Anatomical changes of the beetle digestive tract during metamorphosis correspond to dietary changes

Abstract

During pupation, the tissues of holometabolous insects change in preparation for the adult lifestyles, although little literature exists examining this hidden process in detail. Using beetles as a model, we hypothesized that species where the adult and larva have the same diets will show less pronounced changes of the digestive tract during metamorphosis than species where the adults diets differ. We also wanted to observe these changes and document them at a level of detail missing from the current record. We compared the structure of the digestive tracts of scarab beetles Oryctes rhinoceros, Thaumastopeus shangaicus, and Protaetia spp. (Coleoptera: Scarabaeidae)—where the larvae eat wood, soil, or compost while the adults feed on soft plant matter, tree sap, and rotting fruits—with the tortoise beetle, Cassida circumdata (Coleoptera: Chrysomelidae), which feeds on leaves as both larva and adult. In the scarab beetles we observed considerable changes in the digestive tracts during the pupal stage, which we could divide into distinct stages, while in the leaf beetle pupae, the gut did not change. This information can provide new insight into metamorphosis, and the illustrations of what occurs during pupation are novel contributions to this field that will facilitate future work.

Evidence for the independent evolution of a rectal complex within the beetle superfamily Scarabaeoidea

“…It could therefore be considered that they from a unique structure: a hindgut fermentation chamber complex. The posterior rectum being enclosed by infoldings of the fermentation chamber has also been noted in larval Protaetia species and Thaumastopeus shangaicus (Cetoniinae) (Chiang and Shelomi, 2023), and in the case of Protaetia cuprea , sinuous MpTs surrounding the rectum have been described (Werner, 1926), consistent with our findings.…”

“…Dramatic remodelling of the gut during pupal metamorphosis has been documented in O. rhinoceros (subfamily Dynastinae), as well as Thaumastopeus shangaicus and Protaetia species (subfamily Cetoniinae), which are all members of the Scarabaeidae family. It has been proposed that this is an adaptation to their radically different larval and adult diets (Chiang and Shelomi, 2023). Our observations show that there are also dramatic reorganisations of the MpTs and their relationship to the gut in Scarabaeoidea.…”

Coconut rhinoceros beetle digestive symbiosis with potential plant cell wall degrading microbes

“…PCWDE activity of digestive tract contents from CRB late instar larvae (Fig. 1b ), pupae 28 , and adults (Fig. 1c ) was examined by using plate assays with four different substrates: carboxymethylcellulose (CMC), xylan, xyloglucan, and glucomannan (Supplementary Fig.…”