Abstract
Copepods are dominant members of the marine zooplankton. Their diets often comprise large proportions of diatom taxa whose silicified frustules are mechanically stable and offer protection against grazers. Despite of this protection, many copepod species are able to efficiently break even the most stable frustule types. This ability requires specific feeding tools with mechanically adapted architectures, compositions and properties. When ingesting food, the copepods use the gnathobases of their mandibles to grab and, if necessary, crush and mince the food items. The morphology of these gnathobases is related to the diets of the copepods. Gnathobases of copepod species that mainly feed on phytoplankton feature compact and stable tooth-like structures, so-called teeth. In several copepod species these gnathobase teeth have been found to contain silica. Recent studies revealed that the siliceous teeth are complex microscale composites with silica-containing cap-like structures located on chitinous exoskeleton sockets that are connected with rubber-like bearings formed by structures with high proportions of the soft and elastic protein resilin. In addition, the silica-containing cap-like structures exhibit a nanoscale composite architecture. They contain some amorphous silica and large proportions of the crystalline silica type α-cristobalite and are pervaded by a fine chitinous fibre network that very likely serves as a scaffold during the silicification process. All these intricate composite structures are assumed to be the result of a coevolution between the copepod gnathobases and diatom frustules in an evolutionary arms race. The composites very likely increase both the performance of the siliceous teeth and their resistance to mechanical damage, and it is conceivable that their development has favoured the copepods’ dominance of the marine zooplankton observed today.
Highlights
Crustaceans of the subclass Copepoda (Figure 1) inhabit an impressively large variety of aquatic habitats [1]
The diet of many copepod species contains large proportions of phytoplankton, and copepods are an important food source for various fish species and a large number of other organisms feeding on zooplankton
Diatoms account for a large proportion of the phytoplankton ([5,7,8] and citations therein). For this reason they often are an important food source for copepods, and the knowledge of feeding interactions between these two groups of organisms is essential for the understanding of processes related to the food web and energy and particle fluxes in the marine pelagial
Summary
Crustaceans of the subclass Copepoda (Figure 1) inhabit an impressively large variety of aquatic habitats [1]. Diatoms account for a large proportion of the phytoplankton ([5,7,8] and citations therein) For this reason they often are an important food source for copepods, and the knowledge of feeding interactions between these two groups of organisms is essential for the understanding of processes related to the food web and energy and particle fluxes in the marine pelagial. Prominent examples for such a specialisation are the gnathobases of the calanoid copepod genus Heterorhabdus They possess only a small number of teeth, and their ventral tooth exhibits a complex morphology that is comparable to the architecture of hypodermic needles and is strongly adapted to catching, anaesthetising and killing prey organisms [25]. In the case of the hollow diatom frustules the application of such a punctual pressure seems to be advantageous over a grinding mechanism and likely leads to a more effective disruption of the frustule structures
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