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（inbreeding）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。这类基因型-环境互作（Genotype-Environment Interaction，G×E）已在多种类群（taxa）中结合不同环境条件得到探究。此类研究通常在成体阶段或个体整个生命周期中操控环境条件，而仅在发育阶段经历胁迫环境、后续如何影响近交对成体性状（adult traits）的效应的相关研究则少得多。

研究结果：本研究对近交和远交的幼年东部食蚊鱼（Gambusia holbrooki）进行为期3周（第7-28天）的日粮操控（对照组vs低食物组），以验证生命早期经历的胁迫环境是否会影响其后续生长及成体表型。对照组采用标准实验室饲喂方案，低食物组的饲喂量不足对照组的25%。出乎意料的是，尽管本研究样本量较大（237个家系，908只后代），且全同胞（full-siblings）交配产生的近交后代的全基因组杂合度（genome-wide heterozygosity）较对照降低了23%（近交系数f=0.25），但近交及其与早期日粮的交互作用均未对生长轨迹、幼体存活率或成体体型产生显著影响。个体并未通过“补偿生长（compensatory growth）”（即低食物处理结束后加快生长）来弥补生命早期的不良营养条件，但它们通过延迟成熟表现出“追赶生长（catch-up growth）”。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食物日粮条件下，近交也未对生长或成体体型产生可检测的影响。据此，本团队此前另一项研究中揭示的、由雄性繁殖成功率下降导致的近交长期成本，似乎与当前研究中成年雄性体型或生长速率相关的近交衰退无关。