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Coevolution predator and prey, a siliceous arms race in pelagic plankton

NEWS - Aquatic life is very metropolitan with a variety of small plankton and plays an important role as a starting point in the food cycle to support the survival of larger species above it up to the very large fin whale (Balaenoptera physalus).

Coevolution predators and prey, a siliceous arms race in pelagic plankton

Recently Bejder el al (2024) placed humpback whales (Megaptera novaeangliae) as one of the sophisticated animals that created and modified tools for hunting prey in the form of bubble nets, meanwhile Shoham et al (2024) reported Theonella conica and Entotheonella symbiosis produces high levels of poison to repel predators.

The coevolution of predators and prey plays a major role in shaping the pelagic region and may have significant implications for marine ecosystems and nutrient cycling dynamics. Siliceous diatom frustules are often assumed to have co-evolved with silica-coated copepod teeth, but empirical evidence on how this relationship drives natural selection and evolution is lacking.

Is the predator-prey arms race a driving force in planktonic evolution and diversity? Fredrik Ryderheim from the Technical University of Denmark and the University of Copenhagen and his team show that feeding on diatoms causes significant wear on copepod teeth and that this causes copepods to become selective feeders.

The teeth of copepods that feed on thick-shelled diatoms are more likely to break or crack than those that feed on dinoflagellates. When feeding on large diatoms, all teeth analyzed had visible wear. The findings underline the importance of predator-prey relationships in planktonic evolution and diversity.

The mandibles of copepods that feed on Coscinodiscus radiatus or Thalassiosira weissflogii are five times more likely to break or crack than those that feed on dinoflagellates. The structure of the mandibles is closely related to the diet. The researchers have videotaped how copepods eat or reject individual cells that they have captured.

The thicker shells provide better protection against copepod predation. However, most importantly, copepods become more selective in their choice of prey and increased food selectivity is an adaptive force for diatoms. A selective advantage for diatoms to grow thicker shells.

In effect, the copepod-diatom arms race resembles the insect-grass arms race also by leaf silification and the consequent wear and tear on insect jaws. Their arms race and any associated trade-offs are one of the driving mechanisms for the enormous diversity among these organisms.

Original research

Fredrik Ryderheim, Jørgen Olesen, and Thomas Kiørboe (2024). A siliceous arms race in pelagic plankton. Proceedings of the National Academy of Sciences 121 (35) e2407876121 DOI:10.1073/pnas.2407876121

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