Stick insects make a certain amount of sense, evolutionarily speaking. They look like sticks, or twigs, or leaves; thus camouflaged, they presumably have a better chance of avoiding predators, reproducing, and passing on their stick-resemblance genes to their offspring. Except that birds still eat them, a lot. Stick insects don’t run fast, most don’t fly, and the females typically don’t lay eggs in large numbers. So there’s a mystery: How do they manage to persist from generation to generation? Why, having managed to exist, do they continue to do so?
A study in a recent issue of Ecology offers an unusual possibility: the eggs of stick insects can survive passage through a bird’s digestive tract, making the bird both a predator and a reproductive aide. That’s essentially the role that birds play for many plants: they eat their fruit and then, later and elsewhere, excrete the still-intact seeds. (If you have, say, an elderberry tree in your yard and a picnic table nearby, you know what this looks like.)
In fact, the eggs of many stick insects are similar to seeds in size, color, shape, and texture. They are also surprisingly hard-shelled, with a coating, unique among insects, made of calcium oxalate—a substance that dissolves only under acidic conditions such as, for instance, in a digestive tract. This got the authors, a team of researchers led by Kenji Suetsugu, of Kobe University, thinking. If they could persuade a bird to eat some stick-insect eggs, would any of the eggs survive the trip and hatch?
The study, “Potential Role of Bird Predation in the Dispersal of Otherwise Flightless Stick Insects,” was a modest success. The bird—a brown-eared bulbul, a common predator of stick insects in Japan—was fed a diet into which were mixed a few dozen eggs of three different species of stick insect…
Read the whole post here.