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The evolutionary origin of hermaphrodites in insects


School of Biological Sciences

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

About the Project

Interested individuals must follow Steps 1, 2 AND 3 at the link on how to apply www.ed.ac.uk/schools-departments/biology/postgraduate/pgr/how-to-apply

Why there is such great variation in the ways that animals reproduce remains an unsolved mystery in evolutionary biology. This project aims to study this question by focusing on a group of insects whose reproduction is incredibly variable and in which evolutionary innovations have reduced the importance of males (Ross et al. 2010). Specifically it focuses on a small plant feeding insect - the cottony cushion scale insect Icerya purchasi - in which evolution appears to have driven the male to become a parasite living in the body of the female, producing sperm and fertilising her from within. This turns females into functional hermaphrodites. Recent evolutionary theory suggests that this system might have evolved from conflict between males and females over how many eggs a male gets to fertilize (Gardner and Ross 2012). However many questions remain: based on our current understanding we would expect that all reproduction happens through self-fertilization of hermaphrodites. However we do find true males in natural populations, and these males have been shown to mate with the hermaphrodites in the laboratory. This raises the question, can the sperm of these males compete with the sperm already present within the hermaphrodite and can these male infect their daughters with new parasitic male tissue? Other questions include, the role of bacteria living within the cells of Icerya purchasi and why and when mothers produce sons instead of hermaphrodites.

This project will combine laboratory experiments and genetic analyses. Depending on the interest of the student these results can be combined with observations of mating behavioural, microscopy of early embryogenesis to study the establishment of the male cells, antibiotics experiments and evolutionary theory.


References

Gardner, A. & Ross, L. (2011) The evolution of hermaphroditism by an infectious male derived cell lineage. American Naturalist 178,191-201

Ross, L., Pen, I. & Shuker, D. M. (2010). Genomic conflict in scale insects: the causes and consequences of bizarre genetic systems. Biological Reviews 85, 807-828.

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