Roberts Reade B, Moore Emily C, Kocher Thomas D
Department of Biological Sciences, North Carolina State University, 3510 Thomas Hall, Raleigh, NC, 27695, USA.
Keck Center for Behavioral Biology, North Carolina State University, 3510 Thomas Hall, Raleigh, NC, 27695, USA.
Mol Ecol. 2017 May;26(10):2625-2639. doi: 10.1111/mec.13975. Epub 2017 Jan 21.
Despite long-standing interest in the evolution and maintenance of discrete phenotypic polymorphisms, the molecular genetic basis of such polymorphism in the wild is largely unknown. Female sex-associated blotched colour polymorphisms found in cichlids of Lake Malawi, East Africa, represent a highly successful polymorphic phenotype, found and maintained in four genera across the geographic expanse of the lake. Previously, we identified an association with an allelic variant of the paired-box transcription factor gene pax7a and blotched colour morphs in Lake Malawi cichlid fishes. Although a diverse range of blotched phenotypes are present in Lake Malawi cichlid species, they all appeared to result from an allele of pax7a that produces increased levels of transcript. Here, we examine the developmental and genetic basis of variation among blotched morphs. First, we confirm that pax7a-associated blotch morphs result primarily from modulation of melanophore development and survival. From laboratory crosses and natural population studies, we identify at least three alleles of pax7a associated with discrete subtypes of blotched morphs, in addition to the ancestral pax7a allele. Genotypes at pax7a support initial evolution of a novel pax7a allele to produce the blotched class of morphs, followed by subsequent evolution of that pax7a blotched allele to produce additional alleles associated with discrete colour morphs. Variant alleles of pax7a produce different levels of pax7a transcript, correlating with pigmentation phenotype at the cellular level. This naturally selected allelic series should serve as a case study for understanding the molecular genetic control of pax7a expression and the evolution of sex-associated alleles.
尽管长期以来人们对离散表型多态性的进化和维持感兴趣，但这种多态性在野生环境中的分子遗传基础仍 largely unknown。在东非马拉维湖的丽鱼科鱼类中发现的与雌性性别相关的斑驳颜色多态性，代表了一种非常成功的多态表型，在该湖地理范围内的四个属中都有发现并得以维持。此前，我们在马拉维湖丽鱼科鱼类中发现了配对盒转录因子基因pax7a的一个等位基因变体与斑驳颜色形态之间的关联。尽管马拉维湖丽鱼科物种中存在多种斑驳表型，但它们似乎都源于pax7a的一个等位基因，该等位基因产生的转录本水平增加。在这里，我们研究了斑驳形态间变异的发育和遗传基础。首先，我们证实与pax7a相关的斑驳形态主要是由黑素细胞发育和存活的调节导致的。通过实验室杂交和自然种群研究，我们除了发现祖先pax7a等位基因外，还确定了至少三个与斑驳形态离散亚型相关的pax7a等位基因。pax7a的基因型支持一个新的pax7a等位基因最初进化产生斑驳形态类别，随后该pax7a斑驳等位基因进一步进化产生与离散颜色形态相关的其他等位基因。pax7a的变异等位基因产生不同水平的pax7a转录本，在细胞水平上与色素沉着表型相关。这个自然选择的等位基因系列应作为一个案例研究，用于理解pax7a表达的分子遗传控制以及与性别相关等位基因的进化。
