Social behaviours and public goods in fruit flies: Effect of egg-laying substrate and social environment on oviposition decisions and the expression of ‘public goods’ related genes in Drosophila melanogaster fruit flies

Lofthouse, Harold John (2023) Social behaviours and public goods in fruit flies: Effect of egg-laying substrate and social environment on oviposition decisions and the expression of ‘public goods’ related genes in Drosophila melanogaster fruit flies. Masters thesis, University of East Anglia.

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Cooperative behaviours are common across various taxa, but not always well understood. For example, the idea of the ‘tragedy of the commons’ shows that, among groups of non-relatives, there is expected to be strong selection for non-cooperative cheats. Fruit flies (Drosophila melanogaster) have been observed to oviposit their eggs in clusters of mixed maternity. I hypothesised that this could potentially be due to the production of ‘public goods’, in which mothers could coat the surface of the eggs they lay with beneficial, diffusible protective compounds which could thus also benefit adjoining eggs. Two types of potential public goods were identified. The first was the sex pheromone 7,11-HD, which is present around the outside of D. melanogaster eggs and has been found to protect eggs from cannibalism. The second was antimicrobial compounds. For example, female medflies (Ceratitis capitata) are known to provision their egg surfaces with anti-microbial peptides (Marchini et al., 1997). It is not yet known though whether D. melanogaster has any equivalent antimicrobials. Such pheromones and peptides could potentially act as public goods if they diffuse into the medium and protect the eggs of other females that are laid nearby within egg clusters. This idea sets up the following predictions: that (i) females housed together in groups have the potential to gain public goods benefits by clustering their eggs with those of others, (ii) some, but not all females housed in groups would activate potential egg surface public good genes. I investigated these predictions by measuring the egg clustering decisions and potential ‘public goods’ gene expression patterns of females held in groups versus those that were socially isolated. I simultaneously tested the effect of two egg-laying substrates, of good and poor nutrient quality, on the basis that eggs laid on a poor food substrate are more likely to be cannibalised. Through this, how diet and social environment affected oviposition behaviour (egg clusters) and the expression of ‘public good’ related genes, was investigated. In contrast to the prediction, I found that there was no effect of the social environment on the proportion of eggs laid in clusters and that females were even less likely to cluster their eggs on the poor oviposition substrate. Therefore, there was no evidence that females clustered their eggs in a manner that would be predicted by public goods benefits. The effects on gene expression of potential public good genes showed variable support for the public goods hypothesis. Females laying eggs on a poor food substrate had higher levels of gene expression in anti-microbial genes Dif and Mtk, compared to females laying on the standard food substrate. Thus, the detection of poor egg deposition substrates activated the expression of antimicrobial protective molecules. Females kept in the grouped environments also showed significantly increased expression of all the tested genes related to 7,11-HD production (Fad2, fatp1, desat1) over those maintained alone. However, there was minimal evidence that females showed significant heterogeneity in gene expression as would be predicted if group females were comprised of cooperators and cheaters. These results provide an insight into the nature of egg clustering decisions and how 7,11-HD and anti-microbial peptides are affected by substrate quality and social environment. The results suggest that the expression of antimicrobial and sex pheromone genes is responsive to egg-laying substrate and social groupings, respectively. However, there was no evidence that potential public goods could be dispersed through the mechanism of egg clustering. Further work is needed to determine whether these compounds are ‘public goods’ and to explore alternative explanations.

Keywords: Cooperation, Public goods, Oviposition, Gene expression, Social Behaviour, Drosophila.

Item Type: Thesis (Masters)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 19 Dec 2023 08:31
Last Modified: 19 Dec 2023 08:31


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