Disclosure: Some links may be affiliate links. If you buy an item via links on our site, we may earn a commission. Learn more.
While humans and many animals depend on sexual reproduction to create offspring, there are numerous organisms in nature that can reproduce asexually. Asexual reproduction is a widespread and intriguing aspect of biology, found in everything from single-celled organisms to complex plants and animals.
Although there are both benefits and drawbacks to this method of reproduction, it has played a crucial role in the evolution and survival of many species. This article will explore the mechanics of asexual reproduction, its different forms, and the impact it has on the environment and evolution of species.
What is Asexual Reproduction?
When most of us imagine reproduction, we think of the need for two parents; a male and a female. But that applies only to sexual reproduction. In the case of asexual reproduction, offspring can be produced with a single parent.
During this type of reproduction, there is no need for any sex cells or fertilization and instead relies on cell division. As a result of this, the offspring is considered to be a clone of the parent and will have the exact same DNA.
Because of the simplicity of this type of reproduction, it is largely only seen in primitive and more simple organisms.
Types of Asexual Reproduction
What’s fascinating about asexual reproduction is that it can occur in one of several ways. There are seven different types of asexual reproduction; let’s take a closer look at how each one works.
Most would agree that binary fission, sometimes just called fission, is the most simple form of asexual reproduction. This occurs when an organism splits itself into two equal pieces. These same size pieces contain the exact same DNA but are no longer just one organism. Instead, they will individually develop and regenerate into two fully-fledged individuals. The two parts are known as daughter cells.
Budding is a form of asexual reproduction whereby the organism forms small buds on its body. These buds, which are bubble-like growths, remain attached to the parent while they develop. Once fully grown, they can then detach and become individuals. This type of reproduction is commonly seen in the hydra and is considered to be a type of clone because of the offspring sharing its parent’s DNA.
Starfish are among the many creatures that rely on fragmentation as a form of reproduction. This is similar to the aforementioned fission but instead of breaking into two equal pieces, the organism may break into several pieces.
In some cases, such as starfish, just a portion of the animal may break away; for example, a limb. This can then form new body parts and continue life as an individual. This type of reproduction is also seen in worms as well as in the plant world with things like lichen.
Vegetative propagation occurs only in plants and is a type of asexual reproduction in which there is no need for a spore or a seed. Instead, the plant will form things like plantlets, tubers or bulbs, which contain everything they need to form a new member of these species. However, the offspring are direct clones of the parents, so there’s no genetic diversity.
Spore Formation (Sporogenesis)
When an organism undergoes sporic meiosis, they’re able to produce spores which in turn develop into new members of the species. This is very common among algae and fungi and is a process that doesn’t require any fertilization.
Parthenogenesis is not truly considered a form of asexualism since it is often referred to by scientists as being a result of the breakdown of sexual mechanics.
Most creatures that use this method of reproduction are able to produce offspring sexually but will turn to parthenogenesis when they are forced to, such as when separated from a male partner. However, there are obligate parthenotes such as the whiptail lizard.
It involves an egg developing into an embryo without any sperm, and it’s thought that around 2000 species reproduce this way.
Agamogenesis refers to any type of asexual reproduction that does not require a male mate. This includes parthenogenesis as well as a process used by plants called apomixis.
Advantages of Asexual Reproduction
One of the most obvious reasons that asexual reproduction is beneficial is the need for just one parent. However, the advantages of this process are much broader, so let’s take a look.
During asexual reproduction, the process of meiosis is not needed. Instead only mitosis is needed and this is a much faster way to reproduce.
For species where rapid reproduction is key to their survival, this is hugely beneficial. For example, some species of bacteria could be entirely wiped out if it weren’t for their ability to asexually reproduce at a fast rate.
Only One Parent Needed
Finding a mate in the animal kingdom is fraught with challenges, but this isn’t a problem for species that use asexual reproduction. Not only is this easier on the cells involved in creating offspring, but it requires a lot less energy from the organism.
Ability to Colonize New Habitats
With rapid reproduction and the ability to produce many more offspring, organisms that reproduce this way are much more easily able to colonize new habitats. The clear benefit of this is that it ensures the survival of the species.
