Scientists Discover Coral Algae Reward and Punishment System

Experimental and sampling design. A Nutrient and light cycling conditions (yellow on, gray off) during the hours of the pulse hunting experiment. Samples were processed at 84 h. B Sample processing scheme for qPCR and subsequent stable isotope analyses. Host and symbiont tissues for each recruit were separated and a subsample was used for quantitative analysis of each symbiont type. Using the relative ratio of symbiont types, recruits from groups 8–10 were assigned and host or symbiont tissues were combined in a fiberglass filter (GF/F). Credit: Microbiome (2022). DOI: 10.1186/s40168-022-01382-0

In human society, reward and punishment are introduced as an incentive for cooperation. However, some people still try to cheat to win. So, is there a system with clear rewards and punishments in the world of other organisms? The answer is yes.”

The corals can “punish” the algae that live inside it by cutting off their food supply if that algae becomes selfish and forfeits the resource sharing agreement with the coral as part of their symbiosis – a mutually beneficial relationship. beneficial. These are the findings of Dr. Shelby Mcilroy of the Swire Institute of Marine Science (SWIMS) and the School of Biological Sciences at the University of Hong Kong (HKU) and his collaborators.

In the coral-algae relationship, both parties, the host coral and the algal symbiont, share and recycle nutrients they cannot access on their own. But this relationship is open to abuse. Corals can host several species of symbiotic algae at the same time, but not all algae species are honest.

Some take advantage of their host by saving more nutrients for their own needs instead of passing them on to the coral. In this way, selfish algae gain an advantage over more beneficial species that grow more slowly because they share their nutrients more generously. This cheating ultimately harms the long-term health and growth of the coral itself.

In other symbiotic relationships, for example between trees and fungi, deceived hosts can interfere and punish dishonest partners. However, until McIlroy’s latest research was published in the journal Microbiome, it was unclear if or how corals could do the same with their algae.

Credit: University of Hong Kong

Using stable isotope techniques, McIlroy was able to unravel the flow of nutrients between different species of algae in their host, a species of Caribbean coral. “Stable isotopes combined with genetic techniques allow us to track the exchange of currencies between partners. In this case, the currency is nutrients, in the form of carbon and nitrogen,” McIlory explained.

The results showed that coral could indeed punish cheaters and reward honest partners. “Our study showed that corals appear to limit the supply of nutrients to symbiotic algae that are less beneficial to them, as a way to foster more beneficial algal symbionts,” McIlroy added.

Understanding how corals control and manipulate their symbiotic algae is now of critical importance to coral survival. Due to climate change, the seas are getting too warm for the algae living inside the coral. As the water temperature rises, the algae die, as does the coral itself, a phenomenon known as bleaching. Bleaching events are becoming more frequent and most of the world’s coral reefs are now threatened.

If scientists could get coral to host the species of algae that can withstand higher temperatures – a form of “coral probiotics”, it could prevent bleaching and buy corals threatened by warming temperatures more time. oceans.

“We may have the ability to intervene and help corals resist bleaching by exposing them to more thermally tolerant partners. But we need to understand the biology of corals and how they might respond to these interventions so we can work efficiently and effectively. There is no time to waste,” concluded McIlroy.

More information: Shelby E. McIlroy et al, Nutrient dynamics in coral symbiosis depends on both the relative and absolute abundance of Symbiodiniaceae species, Microbiome (2022). DOI: 10.1186/s40168-022-01382-0

Provided by the University of Hong Kong

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