Periodic Reporting for period 3 - SpeciationBehaviour (The genetic and neural basis of reproductive isolation)
Reporting period: 2023-01-01 to 2024-06-30
The evolution and maintenance of species diversity relies on barriers to gene exchange between populations. Although these barriers can take several forms, many closely related animals remain separate not because they fail to produce viable offspring, but because they ‘choose’ not to mate in the first place. Our project aims to understand how and why these behavioural barriers emerge, both during development and across evolutionary time.
We study the genetics, brains and behaviours of South American Heliconius butterflies. Importantly, past Heliconius research provides a robust ecological framework. In particular, Heliconius have bright warning patterns, which differ between populations, and which are used by males to recognise females of their own species. Heliconius species also differ in habitat use, and we predict that both these ecological axes drive adaptation in the sensory systems and brain.
Establishing the links across ecological, genetic and neural changes is crucial to our understanding of how behaviours, and the sensory systems through which they are mediated, adapt and ultimately contribute to speciation. To do this our project has four major objectives.
1) Characterise how the components of behavioural isolation vary with ecology. We are collecting data on i) different components of the nervous system, ii) mating signals, and iii) behaviours across populations to determine how these vary with major environmental transitions.
2) Assess the role of selection in shaping the sensory periphery and the brain. We are collecting data on components of the nervous system from hybrids to test i) whether the differences we observe across ecological transitions are the result of natural selection, and ii) whether these differences directly relate to changes in sensitivity and integration of visual and olfactory stimuli.
3) Determine the genomic architecture of behavioural isolation. In combination with DNA sequencing, our hybrid data will allow us to ask which regions of the genome contribute to differences in both the nervous system and mate choice behaviours.
4) Link behaviours to the action of individual genes. By combining data from the previous three objectives we hope to identify candidate genes underlying changes in behaviour, which we can target with state-of-the-art genome editing techniques. The ultimate aim is to link genes to behaviour, and the sensory systems through which they are mediated.
We study the genetics, brains and behaviours of South American Heliconius butterflies. Importantly, past Heliconius research provides a robust ecological framework. In particular, Heliconius have bright warning patterns, which differ between populations, and which are used by males to recognise females of their own species. Heliconius species also differ in habitat use, and we predict that both these ecological axes drive adaptation in the sensory systems and brain.
Establishing the links across ecological, genetic and neural changes is crucial to our understanding of how behaviours, and the sensory systems through which they are mediated, adapt and ultimately contribute to speciation. To do this our project has four major objectives.
1) Characterise how the components of behavioural isolation vary with ecology. We are collecting data on i) different components of the nervous system, ii) mating signals, and iii) behaviours across populations to determine how these vary with major environmental transitions.
2) Assess the role of selection in shaping the sensory periphery and the brain. We are collecting data on components of the nervous system from hybrids to test i) whether the differences we observe across ecological transitions are the result of natural selection, and ii) whether these differences directly relate to changes in sensitivity and integration of visual and olfactory stimuli.
3) Determine the genomic architecture of behavioural isolation. In combination with DNA sequencing, our hybrid data will allow us to ask which regions of the genome contribute to differences in both the nervous system and mate choice behaviours.
4) Link behaviours to the action of individual genes. By combining data from the previous three objectives we hope to identify candidate genes underlying changes in behaviour, which we can target with state-of-the-art genome editing techniques. The ultimate aim is to link genes to behaviour, and the sensory systems through which they are mediated.
Within the constraints imposed by the global pandemic, we have made significant progress towards meeting our four objectives.
1) Characterise how the components of behavioural isolation vary with ecology.
We have established breeding stocks for Heliconius populations spanning a major ecological transition from low-altitude humid to higher-altitude Andean forest in both Colombia and Ecuador. We have tested hundreds of butterflies in mate preference and other behavioural experiments, in addition to collecting pheromone samples and wing photographs for future analysis. Our results already show that populations spanning the humid-Andean forest transition show similar differences in development, flight and mate choice behaviours, consistent with natural selection. We have also collected volumetric data from the brains of 73 individual butterflies. These data reveal parallel shifts in brain structure across the humid-Andean forest transition in both Colombia and Ecuador consistent with selection, likely in response to forest type. Populations inhabiting more ‘complex’ humid forests have larger optic lobes, which are associated with visual processing.
2) Assess the role of selection in shaping the sensory periphery and the brain.
We have generated hybrids between populations spanning the environmental transition, and have started to collect tissue for volumetric brain and gene expression analyses. These will allow a sophisticated ‘quantitative genetics’ approach to explicitly test for selection on different components of the sensory systems. We have also run several assays on living butterflies, which reveal that populations from more complex humid forests can resolve finer detail from a given distance. In the next weeks we will start these and other assays on hybrids to determine how volumetric changes in the brain relate to changes in sensitivity and integration of stimuli, and also mating preferences.
3) Determine the genomic architecture of behavioural isolation.
To determine the genomic regions underlying differences in brain and behaviour, we have measured the mating preference of over 100 hybrids, and will begin collecting brain tissue in the coming weeks. We are on track to complete these experiments by the end of 2023.
4) Link behaviours to the action of individual genes.
We have now established Crispr/Cas9 genome editing protocols for Heliconius, potentially allowing us to validate candidate behavioural genes in the final years of the project.
