Many Species, One Ecosystem

The vernal pool ecosystem is a vital and declining part of California's landscape. These temporary wetlands provide a wide variety of ecosystem services to the country's most agriculturally-productive state: 

- Support native grasses, which maintains pasture productivity

- Support native pollinators

- House and feed migratory birds, especially waterfowl. It is estimated that a billion birds per year migrate along the Pacific Flyway. Hundreds of thousands rely on the water, shelter and food abundant in California's vernal pools.

- Provide breeding habitats for native amphibians

- Sequester carbon

and more!

 

Branchiopods are small freshwater crustaceans commonly called "fairy shrimp" and "tadpole shrimp". They are important vernal pool community members. They feed on algae and detritus in vernal pools, and in turn are eaten by larger predators including salamanders and waterfowl. They are specially adapted to the wet-dry life cycle of temporary pools and can survive dry summers as "cysts" - fertilized, dormant eggs. These cysts are also the secret to moving around the landscape - birds will eat the shrimp, which contain the cysts, and then fly off to the next pool. There are other ways they can move, too. Cattle (or in the past, Bison or Bighorn Sheep) will wade and wallow in the pools, and move the cysts in the mud in their hooves. They can be moved short distance by wind in the summer and flooding in the spring. And now that we're here, humans probably move them around too, in our boots and tire tracks when we move through vernal pools.

 

It is estimated that 95% of the vernal pools present in California at the time of Spanish settlement have already been lost. Remaining vernal pool habitat is fragmented, and only a portion is protected. However, the U.S. Fish and Wildlife Service has been attempting to protect, conserve and recover vernal pools in California and Southern Oregon (recovery plan link). Part of that protection has been listing vernal pool organisms as threatened or endangered and researching them in order to improve their conservation and management. We picked five vernal pool species of conservation concern and carried out RAD-sequencing on individuals from across their respective ranges in order to answer questions and help inform management decisions.

 

Key Questions

1. Within species, how genetically isolated are populations of vernal pool branchiopods?
2. How do these patterns compare between species?
3. Where are the species most genetically diverse? Do these sites overlap? Can they be prioritized for protection, or can they be characterized ecologically?
4. Are there corridors of connectivity that link distant populations? Can these corridors be characterized and prioritized for conservation?
5. Is there contemporary migration between populations? At what geographic scale?
6. What is the evolutionary history of these populations? Of these species?
7. What do these results tell us about how passively-dispersed, patchily distributed species move and persist in an urbanized landscape? How can they help us prepare to manage these species into the future?

Methods

More than 1000 individuals from these five species were collected all across California during the wet seasons of 2018 and 2019. This sampling was a huge undertaking led by grad student Shannon Kieran, who designed the sampling scheme by identifying historical locations using the California Natural Diversity Database and then worked with a huge network of land managers, field biologists and government agencies to collect samples during a series of short seasonal inundation windows.

 

This field work was a hugely collaborative effort and would not have been possible without help and assistance from a wide range of folks. The GVL would like to take this opportunity to thank some of the incredible humans who made this happen:

- Mo Kolster, former director of  the UC Merced Vernal Pool and Grasslands Reserve, who worked tirelessly to support all the research done at this incredible preserve.

-Francesca Cannizzo, biologist with UC Merced

-Brent Helm, director of the Tansley Team, who saved me more times than I can count

-Carol Witham, heart of the Sacramento-area vernal pool community

-Tara Collins and Matt Gause at Westervelt Ecological Services, who were incredibly knowledgable and accomodating

-The DOD researchers who took me out to bases across the state: Jason Bachiero, Kirsten Christopherson, and Ellen Pimentel

- The folks at Center fo Natural Lands Management, especially Bobby Kamansky, Erik Gantenbein and Deborah Rogers

- Geoffery Grisdale with USFWS down at Kern-Pixley

- John Battistoni at CDFW

- Paul Benton (Oregon DOT) and Molly Morrison (The Nature Conservancy) who helped me access Oregon pools and samples

-Bruce Delgado with BLM out at Fort Ord, who also gave an unforgettable lesson about all the good eating in the California coastal scrublands

- Jason Peters and Sean O'Brien for their help in the trenches

 

 

 After collecting so many specimens, we produced a number of RAD-sequencing libraries using the sbf1 restriction enzyme. A restriction enzyme is a protein that cuts DNA at a specific sequence anywhere that sequence occurs. We can use this by creating a library of sequences that all start with the same known sequence.

 

We used these RAD seq assemblies to examine the genetic diversity, differentiation and migration of each species. We also produced neighbor-joining trees, performed Mantel tests to determine the relationship between geographic and genetic distance, and looked for any obvious outlying populations.

Results and Publications

We found that there are two distinctly different populations of B. lynchi - one from Oregon, which is geographically isolated by at least 300 miles from other populations, and the other from Alameda County, CA. This centrally-located population is a special preserved property on Brushy Peak called the Vasco Caves, a series of weathered limestone rock formations full of indentations where water has eroded them away. These indents fill with water every winter, which in turn fill with B. lynchi and other vernal pool species. Nowhere else is B. lynchi found in rockpools.

These dramatically-different pools are nonetheless surrounded by regular, soil-bottomed vernal pools in the lowlying areas around Brushy Peak and the area is home to birds, amphibians and grazers who theoretically might move them around. Nonetheless, these shrimp are genetically distinctive, suggesting that ecology can drive differentiation in this species.

This result and many, many more were published in a technical report for the U.S. Fish and Wildlife Service in 2020, and will be published in an upcoming peer-reviewed paper coming in 2022.