Helps to Conserve Energy
The act of finding a mate involves many rituals like fighting, chasing, dancing, and many other things which use up a lot of energy for an animal. Even when that’s over, there’s the issue of the body producing sex cells and, for females, incubating eggs or growing a fetus. Asexual reproduction requires much less energy expenditure.
Maintenance of Favorable Traits
Since asexual reproduction mainly produces exact clones or, if not, very close copies of the parents, any favorable traits will be passed down through generations. While this doesn’t ensure genetic diversity, it could still be responsible for the species’ survival.
Disadvantages of Asexual Reproduction
It’s evident that there are a lot of benefits to asexual reproduction, but it’s not perfect. With that in mind, let’s explore some of the drawbacks.
No Genetic Variety
One of the biggest downsides to asexual reproduction is that the DNA of the parent and offspring remain the same. This leads to no genetic variation, which studies have shown could lead to problems with the future evolution and adaptation of various species.
Susceptible to Environmental Change
Because of the lack of genetic diversity, any species that are prone to being affected by changes in the environment or by things like disease will pass these traits onto their offspring. If the offspring is not suited to the environment, which could change over time, this could lead to the extinction of the species.
Accumulation of Harmful Mutations
While most asexual offspring will be a clone of its parent, there is the risk of a mutation, just as there is in sexual reproduction. However, scientists have discovered that mutations within asexual species could be more harmful. This has led them to the conclusion that this is why asexual reproduction is much rarer than sexual reproduction.
As I have already discussed, the lack of genetic variation within asexual species means that they have less potential to adapt to their environment. With constant shifts occurring because of things like climate change, it’s essential for species to be able to move and evolve with this.
Vulnerable to Disease
Another issue that rises from the lack of genetic diversity is the species’ ability to be able to withstand disease. The Irish potato famine occurred because almost all crops were wiped out because of one disease.
Organisms that Reproduce Asexually
There are more than 2000 known species that rely on asexual reproduction, and some of them may surprise you.
The starfish, which is not a fish at all, is a special creature since it is able to reproduce using both sexual and asexual methods. However, while there are around 1800 starfish species, only 24 of these use the following method.
The way the starfish reproduce is quite shocking, and some will break themselves into two pieces, thereby creating two individuals. Each of these individuals will then regenerate new limbs and grow into a new starfish. In other cases, where a limb is lost or intentionally broken off, that limb will live as a ‘comet’ and can then go on to regenerate and continue to live as an individual.
It might sound extreme but through this process of cloning, it’s been shown that starfish actually have a longer lifespan than those that rely on sexual reproduction.
The hydra is a small marine creature that’s often confused with jellyfish. While they are from the same family, cnidarians, they differ because hydras only have one life stage, whereas jellies have several.
So, what about reproduction? Well, the hydra uses a method called budding in which small buds will develop on their bodies. Eventually, these buds will grow their own tentacles and drop off of their parent, forming new clones.
In the right conditions and with plentiful food supplies, hydras may develop buds as frequently as every couple of days. However, these animals do have sexual organs and are able to use these for reproduction when conditions are not right for budding.
It seems there are huge populations of aphids; if you’re a gardener, you’ll be super familiar with this. But where do they all come from? The answer is that they can reproduce without a mate and they do so at an alarming rate. Females typically live for around 25 days, during which time she may have as many as 80 babies.
When female aphids are born, they already have developing embryos inside them. There’s no need for males which is why so many populations are female only.
However, these insects are also able to reproduce sexually and may do so once a year during the fall. While sexual reproduction isn’t necessary for their survival, it can help to increase genetic diversity in aphid populations.
When you think of asexual species, you might not immediately imagine a bird. However, the Californian condor has shocked scientists after a few individuals have experienced virgin births. The first instance of this was in 2001, and another incident occurred in 2009, both at the San Diego Zoo.
This happened because of parthenogenesis, but what’s unusual is that this is something typically only seen in species where the female does not have access to a mate. In both of these cases, the females had not only previously sexually reproduced but had always had access to males.
Despite what many people think, coral is actually an animal and not a plant species. It’s also an animal that benefits from using asexual reproduction despite the fact that it is able to reproduce with a mate.
