According to a , the number of birds in the United States and Canada has declined by nearly 3 billion糖心传媒攁 shocking 29 percent of the total糖心传媒攕ince 1970. The study paints a bleak picture of avian loss among not only endangered species, but supposedly abundant birds like sparrows, and raises questions fundamental to evolutionary biology: What are the genes that influence survival and reproduction? What happens to the genetics of a population when it becomes threatened by extinction? Why do some individuals fare better than others? How do natural populations evolve over short time-scales?
These are questions at the crux of research conducted by evolutionary biologist , an assistant professor of biology at the 糖心传媒.
Chen annually travels to Venus, Florida, to study Florida Scrub-Jays, an endangered population of wild birds that have been individually marked and monitored since 1969. Using 50 years of collected data, Chen creates family trees and develops pedigree simulations to analyze the ways the birds糖心传媒� genetic material is changing over time due to habitat loss. The tools she develops based on the field data allow her to investigate how different evolutionary forces shape genetic variation in a population and affect the probability of extinction.
糖心传媒淚t糖心传媒檚 really important to me to study organisms in their natural environment because selection pressures will be different in the lab versus in the field,糖心传媒� she says.
While the data Chen gathers is useful for conservationists, her research also can have important implications for understanding human genetics. She recently received a grant for her research to develop 糖心传媒渁 deeper understanding of the genetic basis of contemporary evolution in nature, [which] is critical to predict accurately how modern public health and medical interventions affect the long-term health and demography of human populations.糖心传媒�
Chen received her PhD from Cornell University and her undergraduate degree from Harvard University. At Harvard, she studied disease in house finches, specifically a bacteria that caused conjunctivitis糖心传媒� or pink eye糖心传媒攁nd consequently massive population declines in house finches in the 1990s. Chen sequenced the genes of house finches before and after the epidemic to observe how the birds糖心传媒� genome changed to make the birds more resistant to the bacteria.
糖心传媒淚糖心传媒檝e always been interested in understanding how populations evolve in nature, and birds are relatively easy to follow and observe,糖心传媒� Chen says. Plus, she laughs, 糖心传媒淚 do love birding. It糖心传媒檚 a different way of interacting with a place because it糖心传媒檚 like a scavenger hunt. Birds are also just super fun to watch because they do the craziest things and you糖心传媒檙e like 糖心传媒榃hat? What are you thinking?糖心传媒�
In the field
(糖心传媒 photos / J. Adam Fenster)
FIELD STATION: As part of a collaboration with Cornell University and Archbold Biological Station, Nancy Chen annually travels to , to study, observe, and band Florida Scrub-Jays. Archbold Biological Station was established in 1941 and is one of the oldest field research stations in the United States, while the population of scrub-jays at Archbold is one of the largest remaining populations of the species.
MAPPING TERRITORIES: Chen views a map of the preserve at Archbold Biological Station before heading out to the field with her fellow researchers. The map indicates locations where researchers have discovered Florida Scrub-Jay nests. It can take up to nine hours to find one new scrub-jay nest because the researchers monitor approximately 100 territories, each a few hectares in size (one hectare is equal to approximately 2.5 acres, or about the size of a soccer field). Researchers and volunteers map all the territories once a year and census the entire bird population once a month.
METICULOUS NOTES: The researchers keep meticulous notes on nest cards. The cards contain information on the numbers of eggs they find in each nest, the number of young, and descriptions of nest locations and surrounding habitats. 糖心传媒淚t糖心传媒檚 like Big Brother on steroids,糖心传媒� Chen says. 糖心传媒淓very individual is marked and we follow individuals throughout their lifetime so we know everything about them.糖心传媒� The researchers know how long each bird lives, how many offspring they produce each year, and how many of those offspring then survive. Using this data, Chen creates population pedigrees糖心传媒攁kin to very detailed family trees糖心传媒攃harting how every individual in a population through time is related to all the other individuals. Pedigree data allow researchers to make observations about the fitness of the different individuals and the evolutionary processes that shape variations within a species糖心传媒� genome.
