From Animals to Humans: Unlocking the Future of Human Regenerative Therapy

Why can salamander lose an entire limb and grow it back, while humans generally heal with a scar? Although humans possess some regenerative abilities, these are much more limited than those observed in certain species that have develop a remarkable ability to heal and regrow entire body parts. In this article, we will explore which species possess these abilities, the mechanisms involved and how they could help scientists develop novel therapies to be implemented in human regenerative medicine.

By Ricardo Ribas

What animals can regenerate body parts?

Across the animal kingdom, species have evolved remarkable adaptations to survive and thrive in their habitats, some of which possessing the extraordinary capacity to regenerate, repair and even regrow entire parts of their bodies. Salamanders, and the Mexican axolotl in particular, are remarkable examples, having been the focus of extensive research because of their ability to regrow entire limbs, tails, and regenerate complex tissues and parts of their organs, including skin, spinal cord, brain, heart and jaw.

Some types of starfish have also developed similar capacities, showing ability to regrow entire limbs after these become detached from the central body. There are even some starfish able to regrow the entire body from one single limb.

Other examples of aquatic species with remarkable regenerative abilities include the sea cucumber, which can regenerate internal organs following injury or evisceration and the zebrafish, an important model for regenerative medicine research due to its capacity to regenerate parts of its heart, fins, retina and spinal cord. Flatworms can regenerate an entire organism from fragments of their bodies. The Mexican tetra, a surface- dwelling freshwater fish, is capable of regenerate heart tissue after injury. Lobsters can shed or discard limbs when threatened and subsequently regenerate claws, legs and antennae. Sharks possess an equally impressive ability to continuous replace teeth throughout their life, with multiple rows of replacement teeth behind those currently in use. In some species, new teeth can emerge in as little as an hour. Octopuses can also completely regenerate lost arms following injuries or attacks by predators, rebuilding complex structures including muscles, skin, suckers, blood vessels and nerves over a period of weeks or months.

However, regenerative abilities are not limited to aquatic animals. Deer can regrow antlers annually making antler tissue one of the fast regenerated tissues in mammals. Similarly, certain types of bats and mice can regenerate specific tissues, such as parts of their wings and ears, although their regenerative capacity is considerably more limited than that observed in salamanders.

How Can Animals Regenerate Body Parts?

Regeneration is the ability to replace or restore tissues or organ that have been damaged or lost often without the creation of scar tissue. It differs from normal healing, which mainly repairs a damaged tissue instead of fully replacing it. Across species, regeneration can occur through different strategies, although some underlying biological mechanisms are shared. Initially, the cells around the injury site receive signals informing them that something is missing and that new tissue needs to be built. Regeneration often involves stem cells, a specialised type of cells capable of dividing and developing into a specialised cell type, such as muscle, skin, nerve cells but also mature cells that become more flexible to take up on new roles. In species capable of major regeneration, such as salamanders, a group of rapidly dividing cells called blastema forms at the site of injury that then grows and develops into a missing body part. Regeneration also involves switch on and off some genes that regulate control growth, repair and tissue formation. At the same time, the immune system helps manage the injury and creates the right environment for the regeneration to take place instead of simply forming a scar.

But how do the cells know what to rebuilt, where, in what shape and size? Researchers are studying how chemical and electrical signals can guide the cells during regeneration, so it may help develop similar strategies in humans. The ability to regenerate varies greatly between species, tissues and age, with younger individuals often exhibiting greater regenerative capacity.

Could animal regeneration eventually help human medicine?

By studying how animals regenerate damaged and lost body parts, scientists can gain insight of the cellular, molecular and signalling mechanisms involved in tissue regeneration and answer questions such as how cells know what to become, where to grow and when to stop. This knowledge could eventually help researchers develop new ways to improve wound healing, reduce scarring, promote the repair of damaged tissues, and potentially encourage the regeneration of human tissues. This research may also identify biological processes that are conserved across species as well as the ones that are regulated differently in humans to provide valuable insights for human regenerative medicine and treatments.

By Ricardo Ribas, Veterinary Doctor, doctorate in veterinary sciences and scientific researcher.

