Gila monsters use osteoderms to protect themselves during fights

A recent study published in the journal Royal Society Open Science has shed light on the intriguing behavior of female Gila monsters, large venomous lizards. The research, conducted by Professor A. Kristopher Lappin from Cal Poly Pomona, reveals that female encounters are significantly more intense and violent compared to interactions between males.

According to the study, when male Gila monsters engage in combat, it is primarily a ritualized contest involving wrestling and occasional nipping. However, the researchers discovered that female Gila monsters display much more aggressive behavior towards one another, involving violent biting. In fact, in three out of four interactions observed, the encounters had to be intervened to prevent severe harm.

This is the first scientific paper documenting such behavior in the iconic Gila monster species, which is indigenous to the American Southwest and northwestern Mexico. Gila monsters are known for their distinctive orange and black appearance, bead-like scales, and formidable teeth. They can reach lengths of nearly two feet, making them the largest native lizard species in the United States.

The study involved adult Gila monsters from two captive colonies. The researchers combined behavioral observations with bite-force experiments to investigate whether the lizards’ osteoderms, which are well-developed bony deposits in their skin, serve a protective function during aggressive interactions.

During the trials, the female Gila monsters displayed a sequence of behaviors, including tongue flicking, hissing, nudging, scratching, and body inflation. As the aggression escalated, sustained biting occurred, followed by a behavior resembling the “deathroll” seen in crocodiles, known as lateral rotation (LR). Whenever LR was observed, the trial was halted to prevent potential serious injuries. Fortunately, no Gila monsters were permanently harmed during the experiments.

Although the researchers expected some degree of aggression among females, they were surprised by how quickly and intensely the aggressive behavior was initiated. Additionally, despite the growing body of literature on venom self-resistance in animals, the Gila monsters that were bitten and envenomated exhibited noticeable behavioral and physical compromise for an extended period. However, the lizards fully recovered without the need for medical intervention.

This study provides valuable insights into the unique social dynamics and aggression patterns exhibited by female Gila monsters. Further research is needed to explore the underlying reasons behind this behavior and to understand the potential adaptive advantages it may confer to these fascinating creatures.

A team of researchers, including lead author Gordon Schuett, an adjunct professor of biology at Georgia State University, recently conducted a study shedding light on the understudied behavior of Gila monsters, the iconic venomous lizards found in the southwestern U.S. and northern Mexico. The research team, which also included co-authors from Cal Poly Pomona, noted that despite their iconic status, Gila monsters have been relatively neglected in scientific research.

One interesting aspect highlighted by the study is that components of Gila monsters’ venom have been used in the development of drugs for type-2 diabetes since the early 2000s. Therefore, in addition to providing insights into the social structure of this cryptic and threatened species, this study offers valuable information on a lizard species that has potential pharmaceutical implications.

While aggression among female lizards is often associated with territorial defense, mate defense, and parental care in other species, the authors hypothesize that in the case of Gila monsters, female aggression may be linked to nest defense and serve as a means to prevent cannibalism. Gila monsters are nest-raiding specialists, preying on eggs, nestlings, and newborn mammals, which could explain the heightened aggression observed among females.

The study involved researchers from Cal Poly Pomona, including corresponding author A. Kristopher Lappin, as well as other individuals with affiliations to the Chiricahua Desert Museum in Rodeo, New Mexico. The team hopes that their findings will encourage further research on this intriguing behavior, not only in Gila monsters but also in other animal species.

The aggression displayed by female Gila monsters offers valuable insights into the nature of aggression itself, showcasing its extreme manifestations and highlighting its crucial role in animal social behavior. By studying the aggression between females, researchers can gain a deeper understanding of the functions it serves in terms of social structure and reproduction. The researchers aim to inspire more comprehensive investigations into this behavior, both within the iconic Gila monster species and across a broader range of animals.

Source: California State Polytechnic University

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