Our Research

About half of all insect and spider species carry specialised symbiotic bacteria that are transmitted from mothers to offspring (“inherited symbionts”) and typically cannot reproduce outside their arthropod hosts. Inherited symbionts may affect their hosts in profound ways: they contribute to nutrition, alter reproductive output, or provide protection from pathogens. Key to the success of inherited symbionts and the reason for their ubiquitous nature is their ability to shift hosts, i.e., establish in novel host species. While we know how novel symbionts may impact arthropods, we have a very limited understanding of symbiont properties important in host shifts: We do not know why some symbionts are better host shifters than others and how the process of establishing in novel hosts impacts symbionts. These questions are fundamental for our appreciation of symbiont ecology and evolution as well as arthropod biology. This project addresses these issues by consolidating experimental evolution of highly evolvable Spiroplasma symbionts with genomic surveys of Wolbachia symbionts in natural populations of solitary bees.

Spiroplasma is a genus of Mollicutes, cell-wall-less bacteria that are pathogens or inherited symbionts of arthropods. As symbionts, Spiroplasma have the ability to kill male offspring in order to enhance their own spread via females. They may also provide protection from parasitoids and parasites through specific toxins. Through a preliminary screen, we recently found that many neotropical Drosophila species harbour a Spiroplasma variant that differs from all previously studied strains by its very low titre, absence of induced phenotypes, and very high incidence - all tested neotropical Drosophila species appear to harbour the same strain. We hypothesise that our newly discovered variant is a “cryptic” strain with a high degree of adaptation to its hosts, and possibly a long evolutionary history with neotropical hosts. This would be in contrast to all previously studied Spiroplasma, that are often costly reproductive manipulators (“pathogenic”) Spiroplasma. In this project, we will comprehensively characterise the evolutionary dynamics and phenotypic potential of our newly discovered cryptic Spiroplasma symbionts in neotropical Drosophila species. This will be achieved through comparison of cryptic with pathogenic Spiroplasma with respect to incidence, diversity, tropism, transmission dynamics, genomic architecture and evolutionary history, and through assessing phenotypes and ability for host shifting.

Psyllids, commonly known as jumping plant lice, are a small group of phloem-feeding insects that have evolved intimate associations with a variety of bacterial symbionts. These symbiotic relationships often contribute to the insect’s diet by making the nutritionally unbalanced plant sap exploitable and enabling the host to adapt to diverse ecological niches. The acquisition of essential nutrients, particularly amino acids and vitamins, through symbiotic associations is a key aspect of these interactions, influencing psyllid fitness and reproductive success. The co-evolutionary dynamics between psyllids and their symbionts have shaped the genomic structure of both parties, leading to intriguing adaptations and molecular interdependencies. However, the relationships between insects and their symbiotic partners are dynamic as symbionts can be frequently acquired, replaced, or lost. In this project, we aim to reconstruct the co-evolutionary history of psyllids with their symbionts and to identify events of symbiont co-diversifications, losses and replacements across the psyllid tree of life. Several disctinct lineages of psyllids have evolved a gall-inducing lifestyle, which likely also lead to differences in nutrition compared with their free-living relatives. We will therefore investigate how the evolution of this lifestyle has impacted the community of nutritional symbionts in psyllids.