The importance of gene flow in speciation of Heliconius

I propose to use modern high-throughput sequencing technologies coupled with ecological data to address one of the major questions in speciation research: the importance of gene flow in speciation. Speciation is the fundamental route to the generation of new species biodiversity. However, the importance of gene flow in speciation, and the role of selection in this process are not well understood. Gene flow can have two diametrically opposite influences on speciation:

1) Gene flow is an obvious hindrance to speciation as it will tend to break down co-adapted gene combinations and homogenize populations. Recent theoretical papers conceptualise the progress of species divergence in a four-phase model of islands of divergence amidst a sea of gene flow. While appealing, empirical support of this theoretical model of speciation remains elusive.

2) In some cases gene flow between taxa could trigger the formation of new species in a process known as hybrid speciation. However, there are few convincing examples of hybrid speciation, particularly among animals.

I will investigate these two effects of gene flow on speciation in Heliconius. Neotropical Heliconius butterflies have long been a model system for studying speciation owing to the the presence of taxa representing the entire speciation continuum from freely hybridizing races differing in wing patterning, through sympatric species that occasionally hybridize in nature, to fully reproductively isolated species. With the publication of the first Heliconius genome sequence, Heliconius now provides one of the few systems suited for comprehensively studying the importance of gene flow in speciation.

The proposed research focuses on three Heliconius species: H. elevatus, H. pardalinus and H. melpomene. My recent work has demonstrated the introgression of colour pattern genes between the species H. melpomene and H. elevatus. H. elevatus is genetically very closely related to H. pardalinus, but the two are distinct species with largely overlapping distributions and known differences in behaviour. Preliminary data suggest that the genome of H. elevatus is of hybrid origin, comprising H. melpomene colour pattern genes embedded in a background of H. pardalinus.

I will gather whole genome sequence data and carry out ecological field experiments on races of H. elevatus and its two putative parental species, H. pardalinus and H. melpomene. These resulting data will allow us to test hypotheses on the importance and extent of gene flow in speciation. I have four main objectives:

1) My taxon sampling will allow empirical testing of the islands-of-divergence hypothesis of speciation with gene flow.
2) I will genetically map traits responsible for the early stages of speciation in H. elevatus and H. pardalinus.
3) The experimental design will allow rigorous testing of whether H. elevatus formed as a result of hybrid speciation.
4) I will test whether H. elevatus was formed from a single or multiple introgression events from different races of H. melpomene.

Speciation is a basic evolutionary process that shapes all ecosystems, and the findings of this research will add significantly to our understanding of the genomic processes underlying the formation of new species.

The proposed research will provide impact in two areas:
1) Contributing to increasing public awareness and understanding of science
2) Training of skilled people for non-academic professions.

1) Contributing to increasing public awareness and understanding of science.
Colourful tropical butterflies are charismatic organisms that are popular with the public. As such they are perfect species for public education about evolution, biodiversity, conservation, genetics, genomics and science in general. As a model system for studying speciation, Heliconius butterflies are also ideal for disseminating the research to professional biologists, school pupils, postgraduate students and undergraduate students. The following beneficiaries have been identified:

1a) Butterfly houses and museums - Heliconius butterflies are relatively easy to keep in captivity, they are ubiquitous species in 'tropical butterfly houses' in the United Kingdom and the rest of the world. During the grant period, at least two butterfly houses (Tropical Butterfly House and Magic of Life Butterfly House) will benefit directly from the proposed research through professionally designed and produced posters. If these posters prove to be popular, in the medium term (3-5 years) there will be a good case for widening distribution of these and further posters to butterfly exhibits and museums throughout the UK and other countries.

1b) School pupils - During the grant period we will visit Bootham College (York) twice a year to provide short research talks and talks on curriculum-related biology topics to 14-16 year old students.

1c) Outreach in Peru - We will provide information about Heliconius butterflies to the Peruvian public through our links with the local Peruvian NGO URKU.

1d) Undergraduate and postgraduate - Heliconius butterflies are already examples of speciation and mimicry in evolutionary biology textbooks at both undergraduate and postgraduate levels within the UK and internationally. The results produced will be incorporated immediately into second and third year teaching modules at York. In the medium term (3-5 years) the results produced in the course of the proposed research are likely to further increase the value of the Heliconius system for teaching evolutionary principals.


2) Training of skilled people for non-academic professions.
The proposed research will providing scientific skills training, transferable to non-academic professions, for the people involved in the project. The following beneficiaries have been identified:

2a) Post doctoral research assistant - Project management in a field setting, managing the latest sequencing technologies, bioinformatics, data-handling, statistical analysis and communication skills. These skills are widely transferable to any research area including applied biology, and have wide applicability in industry as well as non-scientific fields.

2b) Technician - Making libraries for high-throughput sequencing. This valuable wet lab experience will be increasingly in demand in the coming years in many non-academic molecular biology sectors.

2c) Field assistant - Tropical fieldwork experience and training in the scientific method.

2d) Final year undergraduate students - A total of nine undergraduate students will receive training in aspects of bioinformatics, statistics and the scientific method through six month final-year research projects using data generated in this proposal.