Cooperation-mediated plasticity in dispersal and colonization

Abstract

Kin selection theory predicts that costly cooperative behaviors evolve most readily when directed toward kin. Dispersal plays a controversial role in the evolution of cooperation: dispersal decreases local population relatedness and thus opposes the evolution of cooperation, but limited dispersal increases kin competition and can negate the benefits of cooperation. Theoretical work has suggested that plasticity of dispersal, where individuals can adjust their dispersal decisions according to the social context, might help resolve this paradox and promote the evolution of cooperation. Here, we experimentally tested the hypothesis that conditional dispersal decisions are mediated by a cooperative strategy: we quantified the density-dependent dispersal decisions and subsequent colonization efficiency from single cells or groups of cells among six genetic strains of the unicellular Tetrahymena thermophila that differ in their aggregation level (high, medium, and low), a behavior associated with cooperation strategy. We found that the plastic reaction norms of dispersal rate relative to density differed according to aggregation level: highly aggregative genotypes showed negative density-dependent dispersal, whereas low-aggregation genotypes showed maximum dispersal rates at intermediate density, and medium-aggregation genotypes showed density-independent dispersal with intermediate dispersal rate. Dispersers from highly aggregative genotypes had specialized long-distance dispersal phenotypes, contrary to low-aggregation genotypes; medium-aggregation genotypes showing intermediate dispersal phenotype. Moreover, highly aggregation genotypes showed evidence for beneficial kin-cooperation during dispersal. Our experimental results should help to resolve the evolutionary conflict between cooperation and dispersal: cooperative individuals are expected to avoid kin-competition by dispersing long distances, but maintain the benefits of cooperation by dispersing in small groups.

Genetics of dispersal

“…They found that 43% of the variance in dispersal propensity was explained by G, 13% by E and 2% by G × E, with reaction norms (Appendix I) to density varying among genotypes from negative to positive density dependencies (see also Fronhofer, Kropf & Altermatt, ). A recent study showed that this significant G × E interaction could be explained by other traits like cooperation and result in the variation of dispersal syndromes along a density gradient (Jacob et al, ). In the spider Erigone atra , temperatures during development affected both long‐ and short dispersal strategies (Bonte et al, ).…”

“…Consequently, different syndromes among populations could emerge and be maintained (Clobert et al, 2009;Cote et al, , 2017aRonce & Clobert, 2012). Conditional dispersal syndromes have now been reported in several studies (Byers, 2000;Gilliam & Fraser, 2001;Cote & Clobert, 2007;Bonte et al, 2008;Bolnick et al, 2009;Cote et al, 2013;Bestion et al, 2014Bestion et al, , 2015Pennekamp et al, 2014;Myles-Gonzalez et al, 2015;Jacob et al, 2016). However, although the strength of genetic and environmental components of dispersal syndromes and their interactions will undoubtedly influence the eco-evolutionary outcomes of dispersal (Legrand et al, 2017), they remain almost unexplored.…”

Ecological and demographic correlates of cooperation from individual to budding dispersal

“…A common thread across these studies is the existence of budding or some form of group dispersal (e.g. Heinsohn et al ., ; Williams & Rabenold, ; Bradley et al ., ; Sharp et al ., ; Jacob et al ., ). This observation has led us to advance the central hypothesis of our study where we propose that budding may mediate a shift in the ecological and demographic variables shaping the evolution of cooperation.…”

“…For example, using a ciliated protozoan model system ( Tetrahymena thermophila ), Jacob et al . () found that the aggregative behaviour of the strain (determined by their genotype) altered the plastic reaction norms of dispersal behaviour. Specifically, cooperation and dispersal are maintained via the avoidance of kin competition through long‐distance dispersal, and the maintenance of kin structure through group dispersal.…”

Evolution under pH stress and high population densities leads to increased density‐dependent fitness in the protistTetrahymena thermophila

“…; Jacob et al. ). T. thermophila is characterized by a high mutation rate in the macronucleus (Brito et al.…”