Alkaloid-based chemical defenses and diet in six species of Australian poison frogs in the genus Pseudophryne (Myobatrachidae)

Abstract

Poison frogs are well known for their ability to sequester alkaloids from their diet of leaf-litter arthropods for use in defense against predators and pathogens. Australian frogs in the genus Pseudophryne (Myobatrachidae) represent an understudied lineage of poison frogs, with a unique ability to both sequester dietary alkaloids and synthesize pseudophrynamine alkaloids. Herein, we describe the alkaloid profiles and diet of six species of Pseudophryne (P. guentheri [Boulenger, 1882], P. occidentalis [Parker, 1940], P. semimarmorata [Lucas, 1892], P. dendyi [Lucas 1892], P. bibronii [Günther, 1859], and P. coriacea [Keferstein, 1868]) to gain a better understanding of how alkaloid defenses and diet are related within and among species. We characterized and quantified alkaloids using Gas Chromatography-Mass Spectrometry (GC-MS), and assessed diet by way of dissection and examination of stomach contents using light microscopy. We found that alkaloid profiles varied significantly among species, with pumiliotoxins (dietary-derived) and pseudophrynamines (biosynthesized) being the most abundant alkaloids. Pseudophryne bibronii and P. dendyi contained mostly dietary-derived alkaloids, whereas P. coriacea, P. guentheri, P. semimarmorata, and P. occidentalis possessed mostly biosynthesized alkaloids. The stomachs of all the studied species were largely empty, containing mostly soil and few partially digested insects. Our data suggest that frogs eat minimally during the breeding season. Therefore, a decrease in dietary alkaloids may be compensated by the biosynthesized pseudophrynamines, which could allow Australian poison frogs to remain defended from predators during this vulnerable time period.