Evolution and its related real-time complexities

Esha Mukherjee, Amity University Noida

Growth in groups of undifferentiated cells followed by differentiation into soma and germ-like cells is a common feature of the evolutionary transition to multicellular life. According to theory, a convex trade-off between survival and reproduction aids germ soma differentiation.

The present study of interest:

The research team of Professor Lutz Becks at the Limnological Institute of the University of Konstanz has made significant progress in describing this extremely complex process. The differentiation of somatic and germ cells is a crucial step in the evolution of multicellularity, in which body cells (soma cells; cell group) must play an ecological role (e.g., predation avoidance, motility that increases access to resources) while also initiating the next generation of bodies (germ-like cells; single cell). Because of an inherent fitness trade-off between survival and fecundity, differentiation into germ and soma cells may be preferred. A theoretical study examining this trade-off revealed that when the costs of expanding cell group sizes exceed the benefits of staying in cell groups or aggregates, the survival-fecundity trade-off could lead to the differentiation of soma and germ cells.

Experimentally, the evolution of cell group growth by evolving populations of the unicellular C. reinhardtii in various environments was investigated. This was done to characterize their phenotypes and identify mutations that are likely to be involved in the observed phenotypes. C. reinhardtii was the best potential species for the tests since it has likely never had a multicellular progenitor and resembles the volvocales’ unicellular ancestor. It was specifically examined for the curvature of the trade-off between survival in the presence and absence of a predator and algal cell reproduction, as the curvature was thought to influence whether cell groups may develop further to specialise into soma and germline cells.

What did the study find?

It was found that isolates of algal clones selected under rotifer predation were more likely to grow as cell groups, had a lower growth rate, and had a higher level of protection against predator eating, i.e., survival. As predicted, a convex trade-off curve between reproduction and survival was discovered. The majority of cell groups examined grew in groups and had higher survival rates when confronted with a predator. A lower percentage of isolates grew as a mix of groups and single cells, although it’s unclear if these represent distinct life phases of a cell group or fragments of cell groups, as other researchers have found.

Significance of the study:

There was a significant difference in gene expression between cell groups and single cells, regardless of the environment. It was found that common expression changes between cell groups and those previously described when the transition to multicellularity life cycle was induced, pointing to potential commonalities in impacted metabolic pathways. Further analyses are required to identify the underlying mechanism.

Also read: Steroid hormones: Their implications on breast cancer treatment

References:

1. Bernardes, Joana P., et al. ‘The Evolution of Convex Trade-Offs Enables the Transition towards Multicellularity’. Nature Communications, vol. 12, no. 1, July 2021, p. 4222. www.nature.com, doi:10.1038/s41467-021-24503-z.
2. Shelton, Deborah E., and Richard E. Michod. ‘Group Selection and Group Adaptation During a Major Evolutionary Transition: Insights from the Evolution of Multicellularity in the Volvocine Algae’. Biological Theory, vol. 9, no. 4, Dec. 2014, pp. 452–69. Springer Link, doi:10.1007/s13752-014-0159-x.

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