Reference Sources

1. Harry Lye. Five animals that can regenerate. November 2018. The Guardian. https://www.theguardian.com/technology/2018/nov/25/five-animals-that-can-regenerate-salamander-starfish

2. Liz Langley. Pictures: 5 Animals That Regrow Body Parts. August 2013, National Geographic. https://www.nationalgeographic.com/animals/article/axolotl-regrow-regeneration-body

3. Regeneration (biology). Wikipedia. Wikipedia Foundation. August 2026. https://en.wikipedia.org/wiki/Regeneration_(biology)

4. Admin. How do animals regenerate limbs. Deep Sea World. March 2024. https://www.deepseaworld.com/blog/how-do-animals-regenerate-limbs/

5. Katherine Harmon. How octopus arms regenerate with ease. August 2013. Scientific American. https://www.scientificamerican.com/blog/octopus-chronicles/how-octopus-arms-regenerate-with-ease/

6. Fumagalli, M.R., Zapperi, S. & La Porta, C.A.M. Regeneration in distantly related species: common strategies and pathways. npj Syst Biol Appl 4, 5 (2018). https://doi.org/10.1038/s41540-017-0042-z

7. Huang, L., Ho, C., Ye, X., Gao, Y., Guo, W., Chen, J., Sun, J., Wen, D., Liu, Y., Liu, Y., Zhang, Y., & Li, Q. (2024). Mechanisms and translational applications of regeneration in limbs: From renewable animals to humans. Annals of Anatomy, 255, 152288. https://doi.org/10.1016/j.aanat.2024.152288

8. Vieira, W. A., Wells, K. M., & McCusker, C. D. (2020). Advancements to the axolotl model for regeneration and aging. Gerontology, 66(3), 212–222. https://doi.org/10.1159/000504294

9. Menger, B., Vogt, P. M., Kuhbier, J. W., & Reimers, K. (2010). Applying amphibian limb regeneration to human wound healing: A review. Annals of Plastic Surgery, 65(5), 504–510. https://doi.org/10.1097/SAP.0b013e3181d376f9

10. Griffiths, J.R., Miller, M., Duerr, T.J. et al. A characterization of axolotl digit regeneration: conserved mechanisms, divergent patterning, and a critical role for hedgehog signaling. npj Regen Med11, 28 (2026). https://doi.org/10.1038/s41536-026-00461-2.

11. Wu SYC, Whited JL. How axolotl cells ‘remember’ development to rebuild a lost limb. Nature. 2025 Jun;642(8068):573-574. doi:10.1038/d41586-025-01447-8.

12. Haas BJ, Whited JL. Advances in Decoding Axolotl Limb Regeneration. Trends Genet. 2017 Aug;33(8):553-565. doi: 10.1016/j.tig.2017.05.006.

13. Bangru, S., Diegmiller, R., Di Talia, S. et al. Signal control during tissue regeneration in adult animals. Nat Rev Mol Cell Biol27, 316–335 (2026). https://doi.org/10.1038/s41580-025-00917-1

14. Arenas Gómez CM, Sabin KZ, Echeverri K. Wound healing across the animal kingdom: Crosstalk between the immune system and the extracellular matrix. Dev Dyn. 2020 Jul;249(7):834-846. doi: 10.1002/dvdy.178. Epub 2020 May 4. PMID: 32314465; PMCID: PMC7383677.

Disclaimer

The material, ideas and prevention measures discussed on this article are for informational purposes only. For more information consult a vet or a professional in the area. Whilst every effort is made to make sure the article is accurate at the time of publication, I take no liability for any new developments on the subject as well as any errors or omissions.

Monkeypox, a new health scare?

As the world unwinds from Covid-19, a new scare knocks at our door, monkeypox. Could this viral disease become the next pandemic? Learn more about this disease and its capacity to jump from animals to humans.

By Ricardo Ribas

What is Monkeypox?

Monkeypox is a rare viral infectious disease that affects both animals and humans. The agent, an Orthopoxvirus, is an enveloped double-stranded DNA virus usually endemic in the tropical forests of Central and West Africa and a close relative from the smallpox viruses, a family with a tendency to attack skin cells. Monkeypox is not a recent disease, the virus was first identified in 1958 in laboratory monkeys in Denmark and subsequently in humans in the 1970s in the Republic of the Congo. In contrast to what the name indicates, the natural reservoir of this virus is not the monkey and scientists are still unsure which animal would be, but there are some indications that it might be a rodent. It is known, however, that the monkeypox virus can affect a broad range of animals including rope squirrels, Gambian pouched rats, mice, dormice, non-human primates and humans. There are two known types of monkeypox in humans: one predominantly found in West Africa and responsible for a mild disease (with a fatality rate of about 3-4%) and a second one prominent in Central Africa (Democratic Republic of Congo) and responsible for more severe disease with a fatality rate reaching 10%. Recent studies confirmed that the 2022 outbreak is related to the West African variant and as of the date of this publication, no deaths have been recorded during the current outbreak of the disease.

How is monkeypox transmitted?

The routes of transmission from animals to humans is usually by direct contact with blood, body fluids and the cutaneous lesions (blisters and scabs) as well as by the consumption of uncooked meat or other products from infected animals.

