Testing repeatability in the evolution of complex traits: the genetics of convergent structural colour

进化过程的可重复性如何？相同的进化路径是否总是被用于达到给定的终点？最近对野生环境中负责适应的基因的研究表明，某些基因特别有可能成为选择的目标。这可能是因为这些基因对被选择的性状有很大的影响，而对其他性状没有影响。然而，一些适应性差异是由于许多基因的综合作用。在这些情况下，我们不太清楚进化过程的可重复性如何，以及在进化相似的特征时是否会使用相同的基因组。趋同于相似表型的生物体可以帮助我们回答这些问题，因为它们代表着走向同一终点的独立进化轨迹。Heliconius蝴蝶是进化趋同最显著的例子之一。它们有鲜艳的颜色图案，可以警告捕食者它们的恶心，而且有几个物种的颜色图案几乎相同。这减少了捕食者必须学习的模式的数量，从而使所有共享模式的个体受益。这提供了一个“自然实验”来测试在进化相同的表型时是否使用了相同的基因。该系统的结果表明，两个物种独立地使用了相同的主要开关基因来产生相同的颜色图案。然而，这些基因并不能解释所有的进化变化。这两个物种的一些种群进化出了由许多基因控制的彩虹蓝色。我将确定这些基因是什么，以及它们在不同物种之间是相同还是不同。如果相同的基因在两个物种中被独立使用，这将表明进化是可预测的，所以当进化出某种特征时，一组特定的基因很可能总是被使用。另一方面，如果使用不同的基因，那么这将表明由多个基因控制的性状在其进化中更加灵活。考虑到许多重要的特征是由大量基因控制的，比如体型和行为，这对我们理解进化过程具有重要意义。如果进化可以通过多种途径到达同一个终点，那么它可能比限制使用特定基因更容易、更快。像孔雀和蓝色大闪蝶这样的彩虹色是动物王国中最壮观的颜色之一。它们是由亚微米级结构产生的，这种结构引起光的相干散射，而不是由颜料吸收光。虽然这些颜色经常用于动物信号，但目前对控制它们的基因一无所知。确定在Heliconius中负责控制这些颜色的基因将为这些性状的遗传和发育提供一些启示，并为其他系统中的控制这些性状提供候选基因。人工复制这些类型的颜色，用于防伪和先进的材料技术，具有商业利益。如果能够理解这些特征的遗传基础，这将是理解这些结构如何在自然系统中组装的重要一步，这将允许如何从一个全新的角度来处理具有类似特性的合成材料的问题。

How repeatable is the evolutionary process and would the same evolutionary pathways always be used to reach a given end-point? Recent work on the genes responsible for adaptation in the wild suggests that certain genes are particularly likely to be the target of selection. This may be because these genes have large effects on the traits under selection without having effects on other traits. However, some adaptive differences are due to the combined effects of many genes. In these cases it is less clear how repeatable the evolutionary process will be and if the same sets of genes will be used when evolving similar traits. Organisms that that have converged on similar phenotypes can help us to answer these questions because they represent independent evolutionary trajectories towards the same endpoint.The Heliconius butterflies are one of the most striking examples of evolutionary convergence. They have bright colour patterns that warn predators of their distastefulness and several species have converged on near identical colour patterns. This reduces the number of patterns that predators have to learn, so benefitting all individuals that share them. This provides a "natural experiment" in which to test whether the same genes are used when evolving the same phenotypes. Results from this system have shown that the same major switch genes have independently been used in two species to produce the same colour patterns. However, these genes do not explain all of the evolutionary changes. Some populations of these two species have evolved an iridescent blue colour, which is controlled by many genes. I will identify what these genes are and if they are the same or different between species. If the same genes have been independently used in both species it will suggest that evolution is predictable, so when evolving a certain trait a particular set of genes are likely to always be used. On the other hand if different genes are used then it will suggest that traits that are controlled by multiple genes are more flexible in their evolution. Given that many important traits are controlled by large numbers of genes, such as size and behaviour, this has important implications for our understanding of the evolutionary process. If evolution can proceed down multiple routes in order to arrive at the same endpoint, then it is likely to be easier and faster than if it is constrained to use particular genes. Iridescent colours like those of the peacock and blue morpho butterfly are some of the most spectacular in the animal kingdom. They are produced by sub-micron-scale structures that cause coherent scattering of light, rather than the absorption of light by pigments. Although these types of colours are often used in animal signalling, nothing is currently known about the genes controlling them. Identifying the genes responsible for controlling these colours in Heliconius will shed some light on the genetics and development of these traits and provide candidate genes for their control in other systems. There is commercial interest in replicating these types of colours artificially, for use in anticounterfeiting and advanced materials technologies. If the genetic basis of these traits can be understood, this will be an important step towards understanding how such structures are assembled in natural systems, which will allow the problem of how to synthesise materials with similar properties to be approached from an entirely new angle.