Coral reproduce asexually by splitting themselves into pieces in a process called fragmentation. Each fragment that breaks away from the parent organism is an exact copy and, in the right conditions, can thrive as an individual.
It’s not known exactly how many types of fungi there are, but it’s thought to be somewhere between one and five million! What all of these species have in common is the way that they reproduce, and that’s through spores, budding, or fragmentation.
Spores come in all shapes and sizes, from single-celled spores to those with radiating arms and coiled spores or even those that resemble thread. These spores are then released into the environment where, under the right conditions, they will form a new fungus.
However, it is possible for some fungi to reproduce sexually using their mycelia.
The whiptail lizard, sometimes called the New Mexico whiptail, uses a process known as parthenogenesis to produce offspring.
The lizard is able to produce young from an unfertilized egg but there’s a difference compared to many other animals in that the DNA of the offspring is not identical to the mom’s.
Instead, scientists have noticed that there are slight variations in the DNA of the young which means continuing genetic diversity among the species.
Jellyfish have been around for millions of years, and they’re some of the most primitive animals on the planet. They have a five-stage life cycle that takes them from a larva to an adult medusa.
In the polyp stage of life, reproduction occurs and this is done asexually. This happens when the polyp segments itself in order to create clones in a process known as strobilation. As this happens, the tentacles disappear and are replaced by little buds which later split from the polyp.
The detached organism is known as an ephyra and is the final stage before the creature develops into its adult form. A single polyp could produce up to a dozen ephyrae, although this can vary depending on the species of jellyfish.
The spider plant is a popular house plant that many of you may have in your homes. But did you know that these plants could reproduce asexually without a mate?
These plants can reproduce through the production of plantlets that emerge from the mother plant.
If you have a spider plant that has produced plantlets, you can wait for them to develop roots, cut them off, and plant them in their own pots.
Strawberries are a type of plant that can reproduce asexually through the production of stolons or ‘runners’ that grow along the ground and produce new plants that are genetically identical to the parent plant.
However, strawberries produce fruits that are not considered true fruits but rather ‘accessory fruits’, which develop from the swollen receptacle that holds the tiny achenes or seeds. These fruits are produced from the fertilized ovaries of the flowers, but this process is not considered ‘sexual reproduction’ in the same way that animals reproduce. Instead, strawberries rely on cross-pollination to fertilize their flowers and produce fruits.
The potato grows underground with just a small amount of leaves above the surface which would make it difficult for the plant to use sexual reproduction. Instead, tubers form under the ground which are filled with energy and nutrients enough to propagate another plant. This process is called vegetative propagation.
Amazingly, potatoes are able to propagate even in very harsh conditions but despite this, they are still very susceptible to disease.
An obscure-looking creature, the smalltooth sawfish normally reproduces sexually. However, scientists have seen the first virgin birth in a wild vertebrate in this very species. And it isn’t just an anomaly; it’s thought that as many as 4% of these fish in the Florida area have been born with just one parent.
Through the process of facultative parthenogenesis, many female smalltooth sawfish are thriving without the need for a mate. As with many species, it has been theorized that these sawfish have turned to asexual reproduction because of a lack of males and is a viable way of the animals avoiding extinction.
The Amazon molly is a unique species of fish that reproduces through a process called gynogenesis, which is a type of asexual reproduction.
Unlike most species, Amazon mollies are all female and require a male of a closely related species to trigger the development of eggs. However, the male’s genetic material does not contribute to the creation of offspring, which are genetically identical to their mother.
It’s believed that this species has been reproducing asexually for tens of thousands to millions of years. Despite their unusual reproductive strategy, Amazon mollies are doing well in the wild and are a popular aquarium fish.
Sharks usually rely on sexual reproduction but there was one zebra shark that amazed scientists by being the first of her species to switch from one type of reproduction to another.
This happened in Australia in 2017 with a shark named Leonie, who had been kept in captivity and away from any males for the previous five years. However, she still went on to produce three offspring from unfertilized eggs.
This is a process known as parthenogenesis and has previously been seen in other shark species, such as the hammerhead.