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What’s on a horned lizard’s menu? Grant will aid Richards' study
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Filed under Public Information on Thursday, May 31, 2018 by Author: Public Information.

Hannah Richards knows the digestive systems of Texas horned lizards inside and out. She studies what goes in, and what comes out. Her work with the iconic lizard has earned her a grant from the Horned Lizard Conservation Society (HLCS), and her findings may help zoos save funds on the lizards’ upkeep.

Richards, who earned her master’s in biology from Midwestern State University this spring, received the grant from the HLCS to extend the research performed for her thesis titled “The digestive efficiency of Texas horned lizards fed different species of prey.” The work is intended to determine the effects of declining traditional prey and the physiological effects of diet on wild versus captive animals.

Historically, horned lizards feasted on harvester ants, but that population may be declining. Richards wondered what other prey could take their place and if a substitution would affect the lizard. Charles M. Watson, Associate Professor of Biology and Richards’ mentor, said that lizards in the area also eat beetles, and that they may digest beetles more efficiently, getting more energy from beetles than ants.

As part of her studies, Richards has been monitoring the lizards on a nearby ranch to investigate the diet composition and available prey. She also is working with the Dallas Zoo to determine the digestive efficiency of the lizard when fed different prey items. By studying their intake and output, she will determine how efficient these lizards are at deriving energy from their primary prey (harvester ants) and prey they eat in smaller amounts (beetles). She is also investigating whether lizards supplement their ant diet with beetles or if the beetles are incidentally eaten while feeding upon ants.

At the zoo, Richards feeds horned lizards different insects then studies their feces to determine the digestive efficiency. “The zoo spends a lot of money to feed them ants when other more available insects may be just as good or better,” Watson said.

The grant will allow her to continue the research with the zoo throughout the summer. When complete, the study will make predictions on the evolution of nutrition adaptability with the decline of the harvester ant and increased nutrition from other prey. The study will also provide information to help find new places to relocate the lizards. The Texas horned lizard is listed as threatened in the state of Texas, but not listed as a federally endangered species.

This spring, Richards was named Outstanding Graduate Student in the College of Science and Mathematics, and was recognized as the top graduate student by the Biology Department.

Richards presented her research at the Society for Integrative and Comparative Biology meeting in San Francisco, and to other zoos and state agencies to discuss the diet of Texas Horned Lizards and the implications of other insects being fed to the lizard.

The Horned Lizard Conservation Society is dedicated to protecting horned lizards by documenting and publicizing their values and conservation needs, promoting horned lizard conservation projects, and assisting with horned lizard management initiatives. The HLCS annually sponsors research that has direct conservation applications.

Contact Watson at for more information.

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