Date of Award:

8-2026

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Carol D. von Dohlen

Committee

Carol D. von Dohlen

Committee

James P. Pitts

Committee

Moria L. Robinson

Abstract

Taxonomy is the practice of identifying, classifying and categorizing species, providing structure for the vast diversity of life. Aphids are an ecologically important group of soft-bodied insects, but they can be difficult to identify because of their tiny anatomical size, reduced or simplified morphological features, and morphological variation within a single species across different generations. In this study, the taxonomy of the spiny witch-hazel gall aphid, Hamamelistes spinosus, is revised. The complex multi-generational life cycle of the aphids, which alternates between witch-hazel and birch trees, has led to confusion regarding past descriptions. Scientists in the late 1800s who were unaware of each other’s work described the different generations of the life cycle as two different species. Since then, other researchers merged the two species under the name H. spinosus Shimer. In this thesis, I revisited the question of one versus two species, leveraging modern molecular methods and details of morphology. I sequenced mitochondrial DNA, which showed species-level differences between distinct populations of H. spinosus aphids. In addition, I sequenced a nuclear gene to provide further evidence to support reinstating the two species. Differences between their host preferences exist as well. Lowland/southern populations of the species use river birch (Betula nigra) as the birch host, while highland and northern populations feed on birch species other than river birch. I also conducted detailed analyses of the aphids’ external physical features. The morphology of the two populations was somewhat divergent but had overlapping features, which is typical of recently diverged species. Multivariate analyses of the morphology indicated minor, but distinct differences between the populations in corroboration with the molecular and ecological differences. Morphs with wings were more likely to be accurately assessed than the wingless morphs with more reduced morphology. I conclude that these populations of H. spinosus warrant splitting of the species, reinstating the highland and northern populations with the historical name of H. papyraceae (Oestlund) and retaining H. spinosus Shimer for the lowland/southern population. This study underscores the importance of integrating ecological, molecular, and morphological data in resolving complex taxonomic issues.

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Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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