Scientists have taken one of their closest looks at evolution in action in a wild animal. In a study presented last week at the Biology of Genomes meeting in Cold Spring Harbor, New York, researchers reported some intriguing insights into the changing DNA of a dozen generations of the Florida scrub jay. The work, made possible by powerful advances in genetic sequencing and a 45-year data set, has revealed how the jay’s environment has favored small changes within the genome. The findings may help conserve this and other endangered species in the future.
“All the sudden you can do these sorts of studies in scrub jays and other animals that are not a [laboratory] organism,” says Joseph Pickrell, an evolutionary geneticist at the New York Genome Center in New York City, who was not involved with the work. As a result, “there are long-standing ecological and evolutionary questions that you can address.”
Florida scrub jays (Aphelocoma coerulescens)—endangered, 20-centimeter-long bluish birds, first attracted biologists’ attention almost 50 years ago because the young often stick around the nest to help the parents raise subsequent generations of offspring, a rare breeding arrangement among vertebrates. They tend to be homebodies, with generation after generation rarely straying 10 kilometers beyond their predecessors’ nests. As a result, researchers at the Archbold Biological Station in Venus, Florida, have been able to build a detailed family tree for jays there that spans 12 generations. And for the past 45 years, they have kept records on the life span, number of eggs and offspring produced per year, and other traits; they’ve also taken blood samples from every member of the group over the past 25 years.
Graduate student Nancy Chen, a population genetics fellow now at the University of California, Davis, started by sequencing the full genome of a reference scrub jay, and then assessed the genetic differences of all 3800 individual birds followed by the Florida group. Among the 15,000 places in the genome she studied, the vast majority of changes seemed evolutionarily neutral—but there are 67 places where one variant was favored over another, likely because it conferred a survival or reproductive advantage, she reported at the meeting.
In a follow-up analysis, she and her colleagues at Cornell University tried to pinpoint when in a bird’s life these variants gave jays their boost. They found 21 variants that seem to help female birds ages 11 days to 90 days old—comparable scrub jays lacking those variants didn’t live as long. And in sperm, there were four changes in DNA that affected which fertilizations were successful; the research team found some variants were passed on to the next generation more than others.
At this point, Chen doesn’t know how these DNA differences alter survival, but what the studies do reveal is that there are genetic variants that are favored in some parts of the life cycle and not others. Evolutionary biologists have long wondered why genetic variation is maintained, when there should be a “best” variant for each gene. Now, they have an answer: One variant may be beneficial for a certain part of the life cycle and the other may be beneficial at another part, Chen explains. Overall, maintaining genetic diversity may help a species survive changes in their environment, she says.
Chen and others see the scrub jay work as an illustration of the power of applying genomics to long-term field studies. For species such as scrub jays, once conservationists know which genes work best and when, they can in theory be better matchmakers in breeding endangered animals.