From offense to defense
The venom in snakes is largely used to subdue and / or kill prey, and most poisons have clear actions that facilitate death or paralysis. However, the venom has evolved in one group of snakes and has switched from predation to protection. Specifically, in three different subspecies of “spitting” snakes, the venom is used to deter predators. Kazandjian Et al. He showed that similar adaptations occurred within these strains that convert cytotoxic components into a mixture that acts on mammalian sensory neurons and causes pain. The authors argue that the increased predation on these strains led to similar shifts in venom function.
ScienceThis case p. 386
Convergent evolution provides insights into the selective drivers behind evolutionary change. Snake venoms, with a direct genetic basis and clearly defined functional phenotype, provide a model system for exploring the repeated evolution of adaptations. While snakes primarily use venom for predation, and the composition of the venom often reflects the specificity of the diet, three subspecies of cobras have independently developed the ability to spit out venom on enemies. Using genetic, protein, and functional analyzes, we show that the three spit strains possess toxins that are characterized by higher up-regulation of phospholipase A2 (The Chinese People’s Liberation Army2Toxins, which enhance the action of pre-existing cytotoxins to activate mammalian sensory neurons and cause increased pain. These frequent independent changes provide a great example of convergent evolution across multiple style levels driven by choice for defense.