Infection between humans is often a result of sharing clothing, bedding and towels used by someone infected with the virus particularly when suffering from rashes, blisters and scabs. Contamination is also possible through droplets of respiratory particles during coughing or sneezing. Recent research also suggests the possibility for vertical transmission between mother-to-child.

Given the high frequency of human to human transmission observed in the current outbreak of the disease, together with the fact that most of the patients are young adults and middle-aged men who have sex with men, scientists suspect that the close contact during sexual activities might be the main route of transmission. It is, however, important to note, that monkeypox is not a sexually transmitted disease.

Image from SamuelFrancisJohnson, pixabay.con

So, what are the symptoms?

The incubation period for monkeypox (time between the infection and the appearance of the first symptoms) is between 5 to 21 days. In the first stages, the person will show fever, headache, muscle aches, shivers, swollen gland and tiredness, followed by a rash a few days later. The rash is characterized by the presence of raised spots often starting in the face and later spreading throughout other parts of the body and genitals. The spots eventually turn into small blisters filled with liquid and then into scabs that will fall off within a few weeks. The duration of the symptoms are approximately 2-4 weeks.

Children, immunocompromised individuals and pregnant women are more susceptible to develop severe forms of the disease as well as to suffer complications and a higher fatality rate. Scientists are still not sure why the 2022 outbreak is causing milder symptoms than previously observed, but it may relate to the fact that the virus is infecting a healthier and stronger population (mainly men between 20-50 years of age), from countries with better health care systems than previous outbreaks. There is no evidence that the virus has mutated to become less deadly.

How to treat the disease?

The great majority of people infected will recover from the disease without requiring any specific therapy. However, in severe cases involving immunocompromised patients, pregnant women and children, additional therapy may be required. There is currently no specific treatment approved for monkeypox, but a series of antiviral agents developed for patients suffering from smallpox might be effective. Administration of smallpox vaccines also appear to reduce the severity of the disease and should be consider in the most serious cases.

How to prevent from catching monkeypox?

A series of recommendations are important to keep in mind to prevent infection from monkeypox:

• Avoid direct contact with animals infected with the disease or with any of their derived products, such as blood and uncooked meat,

• Avoid contact with any materials that have been in contact with infected animals or humans,

• Thoroughly cook all foods containing animal meat or their parts before eating,

• Humans infected with monkeypox should isolate until all the symptoms are over and the scabs have fallen off,

• Use protective equipment and practice good hygiene (such as wash the hands with soap and water or hand sanitizer), particularly if in contact with infected animals or humans,

• Professional health workers should implement standard infection control precautions,

• Smallpox vaccines appear to be 85% effective against monkeypox and it can be used as a post-exposure prophylaxis for close contacts of known cases,

• Preferably select people already vaccinated against smallpox to care for animals and patients infected with the disease.

• The governments should improve regulations for animal trade and importation of rodents and non-human primates, such as promotion of isolation and quarantine of animals.

New Outbreak 2022

Monkeypox is generally a mild disease, confined to Central and West Africa, often endemic in Benin, Cameroon, Central African Republic, Democratic Republic of the Congo, Ghana, Ivory Coast, Liberia, Nigeria and Sierra Leone. While it is not the first time that monkeypox spreads to regions outside Africa, this is quite rare. For instance, in 2003, the West African strain managed to reach 70 humans in the United States. This was linked to the direct contact of humans with infected pet prairie dogs who have been housed with Gambian pouched rats imported from Ghana. All 2003 cases resulted from an animal to human contact and there was no evidence of human to human transmission.

The recent 2022 outbreak appears to be the result of the importation of the disease through infected humans with the first case reported in England in an individual recently arrived from Nigeria. As of the day of this publication, more than 1300 cases have been reported throughout Europe, North America, Middle East and Australia, the majority of which as a result of human to human transmission particularly affecting men who have sex with men. Scientists are trying to understand the reason for the spread of the disease outside Africa but are concerned that human monkeypox virus may have already been established as a reservoir in non-African wildlife species creating the perfect environment for future outbreaks and the opportunity for the virus to mutate to more dangerous and transmissible variants.

By Ricardo Ribas, Veterinary Doctor, doctorate in veterinary sciences and scientific researcher.

