Exploring the interplay between tanning, desiccation resistance, and calcium metabolism in cockroaches

The successful terrestrial adaptation of insects has been recently suggested to be significantly influenced by a novel cuticle modification mechanism mediated by the Laccase 2 (Lac-2) enzyme, introducing a new hypothesis in insect evolutionary biology. This enzyme enables rapid recovery following exoskeletons shedding during moulting and reduces the reliance on calcium sources. Although most insect species have abandoned mineral reinforcement in favour of Lac-2-driven tanning, some insects continue to use both processes concurrently, with a possible interplay between them. In this study, we investigated Lac-2-mediated tanning in Blattella germanica , a global pest and model organism, with a particular focus on its potential interactions with calcium metabolism. Our results show that cuticular maturation after moulting shows a trend of increasing duration throughout development. Notably, the timing of BgerLac-2 expression peak differs between early, middle, and late instar nymphs and does not always coincide with the pre-moult phase. Deficiency of BgerLac-2 had a significant impact on survival. However, supplementing the diet with high calcium content reduced the severity of these effects. The desiccation associated with BgerLac-2 deficiency altered elemental calcium level in both the haemolymph and the cuticular surface in B. germanica on a high calcium diet. Since the molecular mechanisms underlying insect calcium metabolism are unexplored, we attempted to identify genes related to those involved in crustacean calcification. Among them, BgerDD5 -like demonstrated a positive correlation between its expression and desiccation in the context of a calcium-rich diet.