Data from: The nature of nurture in a wild mammal’s fitness

Genetic variation in fitness is required for the adaptive evolution of any trait but natural selection is thought to erode genetic variance in fitness. This paradox has motivated the search for mechanisms that might maintain a population’s adaptive potential. Mothers make many contributions to the attributes of their developing offspring and these maternal effects can influence responses to natural selection if maternal effects are themselves heritable. Maternal genetic effects on fitness might, therefore, represent an under-appreciated source of adaptive potential in wild populations. Here we used two decades of data from a pedigreed wild population of North American red squirrels to show that maternal genetic effects on offspring fitness increased its evolvability by over two orders of magnitude relative to expectations from direct genetic effects alone. Maternal genetic effects are predicted to maintain more variation than direct genetic effects in the face of selection, but we also found evidence of maternal effect trade-offs. Mothers that raised high-fitness offspring in one environment raised low-fitness offspring in another environment. Such a fitness trade-off is expected to maintain maternal genetic variation in fitness, which provided additional capacity for adaptive evolution beyond that provided by direct genetic effects on fitness.

任何性状的适应性演化均需以适合度的遗传变异为基础，但自然选择通常被认为会削减适合度的遗传方差。这一悖论推动学界探寻维持种群适应性演化潜力的潜在机制。
母体对发育中子代的性状具有多重贡献，若母体效应（maternal effects）本身可遗传，则其可影响种群对自然选择的响应。因此，针对适合度的母体遗传效应（maternal genetic effects），或许是野生种群中未被充分认知的适应性演化潜力来源。
本研究利用北美红松鼠这一具有谱系记录的野生种群长达二十年的监测数据，证实针对子代适合度的母体遗传效应，可使种群的可演化性较仅考虑直接遗传效应（direct genetic effects）的预期提升两个数量级以上。
理论预测，面对自然选择时，母体遗传效应相较于直接遗传效应，能够维持更多的遗传变异，但本研究同时发现了母体效应权衡（maternal effect trade-offs）的相关证据。
在某一环境中抚育出高适合度子代的母本，在另一环境中则会产出适合度较低的子代。这类适合度权衡（fitness trade-offs）被认为可维持适合度相关的母体遗传变异，从而为适应性演化提供了超出直接遗传效应所能提供的额外潜力。