of Biology, John Carroll University, 1 John Carroll brates, members of five different families of poison frogs have Boulevard, University Heights, OH 44118, USA evolved the ability to use alkaloids obtained from dietary ar- 2 Department of Environmental Science, Policy, and Management, thropods as a mode of defense. These include the dendrobatids University of California at Berkeley, 130 Mulford Hall #3114, (Dendrobatidae) from Central and South America, bufonids Berkeley, CA 94720, USA (Melanophryniscus) from South America, mantellids (Mantella) from Madagascar, myobatrichids (Pseudophryne) The dendrobatid frog Oophaga pumilio is characterized by from Australia, and certain eleutherodacylids particularly variable alkaloid defenses throughout its geo- (Eleutherodactylus) from Cuba (Saporito et al. 2012). graphic range from southern Nicaragua through northwestern Vertebrates dependent on dietary sources for their chemical Panama, differing in defense among populations, between defenses often exhibit tremendous variation in the type and sexes, among life stages, and over time (Saporito et al. 2006, quantity of their sequestered defenses (Saporito et al. 2009; 2007a). More than 232 different alkaloids have been identified Savitzky et al. 2012; Speed et al. 2012). Variation in defense in O. pumilio (categorized into 24 structural classes), and in- can occur geographically and temporally, and is largely attrib- dividual frogs possess between 4 and 44 different alkaloids uted to differences in food availability, but also include age, (Saporito et al. 2007a). Ants and spiders are important natural size, and sex (Jeckel et al. 2015;Saporitoetal.2007a, 2012; predators of this species (Hovey et al. 2016; Murray et al. Speed et al. 2012; Stynoski et al. 2014a). Variation in diet for 2016; Santos and Cannatella 2011), both of which use chemo- vertebrates that sequester chemical defenses are hypothesized reception to detect prey and therefore may be particularly to result in differences in the ability of individuals, popula- sensitive to differences in alkaloid defenses. Recently, tions, and/or species to protect themselves from predation Murray et al. (2016) investigated differences in predation by (Bowers 2003;Broweretal.1968; Saporito et al. 2007a; bullet ants (Paraponera clavata) and red-legged banana spi- Savitzky et al. 2012); however, relatively little empirical work ders (Cupiennius coccineus) on different life stages of has tested how variation in chemical defenses might function O. pumilio, and provided evidence that ant predators are sen- as a defense against natural predators (however, see Murray sitive to differences in alkaloid defenses; however, it is not et al. 2016). Recently, theoretical studies have proposed that known how alkaloid variation among populations of variation in prey defenses are only important if predators are O. pumilio translates to predator avoidance. The extensive able to detect and respond to this variation (Speed et al. 2012; population-level variation in chemical defenses in Summers et al. 2015). Therefore, experimental studies are O. pumilio, coupled with the fact that their natural arthropod necessary to fully understand the ecological and evolutionary predators use chemoreception, makes it an ideal species to importance of variable chemical defenses in vertebrates. study how alkaloid variation in dendrobatids is perceived by Conspicuously colored dendrobatid frogs represent a well- arthropods. studied group of vertebrates that acquire defenses from a diet Investigations on variable alkaloid defenses in O. pumilio of mites, ants, beetles, and millipedes (Daly et al. 2002; have been predominantly focused on measuring alkaloid tox- Saporito et al. 2007a, b, 2009). Due to differences in the dis- icity to laboratory mice in minimum lethal dose, LD50,or tribution, abundance, and availability of these dietary arthro- irritability assays. Overall, these studies have shown that var- pods, dendrobatids often exhibit tremendous alkaloid variabil- iation in alkaloids is related to differences in toxicity (Daly ity within and among populations, between sexes, throughout and Myers 1967; Darst et al. 2006; Maan and Cummings life stages, and over time (Daly et al. 1978, 1987, 2002;Daly 2012). Daly and Myers (1967) investigated alkaloid toxicity and Myers 1967;Saporitoetal.2006, 2007a, 2010a, 2010b, in terms of minimal lethal dose for several populations of 2012; Stynoski et al. 2014a). Given the large degree of varia- O. pumilio from Bocas del Toro, Panama. These assays were tion in dendrobatid defenses, it is possible that predators per- performed by injecting mice subcutaneously with naturally ceive differences in alkaloids as a spectrum of palatability occurring alkaloids dissolved in saline, which served as a (Fritz et al. 1981;Murrayetal.2016; Saporito et al. 2007a; proxy for quantifying toxicity. Daly and Myers (1967)found Szelistowski 1985). For example, chemically defended arthro- considerable variation

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