Understanding the extinction vortex: inbreeding in haplodiploids

Around 20% of all animals - including all the bees, wasps and ants that are important pollinators and seed dispersers - are haplodiploid (Heimpel and de Boer, 2008). That is, females are diploid and males are haploid. However, the mechanism underlying haplodiploidy, known as complementary sex determination (csd), means that low genetic variation and/or inbreeding can detrimentally reduce reproduction (Zayed and Packer, 2005). This is because diploid offspring erroneously develop as males rather than females (Harpur et al., 2013). Such reduced reproduction lowers population size further, exacerbating the effects in a feedback loop: the extinction vortex. Given human induced habitat degradation and climate change, insect populations – including many of those with haplo-diploid sex determination - are declining and fragmenting (Sanchez-Bayo and Wyckhuys, 2019). Understanding the extinction vortex is therefore a priority.

The objectives of the PhD project are as follows (the emphasis on each element can be tailored to your interests & how the project develops).

1.      Model the effects of inbreeding and diploid male production in haplodiploids. Although there is some theoretical work on the impact of inbreeding and diploid male production on population persistence, you will extend this theory to investigate how life history variation influences outcome. 

2.      Estimate inbreeding & diploid male production in a model ant species. You will estimate diploid male production in the well-studied ant, Leptothorax acervorum (Figure 1C), and test if this correlates with effective population size (current and historical) estimated from genetic data. In the southern part of their range (Spain) this species is attitudinally limited being restricted to >1500m (Figure 1B). Populations are often small, have limited gene flow and so population isolation and inbreeding is a real issue and diploid males are regularly produced (Hammond, unpublished data)

3.      Model habitat patch size, occupancy and fragmentation. You will use spatial data to discover suitable habitats for L.acervorum in Spain. This will allow us to estimate patch size and connectivity and to interpret data gained from objective 2. It will also find new populations to sample for part 2.

Methodology:

1.      Modelling: You will develop mathematical models of diploid male production that consider: solitary vs social living, for social species the type of colony founding, mating frequency of females, colony size and female productivity, diploid male fertility and triploid female fertility.

2.      Inbreeding / diploid male production: You will collect samples of the ant, L.acervorum, from known locations, and locations identified by GIS modelling (see 3), in Spain. You will estimate population genetic variation using reduced representation sequencing and the proportion of diploid males will be identified genetically. This will involve molecular genetic lab work and bioinformatic analysis.

3.      Habitat patch size: You will develop GIS models to identify suitable habitat/altitude/aspect patches. This will be done using data derived from known populations / published records and using state of the art GIS software and modelling (e.g. ArcGIS Pro, R).

For details of entry requirements and how to apply please refer to:

https://le.ac.uk/study/research-degrees/funded-opportunities/centa-phd-studentships