Animal genitalia: amphibians, reptiles and mammals

After the first post on the genitals of birds and fish, we close chapter on the curiosities of the penises, vaginas and other reproductive organs of amphibians, reptiles and mammals.

GENITALS IN AMPHIBIANS

As we saw in a previous post, the cloaca is the hole where the digestive, reproductive and excretory systems converge. All amphibians possess cloaca, as well as reptiles, birds and some fish (sharks and rays) and mammals.

Larvae of amphibians are characterized by a great transformation known as metamorphosis .
Do not miss the successful post about amphibious sperm thieves .

ANURA

The anurans (amphibians without tail, such as frogs) have external reproduction and mating occurs usually in the water. The male, who is smaller than the female, grips the female firmly. This embrace  is called amplexus.

Amplexus of Litoria xanthomera. Photo: Rainforest harley

The contractions of the female when expelling the eggs stimulate the male to spray them of sperm in the same moment that they are expelled. The eggs are joined by a gelatinous mass that takes different forms depending on the species.
The male frogs of the genus Ascaphus have a false tail that is nothing but an extension of the cloaca.

Tailed frog (Ascaphus truei). Photo: Mokele

URODELA

Almost all urodela (amphibians with tail, such as salamanders and newts) have internal fertilization. The male is placed in front of the female and releases sperm packages (spermatophores) containing the sperm. The female walks over one of them, collects it with the lips of the cloaca and places them in the spermatheca, a cavity where the sperm wait for the eggs to pass through the cloaca to make them fertilize. The female lays the fertilized eggs one by one beating them in aquatic plants, except in some species of salamander, in which the female retains them and they are born live larvae (ovovivivarism).

Salamander spermatophores (Ambystoma sp.). Photo: Placeuvm

APODA

Apoda or caecilians are amphibians without legs with internal fertilization, but unlike in anura, internal insemination occurs. This is possible thanks to a pseudo-phallus (phallodeum) that have the males, which they insert in the cloaca of the female for two or three hours. In oviparous species (25%) the eggs are kept by the mother, the rest of species are ovoviviparous (75%).

Caecilia phallodeum. Photo used under permission by: Danté Fenolio

In some ovoviviparous species the offspring are born metamorphosed, in others as larvae. During their stay inside the mother, they feed on oviduct cells, which they scrape with their special teeth. In the case of the oviparous species Boulengerula taitana, the larvae feed on the mother’s skin allowing them to grow 10 times their size in a week.

GENITALIA IN REPTILES

 SCALED REPTILES

Scaled reptiles (Squamata order), as lizards and snakes have the penis divided into two: this is known as  hemipenis. It is kept inside the tail and exits to the outside during intercourse thanks to the erectile tissues. In spite of being double, during intercourse they only introduce one of the parts into the female, although they can do it alternately. The ends can be smooth or have spikes or structures to ensure grip to the female’s cloaca.

Viviparous lizard (Zootoca vivipara) showing its hemipenis. Photo: Charlesjsharp

 

TURTLES

In some sea turtles, the cloaca retains the ability to exchange gas, in other words, to breathe. The water slowly passes through it, which allows to collect the oxygen and take it to the lungs.

The male tortoises have a simple penis that is folded in two in the cloaca, inside the tail, reason why the tail of the males is thicker and longer than the females’. During the erection, it fills with fluid, deploys and exits, reaching a comparatively larger size.

Mediterranean tortoise penis (Testudo hermanni). Source

CROCODILES

Crocodiles have a rigid penis (always in erection) hidden inside the body that, shot out like a spring to the outside at the time of copulation and is hidden again at the same speed. According to this study , fibrous tissue and collagen makes unnecessary the erection and detumescence in the American alligator.

GENITALIA IN MAMMALS

MONOTREMES

Monotremes are the most primitive mammals, with some reptilian characteristics, like the laying of eggs and the presence of cloaca. Platypus and echidnas are the best known representatives.

Monotremes penises have 4 heads, although not all can work simultaneously. It uses only half, that is, two heads at a time. In the case of the platypus only the left side works, since the female only has functional the left ovary.

Echidna penis’. Source

MARSUPIALS

The marsupials are those mammals in which the breeding ends its development in a pouch, a kind of bag that own the females and where the breasts are. The best known marsupials are kangaroos, koalas, opossums and the extinct thylacine.

Opossum’s penis. Photo: Ellen Rathbone

Generally females have two vaginas, which fit with the bifurcated penises of males, which retract into the S-shaped body, In the case of kangaroos, females have three vaginas and two uteri . The two lateral vaginas lead the sperm towards the uterus and the central one is where the brood descends during the delivery.

Reproductive system of marsupial femanel. Photo: National Geographic

PLACENTAL

  PENILE BONE AND ERECTION

In placental mammals, such as humans, the offspring develops in the uterus and is nourished by the placenta. Many placental males have a penile bone (baculum). This bone would allow copulation even if there is no erection. Some placentals have lost their baculum: humans, hyenas, equines (horses, zebras, etc.) and lagomorphs (rabbits, hares …). In them, erection is possible thanks to the blood filling of the corpora cavernosa.

A dog’s baculum.The arrow shows the uretral hollow. Photo: Didier Descouens

DOLPHINS

In the case of dolphins, their penis is prehensile and sensory. The end is rotatory and it is not uncommon to see them feel the seabed with their penis. This has led to false myths such as that the dolphins are always excited and try to copulate with anything that gets them ahead. This tactile ability would also allow them to strengthen social bonds between them, even among males. This behavior is also observed in orcas.

The dolphin’s vagina is full of folds and corners to make sperm access to the egg difficult, either from rival males or males with which the female did not want to mate. If you want to see how the penis fits in the intricate dolphin’s vagina, click here.

