Mutation, Duplication, and More in the Evolution of Venomous Animals and Their Toxins

Abstract

Toxins represent one of the fastest evolving types of protein to be found in animal systems, sharing many of their features with other protein families that respond to extrinsic factors, such as those involved in immunity, and detecting and responding to the environment in which they live. However, studies on toxin genes have been lagging behind those on other gene families as until very recently, no fully sequenced genomes from venomous animals have been available. In this chapter, the molecular forces acting on toxin gene sequences are compared to those acting on other non-toxin genes, addressing in particular several features that have been stressed in the toxinological literature, i.e., their hypervariability, accel-erated evolution, and apparent focal mutagenesis centering on the active site of the toxins. The accepted paradigm that the birth-and-death model underlies toxin multigene family evolution is challenged by studies that show both concerted evolution and birth-and-death can give rise to similar patterns following gene duplication and that both models may operate simultaneously. Much of the dynamics of gene duplication and the fate of duplicated genes seem to depend on the genomic and biological context in which they occur. Therefore, there is no reason to expect toxin-encoding genes from diverse animal groups to show common mechanisms of evolution.