Sharks

One of the coolest things people never discuss is the idea of a “virgin birth.” Among humans, this is impossible. At least, not without a little help from the main upstairs. In other species though, it is not abnormal at all. Sharks, for example, can be asexual and still have children. In one situation, female sharks from at least two different species of shark that had been separated from males had pups (baby sharks). However, when there is no male to take part in the reproduction process, the pups will only carry the female’s DNA. Thus far, we know that the hammerhead, blacktip, lip, and zebra sharks can have pups through unfertilized reproduction or “parthenogenesis.” In this case, the sharks are not animals that gender-switch entirely. They simply operate as both the mother and father, likely due to an evolutionary survival trait.

White-Necked Jacobins

Female White-Necked Jacobins are disrespected by the males of the species. In fact, they are bullied quite a lot and have access to food sources that females cannot have access to. This species is known for picking fights and fiercely defending its food sources. They don’t even mind doing this to the death! The males also claim territories prime for breeding. While they do not mind if some females trespass, they will bully them the entire time. All females will look greenish with a gray-dabbled chest while males will have a flashy blue and white plumage. However, the females start out looking like adult males but this usually changes. Around 80% will shift into drab plumage but the 20% remaining can win out. They’ll get less social harassment from males, which allows them to do as they please and face fewer issues with other males.

Hawkfish

The Hawkfish is pretty interesting. They are known to be protogynous, where they start off entirely as females but will morph into males whenever they need to do so. This essentially means that when you see a Hawkfish, it is likely it will be female. However, when one does switch to being a male, it is due to mating purposes. Hawkfish usually operate in a harem, where one male has “relations” with a lot of other females. When the male takes on too many, another female transforms into a male to give the dude a break. Usually, it is the largest female that makes the turn into a male. When this occurs, the new male takes about half the harem with them. You’d think that would be the end of it, right? Nope. The very same hawkfish can switch back into a female, usually due to the harem’s needs.

Bonobos

While the Bonobo is not technically among the animals that can gender-switch, this is for a good reason. They do not consider these constructs at all when it comes to mating habits. These primates are about as open as it gets. Bonobos are usually in a female-led group and will remain together for quite a long time, if not forever. Within this group, every male will likely have relations with every female. However, every female will have “relations” with every female while every male will get it on with every male too. This pretty much means you’ll never really know who a child belongs to for little chimp child support. However, due to this, the males and females take care of every child like it is their own regardless. We’re assuming this means no one can ever get mad at their mate in these groups.

Moray Eels (Kinda)

Most of the world’s Moray Eel population will be born male or female and remain that way. However, there are at least two types of moral eel known as the Zebra and Dragon moray that differ. These are a few of the animals that can gender-switch due to a group need. They too will begin life as a male or female. Yet if there are not enough males around, females of these species will pick up the slack left behind by those deadbeats and become males. This sequential hermaphroditism is for mating purposes too, not just a random change for no reason. Meaning, they’ll be able to help out to ensure that future Zebra and Dragon moray eels are in this world. It should be noted that only females can transition, as males cannot become females. Well, there is one eel that differs from this.

Ribbon Moray Eel

Say hello to the Ribbon Moray Eel. Like the Zebra and Dragon moray eels we referenced, it too can switch things up. Making it one of the most notable animals that can gender-switch. It is the only eel that can switch from male to female. It’s known for its dynamic color changes as it ages, but age plays a part in its growth too. When a Ribbon eel gets between 23 to 32 inches long, it is now a functioning male that begins to give out sperm. At this point, it’s a lovely light blue with a bright yellow jaw. When it’s at the 33-inch mark, male sex organs stop functioning and female reproductive organs mature and it’ll start to lay eggs. By this point, the eel is entirely yellow or greenish-yellow. They’ll live often up to 25 years and grow as large as 50 inches.

Butterflies

Butterflies have to be one of the most compelling animal species on this list. While most of these species are among the animals that can gender-switch, butterflies can be both all at once. There is one species of butterfly called the Lycaeides that has a rare dual condition known as gynandromorphism. This causes an animal to be male and female at the same time. For these butterflies, both male and female traits can be arranged in a crazy order. Where one side of the butterfly will be female and the other side will be male. While gynandromorphism is technically rare, it actually occurs in one in every 10,000 butterflies. There are millions alive around the world at any one time. Thus, for every million, there are 100 butterflies with this disorder. This can really add up.

