Yes, some geckos are capable of laying eggs that are viable and can develop into full offspring without any genetic contribution from a male. Geckos are small, primarily nocturnal lizards known for their specialized toe pads that allow them to climb almost any surface. While sexual reproduction remains the most common form of procreation among vertebrates, this ability to reproduce asexually is a notable exception found in certain gecko species.
The Biological Mechanism Parthenogenesis
The biological process that allows for this “virgin creation” is called parthenogenesis, a term derived from the Greek words parthenos meaning “virgin” and genesis meaning “creation.” It is a form of asexual reproduction where the embryo develops from an unfertilized egg cell. This mechanism bypasses the need for the male gamete, or sperm, entirely, allowing a female to reproduce in isolation.
In a sexually reproducing animal, the egg cell produced through meiosis contains only half the required set of chromosomes, known as the haploid number. For the egg to become a viable embryo, it must fuse with a sperm cell, which also carries a haploid set, to restore the full, diploid number of chromosomes. Parthenogenesis, however, involves a modification of this cellular process.
The female’s body employs various cellular strategies to restore the full chromosome count within the egg before development begins. One common method is automixis, where the egg fuses with a secondary cell produced during the egg formation process, such as a polar body, instead of a sperm cell. Another mechanism involves premeiotic endoreplication, where the female’s germ cell doubles its entire genome before meiosis even begins, ensuring the resulting egg already has the full diploid set.
The resulting offspring are essentially clones, or near-clones, of the mother, as they inherit genetic material solely from her. Because no new genetic material is introduced from a male, the level of genetic diversity in a population relying on this method is significantly reduced. This lack of diversity can make the species more vulnerable to environmental changes or disease.
Obligate and Facultative Asexual Reproduction
Asexual reproduction in geckos is categorized into two main types based on how consistently a species uses the mechanism. Obligate parthenogenesis describes species where reproduction is exclusively asexual, and males are either extremely rare or non-existent in the population. These all-female lineages rely entirely on this method for survival and propagation.
The Mourning Gecko, Lepidodactylus lugubris, is a prime example of an obligate parthenogen. Females lay clutches of one to two eggs approximately every four to six weeks, and the resulting young are almost always female clones of the mother. The absence of males allows these geckos to establish new populations quickly, as only a single individual is needed to colonize a new area, contributing to their wide distribution across the South Pacific and beyond.
Facultative parthenogenesis occurs in species that typically reproduce sexually but retain the ability to switch to asexual reproduction when a male is unavailable. This ability is often observed in females that have been isolated in captivity for a long time, or in situations where finding a mate is physically impossible. The Gargoyle Gecko, Rhacodactylus auriculatus, for example, has been documented to lay fertile eggs without having ever encountered a male, demonstrating this dual reproductive capacity.
Facultative parthenogenesis has also been observed in other normally sexual species. This switch is often a survival mechanism, allowing a female to produce offspring in the absence of a partner, even if the resulting clones lack the genetic benefits of sexual diversity.
Identifying Fertile and Infertile Eggs
A female gecko can lay eggs without mating, even if she belongs to a species that typically reproduces sexually. However, not every egg laid by an un-mated female is the result of true parthenogenesis. Female geckos, like many reptiles, will frequently lay infertile eggs, sometimes called “duds” or “slugs,” which are simply unfertilized ova that the body expels.
These infertile eggs are not viable and will not develop into offspring, often molding or collapsing shortly after being laid. A key challenge for reptile keepers is distinguishing a truly parthenogenic (viable) egg from a non-viable infertile one. Infertile eggs often appear misshapen, yellowish, or translucent when first laid, and they may not calcify into a perfectly round, firm sphere.
The most reliable way to check for viability is through a technique called candling, which involves shining a bright, focused light source, such as a small LED flashlight, through the eggshell. In a truly fertile egg, a small, pink, or reddish circle representing the developing embryo and its blood vessels can be seen attached to the inside of the shell. This distinct ring, often described as a “cheerio” shape, confirms the egg is developing and must be carefully incubated.
An infertile egg, when candled, will appear uniformly yellow or translucent, showing no distinct dark spot or network of blood vessels. It is important to wait a few days after the egg is laid before candling, as the early stages of embryonic development may not be immediately visible. If an egg remains uniformly yellow and does not show any signs of a developing embryo after a week, it is likely infertile and should be discarded to prevent mold from spreading to potentially viable eggs.