For most species on Earth, the ultimate goal of life is to attract mates and pass on their genes to the next generation. The natural world is filled with fascinating and, sometimes, extreme strategies for attracting partners.
Take the peacock, for example, whose males flaunt their iridescent tail feathers in an elaborate display to win over peahens. The bright plumage and intricate patterns serve as a signal of genetic fitness, making them irresistible to potential mates.
In the deep blue sea, the male anglerfish has a unique approach to reproduction. Lacking the peacock’s visual flair, he instead bites and fuses with a much larger female, becoming a permanent appendage and providing sperm whenever she needs it. This bizarre form of mating ensures that the female always has a ready supply of sperm, crucial in the vast and sparsely populated ocean.
But what if some species could sidestep the mating dance altogether?
Asexual reproduction, where offspring are produced without the genetic contribution of a mate, is most commonly seen in microorganisms such as bacteria and certain plants. These organisms reproduce rapidly and efficiently without the need for mates, which is advantageous in stable environments (like inside your body) where genetic diversity is less critical for survival.
However, in the animal kingdom (especially in vertebrates, where sexual reproduction is the norm) there are rare instances of “virgin births,” or parthenogenesis. Parthenogenesis is a type of reproduction where an egg develops into a new individual without fertilization by sperm. Essentially, the egg activates on its own, grows and divides, creating an offspring that is a genetic clone of the mother.
This rare phenomenon occurs in specific species and often only in certain individuals within those species. It can be triggered by environmental factors, lack of mates or other ecological conditions. Here are two species observed to undergo parthenogenesis.
1. Komodo Dragons
These giant lizards can reproduce without a mate when males are scarce—which is less rare than one would expect. Individuals of this species tend to live in isolation and don’t take too well to company. Female Komodo dragons have been observed laying viable eggs that hatch into healthy, albeit all male, offspring, ensuring the continuation of their lineage even in isolated environments.
An example of this occurred in late 2019, when Charlie, a female Komodo dragon at the Chattanooga Zoo, gave birth to three hatchlings—Onyx, Jasper and Flint. Despite being kept with a potential mate named Kadal, DNA tests confirmed that these hatchlings were the result of parthenogenesis.
2. Hammerhead Sharks
Until relatively recently, instances of “virgin” births in sharks were often attributed to long-term sperm storage by female sharks that had encountered males in the past, rather than genuine parthenogenesis. Traditionally, sharks, as members of the cartilaginous fishes (class Chondrichthyes), were not expected to reproduce via parthenogenesis, with this group thought to exclusively rely on sexual reproduction.
However, increased reports of captive female sharks giving birth, despite prolonged isolation from males, suggested an alternative explanation. In a groundbreaking 2007 study, genetic evidence confirmed that a hammerhead shark had indeed reproduced through parthenogenesis. This discovery not only contradicted previous assumptions about shark reproduction but also expanded the known occurrence of parthenogenesis across vertebrates.
This discovery raised significant concerns about how this type of parthenogenesis could impact the endangered species, reshaping our understanding of how these ancient marine creatures reproduce.
Why Parthenogenesis Is A Concern, Especially For Endangered Species
The mixing of genes through sexual reproduction is essential for producing genetically robust offspring. However, virgin births bypass this natural mixing, leading to offspring that are genetic copies—clones—of their mother.
This lack of genetic diversity can be particularly problematic for endangered species. Take, for instance, Komodo dragons and hammerhead sharks. Both species are endangered and have been observed to undergo parthenogenesis, particularly in environments where males are scarce or absent. While this reproductive strategy can ensure short-term survival by allowing for reproduction when no mates are available, it compromises the long-term health and adaptability of the population. The offspring produced are often less capable of adapting to new challenges or resisting diseases, which could further threaten their survival.
What’s more, in some cases, the offspring resulting from this rare form of reproduction may have reduced fertility or even be sterile, making it difficult for them to contribute to future generations. This can accelerate the decline of already vulnerable populations.
While virgin births in nature are indeed fascinating and highlight the incredible adaptability of some species, they are often a sign of stress within the population and not a sustainable way to maintain genetic health and diversity. Parthenogenesis is not usually a positive sign for the long-term viability of species, especially those facing the threat of extinction, so it’s a good thing they are once-in-a-blue-moon occurrences.