Vega-Trejo Regina, Head Megan L, Jennions Michael D
Division of Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Acton, ACT, 2601, Australia.
BMC Evol Biol. 2016 Apr 1;16:68. doi: 10.1186/s12862-016-0640-1.
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.
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.
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.
近亲繁殖通常与后代适应性下降（“近亲繁殖衰退”）相关。此外，一般认为在压力环境下近亲繁殖的负面影响会加剧。这种基因与环境的相互作用已在许多分类群中不同环境条件下进行了探究。这些研究通常在成年期或个体整个生命过程中操纵环境条件。很少有研究测试仅在发育期间经历的压力环境随后如何影响近亲繁殖对成年性状的作用。
我们对近交和远交的幼年东部食蚊鱼（盖氏食蚊鱼）的饮食进行了实验性操纵（对照饮食与低食物量饮食），为期三周（第7 - 28天），以测试生命早期经历可能有压力的环境是否会影响它们随后的生长和成年表型。对照饮食是标准的实验室食物方案，而低食物量饮食组的鱼所获得的食物量不到该量的25%。出乎意料的是，尽管样本量很大（237个家系，908个后代），并且全同胞交配产生的近交后代的全基因组杂合度量化降低了23%（f = 0.25），但近亲繁殖及其与早期饮食的相互作用均未影响生长轨迹、幼体存活或成年体型。个体并未通过表现出“补偿性生长”（即在低食物处理结束后生长加快）来缓解生命早期的不良开端，但它们通过延迟成熟表现出“追赶生长”。然而，近亲繁殖对追赶生长的程度没有影响。
即使在应会加剧近亲繁殖衰退的低食物量饮食条件下，也未检测到近亲繁殖对生长或成年体型有影响。因此，我们在另一项研究中所显示的由于雄性繁殖成功率降低导致的近亲繁殖的长期成本，似乎与成年雄性体型的近亲繁殖衰退或本研究中报告的生长速率无关。
