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Evolution of inbreeding mating systems in social species: theory on causes and consequences.


Project Description

This project aims at developing new spatially- and genetically-explicit theory to understand (1) evolution of inbreeding mating systems and associated sociality, and (2) its consequences for species adaptation to changing environments and evolutionary potential.
Inbreeding mating systems, that is systems where individuals mate regularly with close relatives and thus are permanently inbred, have evolved multiple times in both animal and plants1,2. Yet, they represent an intriguing evolutionary puzzle. Because of the costs associated with inbreeding (inbreeding depression and loss of genetic diversity), the expectation is that there will be strong selection for mechanisms that allow avoiding inbreeding. However, in situations where the costs of avoiding inbreeding are greater than the cost of inbreeding itself, for example because of extremely high cost of dispersal, tolerance to inbreeding might evolve. Additionally, the transition to permanent inbreeding requires purging of most of the inbreeding load, which represents an even greater challenge for self-incompatible organisms. The mechanisms behind the transition to inbreeding mating systems becomes even more intriguing when it is associated with a transition to sociality. In spiders, for example, the transition from sub-social to social species is associated with loss of pre-mating dispersal and evolution of propagule dispersal, decreased inbreeding depression and chronic inbreeding, female-biased sex ratio and cooperative predation and brood care1. Thus, evolution of inbreeding mating systems represents a fascinating example of eco-evolutionary interactions between dispersal, mating system and sociality, still waiting for theory explaining their occurrence and the role of spatial dynamics and genetic processes in their evolution.
Explaining the persistence and the widespread phylogenetic and geographic distribution of inbreeding mating systems poses a further challenge. In fact, chronic inbreeding dramatically reduces genetic diversity and efficacy of selection2-4, reducing species’ adaptive potential and therefore their ability to colonise new environments, to respond to environmental changes and to fight diseases and parasites. These long-term consequences are so dramatic that inbreeding mating system are hypothesised to be an evolutionary dead-end5. Yet, social species with inbreeding mating system appear to be quite old, which begs the question: are these species inevitably on their way to extinction or are there alternative mechanisms of adaptation that allows them to persist despite having very low genetic variation?
This project will generate new theory to understand under what ecological circumstances inbreeding mating systems evolve in group-living, non-selfing species, and what is the role of dispersal evolution, spatial dynamics and sociality evolution. Further, it will investigate the ecological and evolutionary consequences of such systems and the role of different mechanisms of adaptation to changing environments such as symbiont-mediated adaptation and adaptation through nongenetic inheritance6. These questions are inspired by the empirical work carried out in Prof. Bilde’s Lab on Stegodyphus spiders, which comprise social and sub-social lineages, to understand causes and consequences of inbreeding mating systems1,3,4. Ongoing projects are generating exciting data on the species’ population genetics, genome, epigenome and microbiome, providing multiple opportunities to inform and test emerging theory.
The project is deliberately broad, leaving plenty of scope for the student to develop their own line of research. The student will work closely with the PI and receive excellent training in eco-evolutionary modelling and benefit from the presence of strong groups in the department working on related topics and modelling approaches. Further, the student will be co-supervised by Prof. Bilde and have the opportunity of working closely with her group and the spider system in Aarhus University.

Funding Notes

This studentship is available to UK and other EU nationals and provides funding for tuition fees and stipend, subject to eligibility.

Candidates should have (or expected to achieve) a minimum of 2:1 Honours degree, ideally (but not required) an MSc in ecology, evolution or related, strong quantitative skills and passion and enthusiasm for learning and developing evolutionary theory.

References

1. Bilde, T., Y. Lubin, D. Smith, J. M. Schneider, and A. A. Maklakov. 2005. The transition to social inbred mating systems in spiders: role of inbreeding tolerance in a subsocial predecessor. Evolution 59:160–74.
2. Avilés, L., and J. Purcell. 2012. The Evolution of Inbred Social Systems in Spiders and Other Organisms. From Short-Term Gains to Long-Term Evolutionary Dead Ends? Advances in the Study of Behavior (Vol. 44).
3. Settepani, V., J. Bechsgaard, and T. Bilde. 2016. Phylogenetic analysis suggests that sociality is associated with reduced effectiveness of selection. Ecology and Evolution 6:469–477.
4. Settepani, V., M. F. Schou, M. Greve, L. Grinsted, J. Bechsgaard, and T. Bilde. 2017. Evolution of sociality in spiders leads to depleted genomic diversity at both population and species levels. Molecular Ecology 26:4197–4210.
5. Wright, S. I., S. Kalisz, and T. Slotte. 2013. Evolutionary consequences of self-fertilization in plants. Proceedings of the Royal Society B: Biological Sciences 280:1–10.
6. Bonduriansky, R., A. J. Crean, and T. Day. 2012. The implications of nongenetic inheritance for evolution in changing environments. Evolutionary Applications 5:192–201.

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