Mandibular gnathobases of marine planktonic copepods – feeding tools with complex micro- and nanoscale composite architectures

Abstract

SummaryCopepods 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.

Functional diversity of resilin in Arthropoda

“…Like in the silica-containing teeth of C. hamatus , these resilin-containing structures very likely function as compressible supports reducing the risk of mechanical damages of the teeth during feeding on diatoms with stable frustules. In general, the complex composite systems in the gnathobase teeth are assumed to have co-evolved within an evolutionary arms race together with the diatom frustules [122]. …”

The Initiation and Early Stages of Postmolt Mineralization in the Blue Crab, Callinectes sapidus

“…Reports of silicified mandibles have been reported in copepods (Beklemishev, 1954;Miller et al, 1990;Michels et al, 2012;Michels and Gorb, 2015) and amphipods (Mekhanikova et al, 2012). More recently we described silicified teeth in the gastric mill of the blue crab (Vatcher et al, 2015;Nesbit and Roer, 2016).…”

A review of the ecological affinities of marine organic microfossils from a Holocene record offshore of Adélie Land (East Antarctica)

“…Geographic distribution: Although benthic foraminifera are common around Antarctica and can be quite diverse (Mikhalevich, 2004), they are often not preserved because the Antarctic shelf waters are highly undersaturated with respect to calcite (Expedition 318 Scientists, 2011), and the remineralization of organic matter causes acidic pore waters which dissolve the foraminifera post-depositional. The inner linings of benthic foraminifera within palynomorph assemblages are found more commonly at sites along the Antarctic coast (Wrenn et al, 1998;Warny et al, 2006;Warny, 2009).…”