Altruism, Cheating, and Anticheater Adaptations in Cellular Slime Molds

Abstract

Cellular slime molds (CSMs) possess a remarkable life cycle that encompasses an extreme act of altruism. CSM cells live as individual amoebae until starved, then aggregate and ultimately transform themselves into a multicellular fruiting body. This fruiting body consists of stalk cells (altruists that eventually die) and spores (the beneficiaries of this sacrifice). Altruistic systems such as this are vulnerable to cheaters, which are individuals unrelated to the altruists that obtain the benefits provided by them without reciprocating. Here, we investigate two forces that can maintain CSM altruism despite cheating: kin selection and anticheater adaptations. First, we present new kinship-based models based on CSM developmental biology to evaluate the efficacy of kin selection. These models show that stalk-making genotypes can still be maintained when aggregations are initiated by multiple "founder" spores, provided that spores of stalkless fruiting bodies have low rates of dispersal and dispersal success is a concave function of stalk height. Second, we review proposals that several features of CSM development, such as the chemical suppression of the redifferentiation of prestalk cells into prespores, act as anticheater adaptations.

Evolutionary dynamics of altruism and cheating among social amoebas

“…This component of the model closely follows Hudson et al (2002). We consider a fruiting body that is founded by a total of kZ k 1 C/C k n spores, with trait values a 1 ,.,a n , respectively.…”

“…The selection gradient in equation 3.1 shows that this is possible if mD 0 (0)OD(0). The dispersal success function considered by Hudson et al (2002), equation 2.3, yields mD 0 (0)!D(0) whenever qO1. By contrast, the alternative function in equation 2.4 yields mD 0 (0)OD(0) whenever mqO0; under this condition, clones with stalked fruiting bodies can thus evolve from stalkless ones.…”

“…In this manner, some far-reaching insights could be derived analytically. Hudson et al (2002) analysed a special case of this latter model, and also presented one of the first models of variable-allocation cheating.…”

“…While Armstrong (1984) and Matapurkar & Watve (1997) relied mainly on numerical simulations, Matsuda & Harada (1990) and Hudson et al (2002) only considered evolutionarily stable strategies in chimeric aggregations with fixed sets of founder spores. In this paper, we combine the strengths of these previous approaches by allowing for a probabilistic variable number of founder spores, while retaining analytic tractability to a large extent.…”

Diminishing returns in social evolution: the not-so-tragic commons

“…Models of cooperation typically assess sociality from how much each group member invests in cooperation (e.g. Brown, 1999;Killingback et al, 1999;Avilé s, 2002;Hudson et al, 2002;Le Galliard et al, 2003). Here I focus instead on group performance to measure of the impact of competition and specifically address the problem posed by the tragedy of the commons.…”