Asexual reproduction in Reptiles
by Randy Klabacka
If whiptail lizards could talk, the answer to the question, "mommy, where do babies come from?" would differ depending on the species asking the question. Whiptail lizards, found mostly in the deserts of North America, are a group of over 40 species– 14 of which only contain females. In these 14 species, reproduction happens through a clonal process where hatchlings are genetically identical to their mothers. This phenomenon is known as "asexual reproduction," because it occurs without the need for two parents. While asexual reproduction seems to be the exception in vertebrate animals (of which 99.9% reproduce sexually), multiple groups of lizards and snakes have developed the ability to reproduce asexually.
There are two different types of asexual reproduction. The first type occurs when a female from a species that generally reproduces sexually is able to sometimes have offspring asexually (this is known as facultative parthenogenesis). Zookeepers in the St. Louis Zoo observed this last year when a single female python (who had never been with a male python) laid eggs from which seven healthy little pythons hatched. Facultative parthenogenesis has also been observed in many other reptile species over the past century. The second type of asexual reproduction is when a species reproduces exclusively by asexual reproduction (this is known as obligate parthenogenesis). In these species, all individuals are female. In fact, obligate parthenogenesis was discovered when a researcher in Southeast Asia collected 100 female fox geckos without finding a single male. Since then, multiple instances of obligate parthenogenesis have been discovered in nine families of reptiles.
Just four years ago an asexual reptile was documented for the first time in Alabama– the Brahminy blind snake (Indotyphlops braminus). This non-native snake, sometimes called the “flowerpot snake”, has found its way around the globe due to its low profile (it hangs out underground, sometimes in the soil of potted plants) and its ability to reproduce without needing a mate. If you are scared of snakes, there is no need to fear this harmless garden friend! Blind snakes offer virtually no threat to humans. While no native asexual reptiles are found in Alabama, we do have a resident whiptail lizard (Aspidoscelis sexlineatus, commonly known as the “six-lined racerunner”). This species has several cousins found as close as Texas (such as Aspidoscelis tesselatus, commonly known as the checkered whiptail) that reproduce asexually.
You may be asking yourself, “Why would a species reproduce asexually instead of sexually?” Or perhaps you are wondering, “Why do so few vertebrate animals reproduce asexually?” Researchers (including me) are seeking for answers to questions such as these.
Concerning the first question, some answers have been presented by theoretical biologists. The most “successful” life on earth is found in organisms that pass their genes onto the next generation. The more genes that an organism can pass on to the next generation, the more likely your genes are to persist over time. Although multiplication of your genes is a good strategy, sexual reproduction is the exact opposite– division! In other words, when a sexual parent has one offspring only ½ of their genetic material is passed onto that offspring (for example, you only have ½ of your mother’s DNA). Contrast this with asexual reproduction, where 100% of a parent’s genetic material is passed on to all of their offspring. Theoretical biologists show that because of this benefit asexual populations can quickly eclipse sexual populations.
Pondering answers to the first question leads naturally into the second question, which has caused many scientists to assume that because (A) asexual reproduction is beneficial and (B) asexual vertebrate species are rare, then (C) asexual reproduction must be costly. In other words, the negative consequences of asexual reproduction might outweigh the benefits. To find evidence of negative consequences resulting from asexual reproduction, biologists examine the physiology, morphology, behavior, genetics, and other aspects of asexual species in comparison to sexual species. While much remains to be discovered regarding the negative consequences of asexual reproduction, reptile biologists have made several discoveries. A few examples include (1) increased internal parasites found in asexual lizards, (2) increased external parasites in asexual lizards, (3) decreased genetic diversity in asexual lizards, (4) decreased endurance capacity in asexual lizards, and (5) decreased mitochondrial respiration in asexual lizards. We discovered this last example (decreased mitochondrial respiration) here at Auburn University, and we are actively investigating the genetic causes of this negative consequence of asexual reproduction.
Disclaimer: The views and opinions in this work are those of the author and do not necessarily reflect the views of Auburn University.