Understanding the genetic mechanisms of phenotypic plasticity in insect migration

Lead Research Organisation: Rothamsted Research
Department Name: Agro-Ecology

Abstract

Each year billions of insects migrate thousands of kilometres in search of food, shelter and places to breed. Embarking on such an arduous journey requires physiological, behavioural and morphological adaptations encoded by multiple genes. For many insects, migration is 'switched on' in anticipation of deteriorating habitats, allowing populations to succeed in the face of environmental stress. This ability to respond to environmental cues in a single generation requires a flexible genetic basis that triggers migratory behaviour and is highly likely to be due to changes in gene expression (the process of using genetic information to produce functional proteins) based on similar behavioural plasticity in other insects. The specific genes and biochemical processes which contribute to this phenomenon are poorly understood. This project will address this knowledge gap by studying the genetic basis of migration in response to environmental cues using the global insect pest, Helicoverpa armigera. H. armigera is a noctuid moth present throughout much of Asia, Africa, the Middle East and Europe and is capable of infesting over one hundred host plants including many crops, with the caterpillar stage causing damage through direct feeding. It is the ability of H. armigera to migrate thousands of kilometres between host crops that make it such a major pest. Characterising migration in the laboratory in any organism is not easy. However, by using a computerised tethered flight system, designed and built at Rothamsted Research, it is possible to fly up to 32 moths per night and electronically record the distance, time and speed of each individual flight. This permits an accurate assessment of flight performance which can be used as a proxy for migratory versus sedentary behaviour. The flight propensity of H. armigera collected directly from host plants in China and Greece has previously been characterised. Using a technology called RNA-seq (a high-throughput sequencing tool which determines both the full sequence and the number of RNA molecules present in each sample), over 200 genes have been identified that are differentially expressed between migratory and sedentary flight phenotypes. Many of these genes have potential roles in processes associated with migration biology including flight muscle, the metabolism and hormonal stimulation. It is not known, however, which genes drive facultative migratory behaviour or how their expression is affected by environmental stimuli. The initial objective of this proposal will be to expose larvae of H. armigera to one of three environmental cues (density, photoperiod and nutrition) that are important migratory triggers in noctuid moths. The adults from each of these experiments will be flown on the flight mills to determine the impact of each cue on flight ability. The expression of 50 of the most promising candidate genes will be quantified - from the 200 genes identified using RNA-seq - in individual moths to determine those genes that show the strongest association with flight in response to each cue. RNA interference (the delivery of double-stranded RNA into a cell to inhibit gene expression) will be used to silence the five genes that explain the greatest proportion in flight propensity according to their expression patterns and examine their role in migration on the flight mills. Finally, the same five genes will be expressed in a second organism, the fruitfly (Drosophila melanogaster), to see whether they induce increased flight performance on a modified set of flight mills designed for smaller insects. The combination of these techniques will contribute greatly to our understanding of the genetic basis of migration in H. armigera, and in particular, migration in response to environmental cues. The results will be applicable to other important migratory moths and will set the benchmark for this area of research for the foreseeable future.

Technical Summary

Migration is an essential life-history strategy for several of the world's most damaging agricultural insect pests. For many insects, migration occurs in anticipation of deteriorating habitats allowing populations to succeed in the face of spatial and temporal environmental variability. This facultative behaviour, expressed in a single generation, requires phenotypic plasticity in response to environmental stimuli that is likely to be driven by changes in gene expression. The specific genes involved, however, remain largely unknown. The proposal will fill this knowledge gap in one of the most important and invasive crop pests, the cotton bollworm moth (Helicoverpa armigera). By combining state-of-the-art phenotype characterisation (tethered flight) with forefront genomic and post-genomic technologies the overall aim of the project is to determine the relative contribution of a set of migratory candidate genes - previously identified using RNA-seq - on adult flight activity in response to key sensory cues for insect migration experienced during the larval stage. Three environmental factors (density, photoperiod and nutrition) will be manipulated in the laboratory and the effect on flight phenotypes determined. The contribution of a core set of 50 candidate genes on flight performance will be deciphered using quantitative PCR (qPCR) to measure gene expression in insects from a single family line of H. armigera exposed to each environmental treatment. The five genes that explain the greatest proportion of phenotypic variance in flight will be 'silenced' using RNA interference (RNAi) and the impact of gene knockdown on flight assessed. Finally, functional validation of each gene will be performed by transgenic over-expression in Drosophila and the effect on flight performance assessed using a modified set of flight mills. The results generated from this project will be applicable to other noctuid moth pests and contribute to predictive models for pest forecasting.

