Evolutionary History of Venom Glands in the Siluriformes

Abstract

The order Siluriformes represents a hyperdiverse group of fishes (>3,000 currently recognized species), which has been known to contain venomous species diversity for over 250 years. In spite of this historical knowledge, scientific examinations of the basic characteristics and evolutionary history of these species’ venom glands, and their products, have been extremely sparse compared to those of terrestrial venomous organisms, or even venomous fishes in general. Here, the current state of knowledge regarding the venom glands of catfishes and their products is examined in a review of morphological, pharmacological, and chemical studies of these structures. Several hypotheses regarding the evolution of siluriform venom glands are able to be drawn from the information contained in these studies as well as the limited work that has attempted to study the evolution of these structures in detail. These include selective scenarios to explain the secondary losses of venom glands in several catfish species and families, compositional variation in siluriform venom chemistry, and the derivation of venom glands from secretory cells of the epidermis. Future work directly addressing multiple issues of venom production and composition in catfishes is necessary before investigations of the evolution of siluriform venoms and delivery structures can reach the levels of detail and sophistication seen in other venomous groups. These studies will benefit greatly from the advent of genomic, transcriptomic, and proteomic methods, which have seen wide use in examinations of venoms produced by other taxa, but have yet to be widely applied to analyses of piscine venoms.