Seahorses

By now, most people know the story of the seahorse. They are incredibly unique in the animal kingdom because it is the males of the species that give birth. You read that right, the dudes handle all the egg fertilization and laying stuff. However, there is one big problem that we should probably point out. Once the seahorse lays eggs, he runs back to party with the boys and becomes the ultimate absent father. Seriously, when male seahorses lay their eggs, neither parent sticks around to protect the future seahorse babies. They are on their own literally from day one, and neither parent cares if their offspring live or die. The kids do not even see child support!

Boyd’s Forest Dragon

The Boyd’s Forest Dragon is a relatively small arboreal lizard (those found in trees) that you can see in Queensland, Australia. These are among the most notable animals that can gender-switch, doing so out of simple need. Tom Fair, a keeper of a few dragons, had two females. One mated with a male and laid eggs, which obviously confirmed its female status. Yet it then stopped producing eggs and began to develop traditionally male characteristics. This even included testicles. While the two females were rivals, this slowly began to stop as the larger female turned male. The transition process was so thorough for the new male dragon that ovarian tissue was completely gone and only the now mature testes remained. This was a first, as no other reptile was known to be capable of switching sex completely outside of an egg.

Black Sea Bass

You can find the Black Sea Bass across the east coast of the United States from Maine to Florida. They are one of the most well-known animals that can gender-switch in the animal kingdom. They are technically protogynous hermaphrodites, which is why they can change from female to male. While they are too widespread for scientists to fully study the reproduction process in the wild, it is thought that the change only occurs due to supply and demand. When the black sea bass was studied in captivity, female sea bass would observe how many males were present in the tanks. If they noticed a decrease in males, they’d switch to increase the amount or even up the male population.

Banana Slugs

You have likely seen the banana slug in the past. The species gets its name honestly, as it is typically a bright yellow color similar to that of a banana. These slugs can grow up to 10 inches in length. However, what you might not know about this species is that they are simultaneous hermaphrodites. This means that they technically do not switch back and forth between being a male or female. Rather, they are both male and female at the same time. In fact, both of these reproductive organs work at the same time so they can actually self-fertilize if they want to. Some actually do this, but most banana slugs prefer to find a partner. When they mate, the two slugs curl around the other and both will engage in the exchange of sperm to fertilize each other’s eggs.

Ruff Wading Sandpipers

Ruff Wading Sandpipers actually have four distinct genders: territorial males, satellite males, or female mimics. Along with, of course, normal females. Territorial males usually win out in the mating season. Territorial males are aggressive with dark plumage, satellite males have white plumage, but the mimics do not have any. The territorial male will put on elaborate displays to attract a female, but the satellite males are not as aggressive and even help the territorial male. The female mimics will wait for a female to crouch for mating, then as quickly as possible, hop on her back. Now, the territorial male is on the back of the female mimic and not having relations with the female. Sometimes, the mimics will crouch like a female to draw in males to get them away from other females too.

Humphead Wrasse

The Humphead Wrasse species is yet another of the animals that can gender-switch and operate as a protogynous hermaphrodite. Around the age of nine, the species is able to change from its female stage into a male. With this change, the coloration of the Humphead Wrasse will also change. They start out reddish-orange as females and then become blue-green when they turn into males. The species is known for living relatively long for a fish species at around 30 years. Sadly, overfishing and threats to coral reef habitats have hurt the population. In spite of its ability to change things up, it is currently on the Endangered Species List.

Marsh Harrier

Few species seem to hate the Marsh Harrier as much as the Marsh Harrier species hates itself. Males of the species are known for sometimes severely attacking other males. When the males grow into adults, they usually develop a grey down of feathers and have yellow eyes. However, around 40% do not and will actually resemble females. The females have brown feathers and white eyes, plus they’re larger than males. The female-like down comes in the second year of their life but keep the same build and eyes. Biologists who study the Marsh Harrier claim that this does well with preventing random attacks from other males. It is one of the few bird species that defies gender, yet it does this for an understandable purpose.

