Mandible evolution in dung beetles and adaptations to eating poo

It's no secret... I love dung beetles! So here's some hot-off-the-press research on how their jaws have evolved to feed on poo.

 

Mandible evolution in the Scarabaeinae (Coleoptera: Scarabaeidae) and adaptations to coprophagous habits

The astonishing spectrum of scarabaeine lifestyles makes them an attractive group for studies in entomology and evolutionary biology. As a result of adaptations to specific food substrates and textures, the mouth parts of dung beetles, particularly the mandible, have undergone considerable evolutionary changes and differ distinctly from the presumptive ancestral conditions of the Coleoptera and Polyphaga. The possible functions of dung beetle mouth parts and the evolution of dung feeding have been controversial for decades.

In a recent study by Bai et al. (2015), 187 scarabs representing all tribes of the Scarabaeinae and the major lineages within the Scarabaeoidea, along with three major feeding types within the Scarabaeoidea (omnivory, phytophagy and coprophagy), were studied. Based on geometric morphometric and three-dimensional (3D) reconstruction approaches, morphological differences in mandibles among the three feeding types were identified. The ancestral forms of the mandible within the Scarabaeinae were reconstructed and compared with those of modern species. The most recent common ancestor of the Scarabaeinae fed on soft materials, and the ancestor of the Scarabaeinae and the Aphodiinae was in an evolutionary transition between processing more solid and softer substrates.

Coprophagy originated from omnivorous ancestors that were very likely saprophagous. Furthermore, phytophagy may also have originated from omnivory. In addition, the study addresses the integration and modularity of geometric morphometric data in a phylogenetic context.

Morphological comparison of the mandible from three feeding types (omnivory, phytophagy and coprophagy) based on 3D models. Scarabaeinae: Kheper devotus (a–h); Dynastinae: Allomyrina dichotoma (i–p); Trogidae: Trox sp. (q–x). Lateral view (a, b, i, j, q, r); dorsal view (c, k, s); ventral view (d, l, t); cross-sections in different positions (e–h, m–p, u–x; percentages indicate the cross-sectional area of each position divided by the top 4/6 position) (From Bai et al. 2015).

Morphological comparison of the mandible from three feeding types (omnivory, phytophagy and coprophagy) based on 3D models. Scarabaeinae: Kheper devotus (a–h); Dynastinae: Allomyrina dichotoma (i–p); Trogidae: Trox sp. (q–x). Lateral view (a, b, i, j, q, r); dorsal view (c, k, s); ventral view (d, l, t); cross-sections in different positions (e–h, m–p, u–x; percentages indicate the cross-sectional area of each position divided by the top 4/6 position) (From Bai et al. 2015).

Citation Ming Bai, Sha Li, Yuanyuan Lu, Haidong Yang, Yijie Tong and Xingke Yang, Mandible evolution in the Scarabaeinae (Coleoptera: Scarabaeidae) and adaptations to coprophagous habits, Frontiers in Zoology, Published online 28 October 2015, doi:10.1186/s12983-015-0123-z.

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