Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Biology Dept.


David Angelini

Second Advisor

Johanna van Oers

Third Advisor

Russell Johnson


Natural selection alters genetic pathways over evolutionary time. However, different pathways have been shown to maintain mutations at varying rates, leading to different levels of conservation across developmental pathways. Sex determination pathways, in particular, show vast diversity across animals despite the fundamental conservation of biological sex itself. Here, I investigated the sex determination pathway of the hemimetabolous insect, Oncopeltus fasciatus. The large milkweed bug, O. fasciatus, is part of the order Hemiptera, which provides a relevant outgroup study to other insects in which sex determination has been studied to date. I studied three sex determination genes, intersex, fruitless, and three paralogs of doublesex via a set of phylogenetic sequence comparisons, qRT-PCR gene expression studies, and RNAi functional analyses. I report that somatic sex differentiation requires these genes in a tissue- specific manner. Additionally, the doublesex locus might be less conserved than intersex and fruitless. intersex and all three doublesex paralogs appear to be moderately expressed during key time periods of sex determination in O. fasciatus specimens. Finally, I find that intersex, fruitless, and doublesex-c (or potentially all three doublesex paralogs in males) are required for the determination and development of two sexual dimorphisms in O. fasciatus in tissue-specific combinations. All three target genes appear to be required for sex determination and development in both sexes of O. fasciatus. These results indicate novel functions and/or locus evolution of intersex, fruitless, and doublesex in O. fasciatus compared to other insects, indicating evolution of the sex determination pathway within the insect lineage.


The raw data collected and analyzed as part of this project are available for download at Colby College’s “digital commons” ( in a folder titled “jjust_honors_2019_supplementary”. All sequence alignments, and qRT-PCR and RNAi datasets are available as they were imported into R. In addition, the R-scripts that were used for analysis are provided as well. A text file that describes each file’s contents is included in the folder available for download.


Insect Sex Determination, Evolution and Development, Oncopeltus fasciatus

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Raw Data and Scripts