Giant Australian Cuttlefish

Like the Marsh Harrier, the Giant Australian Cuttlefish also defies gender norms for an understandable reason. This has made it one of the most prominent animals that can gender-switch in the animal kingdom. It should be known that male cuttlefish outnumber the female population by roughly 11 to 1. Needless to say, the competition for finding a female to mate with can be fierce. Males will attack other males in order to stomp out potential competition. This can be tough for the smaller cuttlefish, so they devised a clever plan. They’re able to camouflage into muted brown tones, similar to the female cuttlefish. That allows them to switch through the male-dominated areas without a problem. When doing this, they are not attacked and end up having much easier access to the actual female cuttlefish to mate with.

Komodo Dragons

Usually, Komodo Dragons lay eggs after mating but this is not always the case. In late 2005, a female Komodo Dragon laid eggs at London Zoo. However, she had been separated from any male Komodos for more than two years. Initially, it was thought that she was able to store sperm from a previous male encounter. Then another female laid 11 eggs at Chester Zoo in England, also without being with a male. Seven of those eggs hatched, and oddly, all were male. Unlike the previous Komodo, this female had never been with a male dragon. This essentially proved that female Komodos can be parthenogenetic, which was relatively shocking. However, it’s not exactly uncommon for a female reptile species to lay eggs without mating with a male.

Jellyfish

Jellyfish are probably the most uncomplicated animal species out there. For some jellyfish, they are both male and female at the same time. This means that no specific switch is necessary. However, other jellyfish species are sequential hermaphrodites. This means they are either male or female, but they cannot be both simultaneously sadly. This makes these jellyfish one of the animals that can gender-switch specifically for mating purposes. The switch often occurs out of need. If a jellyfish travels to an area with more male than female jellyfish, it will become female. If it’s the opposite, then it will become male. The best part is that these jellyfish can go back and forth as they please…after a reproductive cycle at least. Funny enough, some jellyfish produce without mating too.

Starfish

Starfish are absolutely incredible. The species is technically a bisexual organism, and will usually regenerate things like arms and tube feet. Yet this regeneration is a method of parthenogenetic reproduction for the species. This takes place via binary fission, where the parent organism’s cell divides completely into two genetically identical daughter cells. During this process, central discs present in the mature starfish break into two pieces. Each part on either side of the disc regenerates the broken parts of the starfish. They do mate, however. Usually, the males will simply release sperm into the water and the females will release eggs. The eggs hatch into a larval form that lives off of plankton for several months before settling on the sea floor to become an adult starfish.

Red & Olive Colobus Monkeys

If you do not want to be kicked out of the house when you turn 18, you might want to take a note from the Red and Olive Colobus Monkeys. When a male of the species comes of age, they are kicked out of their monkey tribe to seek other single males. Where they will form a bachelor’s tribe of sorts. However, not all male monkeys are ready for this. This led them to develop an evolutionary trait. Just before they reach puberty, the area around their anus swells to mimic that of a female colobus in heat. While this might not confuse the males within their own or any related species, it will stop them from being kicked out. The swelling usually stops for the Olive Colobus when they reach full adulthood but the Red Colobus will retain this feature for the rest of their life.

Oysters

Oysters are pretty interesting, as it is known that their reproductive cycle is pretty wild. Young males release sperm into the water while older females release eggs, which can result in sometimes millions of new mollusks. Yet they are also one of the most notable animals that can gender-switch, simply because they have to do so biologically. Every oyster starts their life as a male, but most will change to female after around a year or two and usually do so permanently. The reproductive system for oysters produces both sperm and eggs, so it is possible for them to fertilize their own eggs but rarely do. Yet this is why only young males put sperm in the water for eggs to fertilize with. They’ll become a female after a few years, so they need to give females their sperm before they switch.

Lions

It’s clear that the Lion species is incredibly cool, right? A Lioness, or the female of the species, will have a distinct look that differs her from males. All Lions will look the same in their early life but as males grow up, the males slowly develop the mane. However, in 2016 five lionesses at the Moremi Game Reserve in Botswana grew manes and even adopted male-like behaviors. One even developed a signature roar and mounted other females just like any other male. It was initially unknown why this took place, but there are some theories. A lioness named Emma at the National Zoological Gardens had high levels of testosterone due to an ovarian issue. She too had a mane and male-like traits. When the zoo fixed her ovarian issue, she reverted to a normal Lioness. Therefore, it is likely that elevated T-Levels are playing a part here too.

