Evolution of Olfaction in Bark Beetles and Termites: Gene families and odorant receptor characterization

Jibin Johny

Doctoral thesis

Abstract:

Evolution is the central theme of biology, representing organismal variations in various contexts, from the molecular level to social behavior. The current research explores the variations in the context of the sense of smell, i.e., the evolution of olfaction in two wood-boring insects: bark beetles (Coleoptera: Curculionidae: Scolytinae) and termites (Blattodea: Isoptera). Both have a critical impact on forests and wood structures (Biedermann et al., 2019; Bordereau and Pasteels, 2010) as engineers of the ecosystem and use volatile cues of remarkable diversity for their survival and host selection (Biedermann et al., 2019). In bark beetles, a rapid ‘switching on and switching off’ of specific aggregation pheromone components was observed across Scolytinae (Symonds and Elgar, 2004, 2008; Raffa et al., 2016). Similarly, in termites, a shift from branched primary alcohols and aldehydes to unsaturated primary alcohols was observed in trail-following pheromones from basal to derived lineages (Bordereau and Pasteels, 2010). As such changes in pheromone composition were highly conserved across species, the current research hypothesizes rapid heritable changes in their olfactory perception at the molecular level, i.e., in the expression and function of odorant receptors. To extend our current knowledge on the evolution of olfaction (Hansson and Stensmyr, 2011; Hansson and Wicher, 2016; Thoma et al., 2019) and to test the hypothesis, we expanded the gene tree by identifying chemosensory gene families from three termites and two bark beetle species. The gene families were identified by using antennal transcriptome sequencing and annotations. The phylogenetic analysis revealed the diversification of these gene families. The Drosophila transgenic expression system was used for the functional characterization of odorant receptors. The study reports the multi-step origin of odorant receptors in insects and highlights the standing genetic variations in bark beetle odorant receptors as a possible source of olfactory adaptation. Here, I report the first population-level functional polymorphism in insects other than Drosophila by characterizing two variants of a bark beetle pheromone receptor. The structural predictions conclude that mutations outside the ligand binding sites could alter the ligand selectivity of the receptor. Further research is needed to extend the significance of identified molecular and functional variations to possible olfactory adaptations in the population. Similar functional evolution of termite pheromone receptors is also being explored.

Keywords

Bark beetles, termites, olfactory adaptation, functional evolution, pheromone receptors, forest pest, functional polymorphisms

Jazyk práce: English

Datum vytvoření / odevzdání či podání práce: 4. 10. 2024

Obhajoba závěrečné práce

• Vedúci: Amit Roy, Ph.D.
• Oponent: Eloy Fernández Cusimamani, Ph.D., prof. Ing., Nicolas Montagné, externi, Binu Antony, externi

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme / odbor:
Forestry Engineering / Forest Biology