The question “Are all geckos female?” is a common misconception. While some specific gecko species can reproduce without a male, most of the 2,300 known species have both males and females and reproduce sexually. This diverse group of lizards employs various reproductive strategies, making their biology more complex than a simple “all-female” assumption.
Gecko Diversity and Reproduction
Most gecko species reproduce sexually, requiring both a male and female. Reproduction involves mating, internal fertilization, and egg-laying. Female geckos develop eggs internally, depositing them in suitable locations like under rocks, in crevices, or among leaf litter. Most geckos lay clutches of two eggs at a time, though the frequency of these clutches varies by species.
Sexual dimorphism, or differences between sexes, is common in geckos. For instance, male leopard geckos are typically larger and bulkier, with broader heads and distinct features like pre-anal pores and hemipenal bulges, which are absent or less pronounced in females. In some species, males may also exhibit specific behaviors, such as clucking calls or head-bobbing, to attract females.
Species That Reproduce Asexually
The misconception that all geckos are female likely stems from parthenogenesis, a form of asexual reproduction where females lay fertile eggs without male involvement. In these cases, offspring are typically genetic clones of the mother and are all female. This strategy allows a single female to establish a new population, which is advantageous where finding a mate is difficult or when colonizing new habitats.
Prominent examples of parthenogenetic geckos include the mourning gecko (Lepidodactylus lugubris), which is almost entirely female, and the common house gecko (Hemidactylus frenatus). Other species, such as the Indo-Pacific house gecko (Hemidactylus garnotii) and Bynoe’s gecko (Heteronotia binoei), also exhibit this ability. Male mourning geckos are occasionally born, but are often sterile and do not contribute to reproduction, emphasizing the species’ reliance on parthenogenesis.
Environmental Influence on Sex
Beyond sexual and asexual reproduction, some gecko species exhibit temperature-dependent sex determination (TSD), where the incubation temperature of the eggs determines the sex of the hatchlings. This means that even for sexually reproducing geckos, environmental factors can play a significant role in the sex ratio of their offspring. The specific temperature ranges that produce males or females vary by species.
For example, in leopard geckos (Eublepharis macularius), cooler incubation temperatures (around 26-30°C) tend to produce more females, while warmer temperatures (around 32.5°C) often result in a male-biased sex ratio. However, extremely high temperatures (e.g., 34-35°C) can sometimes produce a female-biased ratio again. This environmental influence on sex highlights the diverse and adaptable reproductive strategies found within the gecko family.