Desert Iguana
The desert iguana is a slim, fast-running lizard from the deserts of the southwestern United States and northwestern Mexico. It is one of the most heat-tolerant lizards in the world. Most lizards retreat to shade when temperatures climb above 35 °C, but the desert iguana keeps on running at 45 °C, when most other animals are hiding. Unusually for a lizard, it is mostly vegetarian, feeding on flowers, leaves and fruits.
- Length40 to 60 cmIncluding the long tail
- WhereMojave and Sonoran desertsPlus Baja California in Mexico
- Heat toleranceActive at 45 °C+One of the most heat-loving lizards
- Main dietPlantsUnusual for a lizard, which usually eats insects
- Lifespanapprox. 15 yearsIn the wild
- Favourite plantCreosote bushEats its yellow flowers in spring
Heat tolerance compared to other lizards
The desert iguana stays active at body temperatures that would kill most other lizards. It is one of the most heat-tolerant land vertebrates on Earth.
What is a desert iguana?
The desert iguana (Dipsosaurus dorsalis) is a medium-sized lizard with a pale tan-grey body, a long slim tail and a row of slightly raised scales running down its back. Adults can be up to 60 cm long including the tail. They are related to the famous green iguanas of Central America but have evolved to handle desert conditions instead of tropical rainforests.
Built for heat
The desert iguana is one of the few lizards that actually prefers extreme heat. Its preferred body temperature when active is around 42 °C, well above most reptiles. To handle the heat, the iguana has several adaptations:
- Pale skin that reflects sunlight better than darker scales.
- Heat shock proteins in its body that protect its tissues from heat damage.
- Specialised blood circulation that helps shed heat through its head and neck.
- Long legs that lift the body off the hot ground when running.
- Burrow access. It uses burrows dug by other animals (like the kangaroo rat) to escape extreme heat at midday and to hibernate in winter.
The result is a lizard that can be active and feeding when other animals (and most humans) cannot survive in the open sun.
Why eat plants?
Most desert lizards eat insects because insects are easier to digest than plants and provide more energy per bite. The desert iguana is unusual in feeding mainly on plants, which take longer to digest and provide less energy. The trade-off is that plants are more reliable in the desert. After spring rains the creosote bushes bloom and provide an abundant food source. Even in dry years, the iguana can find enough green leaves and seeds to survive. Insects, by contrast, may be scarce in drought years.
Reproduction and life
Desert iguanas mate in spring. The female digs a burrow in damp sand and lays a clutch of 3 to 8 eggs. The eggs incubate in the warm sand for approx. 75 days before hatching. The new hatchlings are around 10 cm long and have to fend for themselves immediately; their parents provide no care after the eggs are laid.
Adult desert iguanas live for around 15 years in the wild, which is unusually long for a lizard. They spend the cool winter months hibernating in burrows and emerge for the warm season.
Deeper dive: heat shock proteins, the creosote bush partnership and ecological role
Heat shock proteins (HSPs) are a family of proteins produced by almost all living things when they are exposed to high temperatures. They act like molecular chaperones, helping other proteins maintain their proper shape under heat stress. The desert iguana produces unusually high levels of certain HSPs, even when not under immediate heat stress, which allows it to handle temperatures that would denature (unfold) the proteins of less heat-tolerant lizards. Studying the desert iguana's HSP system has provided insights for biotechnology and for understanding how living things might cope with climate change. Some research is even exploring whether HSP analogues might help protect human transplant organs from heat damage during transport.
The relationship between the desert iguana and the creosote bush (Larrea tridentata) is one of the more interesting interspecies partnerships in North American deserts. The creosote bush is one of the dominant plants of the Mojave and Sonoran deserts and the longest-lived plant in the world (some creosote clones are estimated to be over 11,000 years old). The plant produces leaves with strong-smelling oily resins that protect against herbivory by most insects and mammals. The desert iguana, however, has evolved tolerance for these compounds and feeds heavily on creosote flowers and leaves. In doing so, the iguana helps pollinate the flowers and disperse the seeds. The iguana is just one of several species that have specialised on creosote; the creosote bush also has its own species of grasshopper, gecko and antlion that depend on it.
The desert iguana plays a key ecological role as both a herbivore and as prey. By eating large quantities of flowers and seeds, it influences plant reproduction patterns and helps spread seeds across the desert. At the same time, it is an important food source for desert predators like roadrunners, kit foxes, snakes and birds of prey. Its tendency to be active during the hottest part of the day means that it occupies a temporal niche that few other prey species can fill; predators that have evolved their own heat tolerance (like the roadrunner) get access to a food source that would not otherwise be available. Loss of desert iguana populations therefore has ripple effects through the desert ecosystem.
For other desert animals, see desert animals. For desert ecology, see desert ecosystems.