Graham, Jessica

• Postdoctoral Researcher, Behavioral Ecology Team, Centre National de la Recherche Scientifique 

• Ph.D., Environmental & Conservation Sciences, North Dakota State University

•  B.S., Natural Resource Sciences, Washington State University

The American dipper (Cinclus mexicanus) is unique in being North America's only truly aquatic songbird. They are reliant upon abundant aquatic insect prey associated with fast-moving, clear, cold streams in Western North America, and rarely stray from this optimal habitat. In the Black Hills of South Dakota is a small, geographically isolated population of dippers that is genetically distinct from its neighboring population in the Bighorn Mountains, nearly 250 kilometers away. Historically, dippers could be found along most permanent streams in the Black Hills. However, by 2018, only two remaining creeks around Spearfish canyon were inhabited. 

The breeding population of dippers in the Black Hills is estimated to have fewer that 100 individuals, with relatively low reproductive success. While not considered a federally threatened or endangered species, the state of South Dakota has listed the dipper as threatened. Low reproductive rates and a small population size compete with continuing threats of urbanization, water pollution, and invasive species. South Dakota's Game, Fish, and Parks (SD GFP) would like to see evidence of a self-sustaining population for at least 5 years in a 6-year period, but in order to meet this goal, the specific factors affecting reproductive rates and survival need to be identified and addressed. Studies conducted in larger populations of dippers provide some insight into potential causes of low reproductive rates. However, the role these factors play in the Black Hills population have not been established.

Heavy gold mining activity near the towns of Lead and Deadwood has heavily affected the drainage basins of Spearfish and Whitewood creeks, resulting in high selenium concentrations. Based on previous studies, these values are concerning for dippers. Primary producers take up selenium from water, introducing it into the food web where it accumulates in species like dippers that consume aquatic invertebrates. Dietary selenium intake in wild aquatic birds can delay egg laying, and delayed reproduction is associated with reduced reproductive success in many species, including the Black Hills dippers. Aquatic birds also experience factors like increased mortality and impaired reproduction in response to toxic levels of selenium. When enough selenium accumulates in eggs, hatch rate is reduced by as much as twenty percent. Whether these concerning levels are occurring in this particular population is unknown. 

Telomeres are repetitive, noncoding DNA sequences that form protective caps at the ends of linear eukaryotic chromosomes, being conserved in may organisms. Telomere dynamics and environmental conditions have been linked in numerous studies, suggesting they are useful biomarkers of biological aging, and also predictive of longevity. Exposure to environmental stressors accelerates telomere shortening beyond what occurs during normal cell division. Examples of stressors previously shown to shorten telomeres include heavy metal pollution. A recent study found that lizards from threatened populations are being born 'old'. That is, exposure to chronic stress is shortening telomeres in breeding adults, who then pass short telomeres to their offspring. This is considered the aging loop hypothesis and progressively leads to biologically old individuals as the population moves toward potential extinction. Telomere dynamics have never been reported in any population of American dippers but may be an important physiological indicator of stress and  aging within this population.

My current research is focused on bioaccumulation of the heavy metal, selenium, as  a potential cause of low reproductive rates in American dippers and exploring how this stressor significantly impacts aging and longevity via telomere degradation. American dippers serve an important role as bioassessment indicators for mountain streams. Addressing declines in the dipper population can also substantially impact stream biodiversity and water quality to protect human health.