Understanding temperature adaptation in tropical insects

Lead Research Organisation: University of Sheffield
Department Name: School of Biosciences

Abstract

Understanding thermal adaptation is a priority if we wish to understand and mitigate the impacts of climate change. Organisms' current tolerances and their ability to adapt or move to new areas will determine whether they survive warming environments or not. There is currently a relative paucity of data on thermal adaptation in tropical as compared to temperate species. Tropical insects make up a large proportion of the Earth's biodiversity, but little is currently known about their ability to respond to climate change.

We propose to use a well-studied group of tropical ectotherms, the Heliconius butterflies, to assess thermal adaptation across altitudinal gradients, to determine the contributions of genetic and environmental variation to these traits, and to identify the underlying genetic loci. Within Heliconius there are several instances of subspecies that also show structuring by altitude. Using population genomic sequence data and the reference genome for H. melpomene we recently showed that three subspecies pairs of H. melpomene and H. erato across altitudinal gradients exhibit divergence in regions of the genome that contain candidate genes for thermal adaptation such as metabolic enzymes and heat shock proteins. We will characterise the ecophysiology of these species, through characterisation of the physiological differences found between populations and species. Within Ecuador these species have parallel altitudinal clines on the east and west side of the Andes allowing us to assess the replicability of any trends we identify.

Temperature can also be an important factor in delimiting the ecological niche and so in driving divergence and speciation. Research on the Heliconius system has largely focussed on the role of colour patterns in driving divergence between populations and species, but habitat differences are also present and thought to contribute to divergence. For example, the species pair H. melpomene and H. cydno on the western side of the Andes, which have become a classic system in speciation research, show divergent altitudinal ranges. The phenotypic differences driving divergence in habitat use have yet to be investigated, but physiological adaptations to temperature seem highly likely. Therefore, we will experimentally test for thermal adaptation differences between the sister clades H. melpomene and H. cydno/timareta, to assess the importance of temperature in determining altitudinal range and species distributions in these species.

We will use the extensive genomic resources available for Heliconius to perform genome scans and detailed association mapping analyses to identify loci responsible for thermal adaptation within H. melpomene. Identifying these loci will then allow us to address the question of whether genes involved in temperature adaptation show evidence for either introgression or divergent selection between species. Sharing of temperature adaptation genes between species could allow rapid adaptation to novel environments, while divergence would suggest thermal adaptation is important in maintaining species identities.

Research on Heliconius has flourished in recent years leading to many insights into the process of divergence and speciation in the genome. However, the ecological characters investigated have remained largely restricted to colour pattern. This project will be a major step towards establishing Heliconius as a more comprehensive model system for ecological genetics, making use of the existing knowledge, genomic resources and techniques available in this system to investigate broader ecological issues in the tropics.

Planned Impact

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 science education

1.3 This research will benefit wider society through increased engagement with science and conservation issues

2. How will they benefit from the research?

2.1 Losses of biodiversity due to habitat destruction and climate change are a major concern. Tropical insects make up a large and under-appreciated proportion of this diversity. Understanding adaptation to temperature and genetic structure in these species is necessary to predict how they may respond to climate change. This work will be among the first to directly address this. In particular in will help us understand the importance of altitudinal gradients in driving and maintaining genetic variation in temperature responses. Therefore results of this work may be useful for informing conservation policy and practice to conserve biodiversity, for example by providing information that can be taken into consideration when identifying priority tropical forest areas for conservation.

2.2 Temperature adaptation in butterflies is an excellent system for teaching the principles of evolution because of the appeal of butterflies and the general awareness of the issue of climate change. Our research will give a concrete example showing how environmental and genetic variation can lead to adaptive change. It will therefore provide an excellent evolutionary example for the classroom and one that would link across different areas of the curriculum.

2.3 Butterflies hold a unique place in the public imagination as evidenced by the coverage that previous Heliconius work has received in the popular press, and the enthusiastic responses we have received at outreach events. Butterfly research has been at the forefront of understanding animal responses to climate change and there is a general awareness of resulting changes in UK butterflies. This research would build on that interest and awareness, engaging the public in both the UK and Ecuador with climate and deforestation issues on a global scale and evolutionary biology more generally. The appeal of butterflies and tropical systems as well as the interest in climate change also means that this work has the potential to inspire young people to follow careers in science. This is of general benefit for innovation and society. Further, as the PI and visiting researcher are female scientists, this could be particularly beneficial in attracting women and girls into science.

