Can Frogs Change Gender?

Animals can display some truly unique and interesting adaptations! For example, some can sleep standing up, give birth without males, or hunt for their dinner even though they are blind. There are even animals that naturally change their gender in a process known as sequential hermaphroditism.

Why does gender-changing occur in animals? And can frogs change their gender? This article will explore these two questions and answer your curiosities around gender and reproduction in frogs. It will also cover examples of animals that commonly change their gender and why.

Let’s find out more!

Can Frogs Change Gender?

While it is not a normal occurrence, yes frogs can change their gender. Frogs primarily determine their gender through genetics, relying on specific chromosome combinations (such as XX for females and XY for males). However, certain environmental factors, particularly exposure to endocrine-disrupting chemicals like pesticides and industrial pollutants, can interfere with their hormonal systems.

This interference may lead to sex reversals or the development of intersex characteristics, where genetically male frogs may exhibit female physical traits or vice versa. These changes are usually in response to environmental stressors and are not part of frogs’ natural reproductive biology.

While most instances of gender alteration occur during the early developmental stages, such as in larvae or tadpoles, adult frogs can also undergo sex changes if exposed to significant hormonal disruptions. Unlike some fish species that can naturally and reversibly change sex as part of their life cycle, frogs do not have an inherent ability to switch genders under normal conditions. Instead, any observed gender changes are typically caused by human impacts like climate change and pollution.

Why do Frogs Change Their Gender?

Typically, frogs will change their gender in reaction to changes in the environment that put stress on the frogs normal biological functions. As we’ve said, this tends to be various types of man-made pollution in water or soil. One research study found that human-created pollution that increased the levels of estrogen in suburban ponds led to an increase of female frogs.

Another study by the University of California, Berkeley, found that the pesticide atrazine turned one in 10 male frogs into females. It also reduced testosterone in three-quarters of male frogs, preventing them from reproducing. The female-turned male frogs could not produce female offspring even though they could successfully mate with other male frogs: a situation that contributes to population decline.

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Can Female Frogs Reproduce Without a Male?

All female frogs require a male frog to fertilize the eggs they release for reproduction. Most frogs hatch from eggs into tadpoles, though some species undergo direct development, bypassing the tadpole stage. While many frogs lay their eggs in water, not all do; some lay eggs on land and keep them moist using environmental moisture or secretions like mucus. Additionally, certain species exhibit unique parental behaviors by carrying their eggs in specialized structures such as abdomens or vocal sacs to ensure their protection and development.

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How Do You Tell Female Frogs from Male Frogs?

Most frog species have observable differences between females and males, known scientifically as being sexually dimorphic. Their body color and sizes can differ depending on whether they are male or female. For example, the female American toad (Anaxyrus americanus) is significantly larger than the male.

Other characteristics found in different species include:

• Males have rough patches on their hands called nuptial pads. These pads help males grasp females firmly during mating, ensuring successful fertilization of the eggs.
• Males have loose skin on their throats. This flexible skin allows the vocal sacs to expand when they call. Males call frequently during the mating season to attract females. Most females do not need this loose skin because they do not make calls, only males do.
• Males have larger tympanum, an ear-like membrane that detects sound. In many species, the tympanum is more prominent or larger in males, aiding them in both producing and receiving calls. 

In frog species where the females and males look very similar, scientists often rely on the release call to identify their gender. A male frog will typically produce a release call if another male clasps them for mating.

Why Do Frogs Get Stuck Together?

It’s normal to wonder what is going on when you see two frogs clinging on to each other or stuck to each other. This behavior is known as amplexus and happens during mating. It allows male frogs to place their cloaca closer to the female’s cloaca. The cloaca is the opening on the frog for their reproductive, digestive, and urinary tracts.

Except for a few species, egg fertilization happens externally, so the frogs need to be close enough together for the male to fertilize the female’s released eggs. Frogs can stay stuck together for hours or days, waiting for the female to release one or several hundred eggs.

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Frogs Species That Change Their Gender

While these three frogs are not naturally capable of changing their gender as part of their normal biology, scientific studies have shown that exposure to certain environmental pollutants, such as endocrine-disrupting chemicals like atrazine, can induce sex reversals or intersex conditions in these species. 

1. African Clawed Frogs

Scientific name: Xenopus laevis

The African Clawed frog is an aquatic species native to waterbodies in various African countries but has also been introduced to other countries, such as the United States, United Kingdom, and France. They are commonly used in experiments and scientists have extensively studied the impact of atrazine (an herbicide known for its potential hormone disrupting effects) on gender change in this species. These frogs have distinctive clawed toes and adults can reach up to 5 inches in body length.

2. Green Frogs

Scientific name: Lithobates clamitans

The Northern Green Frog is native to the eastern United States, inhabiting a variety of freshwater environments such as ponds, lakes, marshes, and slow-moving streams. These frogs exhibit a range of colors, including green, brown, and bronze, with a distinctive green lateral stripe that often extends to the upper lip, aiding in camouflage.

While Northern Green Frogs primarily rely on genetic mechanisms for sex determination, environmental factors can influence their reproductive biology. Exposure to endocrine-disrupting chemicals and pollutants may lead to abnormalities in sex development, such as intersex conditions or skewed sex ratios. 

3. Common Reed Frog

Scientific name: Hyperolius viridiflavus

The Common Reed Frog is a tree frog native to the forests and wetlands of central and eastern African countries, including Rwanda, Tanzania, and Uganda. Known for their diverse patterns and colors, these frogs display a range of hues from green and yellow to brown and red, aiding in camouflage and communication within their lush habitats. 

Environmental factors such as exposure to pesticides can lead to abnormal sexual development, including sex reversals or intersex conditions. 

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What Other Animals Can Change Their Gender?

Some of the other fascinating animals that can change their gender, and why, are:

• Clownfish (Amphiprioninae) are protandrous hermaphrodites, meaning they are born as males and can change to females if the dominant female in their group is removed, ensuring the social and reproductive structure of their community.
• Bluehead Wrasse (Thalassoma bifasciatum) are protogynous hermaphrodites that typically start life as females and can change to males in response to social cues, such as the absence of a dominant male in their group, to maintain reproductive functionality.
• Yellow-Bellied Water Snake (Nerodia erythrogaster) can exhibit facultative parthenogenesis, allowing females to produce offspring without male fertilization, particularly when kept alone in captivity.
• Coral: Some coral species begin life as males and later change to females. This shift often occurs in response to environmental stressors or changes in colony dynamics, ensuring the continuity of reproduction within coral reefs.
• Parrotfish (Scaridae): Many parrotfish species begin their lives as females and can later transition to males. This sex change often occurs when the dominant male in a group dies or is removed, allowing a female to take over the role. This strategy helps maintain reproductive efficiency within their social structure.
• Cleaner Shrimp (Lysmata): Certain cleaner shrimp species start life as males and can transition to females as they grow larger. This shift typically happens in response to the absence of dominant females, ensuring that all available shrimp can contribute to reproduction.

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Conclusion

Differentiating between male and female frogs can be challenging due to the subtle differences present in many species. While it is not a common or natural capability, some frogs can exhibit gender changes or sex reversals. These changes are primarily induced by environmental factors, particularly exposure to pollutants such as endocrine-disrupting chemicals from human activities. These changes tend to happen most during the tadpole stage, but adult frogs can also be affected under extreme environmental stress.

It’s important to recognize that gender changes in frogs are not adaptive behaviors but rather adverse effects caused by man-made pollution. These disruptions can lead to imbalanced sex ratios, reduced reproductive success, and potential declines in frog populations, highlighting the critical impact of a clean environment on amphibian health and ability to thrive.