Turid Everitt: Genomic Studies of Local Adaptation and Meiotic Recombination in Social Insects

Abstract

Honeybees have adapted to a wide range of environments across the world but the underlying genetic mechanisms are unclear. On the American continents, hybridization between European and African honeybees has led to important phenotypic changes. The African ancestry proportions vary with latitude, likely related to climate adaptations. In the first study, we analysed climate adaptations related to African ancestry in a different context, by comparing two populations of hybrid honeybees at different altitudes. We found significantly lower African ancestry proportions in the highland population which experienced lower temperatures. This supports a greater generality of the link between African ancestry and climate adaptations. In similarity with the genomic changes across latitudes, we found that a great number of small-effect loci are involved in the altitude adaptation. 

Social insects from the order Hymenoptera, including honeybees, have unusually high recombination rates compared with most other metazoan species. Multiple hypotheses link their high recombination rates to their social behaviours. Recombination rates in social insects from different orders have however not previously been estimated. In the second study, we estimated the recombination rates in termites, which are social insects from the order Blattodea, and found that they are clearly lower than the rates in social hymenopteran species. This means that sociality alone cannot explain the high recombination rates within Hymenoptera. We also found that the locations of recombination events in the termite genomes are clustered in hotspots, a pattern seen previously in various taxa but not commonly in insects. 

In the third study, we investigated the genetic basis of inter-individual recombination rate variation in honeybees. We estimated the recombination rate in 184 honeybee queens by whole genome sequencing of their offspring, 1508 haploid drones. The mean genome wide recombination rate was 23 cM/Mb and the narrow-sense heritability 28%, indicating a high degree of genetic control. In a genome-wide association study of the recombination rate per queen, we found a significant association to the gene MLH1, which has an important function related to recombination in multiple other taxa. This gene is also a candidate for explaining the high recombination rates in social Hymenoptera.