Geckos are reptiles and all are ectotherms, meaning they cannot generate their own body heat and must rely entirely on external sources to regulate their temperature. This biological constraint makes them highly susceptible to environmental cold, as their internal processes slow down dramatically when temperatures drop. While geckos can survive certain cold exposures, their survival depends on the duration and degree of the temperature decrease. A short, moderate temperature dip might be tolerated, but a prolonged or severe cold snap can quickly become fatal.
Ectothermy and Critical Thermal Minimums
The ectothermic nature of geckos dictates that their body temperature directly controls their metabolism, digestion, and immune function. In warm conditions, they are active, quickly digesting food and maintaining a robust immune system. When the ambient temperature falls, the gecko’s metabolic rate declines, resulting in lethargy and a diminished capacity to digest food, which can lead to complications if there is undigested matter in the gut.
Cold exposure eventually leads to the Critical Thermal Minimum (CTMin), the low temperature at which the gecko loses its ability to coordinate movement. Once a gecko reaches its CTMin, it can no longer right itself or move effectively, leading to physiological shutdown and eventual death if the temperature does not rise. The CTMin varies by species and population, but for many tropical house geckos, this limit can be around \(11-12^\circ\text{C}\).
Research on the common house gecko, Hemidactylus frenatus, has shown that individuals stop feeding when temperatures drop below approximately \(17^\circ\text{C}\), indicating a physiological slowdown long before the lethal CTMin is reached. Even short-term cold stress can weaken the immune system, leaving the gecko vulnerable to infections. The inability to maintain coordination below the CTMin means the gecko is essentially immobilized and unable to reach a warmer refuge.
Behavioral Strategies to Survive Seasonal Cold
Geckos that inhabit regions with seasonal temperature drops employ specific behavioral strategies to avoid reaching their Critical Thermal Minimum. The primary method is behavioral thermoregulation, where the gecko actively seeks out warmer microclimates within its habitat. This often involves moving away from the surface cold and into insulated retreats.
Geckos utilize deep crevices, hide under large rocks, or enter burrows, where the ambient temperature is more stable and warmer than the air temperature. These microclimates act as thermal buffers, using the insulating properties of the earth or rock to prevent extreme drops in body temperature. For species in temperate zones, this search for a stable thermal refuge prepares them for a period of dormancy.
This dormancy is known as brumation, a state of metabolic slowdown used by many reptiles during cooler periods. During brumation, the gecko remains conscious but its activity levels, appetite, and metabolism are drastically reduced. While the gecko is inactive, the brumation temperature must remain above freezing to prevent the formation of ice crystals in its tissues, which would be lethal.
Why Cold Tolerance Varies Among Species
The term “gecko” encompasses over 1,500 species, and their tolerance for cold varies widely based on their native environment and evolutionary history. Tropical species, such as the Tokay or Crested gecko, are adapted to environments with consistently high temperatures and relatively narrow thermal ranges. These geckos typically have a higher CTMin, making them highly vulnerable to even moderate temperature drops outside their preferred range.
Conversely, species originating from arid or temperate regions, such as the Leopard gecko or certain European wall geckos, have evolved a greater capacity for cold tolerance. These hardier geckos can acclimate to seasonal fluctuations, exhibiting a lower CTMin than their tropical counterparts. For example, some populations of the common house gecko introduced to cooler, temperate regions have demonstrated an ability to shift their cold tolerance downwards, suggesting a degree of physiological plasticity or rapid local adaptation.
This variation allows some species to survive in surprisingly cool areas, even showing activity at body temperatures as low as \(1.4^\circ\text{C}\) in the world’s southernmost geckos. The ability to endure a cold season is often the result of both inherited genetic traits and the ability to physiologically adjust to the immediate environmental conditions.