1) Characterise how the components of behavioural isolation vary with ecology.
We have established breeding stocks for Heliconius populations spanning a major ecological transition from low-altitude humid to higher-altitude Andean forest in both Colombia and Ecuador. We have tested hundreds of butterflies in mate preference and other behavioural experiments, in addition to collecting pheromone samples and wing photographs for future analysis. Our results already show that populations spanning the humid-Andean forest transition show similar differences in development, flight and mate choice behaviours, consistent with natural selection. We have also collected volumetric data from the brains of 73 individual butterflies. These data reveal parallel shifts in brain structure across the humid-Andean forest transition in both Colombia and Ecuador consistent with selection, likely in response to forest type. Populations inhabiting more ‘complex’ humid forests have larger optic lobes, which are associated with visual processing.
2) Assess the role of selection in shaping the sensory periphery and the brain.
We have generated hybrids between populations spanning the environmental transition, and have started to collect tissue for volumetric brain and gene expression analyses. These will allow a sophisticated ‘quantitative genetics’ approach to explicitly test for selection on different components of the sensory systems. We have also run several assays on living butterflies, which reveal that populations from more complex humid forests can resolve finer detail from a given distance. In the next weeks we will start these and other assays on hybrids to determine how volumetric changes in the brain relate to changes in sensitivity and integration of stimuli, and also mating preferences.
3) Determine the genomic architecture of behavioural isolation.
To determine the genomic regions underlying differences in brain and behaviour, we have measured the mating preference of over 100 hybrids, and will begin collecting brain tissue in the coming weeks. We are on track to complete these experiments by the end of 2023.
4) Link behaviours to the action of individual genes.
We have now established Crispr/Cas9 genome editing protocols for Heliconius, potentially allowing us to validate candidate behavioural genes in the final years of the project.
Our work has already shed light on how ecological, genetic and neural changes influence behavioural adaptation, and how they may ultimately contribute to speciation.
1) Characterise how the components of behavioural isolation vary with ecology
We have now demonstrated that Heliconius populations show parallel changes in both brain structure and behaviours, consistent with natural selection. Completing our data-set of sensory and neural gene expression, mate choice behaviours, and the potential olfactory and visual cues on which they depend will allow a major analysis comparing populations spanning ecological transitions. Experiments to test the relative role of pheromones during mate choice are planned for the second phase of the project.
2) Assess the role of selection in shaping the sensory periphery and the brain.
Our emerging evidence is beginning to suggest that the larger optic lobes of Heliconius inhabiting more humid forests are associated with the ability to visually resolve finer detail, which may aid flight, foraging and mate finding in these visually more complex habitats. We will continue to unravel the role of natural selection in driving differences in sensory and neural gene expression, and volumetric differences in the brain using state-of-the-art statistical techniques based on comparing these traits between populations, and their hybrids.
3) Determine the genomic architecture of behavioural isolation.
Our genetic crosses in Ecuador will allow us to determine the regions of the genome underlying differences in mating behaviours, and for the first time in Heliconius, brain structure. We are also extending the project to include crosses from Colombia, allowing us to ask whether the same genomic regions underlie parallel phenotypic changes across populations.
4) Link behaviours to the action of individual genes.
Analysis of gene expression from the brain and sensory tissue that we have been collecting from our hybrid butterflies, in combination to the analyses planned for objective 3, will identify some of the first candidate genes associated with changes in behaviour in Heliconius. Comparisons with previous work from my lab, on a group of distantly related Heliconius species, will allow us to begin to ask whether certain genes are hotspots for behavioural evolution. Our final aim is to functionally test these candidate genes with state-of-the-art genome editing techniques.
1) Characterise how the components of behavioural isolation vary with ecology
We have now demonstrated that Heliconius populations show parallel changes in both brain structure and behaviours, consistent with natural selection. Completing our data-set of sensory and neural gene expression, mate choice behaviours, and the potential olfactory and visual cues on which they depend will allow a major analysis comparing populations spanning ecological transitions. Experiments to test the relative role of pheromones during mate choice are planned for the second phase of the project.
2) Assess the role of selection in shaping the sensory periphery and the brain.
Our emerging evidence is beginning to suggest that the larger optic lobes of Heliconius inhabiting more humid forests are associated with the ability to visually resolve finer detail, which may aid flight, foraging and mate finding in these visually more complex habitats. We will continue to unravel the role of natural selection in driving differences in sensory and neural gene expression, and volumetric differences in the brain using state-of-the-art statistical techniques based on comparing these traits between populations, and their hybrids.
3) Determine the genomic architecture of behavioural isolation.
Our genetic crosses in Ecuador will allow us to determine the regions of the genome underlying differences in mating behaviours, and for the first time in Heliconius, brain structure. We are also extending the project to include crosses from Colombia, allowing us to ask whether the same genomic regions underlie parallel phenotypic changes across populations.
4) Link behaviours to the action of individual genes.
Analysis of gene expression from the brain and sensory tissue that we have been collecting from our hybrid butterflies, in combination to the analyses planned for objective 3, will identify some of the first candidate genes associated with changes in behaviour in Heliconius. Comparisons with previous work from my lab, on a group of distantly related Heliconius species, will allow us to begin to ask whether certain genes are hotspots for behavioural evolution. Our final aim is to functionally test these candidate genes with state-of-the-art genome editing techniques.