The evolution of cooperation by the Hankshaw effect

Abstract

The evolution of cooperation-costly behavior that benefits others-faces one clear obstacle. Namely, cooperators are always at a competitive disadvantage relative to defectors, individuals that reap the benefits, but evade the cost of cooperation. One solution to this problem involves genetic hitchhiking, where the allele encoding cooperation becomes linked to a beneficial mutation, allowing cooperation to rise in abundance. Here, we explore hitchhiking in the context of adaptation to a stressful environment by cooperators and defectors with spatially limited dispersal. Under such conditions, clustered cooperators reach higher local densities, thereby experiencing more mutational opportunities than defectors. Thus, the allele encoding cooperation has a greater probability of hitchhiking with alleles conferring stress adaptation. We label this probabilistic enhancement the "Hankshaw effect" after the character Sissy Hankshaw, whose anomalously large thumbs made her a singularly effective hitchhiker. Using an agent-based model, we reveal a broad set of conditions that allow the evolution of cooperation through this effect. Additionally, we show that spite, a costly behavior that harms others, can evolve by the Hankshaw effect. While in an unchanging environment these costly social behaviors have transient success, in a dynamic environment, cooperation and spite can persist indefinitely.

Computational complexity as an ultimate constraint on evolution

“…The strength of this ultimate constraint allows us to reason rigorously from disequilibrium to establish positive results. For instance, that costly learning (Baldwin effect [47,48]) can remain adaptive, or that hitchhiking can maintain cooperation (Hankshaw effect [49]) effectively forever. In the case of costly learning, Simpson [48] noted: "[c]haracters individually acquired by members of a group of organisms may eventually, under the influence of selection, be reinforced or replaced by similar hereditary character".…”

“…A similar phenomenon is important for the maintenance of cooperation. Hammarlund, Connelly, Dickinson, and Kerr [49] consider a metapopulation that is not sufficiently spatially structured to maintain cooperation. They augment the metapopulation with a number of genes with non-frequency dependent fitness effects that constitute a static fitness landscape.…”

Resource abundance and the critical transition to cooperation

“…When biofilms enable populations to reach greater densities, cooperation may be further challenged by increased competition among kin (Taylor, 1992;Platt & Bever, 2009). Under these circumstances, cooperation can nevertheless be bolstered by pleiotropy (Dandekar et al, 2012;Mitri & Foster, 2016), policing (Frank, 2003;Wang et al, 2015) or nonsocial adaptation (Asfahl et al, 2015;Hammarlund et al, 2016). In our systems, the environmental disturbance created opportunities for the population to expand, allowing cooperators to escape competition from noncooperators (Video S1; Alizon & Taylor, 2008).…”

The evolution of genetic bandwagoning

“…In the current paper, "quality" is used in the sense of "good genes," that is, "an individual's intrinsic propensity or ability to achieve fitness" (Wang et al, 2017) because it has genetic variants that leave it more or less advantaged in prey and territory acquisition or more or less susceptible to, for example, predation or infection.. Variation in genetic quality is assumed to owe to mutations or epimutations having positive-as in the Red Queen's (Van Valen, 1973;Hartung, 1981;Ridley, 1993;Liow et al, 2011;Brockhurst et al, 2014) and adaptive (Morgan et al, 2012;Waite and Shou, 2012;Hammarlund et al, 2016) racesor negative influences upon quality. An individual's condition may also be used to indicate its genetic quality (i.e., "good genes").…”

“…Genetic bandwagoning is an example of the Hankshaw effect-by which "a property of an allele increases its likelihood of hitchhiking" (Hammarlund et al, 2016(Hammarlund et al, , pg. 1376)-because when copies of a bandwagoning variant induce low-quality individuals to forfeit resources, higher-quality individuals gain resources, facilitating hitchhiking by copies of the variant held by higher-quality individuals.…”