Evolution: These jaws are made for crushing

The precise composition of the mandibles of the tiny crustaceans known as copepods, which allows these creatures to crush the hard shells of the phytoplankton on which they feed, is revealed in a study published in Scientific Reports. The development of these complex mouthparts could have been the basis for the dominance of copepods within the marine zooplankton.

Diatoms are a major group of algae known for the superior mechanical properties of their mineralised shells. Many crustaceans are still able to crush the shells using their mandibles but although some copepod species are known to have silica-containing opal teeth, the detailed material composition of these creatures’ mouthparts has remained uncertain.

Jan Michels and colleagues used a range of microscopy techniques to examine the structure and composition of the hardened bases (gnathobases) of the mandibles of females of Centropages hamatus, a spiny copepod found in the North Atlantic and adjacent seas. The study reveals the existence of complex composite structures, which contain the soft and elastic protein resilin, in addition to silica, and which form opal teeth with a rubber-like bearing. These structures, which could have coevolved with the diatom shells in an evolutionary arms race, probably increase the efficiency of the opal teeth, while minimizing the risk of mechanical damage, the authors suggest.