Hancock’s Flatworm

This flatworm species perhaps has the best name you could get for a species. Known as Hancock’s Flatworm, the scientific name is “Pseudobiceros hancockanus.” You might find that a little odd for a scientific name, and rightfully so. However, it is truly apropos. This flatworm is sort of among the animals that can gender-switch, but not entirely. It is hermaphroditic and actually engages in a form of “male member fencing.” Each worm will attempt to inject sperm into the other with one of its TWO little mal members, all while trying to avoid being inseminated itself. Basically, carrying eggs is a punishment for losing in a sophisticated battle of male member fencing. The flatworm with the best swordsmanship will get out without being injected. Imagine if this was how it worked for humans….that would be an awkward game of tag.

Pacific Cleaner Shrimp

This is an interesting species that usually eats parasites and dead skin off of other marine animals. It actually goes through molting cycles that cause it to change its gender. What is so interesting about the Pacific Cleaner Shrimp is simply how it changes. As one of the animals that can gender-switch, it is the only one on this list that starts as a specific gender and then becomes both. All of the species will be born and start life as males. After a few molts, they will switch from male to hermaphrodites. This, of course, allows the shrimp to be both male and female at the same time. Now you know why we have so many of these things in the Pacific Ocean.

Common Reed Frogs

Scientists have been well aware for years that the Common Reed Frog is among the animals that can gender-switch like it’s nothing. Unlike other species on this list, the changes can be relatively spontaneous. The species was studied in 1989, and they found that 7 out of 24 Common Reed Frogs switched from female to male. Usually, this change will occur when a local population is too heavily skewed toward one version. While normal biological changes are quite common, human beings seem to be contributing to this too. In 2010, a study found that the Atrazine pesticide caused gender changes in every 1 in 10 frogs exposed to it. In addition to this, it emasculated three-quarters of the remaining frogs.

Green Sea Turtles

Green Sea Turtles can actually change their biological gender entirely while inside the egg. This seems to occur due to the temperature they are faced with. The warmer the sand is, the more females will be born. In one study of turtle hatchlings from beaches around the Great Barrier Reef near Australia, temperatures from climate change were particularly intense at the time. Among all eggs that hatched on those warmer beaches, between 86.8% to 99,8$ were born female. Yet on cooler beaches in the same region, between 65% to 69% were born female. It is possible females will mate with males in cooler climates from now on. Which could bring back some balance in the Green Sea Turtle population. The species is already endangered, so if a change does not occur soon, this could get worse.

Spotted Hyenas

Most people do not know that the Spotted Hyena breaks from modern knowledge of gender. While it is not technically among the animals that can gender-switch, it also kind of does. Both the male and female hyenas have testes and a normally “male” member. For both, the member will become erect. For males, this is a function of arousal but for females, it happens due to a sense of familiarity or safety. Technically speaking, the female “member” is actually an elongated clitoris. However, it is so large that biologists had no choice but to refer to it as a pseudo-member. The females urinate, mate, and even give birth through this. When it comes to mating, females will roll up the clitoris to give males permission to access the internal “V-region.” Curiously, the female member is actually longer than the male’s. Well, that hit below the belt.

Honey Bees

It might be surprising to see Honey Bees on this list. However, it is true that honey bees are among the animals that can gender-switch. Of course, this is usually not something they do. Impressive researchers at the Heinrich-Heine University in Germany discovered that disrupting the feminizer gene in the honey bee is enough to fully switch female bees to males. Honey bees exhibit both normal and parthenogenetic reproduction, which is thanks to their haplodiploid determination system. Through this system, females are produced normally from fertilized, diploid eggs. Of course, these females get half of their chromosomes from each parent. However, males arise from unfertilized, haploid eggs. If a Queen lays an egg though, she is able to choose if their child is going to be a worker or a drone bee. Yet nurse bees can only lay drone bees.