Reference Sources

1. Monkeypox, Wikipedia, Wikipedia Foundation, June 2022, https://en.wikipedia.org/wiki/Monkeypox#cite_note-WHONR-19

2. 2022 monkeypox outbreak, Wikipedia, Wikipedia Foundation, June 2022, https://en.wikipedia.org/wiki/2022_monkeypox_outbreak

3. Monkeypox, WHO, June 2022, https://www.who.int/news-room/fact-sheets/detail/monkeypox

4. Monkeypox, NHS, June 2022, https://www.nhs.uk/conditions/monkeypox/

5. Monkeypox. Centers for Disease Control and Prevention. June 2022. https://www.cdc.gov/poxvirus/monkeypox/treatment.html

6. Monkeypox: Cases outside Africa rise to 780 in three weeks. BBC News. June 2022. https://www.bbc.co.uk/news/health-61696974

7. Daniel Payne & Carmen Paun. What researchers do — and don’t — know about monkeypox. Politico. June 2022. https://www.politico.com/news/2022/06/07/researchers-monkeypox-00037620

8. Camille Besombes. Monkeypox: ‘This is an entirely new spread of the disease’. The Conversation. June 2022. https://theconversation.com/monkeypox-this-is-an-entirely-new-spread-of-the-disease-184085

9. Jon Cohen. Concern grows that human monkeypox outbreak will establish virus in animals outside Africa. ScienceInsider. June 2022. https://www.science.org/content/article/concern-grows-human-monkeypox-outbreak-will-establish-virus-animals-outside-africa

10. Jonathan Wolfe, Monkeypox: a Guide. The New York Times, June 2022. https://www.nytimes.com/2022/06/08/briefing/monkeypox-guide.html

11. Jason Gale. Understanding monkeypox and how outbreaks spread. The Washington Post. June 2022. https://www.washingtonpost.com/business/understanding-monkeypox-and-how-outbreaks-spread/2022/06/08/29454880-e78e-11ec-a422-11bbb91db30b_story.html

Disclaimer

The subjects and ideas discussed on this article are for informational purposes only. For more information consult a vet or a professional in the area. Whilst every effort is made to make sure the article is accurate at the time of publication, I take no liability for any new developments on the subject as well as any errors or omissions.

Toxoplasmosis: Be aware of your cat and uncooked meat

Learn about toxoplasmosis, a worldwide and common parasitic disease responsible for serious problems in pregnant women and those with weakened immune system.

By Ricardo Ribas

Toxoplasmosis is a world distributed disease affecting warm-blood species such as birds, mammals and humans. The agent is a single-celled protozoa parasite named Toxoplasma gondii. Whilst studies suggest that the Toxoplasma can be found in approximately 30% of the human population, the disease is rarely a reason of concern in healthy individuals, but can lead to serious consequences in those with weak immune system, such as AIDS sufferers or those undergoing chemotherapy. Pregnant women are also vulnerable and the disease can lead to miscarriage, stillbirth and devastated neurological problems to the foetus.

How is Toxoplasma transmitted?

Most of human and animal infections occur during the consumption of uncooked meat containing toxoplasma cysts or by ingestion of food/water contaminated with eggs. Other less common routes of transmission include blood transfusions, organ transplantation and vertical transmission from the mother to foetus. The World Health Organisation suspects that, just in Europe, there are over a million toxoplasma infections happening each year.

The Toxoplasma’s life cycle

Cats and other felines have a crucial role in the life cycle of the Toxoplasma’s given that they are the only species able to provide the right environment for the parasite to mature sexually and complete its life cycle. The process starts when the felines consume meat (often rodents, birds, and other small animals) carrying the parasite cysts. The cysts will travel to the animal’s stomach where they lose the protective envelop, triggering the start of the process of maturation and replication. Once reach the intestines, the toxoplasma produce eggs that are subsequently released into the environment with the animal’s faeces.

The eggs can remain in the environment for several years and are been able to contaminate food and water. Once ingested by animals or humans, the eggs have the potential to migrate through their bodies and lodge in the form of cysts in many tissues, such as brain, muscles, liver, heart, lungs, eye, etc, generating a new route for transmission to other species that will consume these tissues. Infection during pregnancy is of particular concern both in animals and humans, because the parasite has the potential to trespass the placenta and to lead to the development of neurological problems in the foetus, stillbirth and miscarriage.

What are the symptoms?

While most of the infections by Toxoplasma do not cause any symptoms in healthy animals and humans, complications often occur in pregnant females or individuals with weaken immunity. This is because the toxoplasma is an opportunist parasite that takes advantage of hosts with weakened immunity to spread. In the majority of the cases, people show flu-like symptoms such as fever, tiredness, muscles-ache, lack of appetite and weight loss. However, complication can happen depending of the organs affected. These can include diarrhoea, vomiting, jaundice, coughing, difficulty breathing, pancreatitis, headaches as well as problems in the nervous system and with the eye (reduced or blurred vision, eye pain, redness or tearing) and occasionally death. Recent studies have also suggested a link between Toxoplasmosis and schizophrenia and suicide. Finally, particular care should be given during pregnancy because it can bring catastrophic consequences to the foetus and lead to stillbirths or birth defects such as mental retardation, blindness, hydrocephalus – presence of water in the brain, seizures, etc.

