The Evolution and Diversification of a Symbiotic Bioluminescence Signaling System

American Museum Natural History, New York NY

Investigators

Abstract

A grant has been awarded to Dr. John Sparks of the American Museum of Natural History to examine the evolution, coevolutionary interactions and biogeography of the symbiosis between fishes of the family Leiognathidae (ponyfishes) and the luminous marine prokaryote Photobacterium leiognathi. The fish host is abundant, economically important, and widely distributed throughout the Indo-Pacific. The fish harbors a dense population of the bacterial symbiont in an internal circumesophageal structure, called a light organ, providing the bacteria with oxygen and nutrients, and uses bacterial luminescence in various displays associated with predation, anti-predation and sex-specific signaling. Males of most ponyfish species exhibit greatly enlarged, structurally complex and species-specific light organs, whereas those of females are comparatively poorly developed. It is hypothesized that sexual selection for male luminescence signaling is correlated with morphological diversification of the light organ system (LOS) and speciation in ponyfishes. Although the evolution and functions of a sexually-dimorphic bioluminescent system based on species-specific male signaling are well documented in fireflies, in vertebrates these systems are poorly understood. Ponyfishes provide an excellent system in which to address these questions. The evolutionary relationships of ponyfishes will be reconstructed using DNA sequence data and phenotypic features of the fish's LOS, and examined in light of symbiont patterns of relationship. This project will provide insight into the evolution of luminescence-signaling systems in fishes, the role of sexual selection in ponyfish diversification, coevolutionary interactions in a symbiosis in which the bacterium is acquired with each new generation, and the role of the symbiosis in the biogeographic distribution of the fish and bacterium. The project will provide exposure to fieldwork and training to post-doctoral and student participants in the areas of systematics, symbiosis, ichthyology, coevolution, and biogeography.