Secrets in the soil: NMSU scientists research desert’s tadpole shrimp


Triops occupy a petri dish for NMSU student Rebekah Horn to collect data. (NMSU photo provided by Rebekah Horn)
Triops occupy a petri dish for NMSU student Rebekah Horn to collect data. (NMSU photo provided by Rebekah Horn)

“You look at the soil and you don’t see anything, but you put it in water and it comes to life,” said David Cowley, associate professor in the Department of Fish, Wildlife and Conservation Ecology at New Mexico State University.

Researching a unique crustacean with a fossil record dating to more than 250 million years ago, the tadpole shrimp, Cowley and Ph.D. student Rebekah Horn are uncovering new discoveries about the genetic composition and how these invertebrates reproduce. 

“The goal is to learn about the ecology and how many species there are in the area,” Cowley said. “For evolutionary biologists it’s a real oddity. How does a species persist so long in time and not change substantially? It’s gone through major climate change, glaciation, etcetera, but the species persists!”

The tadpole shrimp colonizes freshwater temporary ponds, such as dry lakes and vernal pools, throughout the Southwest. Females lay eggs that can survive in the sand or dried mud, dormant for several years. When placed in water the eggs hatch over a period of time and the cycle begins again.

“Each pond or playa we have in the desert represents a different population. It’s interesting to me that we have all these ponds relatively close together, yet they’re all so different genetically – however the species themselves look similar,” Horn said. 

Funding for the project came from the Rio Grande Basin Initiative in conjunction with Texas A&M University. A pilot grant from the National Center for Genome Resources in Santa Fe was awarded to Cowley and Horn for their specific work in genome sequencing.

“For the last 20 years people who did research on triops (one genus of tadpole shrimp) agree that there seems to be three reproductive systems,” Cowley said. “One is purely female, one with 30 percent ‘males’ – but we’ve never proven that they’re really males – and one has about 50 percent of both.” 

Looking at the pouch of embryos located on the extension on the 11th leg of the mother, Horn observes and compares the genetic profile to each of her offspring and samples them using mitochondrial and nuclear DNA. Determining the sequence of the mitochondrial genome, which is 15,000 letters long, will aid in her analysis. This method helps Horn in determining the reproductive system being used by the tadpole shrimp. 

Part of Horn’s thesis was recently accepted by the peer-reviewed scientific journal PLOS One, of the Public Library of Science. 

The information on the reproduction of the Triops will be vital to the ecologists involved with crustaceans and evolutionary ecologists, as there is no existing data on how this species reproduces. 

With continued research, Cowley and Horn intend to discern if water chemistry contributes to gene expression among the Triops species.

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