The Evolution of Eels May be Limited by How They Feed

In an examination of physical diversity among eel species, researchers have found that biters are far more varied than eels that use suction to snatch up food. Now it has been suggested that this is an example of how certain feeding habits can limit how a species physically changes over time.

That's at least according to a study recently published in the journal Nature Communications, which details how an analysis of more than 800 species of eel shows that diversity in skull shape adaptations is closely tied to how these electric fish eat.

"When you look at the skulls of biters, the diversity is astounding compared to suction feeders," study author Rita Mehta said in a statement.

According to the study, the biters are in fact about three times more diverse than suction feeders, and this is to be expected. Eels evolved from suction-feeding ancestors, but biting appeared early in their evolution, and the vast majority of eels today are biters. However, some species of eels re-developed the suction feeding strategy later on, and while the skulls of their biting counterparts continue to change, skull development among these suckers practically came to a grinding halt.

"It's an incredible increase in diversity just from a shift in feeding strategy," Mehta added about biters. "The suction feeders evolve the same traits over and over again, whereas the biters go in a lot of different directions."

So what does this mean? The complexity of a specific feeding strategy may have a lot to do with how easily the associated bones and muscles can adapt.

"All these different parts of the anatomy have to work together to generate suction, so there are only a few ways you can evolve suction feeding," Mehta explained. "Biters have hyoids of all different sizes, short and long skulls, all types of teeth in different places in the mouth cavity - it's a much more variable and flexible feeding strategy."

Interestingly, the researchers found that suction wasn't entirely limiting. Changes in sucker species still occurred at the same rate as in biting eels. However, where and to what extent those changes occurred was predictably more limited, showing evolution simply didn't want to mess with the delicate and complicated process of suction feeding.