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The evolutionary genetics of sexual mode switching.

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  • Full or part time
    Dr R Hammond
    Dr E Mallon
    Dr A Gomez
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

Physically separate males and females – known as dioecy - has evolved many times [1] yet the selective and molecular mechanisms underpinning this change are not clearly understood. This is because sex differences are often longstanding so disentangling cause and effect is tricky [2].

In this PhD project you will use a novel approach and a model system developed by the supervisory team [3-5], the tadpole shrimp, (Triops sp.) - a crustacean commonly kept as a pet - to shed light on this fundamental issue. You will investigate gene expression changes that have occurred recently and in the reverse sexual mode switch - from dioecy to hermaphroditism. This change in sexual mode causes a shift from selection being able to optimise male and female function in separate individuals to selection optimising male and female function together in the same individual. Your research will illuminate the selective mechanisms – such as antagonistic selection – that are hypothesised to underpin the evolution of sex differences [6].

We have shown there are multiple independent evolutionary transitions between separate sexes (dioecy) to individuals with male and female function (hermaphrodites) in tadpole shrimps (Triops) [3, 7], so, one of the strengths of your project is that you will use a comparative approach to investigate gene expression changes in multiple species.

Your research will build upon work that has shown sex is genetically determined [5], that has developed sex linked markers, and identified sex linked scaffolds in the three genomes (male, female and hermaphrodite) we have sequenced and assembled (unpublished).

You will develop functional molecular tests – such as RNA interference – to investigate sex determination. Sex determination is poorly understood in crustaceans, an important gap in the wider understanding of the evolution of sex determination [8].

Possible hypotheses to test:

• Are genes with female biased expression in dioecious populations are less biased in hermaphrodites (and vice versa for male baised genes)?
• Is there an effect of genome position (e.g. within or outside the sex chromosome region) of genes on the degree of change in expression bias?
• Do independent evolutions of hermaphroditism show convergent patterns of expression change?

Funding Notes

This studentship is one of a number of fully funded studentships available to the best UK and EU candidates available as part of the NERC DTP CENTA consortium.

For more details of the CENTA consortium please see the CENTA website: www.centa.org.uk.

Applicants must meet requirements for both academic qualifications and residential eligibility: http://www.nerc.ac.uk/skills/postgrad/

Please direct informal enquiries to the project supervisor. If you wish to apply formally, please do so via: http://www2.le.ac.uk/study/research/funding/centa/how-to-apply-for-a-centa-project

References

Further reading:
1. Vicoso B., Kaiser V.B., Bachtrog D. 2013 Sex-biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution. Proceedings of the National Academy of Sciences 110(16), 6453-6458. (doi:10.1073/pnas.1217027110).
2. Wright A.E., Dean R., Zimmer F., Mank J.E. 2016 How to make a sex chromosome. Nat Commun 7. (doi:10.1038/ncomms12087).
3. Mathers T., Hammond R., Jenner R., Zierold T., Hanfling B., Gomez A. 2013 High lability of sexual system over 250 million years of evolution in morphologically conservative tadpole shrimps. BMC Evol Biol 13(1), 30.
4. Mathers T.C., Hammond R.L., Jenner R.A., Haenfling B., Gomez A. 2013 Multiple global radiations in tadpole shrimps challenge the concept of 'living fossils'. PeerJ 1. (doi:10.7717/peerj.62).
5. Mathers T.C., Hammond R.L., Jenner R.A., Hanfling B., Atkins J., Gomez A. 2015 Transition in sexual system and sex chromosome evolution in the tadpole shrimp Triops cancriformis. Heredity 115(1), 37-46. (doi:10.1038/hdy.2015.10).
6. Bedhomme S., Bernasconi G., Koene J.M., Lankinen A., Arathi H.S., Michiels N.K., Anthes N. 2009 How does breeding system variation modulate sexual antagonism? Biology Letters 5(5), 717-720. (doi:10.1098/rsbl.2009.0401).
7. Zierold T., Hanfling B., Gomez A. 2007 Recent evolution of alternative reproductive modes in the 'living fossil' Triops cancriformis. BMC Evol Biol 7. (doi:10.1186/1471-2148-7-161).
8. Kato Y., Kobayashi K., Watanabe H., Iguchi T. 2011 Environmental Sex Determination in the Branchiopod Crustacean Daphnia magna: Deep Conservation of a Doublesex Gene in the Sex-Determining Pathway. PLOS Genetics 7(3), e1001345. (doi:10.1371/journal.pgen.1001345).
9. Harrison M.C., Hammond R.L., Mallon E.B. 2015 Reproductive workers show queenlike gene expression in an intermediately eusocial insect, the buff-tailed bumble bee Bombus terrestris. Molecular Ecology 24(12), 3043-3063. (doi:10.1111/mec.13215).



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