Spatial population expansion promotes the evolution of cooperation in an experimental Prisoner's Dilemma (original) (raw)

2013, Current biology : CB

Van Dyken et al 2013. Spatial population expansion promotes the evolution of cooperation in an experimental Prisoner's Dilemma. Current Biology 26: 919-923 Cooperation in spatially expanding populations 2 Cooperation forms the basis for numerous complex phenotypes, from cell-cell 43 communication and biofilm formation in microbes to nest construction in multicellular 44 species [12, 13]. Explaining how cooperation evolves despite the direct fitness advantage 45 gained by free-riding remains a central challenge in biology and the social sciences [1-3]. 46 This is particularly true in the Prisoner's Dilemma game [1, 4, 5] where cooperators 47 always lose in direct competition with defectors, leading to a "Tragedy of the Commons" 48 [14]. Nearly half a century of research on social evolution has offered insight into this 49 dilemma, with inclusive fitness theory focusing attention on the importance of high 50 genetic relatedness [15], multilevel selection theory highlighting the role played by 51 competition among social groups [16, 17], and spatial games showing the importance of 52 population structure [18-21]. Here we bring these three frameworks together, 53 demonstrating that spatial population expansion creates a setting where both relatedness 54 and intergroup competition are amplified, promoting the evolution of cooperation. 55 Spatial population expansion occurs when a species spreads outward to fill vacant 56 eco-space or to supplant resident species, resulting in increased geographic range. 57 Human migration out of Africa [7] is one salient example, while more generic examples 58 include ecological invasions, epidemics, growth of microbial colonies, and expansion due 59 to habitat modification caused by environmental disturbance or climate change [8-11]. 60 Spatially expanding populations form a propagating density wave called a "Fisher wave" 61 with a constant speed proportional to the square root of the mean growth rate (i.e., 62 Malthusian fitness) of subpopulations at the front [22]. Genetically heterogeneous 63 populations may also form an "allele frequency" wave representing the spatial spread of 64 alleles [22] (see Supplemental Information). 231