Thermal desiccation and expression of HSP90 and osmotic avoidance protein genes in an acorn barnacle, Amphibalanus...

The marine intertidal zone (IZ) is ideal for deciphering the organisms' response to thermally desiccated stress during tidal emersion. The distribution of organisms across horizontal and vertical transects is plasticity of thermal adaptation potential. The acorn barnacle, Amphibalanus amphitrite inhabits the upper and mid rocky intertidal zone, often encountering episodic thermal desiccation during inter-tidal emersion. In order to survive, the desiccated organisms endure the heating effect of the rocky substratum and aerial temperature, which leads to body temperature perturbation, coma response, and differential gene expression. The intraday thermal desiccation stress response in A. amphitrite has not been studied in a way that integrates both ecological and molecular responses under natural conditions. This study observed and experimented the various factors in an intraday of monsoon environment, including aerial and substratum temperature, duration of emersion along with ecological responses such as coma response, and gene expression. This is the first study to design and standardise the primer for the gene Osmotic Avoidance protein (OA). The expression of stress genes, heat shock protein 90 (HSP90) and Osmotic Avoidance protein (OA) were carried out using Real-time qPCR among thermally desiccated Amphibalanus amphitrite inhabiting the intertidal zone of Anjuna, Goa, India. The ecological responses revealed compelling insights into the effects of thermal desiccation on barnacles. After a 4 h of exposure, a slight increase in body temperature from 30.5 °C to 31 °C triggered a staggering 50% increase in coma response among the barnacles. The study highlights the dynamic expression levels of HSP90 and OA, which fluctuated significantly with varying degrees of thermal and desiccation stress. Notably, we observed a sharp increase in the combined expression of HSP90 and OA after 4 h, followed by a temporary decrease at 6 h and a HSP90 resurgence at 8 h where the body temperature was the lowest. Such an upregulation of HSP90 suggests temperature-independent and prolonged aerial exposure-mediated regulation of gene expression. Moreover, the declining expression of OA from the 4th to the 8th h of aerial exposure underscores an impressive molecular regulation, suggesting an establishment of osmotolerance among the desiccated barnacles. This research underscores the resilience and adaptability of barnacles, emphasising the need for continued study in the face of climate variability. Expression patterns of HSP90 and OA provide concrete evidence of the existence of thermal and desiccation stress and tolerance mechanisms among A. amphitrite in the IZ.