Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, USA.
Department of Entomology & Plant Pathology, North Carolina State University, Raleigh, NC, USA.
J Evol Biol. 2020 Apr;33(4):534-543. doi: 10.1111/jeb.13589. Epub 2020 Feb 3.
Social evolution has led to distinct life-history patterns in social insects, but many colony-level and individual traits, such as egg size, are not sufficiently understood. Thus, a series of experiments was performed to study the effects of genotypes, colony size and colony nutrition on variation in egg size produced by honey bee (Apis mellifera) queens. Queens from different genetic stocks produced significantly different egg sizes under similar environmental conditions, indicating standing genetic variation for egg size that allows for adaptive evolutionary change. Further investigations revealed that eggs produced by queens in large colonies were consistently smaller than eggs produced in small colonies, and queens dynamically adjusted egg size in relation to colony size. Similarly, queens increased egg size in response to food deprivation. These results could not be solely explained by different numbers of eggs produced in the different circumstances but instead seem to reflect an active adjustment of resource allocation by the queen in response to colony conditions. As a result, larger eggs experienced higher subsequent survival than smaller eggs, suggesting that honey bee queens might increase egg size under unfavourable conditions to enhance brood survival and to minimize costly brood care of eggs that fail to successfully develop, and thus conserve energy at the colony level. The extensive plasticity and genetic variation of egg size in honey bees has important implications for understanding life-history evolution in a social context and implies this neglected life-history stage in honey bees may have trans-generational effects.
社会进化导致了社会性昆虫明显的生活史模式，但许多群体水平和个体特征，如卵的大小，还没有得到充分的理解。因此，进行了一系列实验来研究基因型、群体大小和群体营养对蜜蜂（Apis mellifera）蜂王所产卵大小变化的影响。在相似的环境条件下，来自不同遗传品系的蜂王所产的卵大小明显不同，这表明卵大小存在着固定的遗传变异，允许适应性进化变化。进一步的研究表明，大群体中的蜂王所产的卵比小群体中的卵要小，而且蜂王会根据群体大小动态调整卵的大小。同样，蜂王在食物匮乏时会增大卵的大小。这些结果不能仅仅用在不同情况下产生的不同数量的卵来解释，而是似乎反映了蜂王根据群体条件主动调整资源分配。因此，较大的卵比较小的卵有更高的后续存活率，这表明蜜蜂蜂王可能会在不利条件下增大卵的大小，以提高幼虫的存活率，并最大限度地减少因未能成功发育而导致的昂贵的卵抚育成本，从而在群体水平上节约能量。蜜蜂卵大小的广泛可塑性和遗传变异对理解社会性背景下的生活史进化具有重要意义，并暗示蜜蜂这一被忽视的生活史阶段可能具有跨代效应。