Copperhead Snakes

Copperhead Snakes seem to be all over the place, and now we might have a reason for that. Did you know that the species is capable of virgin birth? Like the Komodo Dragon, female Copperheads can lay eggs through parthenogenetic reproduction. During this, the female fertilizes her own eggs without a mate. Usually, this will happen when a Copperhead is in captivity or if they are in an isolated area in the wild. Scientists looked into how these snakes are able to have eggs parthenogenetically, considering very few other snakes are capable of that. While not a hermaphrodite, it does have a special cell called a “polar body” that is produced with an egg. This will sometimes act like sperm, thereby fertilizing the eggs to make parthenogenetic reproduction possible.

Mandarin Ducks

This is relatively rare among ducks. However, some Mandarin Ducks are among the animals that can gender-switch. Yet it will not do this due to a lack of a mate or even due to a population issue. A few instances have been recorded where female ducks develop male-like traits and a male-like appearance. If the female was with another male duck, their partner will not leave them and the now trans-duck will not leave their partner for another female. We know that female ducks are born with two ovaries but only one of them develops. It’s usually the left one while the other is filled with a group of cells. If the developed ovary is damaged, oestrogen will usually inhibit the Z chromosome that triggers male characteristics will stop working. Thus, causing the duck to now start developing those traits.

Octopus

These cephalopods are quite interesting. The Octopus is usually pretty solitary, which is probably a good thing. Many females of the species are cannibals, so to battle against this, the males developed a modified arm called a hectocotylus that doubles as a male member. He will initiate “relations” with it. However, to even get to female dens can be tough. For some octopus species, big males will guard female dens. To get past the much larger and stronger octopi, some males will gender-swap by hiding their hectocotylus from the other males. After sneaking by, they can drop the act and start the mating process.

Deep-Sea Squid

While its cephalopod cousin the octopus has to go through quite a bit to mate with a female, the Deep-Sea Squid has less to worry about. Mating is not nearly as complicated for species. Due to the fact that these squids live so deep, it is incredibly dark for them most of the time. While they have developed special abilities to see in this near-pitch-black territory, it is still tough to see what’s going on even for them. This is why evolution has allowed both males and females to have sperm from different mates in their bodies. Thus, females can technically impregnate other females and males can mate with other males. Allowing Deep-Sea Squid to pretty much get it on with either males or females.

Cardinals

For Cardinals, gynandromorphism, or when an animal has strong dimorphism (as in strong features separating genders), can show up. This particularly happens among the North Cardinal species. The males and females have different coloration, so it’s pretty clear when you’re seeing a gynandromorph. Usually, this Cardinal will have brown-gray “female” feathers on one half along with bright red “male” feathers on the other. The gynandromorph cardinals might look different but they also differ in how they act too. When one was being studied, researchers noticed it was never seen vocalizing or mating. However, other cardinals never seemed to mistreat the odd-looking cardinal and it was accepted among its cardinal peers. We could learn from that type of acceptance.

New Mexico Whiptail Lizards

While we’d love to tell you that the New Mexico Whiptail Lizards are among the animals that can gender-switch, they do not technically do this. Rather, they do things a bit differently compared to most lizards. This happens to be the only lizard species that is entirely female. Seriously, every single one of them is female. However, one might wonder how they mate. Because these lizards do couple off during the mating season. Some assumed they were hermaphrodites for years, which would make sense in theory. Some have hormonal imbalances that can cause some stereotypical male or female social/mating behavior when comparing them to other lizards. In spite of this, all of the eggs are unfertilized but hatch anyway. Even those who do not mate will still reproduce during this period.

Clownfish

Clownfish probably break every norm you can think of. We know what they look like by now, right? Usually bright orange with a few white bars on them. However, this revelation might sadly ruin Finding Nemo for you. Clownfish are sequential hermaphrodites. They are born as one gender but they are able to switch to another whenever necessary. Usually, there will be a need for a female and a male will turn into one entirely. Unlike the two-parent, human-like system…clownfish live in groups. Yet only two members of the clownfish group are mature enough to mate at a time. This will be a large male and an even larger female. If something happens to the female in this breeding pair, her male mate will transform into the next female and select the current biggest male in the group to mate with as their new partner.

SOURCES:

National Institutes of Health

National Oceanic and Atmospheric Administration (NOAA)

United States Environmental Protection Agency (EPA)

World Health Organization (WHO)

World Wildlife Fund

Harvard University

Oxford University

Rutgers University

Oceana

Australian Museum

National Geographic

Scientific American

Smithsonian Magazine

Royal Society Publishing

BBC