Background
In nature, selective forces that forged the origins of complex behaviors and forms vary in strength over space and time. Once evolved, complex traits can later degrade, for example if selection favoring them drops in strength. Penguins lost flight; snakes lost legs.
MyxoEE-1 was designed to ask how Myxococcus xanthus social behaviors evolve, and especially might degrade, when selection favoring them is relaxed.
Design summary: 12 populations recently descended from a single cell grew for 1000 generations in shaken, nutrient-rich broth, with 1% of each population transferred daily into fresh medium.
Highlights
Lost in luxury - Relaxation of selection for proficiency at gliding motility, aggregative fruiting-body development and sporulation leads to systematic loss of these social behaviors. But such loss occurs by phenotypically diverse evolutionary pathways across replicate populations.
Microbes cheat - Gaining a short-term fitness advantage over others by exploiting their costly cooperation while cooperating less oneself - a process often called ‘cheating’ - is found to occur among bacteria.
Negative frequency dependence can stabilize cooperation - In Myxococcus, cheater genotypes that outcompete cooperators at social spore production when cheaters are rare nonetheless lose out to cooperators when the cheaters exceed a threshold frequency. This negative frequency dependence of fitness ranks prevents cheats from driving cooperation to extinction. 2000, 2003, 2009, 2010.
Cheating facilitates an evolutionary transition from cheaters to cheating-resistant cooperators - See MyxoEE-2.
Publications
Velicer, G. J., L. Kroos, and R. E. Lenski. 1998. Loss of social behaviors by Myxococcus xanthus during evolution in an unstructured habitat. Proceedings of the National Academy of Sciences USA. READ IT HERE
Velicer, G. J., L. Kroos, and R. E. Lenski. 2000. Developmental cheating in the social bacterium Myxococcus xanthus. Nature. READ IT HERE
Velicer, G. J., R. E. Lenski, and L. Kroos. 2002. Rescue of social motility lost during evolution of Myxococcus xanthus in an asocial environment. Journal of Bacteriology. READ IT HERE
Velicer, G. J. 2003. Social strife in the microbial world. Trends in Microbiology. READ IT HERE (review article)
Travisano, M. and G. J. Velicer. 2004. Strategies of microbial cheater control. Trends in Microbiology. READ IT HERE (perspective article)
Two “cheaters” used in MyxoEE-2 evolved to become cheaters in MyxoEE-1; most studies listed below relate to MyxoEE-2 but include strains from MyxoEE-1.
Fiegna, F. and G. J. Velicer. 2003. Competitive fates of bacterial social parasites: persistence and self-induced extinction of Myxococcus cheaters. Proceedings of the Royal Society B. READ IT HERE
Fiegna, F., Y.-T. N. Yu, S. V. Kadam and G. J. Velicer. 2006. Evolution of an obligate social cheater to a superior cooperator. Nature. READ IT HERE
Velicer, G. J., G. Raddatz, H. Keller, S. Deiss, C. Lanz, I. Dinkelacker and S. C. Schuster. 2006. Comprehensive mutation identification in an evolved bacterial cooperator and its cheating ancestor. Proceedings of the National Academy of Sciences USA. READ IT HERE
Velicer, G. J. and K. L. Hillesland. 2007. Why cooperate? The ecology and evolution of myxobacteria. In Myxobacteria: Multicellularity and Differentiation, D. Whitworth, editor. American Society for Microbiology Press. READ IT HERE (book chapter)
Kadam, S. V., S. Wegener-Feldbrügge, L. Søgaard-Andersen and G. J. Velicer. 2008. Novel transcriptome patterns accompany evolutionary reversion of defective social development in the bacterium Myxococcus xanthus. Molecular Biology and Evolution. READ IT HERE
Velicer, G. J. and M. Vos. 2009. Sociobiology of the myxobacteria. Annual Review of Microbiology. READ IT HERE (review article)
smith, j., van Dyken, D and P. C. Zee. 2009. A generalization of Hamilton’s rule for the evolution of microbial cooperation. Science. READ IT HERE
Yu, Y.-T. Y., X. Yuan and G. J. Velicer. 2010. Adaptive evolution of an sRNA that controls Myxococcus. Science. READ IT HERE
Chen, I.-.C. K., B. Griesenauer, Y.-T. N. Yu and G. J. Velicer. 2014. A recent evolutionary origin of a bacterial small RNA that controls multicellular fruiting body development. Molecular Phylogenetics and Evolution. READ IT HERE
Velicer, G. J., H. Mendes-Soares & S. Wielgoss. 2014. Whence comes social diversity? Ecological and evolutionary analysis of the myxobacteria. In Myxobacteria: Genomics and Molecular Biology, P. Higgs and Z. Yang eds. Horizon Scientific Press. READ IT HERE (book chapter)
O’Malley, M. A., M. Travisano, G. J. Velicer and J. A. Bolker. 2015. How do microbial populations and communities function as model systems? The Quarterly Review of Biology. READ IT HERE (perspective article)
Yu, Y.-T.N., M. Kleiner and G. J. Velicer. 2016. Spontaneous reversions of an evolutionary trait loss reveal regulators of an sRNA that controls multicellular development in the myxobacteria. Journal of Bacteriology. READ IT HERE
Yu, T.-T.N., E. Cooper and G. J. Velicer. 2017. A conserved stem of the Myxococcus xanthus sRNA Pxr controls sRNA accumulation and multicellular development. Scientific Reports. READ IT HERE
Chen, I.-.C. K., G. J. Velicer and Y.-T.N. Yu. 2017. Divergence of functional effects among bacterial sRNA paralogs. BMC Evolutionary Biology. READ IT HERE
Chen, I.-C. K., B. M. Satinsky, G. J. Velicer and Y.-T.N. Yu. 2019. sRNA‐pathway genes regulating myxobacterial development exhibit clade‐specific evolution. Evolution & Development. READ IT HERE
La Fortezza, M., K. A. Schaal and G. J. Velicer. 2022. Group formation: On the evolution of aggregative multicellularity. In Herron, M. D., P. L. Conlin and W. C. Ratcliff eds. The Evolution of Multicellularity. CRC Press, Boca Raton, FL. READ IT HERE (book chapter)
Cossey, S. M., G. J. Velicer and Y.-T. N Yu. 2023. Ribonuclease D processes a small RNA regulator of multicellular development in myxobacteria. Genes. READ IT HERE