The following post is one of a series previewing the research that will be presented at the SETAC North America 42nd Annual Meeting (SciCon4), 14–18 November.
A guest post by Lauren Gillespie, Central Community College-Columbus
I teach general biology at Central Community College–Columbus (CCC-C) in Nebraska, where I hold ecology lab courses at a nearby creek with students in waders performing water quality tests. This “creek” is a glorified agricultural drainage ditch, bordered by farmland in a state that crop-dusts on a regular basis throughout the summer months. I saw birds nesting underneath the bridge once and decided on a whim to mist net during a lab session. Mist nets are used to capture birds and can only be purchased with proof of a U.S. Fish and Wildlife collecting permit. As students took samples, I extracted the bird—a barn swallow (photo 1, A)—that started this project.
The first barn swallow we caught had unusual coloration on the forehead (photo 1, A, lacking darker pigmentation); there were too many white feathers (photo 1, B) in an area that should have been completely brown (photo 1, D). We first suspected hybridization with cliff swallows that nest under the same bridge, and there was an account of cross-species mating between barn and cliff swallows documented in Nebraska in 2015. I tweeted the photos asking for help identifying the birds, and that tweet led to discussions with barn swallow experts around the country to confirm that our finding was atypical. We presented our discovery with a poster at the American Ornithologist Union annual meeting in 2019, where I met another researcher, Dr. Andrea Bonsoli-Alquati, who saw the same anomaly (photo 2) in his study population in Chernobyl, Ukraine. He documented that his population had genetic damage from radioactive fallout, and those birds exhibited both tail streamer deformations and partial leucism, which is a partial loss of pigmentation, resulting in patchy colored or white skin, hair or feathers. During our 2019–2021 field seasons, we observed approximately 42 birds displaying one or both features in addition to tail streamer asymmetry (photo 1, C), all of which are indicative of genetic damage.
Feather colors serve many purposes in birds as they can signal aggression, health, and reproductive behaviors. Plumage (e.g. feathers) helps insulate birds and can also shield them from heat. Quills of feathers contain both tissue and blood, and many birds sequester heavy metal burdens in their feathers to reduce systemic toxicity. This provides the opportunity to examine a number of questions about physiology and ecotoxicology through non-invasive and non-destructive sampling of pigmented feathers.
I study melanin pigments, specifically the orange-red-brown (phaeomelanic) pigments. Their sister pigment, eumelanin, colors grey and black feathers. All melanin-pigmented feathers have some ratio of both pigments, where one pigment is more dominant than the other depending on which molecular precursor is used—the amino acid tyrosine for eumelanin or cysteine for phaeomelanin. An enzyme, tyrosinase, is the rate-limiting factor in melanin production. Lower levels of tyrosinase can drive phaeomelanogenesis, and copper (Cu) acts as a co-factor promoting tyrosinase-driven melanin production. The production of the phaeomelanic orange-brown color may incur a higher physiological cost. Another metal influencing production is Calcium (Ca), as increased dietary Ca is correlated with increased size of melanin ornaments in zebra finches and increased eumelanin spottiness in barn owls.
Production and dispersal of melanin occurs in cells called melanocytes, and more specifically, within organelles called melanosomes (for my science friends keeping track, yes, there are eumelanosomes and phaeomelanosomes!). After production occurs, melanins migrate to the edges of the cell where they are up taken up by the tissues that will express the pigment. The complexity of this process increases, as melanin pigments must be delivered to specific feather tracks and follicles during molt, a seasonably timed and sometimes recurrent event throughout the year, depending on the species. All said, this is a physiologically sensitive process, with potential or disruptions at multiple levels of pigment production. These pigments act as antimicrobials, they are more durable than non-melanized feathers, and they absorb more light than other pigment types and therefore help with thermoregulation. The unique properties of melanins are due to their molecular structure as they have negatively charged end groups, and these can selectively bind transition metals, in particular, melanosomes in birds can contain elevated concentrations of zinc (Zn), copper (Cu), calcium (Ca), iron (Fe), and other trace metals.
I have predominantly studied the functional applications and hormonal correlates of melanin ornaments in Eastern bluebirds (photo 3), but the capture of some peculiar looking barn swallows in 2018 expanded the scope of my study into melanin pigments. I knew that Fe, Zn, Cu, and Ca can all facilitate melanin production, and thus began our investigation of heavy metal contamination within feathers.
This summer while collecting data, students noticed the same partial leucism in the local cliff swallow population, in addition to a few American robins, a common grackle (photo 5), and multiple Eastern bluebirds (photo 4). While our barn and cliff swallows are migratory, the bluebirds are year-round residents, indicating that there may indeed be local contamination throughout our city related to these plumage anomalies. This past year, we took soil samples from barn swallow nests and from both the creek and ponds at the local park. We also captured aerial insects for heavy metal analyses to get a better idea of how metals might be moving through the food chain.
Given the heavy manufacturing, industrial, and agricultural activities in Columbus, we plan to further examine plasma isolated from barn and cliff swallow blood samples. We will look for the presence and amount of the enzyme tyrosinase, which is intricately linked to melanin production as described above, and we will look for the presence of local pesticides. Varied environmental pollutants can influence melanin production, and the use of ornamental feather colors of birds for environmental assessment and monitoring is not a new idea. Examining ecotoxicology through the lens of melanin pigments may show difficult-to-detect, sub-lethal exposure to pollutants, preventing a crisis before it is too late to remediate.
Session: Partial albinism in Nebraska barn swallow feathers: Elemental composition, heavy metals and possible DNA damage (03.07.21)
Photos: All photos taken by Lauren Gillespie, unless otherwise noted.
Bonus material! Behind-the-scenes info about the testing used in this research and the opportunities for students interested in joining the CCC-C science team.
The CCC-C lab used X-Ray Fluorescence (XRF) Spectrometry to detect the heavier metals and elements in the feathers. The lab has access to this specialized equipment courtesy of a unique, collaborative relationship between CCC-C and the Nebraska Center for Materials and Nanoscience (NCMN), located on the University of Nebraska, Lincoln campus. The NCMN is one of 16 facilities across the country that are part of the National Nanotechnology Coordinated Infrastructure. This year, CCC-C’s relationship with NCMN was lauded as a national model for how these centers can collaborate with community colleges. In addition to teaching biology at CCC-C, I am also co-director of a National Science Foundation-funded S-STEM scholarship program, Growing Pathways to STEM (GPS), where we provide scholarships to low-income students interested in pursuing biology and engineering degrees. An integral part of this scholarship and mentoring program is student participation in applied science and engineering research. We pride ourselves as one of only a handful of community colleges facilitating undergraduate research in this manner, and my colleague and I were recognized by the League of Community College’s Excellence Award in 2020 for our efforts with Project GPS. That same year, I was awarded a Nebraska EbCSOR grant to pay our scholars for their summer research work on this project.