Meta‐population structure and the evolutionary transition to multicellularity

Abstract

The evolutionary transition to multicellularity has occurred on numerous occasions, but transitions to complex life forms are rare. Here, using experimental bacterial populations as proxies for nascent multicellular organisms, we manipulate ecological factors shaping the evolution of groups. Groups were propagated under regimes requiring reproduction via a life cycle replete with developmental and dispersal (propagule) phases, but in one treatment lineages never mixed, whereas in a second treatment, cells from different lineages experienced intense competition during the dispersal phase. The latter treatment favoured traits promoting cell growth at the expense of traits underlying group fitnessa finding that is supported by results from a mathematical model. Our results show that the transition to multicellularity benefits from ecological conditions that maintain discreteness not just of the group (soma) phase, but also of the dispersal (germline) phase.

Ecological scaffolding and the evolution of individuality

“…Periodic collapse of mats marks death events that allow the possibility that new mats arise by dispersal from extant types 7,21 . Precisely this scenario underpinned design of on-going lineage selection experiments exploring the evolution of multicellular life 19,20 .…”

“…Ecological scaffolding underpinned a recent (and on-going) experimental exploration of the evolution of multicellularity 19,20 . Discrete lineages established from the bacterium Pseudomonas fluorescens were propagated under conditions that required, for long-term persistence, repeated completion a two-phase life cycle involving soma and germ-like states.…”

Enhancing Microbial Pollutant Degradation by Integrating Eco-Evolutionary Principles with Environmental Biotechnology

“…This is likely due to the misconception regarding the importance of selection working at levels above the individual (i.e., groups, populations, and ecosystems) [42][43][44] and because of the complexity and scale of artificial community selection experiments. Nevertheless, artificial community selection has been resurrected, with several recent theoretical and experimental studies addressing this topic [45][46][47][48][49]. Here, different strategies and setups of selection experiments using artificial microbial communities have been tested and challenges have been identified [50][51][52].…”

“…We compare this with the approach we favor, where the chosen communities are kept as distinct lineages ('Persistent communities'). The difference seems to be subtle, but it crucially affects the efficacy of the artificial community selection [49]. While the maintenance of inter-community variation is highlighted as one advantage of the 'Transient community' design, we propose that this design also selects for fast growth/high biomass, as the strains that dominate the communities will be rewarded (r-strategists i.e., fast-growing strains).…”

Life history tradeoffs, division of labor and evolutionary transitions in individuality

“…Collective-level traits are most certainly more complex than the arithmetic aggregation of individual quantities measured in the propagule or the fully developed collective. They are rather the result of internal developmental dynamics, i.e., within-collective cellular ecological dynamics (Hammerschmidt et al, 2014;Rose et al, 2020). Selection of developmental mechanisms has long been recognized as an important part of ETIs (Buss, 1987;Michod & Roze, 1997) and can fully be studied by models that explicitly describe the ecological dynamics within collectives (see Ikegami & Hashimoto, 2002;Williams & Lenton, 2007;Xie et al, 2019 for general cell communities; but see Doulcier et al, 2020 for an application to ETIs).…”