Single-cell adaptations shape evolutionary transitions to multicellularity in green algae

Abstract

The evolution of multicellular life has played a pivotal role in shaping biological diversity. However, we know surprisingly little about the natural environmental conditions that favour the formation of multicellular groups. Here we experimentally examine how key environmental factors (predation, nitrogen and water turbulence) combine to influence multicellular group formation in 35 wild unicellular green algae strains (19 Chlorophyta species). All environmental factors induced the formation of multicellular groups (more than four cells), but there was no evidence this was adaptive, as multicellularity (% cells in groups) was not related to population growth rate under any condition. Instead, population growth was related to extracellular matrix (ECM) around single cells and palmelloid formation, a unicellular life-cycle stage where two to four cells are retained within a mother-cell wall after mitosis. ECM production increased with nitrogen levels resulting in more cells being in palmelloids and higher rates of multicellular group formation. Examining the distribution of 332 algae species across 478 lakes monitored over 55 years, showed that ECM and nitrogen availability also predicted patterns of obligate multicellularity in nature. Our results highlight that adaptations of unicellular organisms to cope with environmental challenges may be key to understanding evolutionary routes to multicellular life.

Formation of Microalgal Hunting Nets in Freshwater Microcosm Food Web: Microscopic Evidence

“…We know surprisingly little about the natural environmental conditions that favor the formation of multicellular groups. Adaptations of unicellular organisms to environmental challenges may hold the key to understanding evolutionary pathways to multicellular life [48]. TEM of the microalgal samples provided us the confirmation that the isolated endosymbiotic microalgae may be the base for the microalgal net formation.…”

The effects of CdSe/ZnS quantum dots on autofluorescence properties and growth of algae Desmodesmus communis: dependence on cultivation medium

“…According to Cornwallis et al , 40 multicellularity has allowed new levels of morphological complexity to develop, but it is still unclear what ecological advantages or benefits multicellularity provides. It has been suggested that possible benefits of forming multicellular groups as an adaptation are to protect unicellular organisms from various environmental stressors such as predation and toxins.…”

“…It has been suggested that possible benefits of forming multicellular groups as an adaptation are to protect unicellular organisms from various environmental stressors such as predation and toxins. 40,41 Earlier studies examining the costs and benefits of group formation in algae have produced mixed results. 41,42 According to Lürling et al, 42 multicelled colonies of algae have a higher sinking rate and lower ability to absorb nutrients compared to unicellular algae, but according to Cornwallis et al, 40 they can protect themselves from various stressors.…”

“…40,41 Earlier studies examining the costs and benefits of group formation in algae have produced mixed results. 41,42 According to Lürling et al, 42 multicelled colonies of algae have a higher sinking rate and lower ability to absorb nutrients compared to unicellular algae, but according to Cornwallis et al, 40 they can protect themselves from various stressors. Thus, the formation of four-celled colonies initiated by QDs in the population of D. communis in natural media may be associated with a protecting reaction of the algae to the effects of toxins.…”

Species interactions and food-web context drive temperature-dependent prey evolution

“…We used two protist predators of similar body size, Tetrahymena pyriformis and Glaucoma sp., as the focal predators, and a larger protist Paramecium caudatum, as a competitor for the predators (Fig 1b). All four species are commonly found in freshwater and soil systems (Cornwallis et al 2023;Foissner & Berger 1996).…”