The Early Evolution of Biting–Chewing Performance in Hexapoda

Abstract

Insects show a plethora of different mandible shapes. It was advocated that these mandible shapes are mainly a function of different feeding habits. This hypothesis was tested on a larger sampling of non-holometabolan biting-chewing insects with additional tests to understand the interplay of mandible function, feeding guild, and phylogeny. The results show that at the studied systematic level, variation in mandible biting-chewing effectivity is regulated to a large extent by phylogenetic history and the configuration of the mandible joints rather than the food preference of a given taxon. Additionally, lineages with multiple mandibular joints such as primary wingless hexapods show a wider functional space occupation of mandibular effectivity than dicondylic insects (¼ silverfish + winged insects) at significantly different evolutionary rates. The evolution and occupation of a comparably narrow functional performance space of dicondylic insects is surprising given the low effectivity values of this food uptake solution. Possible reasons for this relative evolutionary "stasis" are discussed.

Morphological determinants of bite force capacity in insects: a biomechanical analysis of polymorphous leaf-cutter ants

“…Implementing either option likely requires substantial changes to head anatomy or muscle physiology, and may therefore only be possible across more distantly related species, where developmental and phylogenetic constraints are relaxed. Indeed, the MA of the mandibular system contains significant phylogenetic signal [82], and extreme variations in outlever such as between male and female stag beetles are matched by corresponding changes in inlever [29], both consistent with this interpretation. Pennation angle: Across worker sizes, the cosine of the average pennation angle ϕ decreases significantly by about 8%, i. e. ϕ increases from about 37 • to 43 • (see Table 1 and Fig.…”

Morphological determinants of bite force capacity in insects: a biomechanical analysis of polymorphic leaf-cutter ants

“…Because this behavioural flexibility is not afforded to L i -which is anatomically fixed-it is functionally sensible to drive systematic changes in MA through changes in inlever length. Notably, both the absolute value of the MA and its variation, 0.27 < MA < 0.32 for the distal outlever, are at the lower end of values reported across numerous insect taxa (typically 0.3 < MA < 0.8, see [58]). Thus, the ants appear to use only a small fraction of the theoretically available scaling capacity-a change from 0.3 to 0.8 across worker sizes would result in MA ∝ m 0.26 , a factor of five in excess of the observed normalized effective area in mm 2 /mg 0.67…”

Ovipositor and mouthparts in a fossil insect support a novel ecological role for early orthopterans in 300 million years old forests

“…The MA of the mandibles, that is, the inlever to outlever ratio, indicates the effectivity of force transmission from the muscles to the food item ( Appendix 1—figure 1 ). Apart from force transmission, the MA can also indicate the dietary niche and feeding habits ( Blanke, 2019 ; Sakamoto, 2010 ; Westneat, 2004 ). The MA was extracted from 43 extant polyneopteran species ( Appendix 1—figure 9 ) including 31 orthopterans and one CFMR of the newly described fossil species (Appendix 1, Sections 1.3.2, 1.4, Appendix 1—table 1 ).…”