Predatory fireflies and their toxic firefly prey have evolved distinct toxin resistance strategies

Abstract

SummaryToxic cardiotonic steroids (CTS) act as a defense mechanism in many firefly species (Lampyridae) by inhibiting a crucial enzyme called Na+,K+-ATPase (NKA). While most fireflies produce these toxins internally, species of the genusPhoturisacquire them from a surprising source: predation on other fireflies. The contrasting physiology of toxin exposure and sequestration betweenPhoturisand other firefly genera suggests that distinct strategies may be required to prevent self-intoxication. Our study demonstrates that bothPhoturisand their firefly prey have evolved highly-resistant NKAs. Using an evolutionary analysis of the specific target of CTS (ATPα) in fireflies, and gene-editing inDrosophila, we find that the initial steps towards resistance were shared amongPhoturisand other firefly lineages. However, thePhoturislineage subsequently underwent multiple rounds of gene duplication and neofunctionalization, resulting in the development of ATPα paralogs that are differentially expressed and exhibit increasing resistance to CTS. In contrast, other firefly species have maintained a single copy. Our results implicate gene duplication as a facilitator in the transition ofPhoturisto its distinct ecological role as predator of toxic firefly prey.One-Sentence SummaryGene duplication and neofunctionalization distinguish firefly predators from their toxic firefly prey.