Researchers study Pennsylvania ruffed grouse population

ruffed grouse

UNIVERSITY PARK, Pa. — Despite decades of decline, a genetic analysis of ruffed grouse reveals that Pennsylvania’s state bird harbors more genetic diversity and connectivity than expected. The findings suggest that the iconic game bird could be maintained in persistent numbers if appropriate protections are implemented.

The study, led by Penn State and Pennsylvania Game Commission researchers, was published in the journal Molecular Ecology. According to the researchers, Pennsylvania’s ruffed grouse populations have declined by up to 70% since the early 1960s, with birds in the southern part of the state particularly affected by West Nile virus, which is spread by mosquitoes and by habitat fragmentation due to development.

Leilton Luna, postdoctoral researcher at Penn State and corresponding author of the paper, said that when an organism’s population size drops too low because of disease or habitat loss, inbreeding can occur, which can lead to a decline in genetic diversity over time.

“Populations with low genetic diversity have a harder time evolving in response to changing environmental conditions and are at greater risk of extinction,” Luna said. “In the case of the Pennsylvania ruffed grouse, due to the sharp population decline, it certainly doesn’t have the same healthy genetic conditions as it did in the past. Even so, the current levels of genetic diversity and connectivity give us great hope for the preservation of this species.”

As an initial step, the team produced the first high-quality reference genome for ruffed grouse. A reference genome is a representative example of a particular organism’s genes, Luna said.

To investigate the population health of the ruffed grouse in Pennsylvania, the research team sequenced 54 individual bird genomes within habitats that were both fragmented by development and intact. The researchers examined the sequence data for evidence of gene flow, which indicates that genetic material is readily exchanged among migrating populations.

He said the team’s DNA analysis provided weak evidence of population subdivision across the state, although the researchers identified reduced genetic connectivity in the south, where the bird’s habitat is fragmented by human development.

“This tells us that the population may not be doing as bad as we expected,” Luna said. “It also helped us to inform wildlife managers which areas would most benefit from the development of habitat corridors. However, it is just a snapshot of the population at this particular moment. In the future, we hope to analyze the DNA of museum specimens so we can compare the genetic diversity and connectivity of today’s populations with those from before West Nile virus was present and before the habitat was so fragmented.”

Surprisingly, the team said, it also stumbled onto the presence of two genetic “anomalies,” called chromosomal inversions. These occur when a segment of DNA breaks off and then reattaches in reverse order.

“The data are very clear,” said co-author David Toews, assistant professor of biology at Penn State. “There are these two large chunks of the ruffed grouse genome that are highly differentiated from the rest of the genome, and they are not associated with any obvious geographic pattern among the birds. It adds a fun ruffle to the story.”

Toews said that chromosomal inversions previously were found in other bird species and were expressed via different plumage patterns or more aggressive behaviors, for example. He said the team does not yet know how the inversions might affect the ruffed grouse. It’s a topic the team plans to further investigate.

In the meantime, Toews said, the chromosomal inversions have important implications for conservation.

“On the surface, all ruffed grouse look fairly similar, but they actually have deep genetic differences,” he said. “In the context of conservation, it may be important to think beyond the species overall to consider protecting individuals with these genetic variations.”

Avery noted that Penn State has a long history of working with state agencies — such as the Pennsylvania Game Commission, Pennsylvania Fish and Boat Commission and Pennsylvania Department of Conservation and Natural Resources — to collect and analyze scientific data that can help inform conservation strategies. He said the team’s findings suggest that certain management interventions may help the bird to maintain healthy populations.

“Not only do ruffed grouse play an important role in the ecosystem, but they are also really interesting,” Avery said. “The males make this drumming sound in the spring to attract mates. You can physically feel the bass when they’re drumming in the woods. They also pair the drumming with a flashy display of ornamental feathers and a spread tail, similar to the over-the-top performance of a male peacock. To top it off, during the fall, ruffed grouse grow these fascinating extensions of their toe scales that may help to increase surface area during the winter months. They’re just beautiful and bizarre, and they deserve our conservation attention.”

(Information courtesy of Sara LaJeunesse, Penn State University.)


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  1. I am an outdoorsman in Mahoning County Ohio. Complete disappearance of wild pheasants and Bob White Quail. Also disappearance of rough grouse in my area and Forest County Pennsylvania where I have a cabin. Steady decline for the last 20 years. The causation of this I believe, is much more sinister than the published explanations.


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