As mammals, our gender is bound by our genetics. Suppose a baby develops XX chromosomes in the mother's womb. In that case, it will continue to grow with the physical characteristics of a female - if it develops XY chromosomes, it will have male characteristics. But the same is not valid for all the animal kingdom.
In fact, a significant number of species - predominantly fish, reptiles, and amphibians can change genders through varying stages of their life. Explore a selection of these sex-swapping animals, discover how and when they change gender, and the benefits it offers to their species.
Frogs
It's a long-known fact that some animals, including fish, reptiles, and amphibians (such as frogs), can change genders throughout their lives. Still, the causes of this phenomenon need to be better understood, and research is ongoing. Past studies suggested that pollution within urban and suburban ponds could be responsible for the gender switch. However, new research highlights the fact that this process still occurs when frogs live in pristine water conditions.
Scientists monitored frogs across 16 populations; within 12 of these habitats, 2-12% of frogs experienced gender reversal. Interestingly there was no correlation to suburban land use, suggesting this process occurs naturally. A more likely hypothesis is that frogs can alter their genders to suit their local environment. And this could include a varied range of factors such as temperature, climate, or gender populations.
Additionally, 11 of these habitats contained "intersex" frogs - mainly males with egg-like cells present in the testes. In one highly forested area, 44% of the frogs possess these intersex qualities, suggesting that there could be an environmental factor that causes XX chromosome (or female) frogs to change genders relatively early in their development.
These gender switches happen during the larvae or tadpole stages - no adult frogs have been witnessed changing genders.
Clownfish
It may surprise you to learn that every baby clownfish is a boy - that's right, all clownfish are born as males. Still, each group of clownfish contains a dominant male, a dominant female, and 1-4 juveniles - so where does the female come from? When the female dies (or leaves the group for any reason), the dominant male changes genders, leaving one of the juveniles to fill his role.
Scientists aren't entirely sure how this happens, but research suggests that dominant males have a functioning pair of testes that can change in ovaries. When the female is no longer present, the testes begin to disintegrate, and ovaries form in their place. One theory is that the female may release some kind of signal into the water to prevent the others in her group from changing genders, but once she leaves, this process is triggered.
Other research suggests that this gender reversal begins in the brain. Females are the dominant sex among clownfish, and when two dominant males fight, the winner becomes a female. Still, the reproductive organs can take months to change, while the brain signals appear to alter sooner.
Turtles
There are approximately 356 species of turtles and 49 species of tortoises living in a variety of environments around the world, from oceans and lakes to forests and deserts.
The gender of most animals is determined during fertilization, but the same is not valid for some species of reptiles, such as crocodiles, alligators, and turtles. Their gender is determined by TSD or temperature-dependent sex determination. If the turtle's eggs incubate at temperatures below 27.7 degrees Celsius, the offspring will be male, but if they incubate above 31 degrees Celsius, the babies will be girls. And research demonstrates that higher sand temperatures give way to increased amounts of female turtles.
Global warming is having a significant impact on the gender of green sea turtles. As temperatures increase, the sex ratio of these animals shifts to become more female-dominated. Complete feminization is sometimes possible, with all offspring being female due to the warmer temperatures. This phenomenon has been observed in many species worldwide and is likely to continue as global temperatures rise.
Snails
You may have read fun facts like “snails don’t’ have feet” or that "all snails are hermaphrodites," but the latter isn't true. Most land-based snails possess the reproductive organs of both genders, but most sea snails are dioecious, meaning they have separate genders. One particularly fascinating species of sea snail is the slipper limpet, found in the Pacific Ocean.
These snails begin life as males, gradually morphing into females as they mature. But, if two limpets grow together and can touch each other, the larger one will change from male to female much more quickly. Scientists believe this could be advantageous in reproduction as the larger snails (females) can hold more eggs while the smaller (male) snails can still produce plenty of sperm.
A male limpet has a relatively large penis that can be longer than the rest of its body! This appendage emerges from the right side of its head. As they morph into females, the penis shrinks until it eventually disappears.
Banana Slugs
Banana slugs don't necessarily change gender, but they are all hermaphrodites born with working male and female appendages. In a unique twist, reproduction depends on the subspecies of a snail; A. dolichophallus, for example, copulates by entwining the penises in an act that can last up to four hours. In contrast, a californicus uses only one penis per ritual, and copulation can be completed within as little as 20 minutes. If necessary, the banana slug can even self-fertilize.
Banana slugs are fascinating creatures, and some of the largest slugs in the world grow up to 10 inches. They are named for their distinct yellow body tone, though coloration can vary depending on diet and habitat. These slugs have a slimy coat that is neither solid nor liquid and is instead a form of liquid crystal. This helps the slug to breathe while protecting them from predators.
Butterflies
Butterflies are like many mammals; they are born either male or female and do not tend to change gender. Still, some butterflies possess a truly unique quality of being half male and half female through a process called gynandromorphism. This creates a split butterfly pattern, where one half adopts the male coloring, and the other half adopts the female coloring.
This usually happens during the early stages of a butterfly's development, when the cells split to form an embryo. If the cells fail to split correctly - for example, an XXYY separating into an X and an XYY instead of an XY, XY - the body will send signals to develop as both genders. The Lexias pardalis is an often-cited example of this phenomenon, as the difference in gender sizes means that each wing forms slightly differently, making the contrast even more apparent.
