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Females of some species can reproduce without males

2021-12-27T20:09:00.356Z


Parthenogenesis or asexual reproduction is more common than previously thought, since it occurs in the females of some species of birds, reptiles, and insects.


California condor breeds without mating 0:58

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(The Conversation) - 

An Asian water dragon hatched from an egg at the Smithsonian's National Zoo, and its keepers were shocked.

His mother had never been with a male water dragon.

Using genetic testing, zoo scientists discovered that the female, who was born on August 24, 2016, had been produced through a mode of reproduction called parthenogenesis.

Parthenogenesis is a Greek word that means "virgin creation", but it specifically refers to the asexual reproduction of the female.

Water dragons are one of the species that can reproduce from parthenogenesis.

Although many people may assume that this behavior only happens in science fiction or religious texts, parthenogenesis is surprisingly common and is found in a variety of organisms, including plants, insects, fish, reptiles, and even birds.

Since mammals, including humans, require certain genes to come from sperm, they are incapable of performing parthenogenesis.

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Create offspring without sperm

Sexual reproduction involves a female and a male, each of whom contributes genetic material in the form of eggs or sperm, to create offspring.

The vast majority of animal species reproduce sexually, but the females of some species are capable of producing eggs that contain all the genetic material necessary for reproduction.

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The females of these species, which include some wasps, crustaceans and lizards, only reproduce by parthenogenesis and are called obligate parthenogens.

More species experience spontaneous parthenogenesis, best documented in animals that live in zoos, such as the Asian water dragon from the National Zoo or a blacktip shark from the Virginia Aquarium.

Spontaneous parthenogens usually reproduce sexually, but may have occasional cycles that produce eggs ready for development.

Scientists have learned that spontaneous parthenogenesis can be an inherited trait, meaning that females who suddenly experience parthenogenesis may be more likely to have daughters who can do the same.

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How can females fertilize their own eggs?

For parthenogenesis to occur, a chain of cellular events must develop successfully. First, females must be able to create eggs (oogenesis) without stimulation of sperm or mating. Second, the eggs produced by the females must begin to develop on their own, forming an early-stage embryo. Lastly, the eggs must hatch successfully.

Each step in this process can easily fail, particularly the second, which requires the DNA chromosomes within the egg to be duplicated, ensuring the full number of genes necessary for developing offspring. Another possibility is that the egg is "fertilized" by cells left over from the egg production process, known as polar bodies. Whichever method initiates the development of the embryo, will ultimately determine the level of genetic similarity between the mother and her offspring.

The events that trigger parthenogenesis are not fully understood, but appear to include environmental changes.

In species that are capable of both sexually reproducing and through parthenogenesis, such as aphids, stressors such as crowding and predation can cause females to go from parthenogenesis to sexual reproduction, but not the other way around. .

In at least one type of freshwater plankton, high salinity appears to cause the change.

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Advantages of self-reproduction

Although spontaneous parthenogenesis appears to be rare, it does provide some advantages to the female who manages to do so.

In some cases, it can allow females to generate their own mating partners.

The sex of parthenogenetic offspring is determined by the same method by which sex is determined in the species itself. In organisms in which sex is determined by chromosomes, such as the female XX and male XY chromosomes of some insects, fish, and reptiles, a parthenogenetic female can only produce offspring with the sex chromosomes that she has on hand, which means that will always produce XX female offspring. But in organisms in which females have ZW sex chromosomes (as in snakes and birds), all living offspring produced will be ZZ, and therefore male, or much more rarely, WW, female.

Between 1997 and 1999, a water snake

Thamnophis marcianus

that lived at the Phoenix Zoo gave birth to two male pups that eventually survived to adulthood.

If a female mates with her parthenogenetically produced child, then we speak of inbreeding, which is the reproduction between individuals of the same lineage or family.

Although inbreeding can lead to a number of genetic problems, it is evolutionarily better than not having any offspring.

The ability of females to produce male offspring through parthenogenesis also suggests that asexual reproduction in nature may be more common than scientists had previously thought.

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Biologists have observed, over long periods of time, that species that are obligate parthenogens are frequently killed by disease, parasitism, or habitat changes.

The inherent inbreeding of parthenogenetic species appears to contribute to their short evolution.

Current research on parthenogenesis seeks to understand why some species are capable of reproducing both through sex and parthenogenesis, and whether occasional sexual reproduction may be enough for a species to survive.

- Mercedes Burns is Associate Professor of Biological Sciences at the University of Maryland, Baltimore County.

Burns received funding from the National Science Foundation.


Published under a Creative Commons license from The Conversation.

Asexual reproductionReptiles

Source: cnnespanol

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