Worms, the most diverse animals

By Lucia Kwan, EEB

Forget the vast array of feathers and fur in the natural world, the most diverse animal is a worm—Caenorhabditis brenneri. Collecting worms from rotting fruits and flowers, researchers isolated 33 genetically different strains from northern South America (Colombia, French Guiana), South Asia (India), and a few other tropical localities.

Focussing on a subset of genes in the genome, the work, led by evolutionary biologist Alivia Dey, compared the genetic diversity both within and across the strains. The findings, published in the Proceedings of the National Academy of Sciences this week, show that the worm is eight times more diverse than the fruit fly, and over a hundred times more diverse than humans; its diversity is more similar to that found in hyperdiverse bacteria.

Dey and her collaborators suggest that the worm’s hyperdiversity is the result of a large population size, and not mutations. We know from theory that more mutations arise in bigger populations leading to more variation. Until now, empirical support for the role of population size in creating diversity has mostly come from microbes, such as those found in the human gut. But this newest finding is in a eukaryote—the group of organisms that includes everything from mushrooms to humans. And not only that, this high diversity is found in a sexually reproducing eukaryote that goes through complex developmental life-stages.

Studying molecular diversity provides insight into genome evolution, such as how genes are regulated, and why some species are more diverse than others. More specifically, on a conservation level, studies like this can help scientists understand the factors that drive and maintain diversity, which is important with the pressures exerted on organisms to adapt to the rapidly changing environments of today.