Planned Impact

The scientific output from this proposal will have economic and societal benefits for the agricultural sector, the crop protection industry, academic stakeholders, collaborating institutes and the wider public. The rationale of the proposal is designed to fill a clear gap in our knowledge - the genetic control of migration in insect pests - using one of the most important pests of global agriculture Helicoverpa armigera as a model species. In the first instance, the project will benefit the agricultural sector using an understanding of migratory genotypes to improve the capacity of integrated pest management programmes to predict and model future outbreaks of invading migratory pests. The research offers a novel strategy for controlling damaging pests and contributing towards sustainable and improved crop yields in the future. Although the proposal will work exclusively with H. armigera, the benefits have both a national and international perspective, as many noctuid moths (including H. armigera) are important or potential immigrant pests into the UK, and the findings from this work will be relevant to other species within this group. The dispersal ability of insect pests has a significant consequence for the spread of insecticide resistance genes (including resistance to Bt cotton in the case of H. armigera) and this research will have clear benefits to academic groups and the crop protection industry trying to limit the evolution of resistance. Results from this project will be disseminated through peer-reviewed publications (at least three open access papers by December 2018), two international conferences (September 2016 & November 2018) and one national conference (Summer 2018) and visits to collaborating institutes (supported by the project). This proposal is at the forefront of a new research field, that of 'migratory genomics', and will be of considerable interest to an international migration research community. The findings will be circulated as widely as possible and facilitated by Dr Chapman's (leader of the Insect Migration and Spatial Ecology Group) extensive network in this area. The project will develop a wide range of molecular techniques which will provide novel resources for H. armigera research including qPCR assays, RNAi and transgenic expression of H. armigera genes in Drosophila.

The research will also appeal to entomology and Lepidopteran enthusiasts and appropriate platforms will be used to share the outcomes and ideas from this work. I aim to target this audience at the annual Royal Entomological Society conference in the summer of 2018. There is a great deal of public interest in animal migration. I will therefore conduct at least one public engagement activity (Summer 2016) to highlight this area as a fascinating part of natural history that is, in some cases (e.g. the monarch butterfly) currently under threat due to climate change. The research also provides an ideal means to inspire young scientists about an exciting area of biology and I will conduct one schools activity (by December 2017) which will hopefully encourage school children to think about a career in biology. Finally, I will write one 'popular science' article (e.g. The Biologist) (by December 2018) to further disseminate the work to a wider non-specialist audience.

