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The mechanical evolution from biting-chewing to piercing-sucking in insects

Periodic Reporting for period 2 - MECH-EVO-INSECT (The mechanical evolution from biting-chewing to piercing-sucking in insects)

Reporting period: 2019-08-01 to 2020-08-31

"Insects evolved an astonishing diversity of different mouthpart and head capsule types optimally adapted to ingest their particular food recourses. Among early winged insects, mayflies (Ephemeroptera), dragonflies (Odonata), and Polyneoptera (including grasshoppers, cockroaches and allies) show biting-chewing mouthparts, while bark and true lice (Psocodea) possess ""intermediate"" mouthparts commonly known as a 'mortar-pestle type'. Thrips (Thysanoptera) and true bugs (Hemiptera) show piercing-sucking mouthparts, together they are known as Condylognatha, the most speciose insect group after Holometabola. How the transition from one mouthpart type to the other could have happened is unclear. The ultimate goal of this project is to explain and quantify to mechanical transition from chewing-biting to piercing-sucking mouthparts in ""basal"" winged insects taking into account recent as well as fossil species. Subsequently, the results will be used to model the head evolution of insects under a range of other factors such as ecology, phylogeny and development in order to better understand the influence of these factors on insect head evolution. A mechanical state-of-the-art characterisation of biting-chewing and piercing sucking insect mouthparts in the context of insect head evolution has not been done so far on a larger scale. Therefore this project will characterize the mechanics in recent biting-chewing insects (Work package, WP1), in recent piercing-sucking insects (WP2), and in selected fossil biting-chewing and piercing-sucking insects (WP3; see Figure 4). In parallel, the PI project (WP4) will deal with the development of algorithms to model evolutionary processes of mouthpart and head capsule change in relation to other factors besides the mechanical ones."
We scanned nearly all specimens necessary for WPs1-4 using micro-computed tomography (nearly 3000 specimens so far). A smaller number of specimens still needs to be scanned but this currently is impeded by the COVID19 pandemic. Geometric morphometric analyses and landmark placement have been carried out for nearly 60% of scanned specimens. Collection of ecological data has been performed for all specimens of WP1 and 50% of WP2 specimens. FEA analyses have been carried out for a small fraction of the specimens. All specimens have been photographed and label information has been extracted. Statistical analyses of a part of the data have started.
This project is unique in its scope. The PI does not know of any other project with such a large database. This database is needed because insects show a diversity which is several orders of magnitude higher than in all other animal groups. If we want to learn about the drivers of insect head shape variation and how mouthpart transitions in insects could have happened, we need data from several thousand species. Therefore data collection needs more time compared to other projects which is the reason why a five year financial support is needed. Now that data collection is nearly completed, the first core papers are in preparation for which we expect publication early next year: One study deals with the head morphology of several groups of Polyneoptera in order to learn more about which ecological factors affect head shape variation in these taxa. Another study, which is almost finished, deals with a detailed analysis of bite forces in insects with an unprecedented taxon sampling of nearly 600 species (more than all vertebrate studies combined) including basic ecological, and morphometric data, as well as the largest phylogeny of insects. A third study will cover the head shape variation and biomechanics of all Polyneoptea and Psocodea, i.e. all non-holometabolous biting-chewing lineages. This study will be complemented by another study with a focus on the non-holometabolan piercing-sucking lineages. A fourth study, which is almost finished, will focus on a detailed investigation of the lever mechanics of the mandibles in biting chewing insects while a fifth study will investigate how mandible and head shape variation are influenced by wing configuration.