Results of a study reveals that cheating algae cells are more vulnerable to environmental stress. This trade-off could help explain the emergence of multicellular organisms, and what keeps cells in algae and cells in the human body cooperating.
Cheating algae cells are more sensitive to stress. This trade-off may shed light on the origin of multicellular organisms as well as what maintains cooperation between human body cells and algae cells.
Volvox Carteri
Aurora Nedelcu from the University of New Brunswick in Canada pointed out that there are always opportunities for individuals to cheat, reaping the benefits of a group without bearing the costs of cooperation, whether within cells or in societies.
Nedelcu and her coworkers looked to the multicellular green algae Volvox carteri to shed light on the mechanisms that keep cheaters in check.
V. carteri has two different types of cells: body cells that do not reproduce and reproductive cells that do. Normally, these cooperate. However, when the regA gene is altered, the body cells begin to reproduce uncontrollably.
It is a member of the morphologically diverse volocine algae and is closely related to the single-celled Chlamydomonas reinhardti, making it a great species for research into the evolution of multicellularity and development.
Body cells outnumber reproductive cells, so they create more new cells overall, each of which has the potential to create more cheaters. Although cheater mutants might initially appear to have an evolutionary advantage, cells in V. carteri eventually cooperate.
The team's findings demonstrate that in V. carteri, somatic cells exhibit the most extreme form of altruism, such as reproductive sterility, and are terminally differentiated. The 2000-4000 somatic cells preserve the individual's motility, which is crucial for survival, by remaining undivided. The 10-16 gonidia, which are non-flagellated reproductive cells, grow rapidly and divide 11-12 times to create fully developed juveniles that are released to begin a new generation.
Nedelcu and her team subjected both the regular V. carteri and the cheater mutant to extreme heat, light, and darkness. Only 50% of the typical algae developed dead cells, compared to 100% of the cheater mutant algae.
This suggests, in Nedelcu's opinion, that cheater mutants are more vulnerable to environmental influences. The cost of lying may be high enough to encourage cooperation, at least in V. carteri.
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The Fail-Safe
Benjamin Kerr at the University of Washington in Seattle, who wasn't involved with the study, describes this behavior as a fail-safe mechanism for policing cheaters. He claims that studies like this one can add to the explanations for why cheaters don't always succeed by demonstrating connections between the common good and individual good.
The same kind of trade-off might deter other varieties of cheaters. All single-celled organisms contain the genes that regulate how reproduction and survival are balanced. RegA is one of many of these genes that are still found in the ancestry of multicellular organisms like plants and animals.
According to Nedelcu, these genes may have played a significant role in the development of multicellularity hundreds of millions of years ago, in addition to supporting the health of multicellular organisms.
The study was published on the website of Royal Society Publishing. Nedelcu collaborated with Adrian Reyes-Prieto, Anajose Reyes-Guevara, Stephan König, and Marybelle Cameron-Pack for the study.
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