Publications

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Montejo-Kovacevich G (2022) Repeated genetic adaptation to altitude in two tropical butterflies. in Nature communications

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Montejo-Kovacevich G (2021) Genomics of altitude-associated wing shape in two tropical butterflies. in Molecular ecology

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Montejo-Kovacevich G (2019) Altitude and life-history shape the evolution of Heliconius wings. in Evolution; international journal of organic evolution

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Montejo-Kovacevich G (2020) Microclimate buffering and thermal tolerance across elevations in a tropical butterfly. in The Journal of experimental biology

 
Description We have 5 major findings so far:
1) We have identified morphological differences between butterflies found at higher altitude and those found at lower altitude, both within and between species. This was published in the Journal Evolution. We have also extended this to determine that these differences are maintained when butterflies are rearer under common laboratory conditions and are therefore genetically determined and identified some candidate loci for difference in wing shape (published in Molecular Ecology).
2) We have characterised differences in microclimate in forest canopy and understory with elevation in forests on the East and West sides of the Andes in Ecuador. We then show that there are differences in thermal tolerance of Heliconius butterflies from high and low elevation populations and communities both within and between species. We find that the within-species differences are not fully maintained when the butterflies are raised in common conditions, suggesting that this difference is largely due to environmental factors (plasticity) rather than genetic differences between the populations.
3) We have identified genetic differences between populations from low and high elevation and found that some of these differences are being shared by interbreeding between populations and even species. This has important implications for how populations may respond to changing temperatures (Published in Nature Communications)
4) Combining common garden and reciprocal rearing experiments, we have identified genetic and environmental contributions to a range of phenotypic differences between populations from different elevations, including differences in developmental rate, size and wing colour. This is being prepared for publication.
5) We have identified differences in gene expression associated with exposure to different temperatures in 3 tropical butterfly species adapted to different thermal environments (analysis ongoing).
Exploitation Route The findings can be used to predict how populations of butterflies in Andes might respond to climate change. The genes and genetic pathways identified can be investigated in other insects, particularly tropical insects, to understand how these may respond to increasing temperatures.
Sectors Agriculture, Food and Drink,Education,Environment,Culture, Heritage, Museums and Collections

URL https://nadeau-lab.sites.sheffield.ac.uk
 
Description I have used this research project as an example in careers and outreach talks at schools in the UK. The research has been conducted in partnership with the Amazonian regional University, IKIAM, in Ecuador. Students and staff at IKIAM are collaborating on the project and have been using examples from the research in outreach and engagement with the local community.
First Year Of Impact 2019
Sector Education
Impact Types Cultural,Societal

 
Title butterfly collections 
Description Collection of wild and captive bred Heliconius butterflies 
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
Impact The collection will be used to explore the physical structures underlying variation in iridescence and its genetic control. Also being used by other research groups studying other aspects of population genetics, dispersal and community composition. Being used for a study of butterfly adaptation to altitude. 
URL https://heliconius.ecdb.io/Default.aspx#ViewID=Unit_ListView&ObjectClassName=EarthCape.Module.Core.U...
 
Description IKIAM 
Organisation Amazon Regional University
Country Ecuador 
Sector Academic/University 
PI Contribution Design and co-ordinate the research project Manage the project budget PDRA, PGRA and PhD student working on the project
Collaborator Contribution Provide access to facilities, including insectaries for butterfly rearing and two temperature-controlled chambers, to all staff and students of the University of Sheffield participating in the project. Hire a research technician to work on the project Help obtain all the necessary legal permits to allow researchers from the University of Sheffield and Ikiam to work and collect data in Ecuador, as well as to export samples. Support the Postdoctoral Research Associate (PDRA) and the Postgraduate Research Assistant (PGRA), hired by the University of Sheffield, to carry out the research and obtain visas and permissions to work in Ecuador Collaborate in the preparation of reports that include the activities in which Ikiam participates.
Impact Contributed to collection of biological specimens, which have been databased. Increasing the Profile of both Sheffield University and IKIAM University
Start Year 2017
 
Description In our time BBC radio 4 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Panel member on BBC Radio 4 programme "In Our Time" episode about hybrids
Year(s) Of Engagement Activity 2019
URL https://www.bbc.co.uk/programmes/m0009t41
 
Description School visit (Doncaster) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Event to encourage girls to pursure careers in science. Spoke to 2 group of about 30 girls in a mixed non-fee-paying school. Participants showed interest and engagement.
Year(s) Of Engagement Activity 2019