by Anthony Herrel
Many among us will probably still remember our days as ungainly clumsy teenagers with bodies growing faster than our nervous system can keep up with. Although the frustration of dealing with growth can cause a few embarrassing moments in the life of a teenager, for many animals, growth and the associated changes in body proportions are something they have to deal with for most of their life. And the consequences of failure are far greater than the few moments of embarrassment we may still remember from our own childhood.
The paper by Maria Laura Habegger is a nice example of a study exploring the effects of growth on bite force, an ecologically relevant and important trait for survival, especially if you’re a barracuda. Fish are different from mammals like us in more than one way. Not only do they have to deal with many fold greater viscosity and density of the medium they live in, but fish, like other most other ectotherms, continue to grow throughout their lives. So why is it that growing can be such a nuisance? Simply put, the changes in mass of the body segments during growth are far greater than the changes in force muscles can generate, thus affecting the speed of movement by which animals can move their limbs or their jaws. Add to that the changes in neural control needed to deal with the changes in the mechanics, and opportunities for failure lurk behind every corner.
So how do fish like barracuda deal with growth while being dependent on the functioning of their feeding system to assure their next tasty morsel. Based on careful dissections, biomechanical models, and an investigation of how muscles are activated during feeding, Habegger and colleagues show that barracudas are able to maintain a similar bite force for their body size throughout much of their life. Although in other fish size-related changes in feeding mechanics often lead to changes in diet during growth, barracudas are faithful to their diet. Consequently, keeping the growth of the jaw muscles up with changes in body size suffices to ensnare a bite of fish the next size up from last month’s one. The ram-based feeding strategy where the fish use their body to power them through the water towards the prey, rather than relying on suction feeding, also helps maintain the ability of these predators to catch elusive prey like fish throughout their lives. Add to that the intricate rotation of the upper jaw bones and the razor-sharp teeth and the success of barracuda as top predators in their ecosystem becomes obvious. And surprisingly enough, barracudas don’t have a big bite, sharp teeth and powerful ram feeding are apparently all you need if you like sushi.