These dragons managed to double the shuffled-around chromosomes after meiosis occurred. But why were the offspring male? You may be familiar with the sex determination system where individuals are female unless they have a Y chromosome which gives an individual male features.
So, if an egg with a single chromosome set had a Z, then managed to double its genetic material, it would end up with two Zs, and therefore hatch a male dragon. Two Ws and it would die, probably. Just saying. But scientists have called into question whether those Komodo dragons and sharks really were occasionally reproducing asexually, or just got lucky after a meiotic accident.
There are some species of lizard that really do reproduce asexually as a rule, like the all-female whiptail lizard. How does that work?
These lizards simply always produce eggs with two full sets of chromosomes. They happen to have twice the number of chromosomes as some other lizard species, reports Scientific American , and a different method of shuffling this genetic material around. This allows them to be more genetically diverse. One meiotic error led to a meiotic requirement, and a mutant crayfish taking over Europe that you may have heard about. Just last week , scientists published a paper about the marbled crayfish, a new all-female species that only evolved 25 years ago through a wacky mutation.
A German collector kept a crayfish as pet in the s, and it had lots and lots of offspring. He gave them away to his friends, and they, too, soon had hundreds of asexually reproducing crayfish on their hands. Soon, the owners were dumping their crayfish in the wild, where they are multiplying like crazy to this day. What happened? Apparently, a female and male must have mated a while back. Meiosis could have crapped out for one of the sex cells and produced a cell with two sets.
In , a brownbanded bamboo shark mother produced an egg that hatched a minimum of 3. Welcome to the world of semen-hoarding. After all, why fill out questionnaires at the sperm bank when you can save a piece of Prince Charming in your body for months at a time? Bamboo sharks are just one of the species known to have this ability, however: The aforementioned swellsharks can also store sperm, and nomadic blue sharks and dusky sharks can do this for months or even years, according to another study.
These aquatic insects reproduce large broods of all-female clones in normal environmental conditions, according to Gerald LeBlanc , a professor of environmental and molecular toxicology at North Carolina State University. But when there isn't enough food to go around, or when there are too many female clones around for comfort, the situation changes. Then, these females will begin producing male offspring as well. The males will then mate with the females, which turn bright copper during these stressful times, LeBlanc said in a release based on a study.
The females then lay more durable eggs, which are more resistant to difficult environmental conditions. Caucasian rock lizards defy any number of attempts at sexual categorization. First, these all-female reptiles that inhabit rocky outcroppings in northern Eurasia don't need a trigger to lay functional eggs.
But the seven-plus different varieties of asexual rock lizards are also the result of inter-species couplings between the many different sexual varieties of rock lizards, according to Susana Freitas , a PhD student in Sheffield University's animal and plant sciences department in the U.
It gets even more complicated. The asexual female hybrid clones sometimes also have a bit of an Oedipus complex—that is, if they mate with males of their father species, they can produce sexual offspring. The asexual species may also outcompete the sexual species in some areas by pushing them out of prime habitat, since they tend to produce more offspring and dominate areas where their range overlaps with their maternal species.
Unisexual mole salamanders have spent about 6 million years perfecting a boycott on traditional reproduction. But, like Amazon mollies, they still need a little help kick-starting their cloning process. Rob Denton , a PhD student and research fellow at Ohio State University who recently conducted a study on these salamanders' fitness , says that these salamanders need to steal sticky sperm packets from related species in order to prompt their reproductive system into action.
But sometimes, genes from the species sneak into the genetic code of the all-female species, giving them properties that can make them look different from their sexual peers. Some female whiptail lizards have learned to "be the man" in their relationships in order to reproduce. Researchers have found that some all-female hybrid clones actually go through the same motions as the males of the sexual variety, gripping a fellow female by the neck and then by the pelvic region.
So why do they do it? Apparently, this pseudo-sex is critical for ovarian development and females in different periods of their ovarian cycle will develop male-like behavior at different times. Editor's Note, March 28, This article initially stated that the Atlantic molly first became a separate species roughly years ago. Joshua Rapp Learn is a D. For millions of years animals have reproduced via parthenogenesis, which first emerged in some of the smallest, simplest organisms.
For more advanced animals like vertebrates, scientists think that the ability to reproduce asexually came about as a last-ditch effort for species facing adverse conditions. That may explain why parthenogenesis is possible in so many desert and island species. Most animals that procreate through parthenogenesis are small invertebrates such as bees, wasps, ants, and aphids, which can alternate between sexual and asexual reproduction.
Parthenogenesis has been observed in more than 80 vertebrate species, about half of which are fish or lizards. No mammals are known to reproduce this way because unlike simpler organisms, mammals rely on a process called genomic imprinting. Like a molecular stamp, imprinting labels which genes are from mom and which are from dad.
For mammals such as humans, this means that certain genes are switched on or off depending on the contributing parent. If there were only a single parent, some genes would fail to activate altogether, making viable offspring impossible. In some very rare cases, animal species reproduce via parthenogenesis exclusively. One such species is the desert grassland whiptail lizard , all of which are female. In certain insects, salamanders, and flatworms, the presence of sperm serves to trigger parthenogenesis.
Sperm cells launch the process by penetrating the egg, but the sperm later degenerates, leaving only the maternal chromosomes. The ability to reproduce asexually allows animals to pass on their genes without spending energy finding a mate, and so can help sustain a species in challenging conditions. If a Komodo dragon arrives on an uninhabited island, for example, she alone could create a population through parthenogenesis.
However, because every individual would be genetically identical, Komodo dragon mothers and their daughters would be more vulnerable to disease and environmental changes than a genetically-varied group. In areas of New Mexico, for example, some populations of female whiptail lizards share nearly-identical genetic profiles. All rights reserved. Creatures big and small For millions of years animals have reproduced via parthenogenesis, which first emerged in some of the smallest, simplest organisms.
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