And how can we treat?

Whilst most animals and humans often recover without any specific treatment, in some cases this is required. A combination of antibiotics and antimalaria drugs are usually recommended in animals and humans to prevent serious complications. Depending on the specific symptoms, a selection of other treatments may be required, such as the use of corticosteroids for those suffering from eye problems.

Preventive Measures

• Ensure meats are well cooked, fresh vegetables are washed thoroughly and avoid consuming unpasteurized milk or any products made from it.

• Avoid handling raw meats without gloves.

• Wash utensils and surfaces that may have been in contact with raw meats to avoid contamination with other foods.

• Clean the garbage daily using disposable gloves.

• Wear gloves and wash your hands thoroughly after handling or cleaning cat faeces. Disinfect the places where the cat may have defecated.

• Prevent cats from eating raw meat or any animals such as mice or birds.

• Avoid touching or handling pregnant sheep or lambs.

• If you intend to become pregnant, it is advisable to take a toxoplasmosis test. If the test is positive, it means that you are already immune. If the test is negative, take extra precautions to prevent infection during pregnancy.

By Ricardo Ribas, Veterinary Doctor, doctorate in veterinary sciences and scientific researcher.

Reference Sources

1. Toxoplasmosis. Wikipedia. Wikipedia Foundation. https://en.wikipedia.org/wiki/Toxoplasmosis. Accessed May 2021.

2. Parasites – Toxoplasmosis (Toxoplasma infection). Centers for disease control and Prevention. https://www.cdc.gov/parasites/toxoplasmosis/. Accessed May 2021

3. Toxoplasmosis. Fact Sheet. World Health Organisation. https://www.euro.who.int/__data/assets/pdf_file/0011/294599/Factsheet-Toxoplasmosis-en.pdf?ua=1. Accessed May 2021

4. Toxoplasmosis. NHS. https://www.nhs.uk/conditions/toxoplasmosis/. Accessed February 2021.

5. Bigna JJ, Tochie JN, Tounouga DN, Bekolo AO, Ymele NS, Simé PS, Nansseu JR. Global, regional and national estimates of Toxoplasma gondii seroprevalence in pregnant women: a protocol for a systematic review and modelling analysis. BMJ Open. 2019 Oct 19;9(10): e030472.

6. Dubey, JP; Lindsay, DS; Speer, CA. Structures of Toxoplasma gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts. Clin Microbiol Rev. 1998 Apr; 11(2): 267–299.

7.Montoya JG, Liesenfeld O. Toxoplasmosis. Lancet 2004; 363:1965- 76.

8. Dickerson F, Stallings C, Origoni A, Katsafanas E, Schweinfurth L, Savage C, Khushalani S, Yolken R. Antibodies to Toxoplasma gondii and cognitive functioning in schizophrenia, bipolar disorder, and nonpsychiatric controls. J Nerv Ment Dis. 2014 Aug; 202(8):589-93.

9. Cook TB, Brenner LA, Cloninger CR, Langenberg P, Igbide A, Giegling I, Hartmann AM, Konte B, Friedl M, Brundin L, Groer MW, Can A, Rujescu D, Postolache TT. “Latent” infection with Toxoplasma gondii: association with trait aggression and impulsivity in healthy adults. J Psychiatr Res. 2015 Jan; 60:87-94.

Disclaimer

The subjects and ideas discussed on this article are for informational purposes only. For more information consult a doctor, a vet or a professional in the area. Whilst every effort is made to make sure the article is accurate at the time of publication, I take no liability for any new developments on the subject as well as any errors or omissions.

The astonishing reproductive life of the animals

The animal kingdom is extremely diverse consisting of a wide-range of anatomies and behaviours. In this article, we will explore the scientific reasons for some of the mind-blowing strategies developed by some species to court, reproduce and produce offspring. Some will leave you speechless!

By Ricardo Ribas

1. Males that get pregnant!!

Seahorses, pipefishes and seadragons have a very peculiar and different reproductive strategy, as they are the only fishes to undergo male pregnancy. Depending on the specie, the males have a pouch located in the abdomen or in the tail where the females deposit the eggs during mating. It is in the male’s pouch that the sperm fertilise the eggs and it is the male’s responsibility to carry and develop the fertilised eggs for a period between 9 and 45 days. The male pouch functions similarly to the mammal’s and human’s placenta, providing protection, the nutrients and the oxygen necessary for the fish development as well as the structure necessary to get rid of the waste products. By the end of the pregnancy, the males can deliver between 5 and 2000 young fish.

