Huylmans/Keller Valsecchi/Foitzik
Sex- and caste determination during termite development
Supervisor: Ann Kathrin Huylmans
Co-Supervisor: Claudia Keller Valsecchi, Susanne Foitzik
Scientific Background
Termites are eusocial insects that, in contrast to well-studied eusocial Hymenopterans, are diplo-diploid. Instead, sex is determined via an XX/XY sex chromosome system and males are present in all three castes: reproductives, workers, and soldiers. Very little is known about the sex determination cascade in termites to date and a master sex determining gene has not been identified, yet. Dosage compensation appears to act on the rather small, differentiated part of the X chromosome but the mechanism and when during development this starts is currently unknown.
Another important difference to Hymenopterans is that termites are hemimetabolous insects. In holometabola, sexual dimorphism increases suddenly during metamorphosis. Currently, fairly little is known about the relationship between sexual dimorphism and sex-biased gene expression. Data for stick insects, the only hemimetabolous species for which sex-biased gene expression has been investigated throughout development, indicates that, in contrast to holometabola, expression differences gradually increase with sexual dimorphism during development (Djordjevic 2022). Also in birds, a correlation between sex-biased gene expression and sexual dimorphism has been observed both across species (Dean et al. 2015) as well as for different sexual morphs (Pointer et al. 2013). As sexual dimorphism in termites is caste-dependent, the gene regulation changes are expected to be regulated via an interplay between the molecular pathways involved in caste- and sex determination.
Project description
The PhD project aims at exploring gene expression throughout development of the termite Reticulitermes flavipes. We are especially interested in sex- and caste-biased gene expression and how the molecular pathways may interact with each other. We hypothesise that during development sex-biased gene expression gradually increases until the worker stage. After that, we predict sex-biased expression to increase again in highly sexually dimorphic reproductives but to decline in the sterile soldier caste. This expression series throughout development enables us also to identify the time when dosage compensation is established as well as identify good candidates for potential master sex determining genes.
Furthermore, we will induce caste differentiation into and assess how and when sexual dimorphism changes. During these transitions, we will perform single-cell RNA-seq for gonad and brain tissues of both sexes to circumvent differences in cell composition between the sexes that are especially pronounced in the gonad and may strongly influence sex-biased gene expression detection (Darolti & Mank 2022). These tissues may be differently influenced by dosage compensation as it is for example the case in Drosophila (Huylmans & Parsch 2015). Thus, the degree of compensation for X-linked genes in these tissues will be assessed and taken into consideration.
What you will learn
In this project you will learn animal handling, developmental staging as well as molecular biology techniques (qPCR, RNAi, molecular sexing). You will perform sequencing (RNAseq, single-cell sequencing, potentially epigenomics) and learn about the downstream bioinformatics and data analyses. According to interest, it is also possible to include more in-depth molecular methods in collaborating such as FISH, etc. In the PhD, you will learn to work in an international team and develop your own research profile, including skills such as experimental design, critical thinking, and taking initiative to push your own project forward. You will learn how to communicate your results in oral and written form while attending international conferences, workshops, and writing papers. Career support is ensured via a wide variety of offers from the GenEvo graduate school, as well as by our group.
Your qualifications
We are looking for an enthusiastic student with a background in evolutionary and/or molecular biology. Interest in developmental biology would be a plus. We work in an international small team, exchange with other groups is a key feature of GenEvo, and this project will closely be associated with others in the group. Hence, we aim to recruit a strong team player interested in combining approaches from multiple angles and disciplines. Prior bioinformatics knowledge is definitely useful but not required.
Publications relevant to this project
Darolti I, Mank JE (2023) Sex-biased gene expression at single-cell resolution: cause and consequence of sexual dimorphism, Evolution Letters, Volume 7, Issue 3 Pages 148–156, https://doi.org/10.1093/evlett/qrad013
R Dean, PW Harrison, AE Wright, F Zimmer, JE Mank (2015) Positive Selection Underlies Faster-Z Evolution of Gene Expression in Birds. MBE 32(10):2646-2656. doi.org/10.1093/molbev/msv138
J Djordjevic, Z Dumas, M Robinson-Rechavi, T Schwander, DJ Parker (2022) Dynamics of sex-biased gene expression during development in the stick insect Timema californicum. Heredity 129:113-122. doi.org/10.1038/s41437-022-00536-y
AK Huylmans, J Parsch (2015) Variation in the X:autosome distribution of male-biased genes among Drosophila melanogaster tissues and its relationship with dosage compensation. GBE 7(7):1960-1971. doi.org/10.1093/gbe/evv117
MA Pointer, PW Harrison, AE Wright, JE Mank (2013) Masculinization of gene expression is associated with exaggeration of male sexual dimorphism. PLOS Genetics 9(8):e1003697. doi.org/10.1371/journal.pgen.1003697