UC Davis Research Spotlight: Madison Armstrong
Urban Pollutants and Pacific Purple Sea Urchins
Maddie is a PhD candidate in her 5th year working with Dr. Rachael Bay. Maddie uses genomics, transcriptomics, and developmental biology techniques to investigate the evolutionary implications of urban stressors on marine invertebrates, using Pacific Purple Sea Urchins as her model organism. She is mainly based on campus at UC Davis but runs some of her experiments at the Bodega Marine Lab. If you want to learn more, feel free to check out her website (https://madisonarmstrong.me/)
Sea Urchins as Model Organisms
Sea urchins are part of a diverse group of marine invertebrates called echinoderms. These marine organisms have been used as model organisms in laboratory studies due to several advantages. They are very easy to spawn in lab conditions, allowing scientists to produce large batches at low costs [1]. They also undergo a rapid well-characterized and observable embryonic growth process–becoming swimming larvae as early as 5 days old–which makes it easy for researchers to study various stages of development within a short period of time [1]. Furthermore, urchins are resilient and adaptive to many environmental conditions, allowing for easy lab maintenance [1]. Lastly, while hardy in survival in the face of difficult conditions, echinoderms are still sensitive to changes in their environment in other ways. In an effort to cope with such stressors, exposure to environmental toxins and pollutants can easily alter echinoderm morphology in both larvae and adult phases. This makes their morphological changes in ecotoxicology experiments easily observable [1].
Maddie Armstrong is currently working with the Pacific purple sea urchin (Strongylocentrotus purpuratus) as her model organism. Their unique purple coloring and high abundance make field collections easy.
Current Research
How does the urban environment affect evolution in marine populations?
To determine how urban environments can affect evolution, Armstrong compares collected urchin spine samples from urban sites, where heavy pollution is expected, to non-urban sites. She is currently examining samples collected from paired urban and non-urban sites in San Diego, Los Angeles, and Victoria, British Columbia.
Back in the lab, Armstrong looks for genetic differences between the urban and non-urban samples. If urban urchin spine samples show genomic variation when compared to their non-urban counterparts, it could indicate adaptation. To determine this, she tests to see if there are any genetic variants, called single nucleotide polymorphisms (SNPs), shared between urchins from the urban areas that are not shared with the urchins from the nearby non-urban areas. Shared SNPs in the urban samples that do not exist in non-urban samples from the same area would indicate that the urban sea urchins may be adapting to stressors in their local environment.
How do urban pollutants affect development?
Armstrong is interested in identifying how larval development and genetic expression change in response to different levels of exposure of an endocrine-disrupting chemical (EDC) called nonylphenol. Nonylphenol is a toxic compound commonly found in urban wastewater outflows which can interfere with the hormonal systems of exposed organisms [2]. It is found in the form of nonylphenol ethoxylates, which have many industrial and household applications, such as in detergents and emulsifiers, due to their cost-effective nature. Because of their extensive anthropogenic usage, nonylphenol ethoxylates reach wastewater and sewage systems in large amounts, eventually degrading into nonylphenol. Known effects of nonylphenol include decreased fertility and survival in aquatic organisms, among other changes to normal physiological functions [3]. Due to their health complications, the use and production of EDC products have been banned in the European Union and are strictly monitored in many other countries such as Canada and Japan [2].
To investigate the effects of nonylphenol on the urchins, Armstrong exposes spawned urchin larvae to varying levels of nonylphenol and observes changes in morphological appearance and gene expression. She will then note any developmental deformities found in the urchin larvae throughout development at three growth phases, the blastula, gastrula, and pluteus phases, and compare these results to urchin larvae not exposed to the chemical. This experiment is ongoing, but preliminary observations have identified some skeletal abnormalities in the exposed group.
Preliminary results indicate the presence of unexpected non-monotonic effects of EDCs, characterized by non-linear responses. Non-monotonic effects refer to phenomena where the relationship between the dose or intensity of a stimulus and its elicited response is not strictly linear or proportional. Instead of a linear increase or decrease in response as the dose changes, there may be instances where the response shows unexpected fluctuations, plateaus, or reversals at certain dosage levels. This can often occur in the context of exposure to substances like hormones or chemicals. In some cases, low doses may produce different effects than high doses, or there may be a threshold beyond which further increases in dose concentration do not result in corresponding changes in the organism response. In this case, lower doses exhibit a higher incidence of abnormalities compared to higher doses. Armstrong administered ecologically significant doses of 100, 500, and 1000 parts per billion. She observed a notable concentration of effects at 100 parts per billion when compared to higher concentrations where the effects are reduced or cutoff. When observed over a week, a higher incidence of abnormalities was evident in the pluteus larvae exposed to 100 parts per billion compared to those exposed to higher doses. Additionally, Armstrong observed a significant variability in how these EDCs affect offspring from different mating pairs, indicating a range of tolerance within the population. She saw size increases as early as the blastula phase, with visible abnormalities becoming apparent during the pluteus phase.
Looking Forward
Armstrong hopes that understanding how sea urchins respond to urban pollution could provide information about the broader impacts of human activities on marine ecosystems. Moreover, the nonylphenol-induced morphological and gene expression changes in Pacific purple sea urchins demonstrate the need for continued monitoring and regulation of endocrine-disrupting chemicals. In the future, Armstrong hopes that her research will eventually provide significant implications for ecological understanding regarding nonylphenol and other endocrine-disrupting chemicals, and thereby inform lasting environmental policy changes. This research not only advances our understanding of the ecological consequences of urban pollution but also provides valuable insight into steps for sustainable environmental management and conservation efforts in the United States.
About the Author: Mirabel Sprague Burleson
Mirabel is a class of 2024 Biological Sciences major with a Global Disease Biology minor. She’s on a pre-med track and plans to pursue a career in healthcare after graduation. Mirabel was born and raised in Alaska and moved to California in 2020 to attend UC Davis. Outside of classes and Aggie Transcript duties, she enjoys working out, hanging out with her dog, and sleeping.
References
Foltz, K. R., & Hamdoun, A. (2019). Echinoderms, Part A. ECHINODERMS, PT A, 150, 125-161.
Soares, A., Guieysse, B., Jefferson, B., Cartmell, E., & Lester, J. N. (2008). Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters. Environment international, 34(7), 1033-1049.
Langford, K., Scrimshaw, M., & Lester, J. (2007). The impact of process variables on the removal of PBDEs and NPEOs during simulated activated sludge treatment. Archives of environmental contamination and toxicology, 53, 1-7.