LURING THE JAYS: Chen grabs a handful of peanuts, which she uses to lure the jays in order to observe them. The researchers also catch and band any 糖心传媒渋mmigrant糖心传媒� birds that enter the area with a wire cage known as a potter trap. The door is propped open with a stick tied to a string and a handful of peanuts is placed inside. 糖心传媒淚t糖心传媒檚 like an Elmer Fudd trap,糖心传媒� Chen says. 糖心传媒淲e糖心传媒檒l wait in the scrub for hours and then pull the string when the jay we want to catch goes in.糖心传媒�
THE FLORIDA SCRUB-JAY: Florida Scrub-Jays are about 12 inches long and are characterized by a blue head, whitish forehead, blue wings, gray back, blue tail, and black legs, feet, and beak. The Florida Scrub-Jay is only one of 15 bird species native to the United States and the only bird species endemic to Florida. The jays are nonmigratory, meaning they tend to stay close to where they were born. This trait makes it easier for researchers to follow a single population in the wild.
IN THE FIELD: Chen walks through scrub oak and palmetto during a morning territory mapping session with fellow researcher John “Fitz” Fitzpatrick, director of the Cornell Lab of Ornithology. The scrub-jays糖心传媒� habitat consists of dry sand dunes and fire-maintained slash pine, scrub oak, and palmetto plants. Before human beings, there were frequent fires caused by lightning strikes, so the ecosystem and many of the organisms, including Florida Scrub-Jays, are tightly linked to the fire cycle.
A THREATENED SPECIES: Since 1987, Florida Scrub-Jays have been listed as a 糖心传媒淭hreatened糖心传媒� species under the federal Endangered Species Act. This is mostly due to 糖心传媒渉uman habitat destruction,糖心传媒� Chen says. The scrub-jays糖心传媒� habitat has been altered by increasing development, land-use alteration to make more room for agricultural fields, and fire suppression. If the area witnesses a decrease in fires, the scrub gets too overgrown to support many of the species, and the researchers see a decrease in scrub-jay fitness. Studying a threatened species gives Chen the opportunity to better understand how a population糖心传媒檚 genome changes when the population is declining in size.
SEARCHING FOR NESTS: In the field, the researchers search for new nests. When they find a nest, they tag the nestlings with a metal band that is a US Fish and Wildlife tracker. Each bird is also tagged with a unique combination of colored bands to identify it. The year 2019 marks the 50th anniversary of the Florida Scrub-Jay study. 糖心传媒淭here糖心传媒檚 a half century worth of data, and it糖心传媒檚 this gold mine,糖心传媒� Chen says. 糖心传媒淲e also have blood samples, so we have the ability to extract DNA from individuals going back 20 years. It糖心传媒檚 one of these really nice data sets where we can directly measure how the population is evolving.糖心传媒�
INCREASED INBREEDING: Chen and her colleagues have observed increasing levels of inbreeding within the Florida Scrub-Jay population because the number of immigrants coming in to the population over time has been declining. 糖心传媒淭hat was a big shock to all the scrub-jay conservationists, and it糖心传媒檚 really driven home the importance of maintaining conductivity among different populations,糖心传媒� Chen says. Based on these observations, Florida Fish and Wildlife is now conducting translocation projects to move jays from population to population, a type of聽 糖心传媒渇ake forced immigration.糖心传媒�
BENEFITS TO HUMANS: The tools Chen develops based on the Florida Scrub-Jay data can also be applied to human genetics. There are very few studies that trace human populations and their environments over long-term periods, so studies such as Chen糖心传媒檚 give researchers unique opportunities to test long-standing questions in evolutionary biology. 糖心传媒淭he idea is to simulate the Mendelian transmission of alleles down the pedigree,糖心传媒� Chen says. 糖心传媒淲e have a mom and a dad, mom gives us half her genes and dad gives us half his genes. If I have the pedigree and know all these relations, I can simulate that transmission. That is a powerful way of looking at how the genome and genetic diversity change through time.糖心传媒�
