Data from: Inbreeding depression does not increase after exposure to a stressful environment: a test using compensatory growth

Background: Inbreeding is often associated with a decrease in offspring fitness (‘inbreeding depression’). Moreover, it is generally assumed that the negative effects of inbreeding are exacerbated in stressful environments. This G × E interaction has been explored in many taxa under different environmental conditions. These studies usually manipulate environmental conditions either in adulthood or throughout an individual’s entire life. Far fewer studies have tested how stressful environments only experienced during development subsequently influence the effects of inbreeding on adult traits. Results: We experimentally manipulated the diet (control versus low food) of inbred and outbred juvenile Eastern mosquitofish (Gambusia holbrooki) for three weeks (days 7-28) to test whether experiencing a presumably stressful environment early in life influences their subsequent growth and adult phenotypes. The control diet was a standard laboratory food regime, while fish on the low food diet received less than 25 % of this amount of food. Unexpectedly, despite a large sample size (237 families, 908 offspring) and a quantified 23 % reduction in genome-wide heterozygosity in inbred offspring from matings between full-siblings (f = 0.25), neither inbreeding nor its interaction with early diet affected growth trajectories, juvenile survival or adult size. Individuals did not mitigate a poor start in life by showing ‘compensatory growth’ (i.e. faster growth once the low food treatment ended), but they showed ‘catch-up growth’ by delaying maturation. There was, however, no effect of inbreeding on the extent of catch-up growth. Conclusions: There were no detectable effects of inbreeding on growth or adult size, even on a low food diet that should elevate inbreeding depression. Thus, the long-term costs of inbreeding due to lower male reproductive success we have shown in another study appear to be unrelated to inbreeding depression for adult male size or the growth rates that are reported in the current study.

研究背景：近交通常会导致后代适合度下降，即近交衰退（inbreeding depression）。此外，学界普遍认为，胁迫环境会加剧近交的负面效应。这种基因型-环境（G×E）互作已在多种类群中、于不同环境条件下得到探究。此类研究通常在成年期或个体整个生命周期中操控环境条件，而鲜有研究探讨仅在发育阶段经历的胁迫环境，会如何后续影响近交对成体性状的效应。

研究结果：我们通过实验操控了近交与远交的幼年东部食蚊鱼（Gambusia holbrooki）的日粮水平，设置对照组与低日粮组，处理时长为三周（第7至28日龄），以探究生命早期经历的推测性胁迫环境，是否会影响其后续生长与成体表型。对照组日粮为标准实验室饲喂方案，低日粮组的摄食量仅为对照组的25%以下。出乎意料的是，尽管本研究样本量较大（237个家系、908个子代个体），且同胞兄妹交配产生的近交子代（近交系数f=0.25）的全基因组杂合度（genome-wide heterozygosity）较对照组降低了23%，但近交及其与早期日粮的互作均未对生长轨迹、幼体存活率或成体体型产生影响。个体并未通过“补偿生长”（即低日粮处理结束后加快生长）来弥补生命早期的不良经历，但它们通过延迟性成熟实现了“追赶生长”；不过近交并未对追赶生长的程度产生影响。

研究结论：即便在本应加剧近交衰退的低日粮条件下，近交对生长或成体体型均未产生可检测到的效应。因此，我们在另一项研究中揭示的、由雄性繁殖成功率降低所导致的近交长期代价，似乎与本研究中所报道的雄性成体体型近交衰退或生长速率无关。