Department of Obstetrics and Gynecology, C. S. Mott Center for Human Growth and Development and Center for Urban Responses to Environmental Stressors, Institute of Environmental Health Sciences, Wayne State University Detroit, MI, USA.
School of Computer Science and Genome Quebec Innovation Centre, McGill University Montreal, QC, Canada.
Front Genet. 2015 Feb 24;6:60. doi: 10.3389/fgene.2015.00060. eCollection 2015.
In a recent perspective in this journal, Herb (2014) discussed how epigenetics is a possible mechanism to circumvent Charles Darwin's "special difficulty" in using natural selection to explain the existence of the sterile-fertile dimorphism in eusocial insects. Darwin's classic book "On the Origin of Species by Means of Natural Selection" explains how natural selection of the fittest individuals in a population can allow a species to adapt to a novel or changing environment. However, in bees and other eusocial insects, such as ants and termites, there exist two or more castes of genetically similar females, from fertile queens to multiple sub-castes of sterile workers, with vastly different phenotypes, lifespans, and behaviors. This necessitates the selection of groups (or kin) rather than individuals in the evolution of honeybee hives, but group and kin selection theories of evolution are controversial and mechanistically uncertain. Also, group selection would seem to be prohibitively inefficient because the effective population size of a colony is reduced from thousands to a single breeding queen. In this follow-up perspective, we elaborate on possible mechanisms for how a combination of both epigenetics, specifically, the selection of metastable epialleles, and genetics, the selection of mutations generated by the selected metastable epialleles, allows for a combined means for selection amongst the fertile members of a species to increase colony fitness. This "intra-caste evolution" hypothesis is a variation of the epigenetic directed genetic error hypothesis, which proposes that selected metastable epialleles increase genetic variability by directing mutations specifically to the epialleles. Natural selection of random metastable epialleles followed by a second round of natural selection of random mutations generated by the metastable epialleles would allow a way around the small effective population size of eusocial insects.
在最近的一篇本杂志的观点文章中，赫布（2014 年）讨论了表观遗传学如何成为一种可能的机制，可以绕过查尔斯·达尔文（Charles Darwin）用自然选择来解释群居昆虫中不育-可育二态性存在的“特殊困难”。达尔文的经典著作《物种起源》（On the Origin of Species by Means of Natural Selection）解释了自然选择如何使种群中最适应的个体能够适应新的或变化的环境。然而，在蜜蜂和其他群居昆虫（如蚂蚁和白蚁）中，存在两种或更多种遗传上相似的雌性类型，从可育的蜂王到多种不育工蜂亚群，它们具有截然不同的表型、寿命和行为。这就需要在蜜蜂群体的进化中选择群体（或亲缘关系）而不是个体，但群体选择和亲缘选择的进化理论存在争议，并且机制上不确定。此外，群体选择似乎效率极低，因为一个群体的有效种群大小从数千减少到一个繁殖的蜂王。在这篇后续观点文章中，我们详细阐述了表观遗传学，特别是可稳定表型等位基因选择，以及遗传学，即选择由所选可稳定表型等位基因产生的突变，如何结合起来为物种的可育成员提供一个增加群体适应性的选择机制。这种“种内进化”假说，是表观遗传定向遗传错误假说的一个变体，该假说提出，选择的可稳定表型等位基因通过定向突变到表型等位基因来增加遗传变异性。随机的可稳定表型等位基因的自然选择，然后是第二轮由可稳定表型等位基因产生的随机突变的自然选择，将为群居昆虫的小有效种群规模提供一种解决方法。