2. Sexual Cannibalism

Some animals use reproductive strategies resembling horror movies. Take as an example the family of black and venous spiders, commonly named as black widows as a result of the females’ gruesome behaviour of killing and eating the males after mating. Scientists believe this form of sexual cannibalism appear to provide the females with an extra source of proteins increasing their chance for reproductive success and offspring survival. Studies have also shown that females who practice this type of cannibalism produce larger eggs and healthier offspring with a better chance of survival, than the females that don’t eat the males. Understandably, some males prefer to court females that have already eaten, even if they are less fertile and fruitful. Scientists believe the males are able to tell how hungry the females are by the presence of pheromone smells in the silk of their cob webs.

There are other examples of sexual cannibalism in nature, such as is the case of the mantises, where females also kill and eat the males during mating. Whilst the purpose for their behaviour is still unknown, studies shown that females with poor diets are more likely to eat their partners, and that, similarly to spiders, it appears to provide them with extra nutrients necessary to improve the chances of reproductive success.

3. Transsexual animals

Other species have the astonishing capacity to change sex throughout lifetime. All clownfish are born male but they carry both male and female reproductive systems. Their school is composed by one female, often the larger animal in the group; a dominant breeding male, usually the second biggest in the group; and several immature males. When the female dies or disappears, the dominant males starts a process of sex change taking about 45 days to be complete, during which the male hormones are inhibited and the female hormones are activated. At the same, one of the immature males becomes the dominant male. Scientists believe this sex-change capacity allows the clownfish to remain in their habitat, circumventing the need to travel and risk their life to find females to mate. Wrasses use the same sex-change strategy as clownfish but in the opposite way. In this case, is the larger female of the group that changes sex and transforms into a male, taking the role of the previous dominant male of the harem upon his death or disappearance.

4. Inflated balloons to attract females’ attention

Male dromedary camels have a very strange and peculiar way to attract females. They hold an organ located in their throat that once inflated turns into a giant pink balloon (often confused with the tongue) that hangs and dangles from one of the sides of the male’s mouth to show their dominance and to attract females. This organ is called dulaa, what means “soft-palate” in Arabic. Male seals have a similar organ also used for sexual attraction and territorial fights, however, in their case, this large pinkish inflated balloon-like sac appears from the animal’s nostrils.

5. Animals with multiple genitals

Some animals own more than one genital. Female marsupials, such as kangaroos, koalas and Tasmanian devils own three vaginas and two uteri, whilst the males have two pronged penises. The two-sided vaginas are used to transport the sperm to their two uteruses, whilst the middle vagina is used for birth. This process allows the females to be constantly pregnant by carrying a baby in their pouch, a foetus developing in one utero and a fertilised egg waiting to be released in the second utero. Marsupials also have the capacity to store sperm for long periods and even delay birth until the pouch becomes free, a great strategy particularly during harsh times of drought and starvation. Due to these reproductive tactics, the population of kangaroos can increase rapidly!!!

Snakes and the lizards are other examples of species carrying multiple genitals. Males own two penises (hemipenes) each one connected to a single testicle and the females have two clitorises (hemiclitoris). Scientists are still unsure why females require two clitorises, but they believe the reason for the two penises is to allow the males to be more flexible and able to mate with the female from either side, particularly during mating aggregations, where as many as 100 males can compete for the same female. Remarkably, female snakes can mate with several males and store their sperm for up to five years and have the capacity to choose which sperm to use to fertilise the eggs.

6. And some without genitals at all

Conversely, there are examples in nature of animals without genitals, such as the squids which lack vaginas. To reproduce, the males store their sperm in enclosed sacs called spermatophores and during mating, they use a special arm to transfer and implant the sacs into the female’s body, generally around her head or near her mouth, where the eggs are waiting to be fertilised. Once fertilised, the female releases the eggs from her mouth or funnel hiding them in the rocks or in holes until they are ready to hatch.

7. Strange Penises

Apart from the kangaroos, snakes and lizards, there are other examples of animals with strange penises. Both ducks and pigs have penis in a shape of a corkscrew or spiral-shaped, which are compatible with a corkscrew-shaped vagina. Boar’s half a meter penis rotates rhythmically during mating and can ejaculate more than half a litter of semen over a period of 15 minutes, whilst duck penises are equally not small, measuring in average about 20cm in length or even half a meter long in the case of the Argentine lake duck. Lucky Donald Duck and Daisy!!

