School of Biological Sciences, University of Bristol, Bristol, UK.
Centre for Biodiversity and Environment Research (CBER), Division of Biosciences, University College London, London, UK.
Nat Ecol Evol. 2021 Apr;5(4):468-479. doi: 10.1038/s41559-020-01382-z. Epub 2021 Feb 15.
Altruism between close relatives can be easily explained. However, paradoxes arise when organisms divert altruism towards more distantly related recipients. In some social insects, workers drift extensively between colonies and help raise less related foreign brood, seemingly reducing inclusive fitness. Since being highlighted by W. D. Hamilton, three hypotheses (bet hedging, indirect reciprocity and diminishing returns to cooperation) have been proposed for this surprising behaviour. Here, using inclusive fitness theory, we show that bet hedging and indirect reciprocity could only drive cooperative drifting under improbable conditions. However, diminishing returns to cooperation create a simple context in which sharing workers is adaptive. Using a longitudinal dataset comprising over a quarter of a million nest cell observations, we quantify cooperative payoffs in the Neotropical wasp Polistes canadensis, for which drifting occurs at high levels. As the worker-to-brood ratio rises in a worker's home colony, the predicted marginal benefit of a worker for expected colony productivity diminishes. Helping related colonies can allow effort to be focused on related brood that are more in need of care. Finally, we use simulations to show that cooperative drifting evolves under diminishing returns when dispersal is local, allowing altruists to focus their efforts on related recipients. Our results indicate the power of nonlinear fitness effects to shape social organization, and suggest that models of eusocial evolution should be extended to include neglected social interactions within colony networks.
近亲之间的利他行为很容易解释。然而，当生物体将利他主义转向关系更远的接受者时，就会出现悖论。在一些社会性昆虫中，工蜂在群体之间广泛流动，并帮助抚养亲缘关系较远的外来幼虫，这似乎降低了包容性适合度。自从 W.D.汉密尔顿提出这个观点以来，已经提出了三个假说（风险分摊、间接互惠和合作回报递减）来解释这种令人惊讶的行为。在这里，我们使用包容性适合度理论表明，风险分摊和间接互惠只能在不太可能的情况下驱动合作漂移。然而，合作回报的递减会在简单的情况下创造出一种共享工人是适应性的情境。我们使用了一个包含超过 25 万个巢室观察数据的纵向数据集，对在高漂移水平发生的新热带黄蜂 Polistes canadensis 的合作收益进行了量化。随着工蜂在其原生群体中的幼虫与工蜂比例的增加，预计对预期群体生产力的边际收益会降低。帮助相关群体可以让工蜂将精力集中在更需要照顾的亲缘幼虫上。最后，我们使用模拟表明，当扩散是局部的时候，合作漂移会在回报递减的情况下进化，从而允许利他主义者将他们的努力集中在相关的接受者身上。我们的结果表明，非线性适合度效应在塑造社会组织方面的力量，并表明应该将真社会性进化的模型扩展到包括被忽视的群体网络内的社会相互作用。
