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Not all animals must have sex with another individual to produce perfectly viable offspring. And neither do humans, thanks to technological breakthroughs in artificial insemination. But what about those critters that do not require masturbation and meat basters to produce babies sans contact with another individual? Remarkably, this is quite common in the animal kingdom, although different animals go about doing it in different ways.
Caenorhabditis elegans, the roundworm that has become a popular model in developmental biology, lives in populations made up almost entirely of hermaphrodites. There are no true females, and only 1% of all individuals are male. A hermaphrodite will usually mate with itself (i.e., they self-fertilize), but the occasional male does get lucky and inseminates a hermaphrodite. Why males even exist is up for speculation, but this is not parthenogenesis.
For a real example of parthenogenesis, we should take a look at the hymenopterans, an order of insects that includes bees, wasps, and ants. Many of these guys are notable for the fact that unfertilized eggs give rise to males, while fertilized eggs gives rise to females. Because the males are born from unfertilized eggs, this is parthenogenesis. The females, on the other hand, are produced the same way most sexually reproducing animals make females — via the combination of a sperm (the male gamete) with an ovum (the female gamete). Therefore, the males are haploid (they have one copy of the genome, inherited from their mother), and the females are diploid (they have two copies of the genome, one from each parent).
Males born via parthenogenesis in hymenopterans can be thought of as half-clones of their mothers, and fathers share their entire genome with their daughters. This leads to interesting relationships between relatives because the genetic relatedness is not reciprocal. For example, while males have 100% of their genome in common with their mothers and daughters (as opposed to 50% in other sexually reproducing organisms), the mothers and daughters are only 50% related to their sons and fathers. Additionally, females are more closely related to their sisters than to their daughters, which may explain why worker females are so cooperative in bee hives.
And there are the exceptional cases, like that of a Komodo dragon last year (see here for a summary of the gory details and speculation on how it happened, and here for a post from Sandy). Unlike the hymenopterans, parthenogenesis in reptiles is not a default state, but results from accidents in the creation of the ovum. In bees, wasps, and ants, the males develop from haploid gametes that have not been inseminated by a male. In reptiles, however, the virgin births result from a misstep in the production of the ovum causing it to be diploid. These reptiles wouldn’t survive as haploids, but, because the ovum has a complete complement of genes and chromosomes, it can develop into a healthy animal.
So, what one means by “virgin birth” determines how someone can answer the question of what’s the deal with it. There are multiple ways to give rise to an animal without mating, only one of which is parthenogenesis. Parthenogenesis can be the default state (as in hymenopterans) or it can be a quirky event that is touted as exceptional (as in reptiles).
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