Characterising the genetic architecture and fitness effects of rapid morphological diversification.

Lead Research Organisation: Oxford Brookes University
Department Name: Faculty of Health and Life Sciences

Abstract

Explaining the diversity of life on earth has long been a goal of biology. However we understand very little about the changes in the genome that underlie variation in the way cells read, interpret and execute the instructions coded in that genome, and how such changes interact in order to produce an organism with a modified shape or size. There is also a paucity of knowledge about whether the genetic changes that affect a given trait also cause in differences in other traits, and even less about their effect on reproductive success.

Male sexual characters are often among the first traits to diverge between closely related species. Characterising the genes involved, their interactions, the evolutionary forces involved and fitness consequences of this rapid evolution offers a great opportunity to understand the processes of animal diversification, reproductive isolation and the evolution of new species.

Among Drosophila species, males exhibit striking differences in genitalia morphology. The posterior lobes and claspers, in particular, differ in size, shape and bristle number between species. Moreover these structures are important for proper attachment of the male to the female during mating. Despite previous mapping studies, none of the genes involved have been identified, which is required to characterise how the underling genetic changes interact, if they also cause differences in other traits, and their effect on reproductive success.

Therefore, in this proposal, we aim to identify the genes underlying variation in the morphology of the clasper and posterior lobe between D. mauritiana and D. simulans. Our preliminary results have already identified several small genomic regions responsible for a large proportion of the variation in posterior lobe and clasper. Here we propose to investigate the role of candidate genes found in those regions of the genome during clasper and posterior lobe development in the model D. melanogaster, and then verify their direct role in the evolution of variation in these structures between D. mauritiana and D. simulans.

Once we have identified the genes responsible for the differences in genital morphology, we will survey natural variation by sequencing those genes in several strains of each species and test if these sequences have evolved under directional selection or just by chance.

Interaction between genes can either facilitate or delay the evolution of a given trait, Therefore, we will test how the D. mauritiana and D. simulans alleles interact with other genomic regions underlying variation in the clasper and posterior lobe to evaluate the contribution of additive and/or non-additive (epistatic) genetic interactions to the divergence of these two traits. Furthermore we will test if the causative genes affect gene expression or morphology, at other stages of development and in other tissues (pleiotropic effects), to evaluate these changes in the wider context of animals development and how this evolves. Finally we will test if the changes in posterior lobe and clasper morphology affect reproductive success.

Our work will serve as platform for further research to test the generality our findings on genital evolution and broaden our knowledge of how the genetic mechanisms underlying developmental programs integrate genotypic information to specify the phenotype and help explain how the vast organismal diversity in the natural world has evolved. Moreover, our study of male genitalia diversity may also help to address questions regarding the genetic architecture of quantitative traits including the role of epistasis and any pleiotropic effects. Given both the prominence of studies relating genes to appearance and behaviour and our general fascination with animal diversity, research such as ours offers an opportunity to not only appreciate this diversity, but explain the genetic nuts and bolts that have shaped it.

Planned Impact

This proposal will have a beneficial impact on individuals and organisations in both private and public sectors through three main mechanisms. First, via collaboration and staff training. Second, through engagement with the children, teachers and members of the public about the aims and importance of our research, and finally basic science in general.

Collaboration and Training
The new collaborations that will be built in the course of this proposal will strengthen ties between two UK universities and between the UK and the USA, which will catalyse further exchange of knowledge in the future benefitting all the countries, institutions and individuals involved. Moreover, scientific progress is often driven by multidisciplinary approaches and consequently there is great demand for scientists with training in different fields and who can approach problems from different perspectives. This multidisciplinary philosophy and skills development is accounted for in this proposal, which relies upon evo devo, population genetics, bioinformatics and systems approaches, and through collaborations with experts in evolutionary biology and behavioural genetics. In addition to this broad scientific training provided, the RCI and technician will have access to a specific training program at OBU and will receive training in transferable skills including oral and written presentations, mentoring, computing, and management. Therefore, public sector areas such as education and private sector research will potentially benefit from the staff training and skills development in this project. The benefits of this training and support for the RCI will ultimately result in a researcher with transferable skills trained for a career in research, teaching or internationally competitive in other employment sectors. In addition, the technician will be trained in state-of-the-art techniques in genetics and molecular biology, and can then contribute to high quality research in academia or industry in the future. Academia and society generally will also benefit from this proposal because it will promote the career of a talented and well trained female RCI, and thus will contribute to widening opportunities for women in science. These opportunities will be maximised by the PI's participation in his departmental team responsible for reviewing and improving working practices for everyone, regardless of gender or ethnicity.

Engagement
Given the success of zoos and natural history museums, it is apparent that the general public is curious about animal diversity. This proposal aims to explore and compare part of the genetic program that builds animals and how this evolves to generate animals of different shapes and sizes.
This proposal, thus, represents an excellent opportunity to further engage children, teachers and the public in how such basic research impacts more applied areas of research such as human biology and medicine, thus widening their interest in evolution, genetics and development, and importantly, how this can impact circumstances in everyday life. Importantly, this also delivers a platform to convey simple evolutionary concepts to the public and call their attention to the pervasiveness of evolution in so many aspects of modern life such as combating bacterial antibiotic resistance and predicting influenza pandemics. Therefore, by engaging the public in the objectives and results of this project through our outreach activities, this proposal will inform and interest children and teachers about basic science, and improve communication between scientists and the public generally to the benefit of both. The general public will benefit from improved science education and clearer understanding of the objectives of basic science, which is likely to benefit charities that fund research from public donations. Science will benefit from a greater public understanding of basic research because this will positively influence funding and policy.
 
Description We have mapped genomic regions underlying differences in male genital morphology (clasper and posterior lobe) between Drosophila mauritiana and D. simulans to high resolution (Tanaka et al. (2015) Genetics). We then carried out RNA interference to test the function of about 100 of these genes in D. melanogaster to find functional candidate genes from among our positional candidates (Tanaka et al. (2015) Genetics). This has allowed us to identify approximately 25 new genes that regulate genital development and to shortlist candidate genes potentially underlying the diversification of genital morphology for further functional analysis using CRISPR/Cas9 in the focal species. We have since map several more regions underlying differences in the posterior lobes and claspers to high resolution and screened further genes using RNAi as well as optimised CRISPR/Cas9 in the focal species.
Exploitation Route Our findings will be of interest to other academics interested in developmental evolution and those interested in developmental regulation.
Sectors Education
 
Description The grant holder and researchers employed on the grant have highlighted the goals and outcomes of the project as part of their outreach activities including school visits, the Oxford Science festival and an event at Oxford Natural History Museum
Sector Education
Impact Types Societal
 
Description Activity stall at Narural History Museum Event 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Our activity introduced families to the diversity of insects and their relatives like spiders and centipedes, including those that live in our houses. This included exploring how the segmental structure of the bodies of these animals underlies the evolution of their different shapes and sizes.
Year(s) Of Engagement Activity 2017
 
Description Science Festival (Oxford) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact We hosted a stall at the Oxford Science Festival "Science in your world" event. During this event we described animal development and diversity to the general public using posters and hands-on activities.
Year(s) Of Engagement Activity 2015