CONTACT: Julie Martinez-Navejar

kajam03@tamuk.edu or 361-593-2590

RESEARCHERS TO DETERMINE

IF HORNED LIZARDS GET MALARIA

KINGSVILLE (April 8, 1999) -- Many Texans have fond childhood memories of seeing and playing with Texas horned lizards. However, over the past 40 or so years, this interesting reptile has seen its population decline across Texas.

Some areas where the Texas horned lizard was abundant are now devoid of this species. Others harbor small isolated pockets of the scaly creatures. Eastern and central Texas seem particularly hard hit. This quick decline led the state to declare the Texas horned lizard a threatened species in 1977. It is also listed as a Species of Concern by the federal government.

Texas horned lizards have been called horned toads or horned frogs, but they are, in fact, lizards. Toads and frogs are tailless amphibians that live in land or water. Toads have rough, warty skin and frogs have smooth skin. Horned lizards are reptiles with tails and a scaled body.

There are currently 13 species of horned lizards, three of which are found in Texas. The Texas horned lizards can be distinguished from other species of horned lizards by the two very sharp spikes that protrude from the back of their heads, two rows of fringed scales on their sides, dark brown to sooty-colored dorsal spots edged with lighter colors and a light-colored stripe down the middle of their back. Adult Texas horned lizards range in length from three to five inches, excluding their tails.

Today, Texas horned lizards are found in the southeastern tip of Arizona and Colorado, southern and eastern New Mexico, most of Kansas and Texas and all of Oklahoma. They are apparently doing well throughout most of their range except in Texas.

Unfortunately, the exact cause or causes of the Texas horned lizard decline are not known. There have been numerous theories as to why they have been declining, including as reduced harvester ant populations caused by competing fire ants. Harvester ants are the preferred food of Texas horned lizards. Other theories suggest that loss of habitat from urbanization, over-collection for the tourist trade prior to 1977 and increased use of pesticides may be important factors.

Although each of these may negatively impact local Texas horned lizard populations, no one cause can account for the state-wide decline in the Texas horned lizard population.

A new study is underway at the Caesar Kleberg Wildlife Research Institute at Texas A&M University-Kingsville to examine a possible previously overlooked factor that may account for the declining Texas horned lizard population -- malaria.

Drs. Scott Henke and Alan Fedynich received a research grant from the Houston Livestock Show and Rodeo Association to survey Texas horned lizards for malaria in rangeland plant communities of South Texas.

"Studies looking at lizard species, such as the western fence lizard, have found that malaria-infected individuals had less stored fat, reduced stamina and smaller clutches, which can ultimately impact productivity," said Fedynich, research scientist for institute.

Fedynich believes that malaria may be a reasonable explanation for the statewide decline in Texas horned lizards.

"If malaria occurs in Texas horned lizards and if it is a fairly recent event in Texas, then one would expect to see statewide declines in the horned lizard population until malaria-resistant horned lizards comprise a significant proportion of the overall population," said Fedynich.

"The first phase of the study is to determine whether or not Texas horned lizards are infected with malaria," said Henke, associate professor in the animal and wildlife sciences department. "If they are, we will assess the disease's impact on several important factors that influence productivity in Texas horned lizards."

The common malarial species infecting lizards in the United States and Mexico is Plasmodium mexicanum. Since blood parasites have been little studied in Texas horned lizards, it is uncertain if they are infected with this parasite or have some other malarial parasite.

According to Fedynich, lizard malarial parasites undergo a cycle in which specific stages occur in the lizards and a blood-sucking insect called a "vector."

In lizard malaria, it is thought that the vector is a mosquito or mite. The vector also transmits the infective stage to other lizards. Basically, a vector ingests these parasites along with the blood when it feeds from an infected lizard. Once in the mosquito or mite, male and female parasites unite and form new cells called sporozoites.

When the vector feeds from another lizard the sporozoites are released into that lizard. Once inside the new host, several stages occur. The ultimate result is the development of male and female parasites contained within the blood cells of the host, which completes the cycle.

The researchers will take a blood sample from horned lizards they capture and test for malaria. The study will start in April or May when the reptiles start emerging from the ground

and end in September, before the lizards begin their winter hibernation.

Fedynich and Henke hope this study will find the missing piece of the puzzle that can explain the overall decline in Texas horned lizards in Texas. If the study does find malaria in Texas horned lizards, the information can be used to help focus recovery attempts by state and federal agencies for the Texas horned lizard.

For more information on the Texas horned lizard contact The Horned Lizard Conservation Society, a nonprofit organization dedicated to the conservation and recovery of the declining horned lizard populations. They publish a newsletter, are active in research and recovery and educate the public about this threatened reptile. They can be contacted at P.O. Box 122, Austin, TX 78767.

-TAMUK-