Evolution: Study Sheds Light On Arms Race Among Venomous Animals

Natural selection pressures have resulted in some interesting and unique evolutionary characteristics. One such feature is venom in animals that have evolved with toxic chemicals as means of protection against predation or a way of incapacitating prey. In a recent study, researchers from the Hebrew University of Jerusalem reveal new discoveries regarding the evolutionary strategies of venomous animals.

Venom, such as that found in some snakes and spiders, is a complex mixture of proteins and other toxic chemicals. Scientists have long believed positive selection, or the process by which a protein changes rapidly over evolutionary time scales, has driven the diversification of animal venoms, according to a news release. This simply means that predator-prey relationships are somewhat governed by an evolutionary arms race, one in which predators have adjusted their venom to overcome the resistance their prey develops to their poison over time.

While this may be how venoms evolve more rapidly today, this was not always the case. In fact, researchers found that ancient lineages of venomous animals had surprisingly low toxin variations.

This means that ancient animal groups evolved more slowly through purifying or negative selection, in which a species evolves without damaging genetic traits. This process has rarely been considered in venom evolution.

For the study, researchers analyzed venom genes for various animals in order to reveal the unique evolutionary strategies of toxin gene families. In total, researchers compared the evolutionary patterns of over 3500 toxin sequences from 85 gene families, including both ancient venomous groups and "young" animals.

From this researchers developed a "two-speed" theory regarding venom evolution. Instead, they believe young venomous animals living in ecological niches experience pressures of positive selection that ultimately diversifies their toxins. Subsequently, this increases their venom's efficiency when it comes to paralyzing prey or defending against predators in a new environment.

They further hypothesized ancient venomous groups already had "optimized" venom for their ecological niche, meaning they accumulated variations more slowing in order to preserve the perfectly suitable toxins.

"The 'two-speed' mode of evolution of animal venoms involves an initial period of expansion, resulting in the rapid diversification of the venom arsenal, followed by longer periods of purifying selection that preserve the now potent toxin pharmacopeia," study researchers Dr. Yehu Moran and Dr. Kartik Sunagar, explained. "However, species that have entered the stage of purification and fixation may re-enter the period of expansion if they experience a major shift in ecology and/or environment."

Their study was recently published in the journal PLOS Genetics.

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