Timely Toxins

Adult Nematostella vectensis polyps

Yaara Columbus Shenkar, The Hebrew University of Jerusalem

Research on venom—a mixture of toxins used by many species to defend against predators or to subdue prey—has been largely focused on the adult stage of development, even though many species undergo dramatic transformations in their life cycles. Adults in the phylum Cnidaria, for example, which includes coral, jellyfish, and sea anemones, are armed with stinging cells that deliver venom from their tentacles. Less is known about their venomous capabilities in the early stages of their complex lifecycles.

A recent study of the sea anemone Nematostella vectensis provides insights into how that species adapts its venom to the unique needs of each life stage. Led by evolutionary biologist Yehu Moran of the Hebrew University of Jerusalem, an international team of scientists used a suite of genetic analysis tools to track changes in the venom-producing cells of Nematostella, from when they were tiny, free-swimming young, to when they become adults fixed in place. They also observed how Nematostella interacted with various predators and prey at different life stages.

The team found that Nematostella’s genetic expression of various types of toxins changes in complex ways across their lifecycle. These changes mean venoms produced in early life have a different composition of toxins than those produced as juveniles, or as adults. The researchers argue that Nematostella’s changing venom arsenal allows them to manage varying interactions with predators and prey encountered at specific points in their development.

For example, at early life stages, when Nematostella are vulnerable to being eaten by predators, their stinging cells are armed with venom and can be activated for defense. This was confirmed when four-day-old Nematostella, at a life stage so small that they are barely visible to the human eye, produced venom potent enough to force the much-larger larva of Atlantic killifish to spit them out when ingested. As Nematostella grow and become predators themselves, their venom composition changes to allow them to catch shrimp and small fish.

The authors suggest that these types of predator-prey interactions, coupled with the likely high metabolic cost of toxin production, probably drove the evolution of these unique venom arsenals. From an evolutionary perspective, sea anemones are now set up to quickly adapt to changing marine habitats, says Moran. “This might be an important factor for the phenomenal success of sea anemones in inhabiting the world’s oceans for the last 600 million years.” (eLife)