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

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.

1. Who will benefit from this research?

1.1 This research will benefit conservation policy makers and practitioners.

1.2 This research will benefit those working in applied uses of structural colours.

1.3 This research will benefit those working in science education, particularly those preparing educational materials, museum and live animal exhibits.

1.4 This research will benefit innovation and wider society by helping to inspire the next generation of scientists (particularly young female scientists).

2. How will they benefit from the research?

2.1 The work will shed light on the evolutionary process and in particular the importance of constraint. This will influence our understanding of how easily organisms can adapt to changing environments and so how best to mitigate human influences on habitats, including habitat destruction and climate change.

2.2 There have been many proposed technological uses for structural colour and much research effort in being channeled into finding ways to synthesise them. An understanding of how these structures are produced in natural systems is currently lacking. By addressing this question this research will provide information that could be used to find novel methods are artificial synthesis of such structures.

2.3 Butterfly wing colour patterns and mimicry are evolutionary examples that have captured the public imagination every since Bates, Darwin and Wallace first described them. Therefore the outcomes of this research will contribute to the public understanding of evolutionary biology and appreciation of the natural world. I will seek to capitalise on this through public engagement activities and direct collaborations with schools to help to incorporate these examples into educational materials (see pathways to impact). In addition, Heliconius butterflies are frequently present in butterfly houses and exhibits. Therefore, the managers of these could increase the educational content of such exhibits by including elements of this research.

2.4 Science is a crucial driver of innovation and the economy. In recent years there has been a decline in interest in science among young people. The vivid and appealing evolutionary examples in this research make it an excellent system for inspiring young scientists. From the outset of the project, I will undertake outreach activities (see pathways to impact). I particular I hope this will help to inspire young women, who are still grossly under-represented in the scientific community, to take an interest in future careers in science.