Effects of temperature on juvenile Dungeness crab, Metacarcinus magister (Dana): survival, moulting, and mTOR signalling and neuropeptide gene expression in eyestalk ganglia, moulting gland (Y-organ), and heart

Abstract

Mechanistic target of rapamymcin (mTOR) is a highly conserved protein kinase that controls cellular protein synthesis and energy homeostasis. We hypothesize that mTOR integrates intrinsic signals (moulting hormones) and extrinsic signals (thermal stress) to regulate moulting and growth in decapod crustaceans. The effects of temperature on survival, moulting, and mRNA levels of mTOR signalling genes (Mm-Rheb, Mm-mTOR, Mm-AMPKα, Mm-S6K, and Mm-AKT) and neuropeptides (Mm-CHH and Mm-MIH) were quantified in juvenile Metacarcinus magister. Crabs at different moult stages (12 d, 18 d or 26 d postmoult) were transferred from ambient temperature (∼15°C) to temperatures between 5 and 30°C for up to 14 days. Survival was 97-100% from 5 to 20°C, but none survived at 25°C and 30°C. Moult stage progression accelerated from 5 to 15°C, but not further at 20°C. In eyestalk ganglia, Mm-Rheb, Mm-AMPKα, and Mm-AKT mRNA levels decreased with increasing temperatures. Mm-MIH and Mm-CHH mRNA levels were lowest in the eyestalk ganglia of mid-premoult animals at 20°C. In Y-organ, Mm-Rheb mRNA level decreased with increasing temperature and increased during premoult and was positively correlated with haemolymph ecdysteroid titre. In heart, moult stage had no effect on mTOR signalling gene mRNA levels; only Mm-Rheb, Mm-S6K, and Mm-mTOR mRNA levels were higher in intermoult animals at 10°C. These data suggest that temperature compensation of neuropeptide and mTOR signalling gene expression in eyestalk ganglia and Y-organ contributes to regulate moulting in the 10°C to 20°C range. The limited warm compensation in heart may contribute to mortality at temperatures above 20°C.