Sea slug’s also use a strange reproductive strategy. They hold three penises and have the capacity to dispose and regenerate one of these penises every time it mates. And scientists seem to know the reason for this perplexing strategy. It appears the sea slugs use their first penis to remove any sperm left inside the female by other males. They then dispose this penis, before using the second penis to inject its own sperm, ensuring that it’s his genes that are passing to the next generation. Miraculously, a few hours later, the male is able to regenerate its first penis and to mate again. Similarly, orb-weaver spiders and other sea creatures also use very similar strategies as the sea slugs.

8. Orphan species

Finally, some animals are orphans from the time they are born. Octopus only go through one single reproductive period and die before their offspring hatch. The males usually die after mating, sometimes killed by the females in an act of cannibalism, whilst the females tend to survive until the eggs are hatched. After fertilization, the female lay the eggs and stand close to them to protect them from intruders, but very soon they stop eating and wastes away starting a process known as programmed death. At later stages some females even go further and start self-mutilation, often slamming against surfaces, tearing off pieces of skin and eating the tips of their own tentacles. By the time the eggs hatch the mother is dead. Scientists are still uncertain why these intelligent animals undergo this process, but it appears it may be an effective strategy to ensure the female does not consume their youngster, particularly since these are remarkable cannibals. Other researchers believe that, since octopus can grow pretty much indefinitely, this may be a strategy to eliminate very big, old and hungry adults that could potential compromise hatchling and to maintain the ecosystem free of massive animals.

Squid use similar strategies during reproduction. Male squid die very soon after mating in order to provide food for the predators that otherwise would feed on the eggs, whilst the female die after releasing the eggs. Similarly, male salmons also die just after spawning but the females survive to guard the eggs, after which they die by exhaustion and the lack of capacity to travel thousands of miles back home to reinitiate their reproductive cycle.

Animals undergo astonish strategies and even ultimate sacrifices, to ensure propagation of their species and generation of viable and healthy offspring. Many more examples exist in nature and these will be part of a future article. Meanwhile, let’s keep observing the world around us and understand the reason behind their complex’s behaviours.

By Ricardo Ribas, Veterinary Doctor, doctorate in veterinary sciences and researcher in the London.

Reference Sources

SeaHorses

1. Foster, S.J.; Vincent, C.J. (2004). “Life history and ecology of seahorses: implications for conservation and management”. Journal of Fish Biology. 65: 1-61. doi:10.1111/j.0022-1112.2004.00429.x

2. Kawaguchi M, Okubo R, Harada A, Miyasaka K, Takada K, Hiroi J, Yasumasu S. Morphology of brood pouch formation in the pot-bellied seahorse Hippocampus abdominalis. Zoological Lett. 2017 Oct 17;3:19. doi: 10.1186/s40851-017-0080-9. eCollection 2017.

3. The biology of seahorses: Reproduction. The Seahorse Project.”The biology of seahorses: Reproduction” Retrieved July 2020

Black Widows

4. Welke, Klaas W.; Schneider, Jutta M. (January 2012). “Sexual cannibalism benefits offspring survival”. Animal Behaviour. 83 (1): 201–207. doi:10.1016/j.anbehav.2011.10.027.

5. Johnson, J. Chadwick; Trubl, Patricia; Blackmore, Valerie; Miles, Lindsay (August 2011). “Male black widows court well-fed females more than starved females: silken cues indicate sexual cannibalism risk”. Animal Behaviour. 82 (2): 383–390. doi:10.1016/j.anbehav.2011.05.018

6. Baruffaldi, Luciana; Andrade, Maydianne C.B. (April 2015). “Contact pheromones mediate male preference in black-widow spiders: avoidance of hungry sexual cannibals?”. Animal Behaviour. 102: 25–32. doi:10.1016/j.anbehav.2015.01.007

Transsexual Animals

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8. Godwin, J.; Thomas, P. (1993). Sex change and steroid profiles in the protandrous anemonefish Amphiprion melanopus (Pomacentridae, Teleostei). Gen Comp Endocrinol 91: 144-157.

9. Liu H, Todd EV, Lokman PM, Lamm MS, Godwin JR, Gemmell NJ. Sexual plasticity: A fishy tale. Mol Reprod Dev. 2017;84(2):171-194. doi:10.1002/mrd.22691

Camels and Seals

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11. Hooded Seal (Cystophora cristata), a weird animal. Drawfluffy.com. https://web.archive.org/web/20101229183024/http://www.drawfluffy.com/hooded-seal.html. Retrieved in July 2020.

