Vertebrates have repeatedly modified skeletal structures to adapt to their environments. The threespine stickleback is an excellent system for studying skeletal modifications, as different wild populations have either increased or decreased the lengths of their prominent dorsal and pelvic spines in different freshwater environments. Here we identify a regulatory locus that has a major morphological effect on the length of stickleback dorsal and pelvic spines, which we term Maser (major spine enhancer). Maser maps in a closely linked supergene complex that controls multiple armor, feeding, and behavioral traits on chromosome IV. Natural alleles in Maser are differentiated between marine and freshwater sticklebacks; however, alleles found among freshwater populations are also differentiated, with distinct alleles found in short- and long-spined freshwater populations. The distinct freshwater alleles either increase or decrease expression of the bone growth inhibitor gene Stanniocalcin2a in developing spines, providing a simple genetic mechanism for either increasing or decreasing spine lengths in natural populations. Genomic surveys suggest many recurrently differentiated loci in sticklebacks are similarly specialized into three or more distinct alleles, providing multiple ancient standing variants in particular genes that may contribute to a range of phenotypes in different environments.

脊椎动物不断改变骨骼结构以适应环境。三刺刺鱼是研究骨骼修饰的绝佳系统，因为不同的野生种群在不同的淡水环境中会增加或减少其突出的背刺和骨盆刺的长度。在这里，我们确定了一个对刺鱼背刺和骨盆棘的长度具有主要形态影响的调节位点，我们将其称为Maser （主要脊柱增强子）。脉塞映射在一个紧密相连的超基因复合体中，该复合体控制着第四号染色体上的多种装甲、进食和行为特征。海洋和淡水刺鱼的Maser天然等位基因有所不同；然而，在淡水种群中发现的等位基因也存在差异，在短刺和长刺淡水种群中发现了不同的等位基因。独特的淡水等位基因会增加或减少正在发育的脊柱中骨生长抑制剂基因斯钙素2a的表达，为自然群体中增加或减少脊柱长度提供了一个简单的遗传机制。基因组调查表明，刺鱼中的许多经常分化的基因座类似地专门化为三个或更多不同的等位基因，在特定基因中提供了多个古老的常备变体，这些变体可能有助于不同环境中的一系列表型。