Publications

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Description The award has helped identify key genes that are responsible for increasing flight performance in important migratory insect pests. These genes are switched on in the migratory animal - in this case the cotton bollworm moth, Helicoverpa armigera. By switching on one of the key genes in the flight muscle of the model organism, Drosophila melanogaster, this insect flew further and faster on a system designed to test insect flight performance - the tethered flight mill. The system was developed as part of the award and can be applied to other insect pests including those of human diseases (e.g. mosquitoes). To determine the impact of the environment on migration (using flight activity as a proxy) moths were flown in response to stressful conditions during the larval stage; (i) nutrition deficiency and (ii) overcrowding. Nutrition (or a lack of) had the largest effect with starved insects flying further as adults while the impact of over-crowding was mixed depending on the origin of H. armigera. This shows that the environment can play a large role on flight performance even when 'experienced' at the juvenile (larval) stage. Finally, field-collected moths from an agricultural site in Central China were flown on tethered flight mills during the migratory season to determine the variation in flight activity of individuals captured whilst on their journey. The DNA of these individuals has been sequenced to determine whether their flight activity is associated with mutations that have been previously been implicated in long-distance flight.
Exploitation Route Academic. Insect migration genomics is a relatively new field of science and this is the first project to tackle this area using a combination of behavioural and genomic technologies. The findings, and specifically the candidate genes for long distance flight, provide genetic targets for a fully understanding of this important trait in crop pests. The experimental design and assays (tethered flight) can be adopted by other researchers in this growing field. Non-academic. The award has highlighted the importance of migration and movement in Helicoverpa armigera and other notcuid moth pests - this is particularly relevant in the Americas where H. armigera has recently invaded and is spreading at an alarming rate causing significant damage to host crops. Insect movement influences the success of integrated pest management and the results from this work show that environment plays a fundamental role in driving movement behaviour. Future work should focus on the impact of temporal and spatial environmental patterns and how they drive migration in this pest in agricultural landscapes.
Sectors Agriculture, Food and Drink

 
Description CSIA seed-funding award (Rothamsted Research)
Amount £22,500 (GBP)
Organisation Newton Fund 
Sector Public
Country United Kingdom
Start 10/2016 
End 03/2018
 
Description Envision: Developing next generation leaders in environmental science
Amount £8,750 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 10/2017 
End 03/2021
 
Title Tethered flight system for 'micro insects' 
Description The tethered flight system is developed for insects up to 5 mm in size. The system can house up to eight insects simultaneously in which insects fly in rotation around a central axle. The speed and duration of individual flights are recorded electronically to determine flight potential. The system can be used to determine aspects on the physiology, biochemistry and genetics of insect flight. 
Type Of Material Technology assay or reagent 
Year Produced 2017 
Provided To Others? No  
Impact Transgenic Drosophila over-expressing a gene with a known role in flight physiology fly further and for longer on the tethered flight system compared with control insects. The results validate the role of a candidate gene in long-distance flight in a migratory pest insects. The assay is now being tested for understanding the flight behaviour of disease-carrying mosquitoes. 
 
Description China partnerships 
Organisation Chinese Academy of Agricultural Sciences
Country China 
Sector Academic/University 
PI Contribution I visited the Chinese Academy of Agricultural Sciences (CAAS), Henan Academy of Agricultural Sciences (HAAS) and Nanjing Agricultural University (NAU) in July 2016 as part of a group of a scientists from Rothamsted to discuss a seed-funding grant application and visit field sites for future experimental work. As part of the visit I participated in a symposium on insect migration in China giving a talk on my work. I will provide expertise in behavioural assays at HAAS in June 2017 as part of one of the objectives of the seed-funding grant. Fieldwork completed in June/July 2017 by myself, research assistant and field technician. Insect samples collected, DNA extracted and sequencing completed per objectives of the award.
Collaborator Contribution HAAS will host experimental work in June 2017 and provide additional staff and logistical support. Members of CAAS and NAU will provide scientific expertise in insect migration in China and contribute to reports/publications from this work.
Impact 'Chasing the high-fliers: Aerial sampling and flight capacity of high-flying migrant insect pests in China' Centre for Sustainable intensification of Agriculture (CSIA; Rothamsted-China partnership funded by Newton Fund) seed-funding project. Fieldwork at HAAS as part of this project due to start June 2017. Fieldwork complete June/July 2017. Project objectives complete with the exception of DNA sequencing analysis.
Start Year 2016
 
