Comparative anatomy of pupal tarsi in caddisflies (Insecta: Trichoptera) with focus on the claw system

Matsumura

Brütt

et al. 2022

Sci Nat

The radula, a chitinous membrane spiked with teeth, is the molluscan autapomorphy for the gathering and processing of food. The teeth, as actual interfaces between the organism and the ingesta, act as load transmitting regions and have to withstand high stresses during foraging — without structural failure or high degrees of wear. Mechanisms contributing to this were studied previously in paludomid gastropods from Lake Tanganyika. For some species, gradients in hardness and Young’s modulus along the teeth were detected, enabling the bending and relying of teeth onto the next row, distributing the stresses more equally. The here presented study on one of them — Lavigeria grandis — aims at shedding light on the origin of these functional gradients. The mechanical properties were identified by nanoindentation technique and compared to the elemental composition, determined by elemental dispersive X-ray spectroscopy (EDX, EDS). This was done for the complete radular (mature and immature tooth rows), resulting in overall 236 EDX and 700 nanoindentation measurements. Even though teeth showed regional differences in elemental composition, we could not correlate the mechanical gradients with the elemental proportions. By applying confocal laser scanning microscopy (CLSM), we were finally able to relate the mechanical properties with the degree of tanning. CLSM is a common technique used on arthropod cuticle, but was never applied on radular teeth before. In general, we found that nanoindentation and CLSM techniques complement one another, as for example, CLSM is capable of revealing heterogeneities in material or micro-gradients, which leads to a better understanding of the functionalities of biological materials and structures.

Section: Discussionmentioning

confidence: 99%

Material gradients in gastropod radulae and their biomechanical significance: a combined approach on the paludomid Lavigeria grandis

Matsumura

Brütt

et al. 2022

Sci Nat

“…This protocol was previously applied to e.g. wings (Ma et al, 2022), foot attachment devices and legs (Peisker et al, 2013;Friedrich & Kubiak, 2018;Beutel et al, 2020), mouthparts (Weihmann & Wip er, 2019;Lehnert et al, 2021), or genitals (Matsumura et al, 2014(Matsumura et al, , 2021. This protocol was previously cross-validated by employing AFM-nanoindentation for hair of foot attachment devices in a lady bird beetle (Peisker et al, 2013).…”

Section: Origins Of the Gradients Of Mechanical Propertiesmentioning

confidence: 99%

Mechanical properties, degree of sclerotisation and elemental composition of the gastric mill in the red swamp crayfish Procambarus clarkii (Decapoda, Crustacea)

Brütt

Gorb

2022

Preprint

The gastric mill of Decapoda is a unique feature consisting of interacting teeth, stabilizing ossicles, and particle sorting setae. As this organ is involved in the mechanical fragmentation of the food, it serves as interface between organism and environment. There is an ongoing debate to which extend structures are shaped due to phylogeny or to ecology. As material properties complement morphology and hold information about functionality and trophic preferences, we here aim at providing a basis for more intensely comparative research on material composition and properties of gastric mill components. Data on the micro-structure, documented via scanning electron microscopy (SEM), on the elemental composition, determined by energy-dispersive X-ray spectroscopy (EDX, EDS), on the heterogeneities in material properties, visualized by confocal laser scanning microscopy (CLSM), and on the mechanical properties hardness and elasticity (i.e., Young’s modulus), tested by nanoindentation technique, of gastric mill components from the red swamp crayfish Procambarus clarkia is here presented. The elemental composition of gastric mill components was studied previously in other taxa, but the mechanical properties were never tested before. As epicuticle and exocuticle could be analyzed individually, due to rather large thickness of the epicuticle, material property gradients, with values decreasing from the interacting surface towards interior, could be determined. Finally, we were able to relate the mechanical property data and the autofluorescence signals with the elemental composition and the degree of tanning.

“…For chiton and limpet radular teeth, functional gradients are in uenced by all parameters [for throughout reviews, see 81, 82, 83], whereas in the less-mineralized paludomid radular teeth the mechanical properties seem to have their origin in the architecture of chitin bres [74] and the degree of tanning [52]. The latter was determined by applying a protocol established on arthropods: for the chitinous insect cuticle, it is common practice to determine the degree of tanning via laser excitation by CLSM, according to the protocol established by Michels & Gorb [110] [see e.g., 111,112,113,114,115]. The emitted auto uorescence signal allows the identi cation of cuticula regions with certain dominating material composition: a red signal is emitted by sclerotized and stiff cuticle and a green signal by the high content of weakly-sclerotized chitin, which is more exible but relatively tough.…”

Section: Discussionmentioning

confidence: 99%

Coping with abrasion and structural failure – diverging composition of radular teeth in two Porifera-consuming nudibranch species (Mollusca, Gastropoda)

Wägele²,

Neumann

et al. 2022

Preprint

Background: Most molluscs forage with their radula, a chitinous membrane with embedded teeth. As teeth are interfaces between the individual and its ingesta, trophic specialisations can be reflected by morphology, composition, and mechanical properties of the radula. Adaptations to the ingesta – especially with regard to mechanisms contributing to the reduction of structural failure and wear – are well studied in the heavily mineralized teeth of Polyplacophora and Patellogastropoda. For the rather chitinous teeth of non-limpet snails, we are however confronted with a large gap of knowledge. Results: For this study, we selected nudibranch gastropods, which are of high interest, when studying trophic specialisations, because taxa are strongly adapted to forage on certain prey types. To shed some light on this type of radula, we here investigated two species – Felimare picta and Doris pseudoargus, which are similar with regard to their food preference (Porifera-consuming). Tooth morphologies were documented using scanning-electron-microscopy and mechanical properties were tested by nanoindentation, to develop hypotheses on functional adaptations of the radula to the ingesta. We found that tooth morphologies and mechanical properties are rather similar in both species, indicating that teeth are similar in their function. In the search for the reasons of the specific mechanical properties, we studied the material composition. Teeth were visualized using confocal laser scanning microscopy (CLSM), to determine the degree of tanning, and analysed with energy-dispersive X-ray spectroscopy (EDX), to determine the elemental composition. Our results show, that the inorganic content and the emitted autofluorescence signal differ between the species. This was especially prominent, when studying the inner and outer sides (leading and trailing edges) of teeth. In F. picta, we detected high proportions of Si, whereas teeth of D. pseudoargus contained high amounts of Ca, which influenced the autofluorescence signal in CLSM. Using nanoindentation we determined high Young’s modulus and hardness values for the leading edges of teeth, which seem to correlate with the Si- and Ca-content. Conclusions: This is a new set of data for non-limpet gastropods, rendering that their teeth can be mechanically enhanced via different chemical pathways to reach similar properties in reducing structural failure and abrasion.