The E3 Lab has published a new paper in the journal Marine Biology. It is titled "Crawl away from the light! Assessing behavioral and physiological photoprotective mechanisms in tropical solar-powered sea slugs exposed to natural light intensities"
Photosynthesizers face a trade-off regarding light: they need enough to maintain high photosynthetic rates (which is good for making energy to fuel cells), yet excess leads to oxidative stress (which can seriously damage cells). The detrimental effects of high light exposure are chronically underestimated. Solar-powered sea slugs (Sacoglossa: Gastropoda) provide the ideal lens with which to study this trade-off, since they steal chloroplasts from algae but do not inherit photoacclimation and photorepair capacities, abilities that help plants and algae regulate the amount of light reaching their photosynthetic machinery.
We collected three slug species in Curaçao during March and December 2022, to compare the:
a) amount of light they receive in nature from the sun (is it too much? just right? not enough?)
b) optimal light intensity (maximizing photosynthesis while minimizing damage from high light),
c) preferred light intensities (do they seek light? avoid it? regulate how much they get?)
We then investigated behavioral and physiological photoprotection mechanisms to determine if and how they regulate how much light their stolen chloroplasts receive. Finally, we examined oxidative activity under optimal and excess light to see if they show signs of damage from exposure to too much light.
All three species were naturally exposed to more light (> 1000 µmol m−2 s−1) than is optimal or preferred. Elysia crispata can retain stolen chloroplasts for > 3 months, and is fully exposed to light in nature but reduces the light reaching its chloroplasts by folding its ruffly foot tissue over its back to shade its chloroplasts. Elysia velutinus retains chloroplasts for ~ 2 weeks and hides in its algal food, which limits light exposure. Both species displayed low amounts of oxidative activity (so no sign of light-caused stress) under optimal light, which increased slightly under excess light. Elysia ornata retains chloroplasts for ~ 3 days, lacked an obvious way of limiting the light its chloroplasts receive and always displayed high levels of oxidative activity (cellular stress), potentially explaining its limited capacity for chloroplast retention. Furthermore, both E.
velutinus and E. ornata display strong light-avoidance behaviors. This study clearly demonstrates links between high light intensities, photoprotection, and oxidative stress, highlighting the need for future studies that examine aquatic photosynthesizers under natural lighting.
Click here to read it: https://link.springer.com/article/10.1007/s00227-023-04350-w
Photos: Lead author Laia Burgués Palau measuring the amount of light these E. crispata specimens are exposed to underwater at Playa Kalki in Curaçao.