Description China partnerships 
Organisation Henan Academy of Agricultural Sciences
Country China 
Sector Academic/University 
PI Contribution I visited the Chinese Academy of Agricultural Sciences (CAAS), Henan Academy of Agricultural Sciences (HAAS) and Nanjing Agricultural University (NAU) in July 2016 as part of a group of a scientists from Rothamsted to discuss a seed-funding grant application and visit field sites for future experimental work. As part of the visit I participated in a symposium on insect migration in China giving a talk on my work. I will provide expertise in behavioural assays at HAAS in June 2017 as part of one of the objectives of the seed-funding grant. Fieldwork completed in June/July 2017 by myself, research assistant and field technician. Insect samples collected, DNA extracted and sequencing completed per objectives of the award.
Collaborator Contribution HAAS will host experimental work in June 2017 and provide additional staff and logistical support. Members of CAAS and NAU will provide scientific expertise in insect migration in China and contribute to reports/publications from this work.
Impact 'Chasing the high-fliers: Aerial sampling and flight capacity of high-flying migrant insect pests in China' Centre for Sustainable intensification of Agriculture (CSIA; Rothamsted-China partnership funded by Newton Fund) seed-funding project. Fieldwork at HAAS as part of this project due to start June 2017. Fieldwork complete June/July 2017. Project objectives complete with the exception of DNA sequencing analysis.
Start Year 2016
 
Description China partnerships 
Organisation Nanjing Agricultural University
Country China 
Sector Academic/University 
PI Contribution I visited the Chinese Academy of Agricultural Sciences (CAAS), Henan Academy of Agricultural Sciences (HAAS) and Nanjing Agricultural University (NAU) in July 2016 as part of a group of a scientists from Rothamsted to discuss a seed-funding grant application and visit field sites for future experimental work. As part of the visit I participated in a symposium on insect migration in China giving a talk on my work. I will provide expertise in behavioural assays at HAAS in June 2017 as part of one of the objectives of the seed-funding grant. Fieldwork completed in June/July 2017 by myself, research assistant and field technician. Insect samples collected, DNA extracted and sequencing completed per objectives of the award.
Collaborator Contribution HAAS will host experimental work in June 2017 and provide additional staff and logistical support. Members of CAAS and NAU will provide scientific expertise in insect migration in China and contribute to reports/publications from this work.
Impact 'Chasing the high-fliers: Aerial sampling and flight capacity of high-flying migrant insect pests in China' Centre for Sustainable intensification of Agriculture (CSIA; Rothamsted-China partnership funded by Newton Fund) seed-funding project. Fieldwork at HAAS as part of this project due to start June 2017. Fieldwork complete June/July 2017. Project objectives complete with the exception of DNA sequencing analysis.
Start Year 2016
 
Description Public Event (Rothamsted Research) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The Public Event was held at the Rothamsted Conference Centre (13th October 2016) and was titled 'Insect and bird migration: revealing the mysteries of flight'. The event was composed of a series of four talks and an exhibition of the latest technologies used by the research group at Rothamsted to understand insect migration. As part of the event I gave a a talk ('Calories, clocks and a compass: ingredients for an insect migrant') and participated in a Q&A session with the general public. Over 200 people attended, mainly from the local area (Hertfordshire), with the intended purpose of highlighting current ongoing research at the institute. The general feedback from the public was positive and there was plenty of interaction during the Q&A.
Year(s) Of Engagement Activity 2016
URL http://www.rothamsted.ac.uk/events/insect-bird-migration-revealing-mysteries-flight
 
Description Radio interview 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Media (as a channel to the public)
Results and Impact Appeared on Radio Verulam (St Albans based radio station) to discuss research on insect migration at Rothamsted.
Year(s) Of Engagement Activity 2016
 
Description Reddit Ask Me Anything 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I participated in the Reddit Science Ask Me Anything series (9th May 2016) to discuss my work on the genetics of insect migration. The platform allows anyone to ask about a research topic online and the host responds to as many questions as possible during a given time. AMA has a global audience and allows a large number of people to view the debate. A total of 25.5k users clicked through the answers to the questions posed and the AMA received 5800 votes. The purpose of the AMA is to reach as wide an audience as possible to disseminate the research.
Year(s) Of Engagement Activity 2016
URL https://www.reddit.com/r/science/comments/4ij3xj/science_ama_series_im_chris_jones_here_to_talk/d2yn...