Developmental and transcriptomic responses of Hawaiian bobtail squid early stages to ocean warming and acidification

Abstract

Cephalopods play a central ecological role across all oceans and realms. However, under the current climate crisis, their physiology and behaviour are impacted, and we are beginning to comprehend the effects of environmental stressors at a molecular level. Here, we study the Hawaiian bobtail squid (Euprymna scolopes), known for its specific binary symbiosis with the bioluminescent bacterium Vibrio fischeri acquired post-hatching. We aim to understand the response (i.e., developmental and molecular) of E. scolopes after the embryogenetic exposure to different conditions: i) standard conditions (control), ii) increased CO₂ (ΔpH 0.4 units), iii) warming (+3°C), or iv) a combination of the two treatments. We observed a decrease in hatching success across all treatments relative to the control. Using transcriptomics, we identified a potential trade-off in favour of metabolism and energy production, at the expense of development under increased CO₂. In contrast, elevated temperature shortened the developmental time and, at a molecular level, showed signs of alternative splicing and the potential for RNA editing. The data also suggest that the initiation of the symbiosis may be negatively affected by these environmental drivers of change in the biosphere, although coping mechanisms by the animal may occur.

Keywords: carbon dioxide; cephalopod; climate change; gene expression; temperature.

Figure 1 –

Hatching success of the Hawaiian bobtail squid reared under different environmental conditions. The proportion of hatched bobtail squid was measured according to the number of days pre-hatching (developmental time). The presence of hatching was verified daily. The Kaplan-Meier survival trajectories illustrate the survival trajectories according to each treatment (the colour code for each treatment is shown in the upper-left quadrant of the figure). The lines represent the rate of hatched bobtail squid, at each given day of exposure. The shaded area shows the 95% confidence intervals. The dashed lines show the hatching time, corresponding to the median developmental time.

Figure 2 –

Principal component analysis on the normalized gene expression data. The ellipses represent the 95% confidence level, and the dots are the data points of each sample.

Figure 3 –

Venn diagram comparing the differentially expressed genes between the ‘control’ and each of the treatment. Green = ‘increased CO₂’, yellow = ‘warming’, brown = ‘increased CO₂ and warming’, ↑ = upregulated genes and ↓ = downregulated genes.