Kangaroos multiple genitals

12. Ed Yong. Kangaroos have three vaginas. National Geograhic. https://www.nationalgeographic.com/science/phenomena/2012/04/17/ kangaroos-have-three-vaginas/. April 17, 2012.

13. Marsupial, Wikipedia. Wikipedia foundation. Updated August 2020. Accessed August 2020. https://en.m.wikipedia.org/wiki/epipubic_bone.

14. Matt Hayes. 10 unexpected examples of animal genitalia. Listverse. https://www.google.co.uk/amp/s/listverse.com/2012/11/29/10-bizarre-animal-genitalia/amp/. 2012

Snakes and Lizards

15. Tina Deines. Why Do Snakes Have Two Penises and Why Are Alligators Always Erect? https://www.nationalgeographic.com/news/2018/02/snakes-alligators-reptiles-genitalia-animals/ National Geographic. February, 2018

16. Friesen CR, Uhrig EJ, Squire MK, Mason RT, Brennan PL. Sexual conflict over mating in red-sided garter snakes (Thamnophis sirtalis) as indicated by experimental manipulation of genitalia. Proc Biol Sci. 2013;281(1774):20132694. Published 2013 Nov 13. doi:10.1098/rspb.2013.2694

17. King, RB.; Jadin, R.C.; Grue, M.; Walley, H.D. Behavioural correlates with hemipenis morphology in New World natricine snakes, Biological Journal of the Linnean Society, Volume 98, Issue 1, September 2009, Pages 110–120, https://doi.org/10.1111/j.1095-8312.2009.01270.x

Squids

18. Morse P, Huffard CL. Tactical Tentacles: New Insights on the Processes of Sexual Selection Among the Cephalopoda. Front Physiol. 2019;10:1035. Published 2019 Aug 21. doi:10.3389/fphys.2019.01035

19. Pharyngula Friday Cephalopod: Undead Squid Penis. Science Blogs. https://scienceblogs.com/pharyngula/2017/08/25/friday-cephalopod-undead-squid-penis. August 2017

20. Stephanie Watson. How Squid Work. How stuff works. https://animals.howstuffworks.com/marine-life/squid2.htm.

21. Squid. Wikipedia. Wikipedia Foundation. Last updated 16 August 2020. Accessed September 2020. https://en.wikipedia.org/wiki/Squid#cite_note-Ruppert-7

Weird Penises

22. McCracken KG, Wilson RE, McCracken PJ, Johnson KP. Sexual selection. Are ducks impressed by drakes’ display?. Nature. 2001;413(6852):128. doi:10.1038/35093160

23. Knox, RV. (2003). The Anatomy & Physiology of Sperm Production in Boars. Published in the internet. http://www.ansci.wisc.edu/jjp1/pig_case/html/library/boara&p.pdf. Department of Animal Sciences. University of Illinois.

24. Rebecca Morelle. Sea slug’s ‘disposable penis’ surprises. BBC news. BBC. https://www.bbc.co.uk/news/science-environment-21431678. February 2013

25. Ed Yong. Sea Slug Amputates Its Disposable Penis, But Has Two Spares. National Geographic.https://www.nationalgeographic.com/science/phenomena/2013/02/12/sea-slug-amputates-its-disposable-penis-but-has-two-spares/. February 2013

26. Sekizawa Ayami, Seki Satoko, Tokuzato Masakazu, Shiga Sakiko and Nakashima Yasuhiro. 2013. Disposable penis and its replenishment in a simultaneous hermaphrodite Biol. Lett.9. 2012.1150. http://doi.org/10.1098/rsbl.2012.1150

Animals who die after giving birth

27. Christina Root. Animals who die giving birth, Petsonmom.com. https://animals.mom.com/animals-die-giving-birth-9247.html. Accessed September 2020

28. Z. Yan Wang, Clifton W. Ragsdale. Multiple optic gland signaling pathways implicated in octopus maternal behaviors and death. The Journal of Experimental Biology, 2018; jeb.185751 DOI: 10.1242/jeb.185751

29. Matt Wood. The grim, final days of a mother octopus. University of Chicago Medical Center. https://www.uchicagomedicine.org/forefront/biological-sciences-articles/the-grim-final-days-of-a-mother-octopus. September 2018.

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31. Anderson RC, Wood JB, Byrne RA. Octopus senescence: the beginning of the end. J Appl Anim Welf Sci. 2002;5(4):275-283. doi:10.1207/S15327604JAWS0504_02

Disclaimer

The material discussed on this article are for informational purposes only. For more information consult a vet or a professional in the area. Whilst every effort is made to make sure the article is accurate at the time of publication, I take no liability for any new developments on the subject as well as any errors or omissions.