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EASTBIO Sex, males, and hermaphrodites in the scale insect Icerya purchasi


School of Biological Sciences

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Dr L Ross No more applications being accepted Competition Funded PhD Project (Students Worldwide)

About the Project

Second Supervisor Andy Gardner University of St Andrews
Organisms reproduce in diverse ways. Yet it is unclear why and how new reproductive strategies evolve. This project focuses on the only case of hermaphroditism in insects: In species of the scale insect Icerya female-like hermaphrodites produce both sperm and eggs and self-fertilize.

Background
Understanding why there is such variability in the way organisms reproduce is one the most important unsolved puzzles in evolutionary biology. This project aims to tackle this question by focusing on the unique and puzzling reproductive strategy of the scale insect Icerya purchasi. This species is the only insect unequivocally described as hermaphroditic; female-like hermaphrodites can produce both sperm and eggs and self-fertilize. But how can a female produce sperm? A recent hypothesis suggests that the sperm present in hermaphrodites seem to have originated from the individuals father “infecting” his future offspring with sperm-producing cells. However, although the data is suggestive, this hypothesis requires further scrutiny. It is also unclear why, while most offspring develop as hermaphrodites, a small number develop as males. Finally, it seems that while hermaphroditism is exceedingly rare in insects, it might have evolved independently in several close relatives of Icerya. This PhD project will explore how and why this unusual reproductive system evolved by using comparative methods across species as well as experimental and genomic analyses in the laboratory. Together this work will help us to better understand what evolutionary forces shape the ways animals reproduce.

The projects sets out to test a number of key questions to better understand the evolution of the only insect hermaphrodite:

1. What is the evolutionary and developmental origin of the sperm produced by female-like hermaphrodites?
2. Hermaphrodites can self-fertilize, so why and how do they occasionally produce male offspring?
3. How frequently did hermaphroditism evolved within the clade of insects and do any ecological factors predict the patterns we observe?
4. How does the reproductive mode of different Icerya species affect the evolution and structure of the genome?

The project will use two main approaches:

The first will focus on collecting insect specimens of different Icerya species, and then use molecular phylogenetic and population genomics methods to determine their evolutionary relationships, and to study transitions between reproductive strategies employed by the different species. This part of the project is in collaboration with Prof. Penny Gullan, The Australian National University, Canberra.

The second part of the project will focus on Icerya purchasi. This will use laboratory experiments and a combination of state-of-the-art cytogenetic and genomic approaches to study different aspects of the reproduction of this species.

Training
A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. Specifically, the student will undertake training in the use of molecular wet lab techniques, the analysis of sequencing data and the use of microscopy and cytogenetic approaches.

Candidates must be highly motivated with a keen interest in evolutionary biology and genetics and a strong motivation to pursue a scientific career. Previous experience working with insects and phylogenetic and genomic analyses would be an advantage.
http://lauraross.bio.ed.ac.uk
https://synergy.st-andrews.ac.uk/gardner/Andy-Gardner/
The School of Biological Sciences is committed to Equality & Diversity: https://www.ed.ac.uk/biology/equality-and-diversity

How to Apply:
The “Institution Website” button will take you to our Online Application checklist. Complete each step and download the checklist which will provide a list of funding options and guide you through the application process.


Funding Notes

This 4 year PhD project is part of a competition funded by EASTBIO BBSRC Doctoral Training Partnership http://www.eastscotbiodtp.ac.uk/how-apply-0. This opportunity is open to UK and International students and provides funding to cover stipend and UK level tuition fees. The fee difference will be covered by the University of Edinburgh for successful international applicants. Please refer to UKRI website (https://www.ukri.org/our-work/developing-people-and-skills/find-studentships-and-doctoral-training/get-a-studentship-to-fund-your-doctorate/) and Annex B of the UKRI Training Grant Terms and Conditions (https://www.ukri.org/wp-content/uploads/2020/10/UKRI-291020-guidance-to-training-grant-terms-and-conditions.pdf) for full eligibility criteria.

References

Bachtrog, Doris, et al. "Sex determination: why so many ways of doing it?." PLoS biology 12.7 (2014): e1001899.
Gardner, Andy, and Laura Ross. "The evolution of hermaphroditism by an infectious male-derived cell lineage: an inclusive-fitness analysis." The American Naturalist 178.2 (2011): 191-201.
Unruh, C. M., and P. J. Gullan. "Molecular data reveal convergent reproductive strategies in iceryine scale insects (Hemiptera: Coccoidea: Monophlebidae), allowing the re‐interpretation of morphology and a revised generic classification." Systematic Entomology 33.1 (2008): 8-50.
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