HYENAS

At first glance we could confuse a male hyena with a female. Female spotted hyenas (Crocuta crocuta) have a long vagina that extends into an external clitoris of the same size as the male penis. The offspring must cross this long channel at birth, who suffers from great tears in the first deliveries and sometimes the puppies die because they can not cross it. In addition, the vaginal lips are also large and full of fat, which could seem testicles.

Spotted hyena’s female genitalia. Source: Quora

 

REFERENCES

• Intimate details of dolphin sex revealed
• Kangaroos have three vaginas
• Do kangaroos really have three vaginas. If so, why?
• Extraños penes animales
• Sistema urogenital de las tortugas
• Terrifying sex organs of male turtles
• The alligator has a permanently erect bungee penis
• Sistema excretor y aparato urogenital de los anfibios
• Nussbaum, Ronald A. (1998). Cogger, H.G.; Zweifel, R.G., eds. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 52–59.
• Cover photo

The thylacine: we extinguished it

Today marks 79 years of the death of the last known thylacine, Benjamin, at the zoo in Hobart (Tasmania). The thylacine, Tasmanian wolf or Tasmanian tiger is one of the classic examples of extinct animals by humans. Its fame is due to its relatively recent extinction, its strange anatomy and the existence of videos of the last thylacine, which transmits certain uneasiness to know that no longer exists. Do you want to know their characteristics, the causes of their disappearance and their cloning project?

THE THYLACINE, A MARSUPIAL

Despite its many names, the thylacine (Thylacinus cynocephalus*) was not related to wolves or tigers (placental mammals), as it was a marsupial animal. Marsupials are a mammals’ infraorder in which the young is born at a very early stage of development, almost in embryonic state. The best known representatives are kangaroos, koalas, wallabies, possums and bandicoots.

One of the few preserved thylacine taxidermy in the world. Museo Nacional de Ciencias Naturales, Madrid. Photo: Mireia Querol

After a very short gestation, newborn moves to one of the mother‘s nipples where is seized several months. In most marsupials, nipples, -and therefore the newborn- are protected by a pouch. When the brood completes its development, it will release the nipple and leave the pouch to explore the outside. Look in the following video the birth and migration of the embryo of a red kangaroo:

DESCRIPTION

The thylacine was native of Australia and Papua New Guinea, but in the seventeenth century (arrival of European settlers Oceania) was found only in Tasmania.

Old thylacine distribution. Map by Discover Life

It was an animal with physical traits of wolf, tiger and kangaroo due to convergent evolution, which made him a unique case and an enigma to science before their taxonomy was known. Its closest relative is the Tasmanian devil (Sarcophilus harrisii).

He looked like a big dog with a thick, stiff tail. Its weight was about 30 kg on average. The fur was short, gray-brown with 13-20 vertical black stripes at the rear. It is estimated that lived between 5 and 7 years in the wild.

Display of taxidermy thylacines. Photo: South Australian Museum

It was capable of bipedal jumps and upright posture for short periods of time. They were also good swimmers. The anatomy of the thylacine when stood up, with its tail resting on the ground, reminds the kangaroo as evidenced by the following filming of 1933:

FEEDING

The thylacine was exclusively carnivorous, feeding on kangaroos, emus, wallabies and wombats. It was a solitary and crepuscular hunter who caught their prey by ambushes, as it was not very fast. It could turn the palm of the leg up like cats do. This increased movement of the leg would have allowed them subdue prey more easily after a surprise attack. In contrast, animals with reduced mobility in the leg, as some canines, prefer the persecution of the ambush and often hunt in herds.

Benjamin gasping similarly to yawning in response to a threat. Hobart Zoo. Photo by David Fleay.

Another unique feature was the ability it had to open its mouth. Equipped with 46 teeth, its powerful jaws could be opened at an angle of 120 degrees, allowing him to swallow large chunks of meat.

The thylacine’s impressive buccal capacity. Photo: video capture by David Fleay

Look in the following video the last moving record of Benjamin (1933), from which was obtained the above screenshot:

To view the 7 videos that remain from this fantastic animal, enter The Thylacine videos.

REPRODUCTION

Thylacines could reproduce from June to December. It were born 2-4 pups per litter, who spent three months in the pouch but were still dependent on its mother‘s milk more than nine months. Unlike many marsupials, in the thylacine pouch opened to the rear of the body.

Only existing photographs of females with brood in the pouch. Photo taken from The Thylacine Museum

EXTINCTION

Australian Aborigines already knew and hunted the thylacine, as seen in their 1000 b.C art. The first possible thylacine footprints discovered by Europeans are from 1642, although it was not until 1808 that a detailed description of the species was made.

Thylacine hunted in 1869. Photo of public domain

There are several hypotheses that point to the extinction of the Tasmanian tiger, in the majority, humans are the main blamable. Like it happens nowadays in Spain, the Tasmanian wolf was quickly accused of killing cattle and hen, so despondent rewards were offered for the animal and was the subject of an intensive hunt. Later research has concluded that its jaw was not strong enough to kill an adult sheep.

Only existing picture of a thylacine with a prey. Later research suggest that is a farce with a taxidermy specimen to give them bad reputation. Photo by H. Burrell (1921)

With the colonization of Australia, the habitat and prey of the thylacine were diminished drastically. They were also victims of introduced species on the continent by humans, such as dogs, foxes and dingoes (wolf subspecies). It is also probably that suffered some diseases that lead them to death.

Last wild thylacine hunted by Wilfred Batty (1930). Photo: unknown (Wikimedia Commons)

In 1920 the thylacine was already on the verge of extinction. In 1930, it was hunted by a farmer the last known wild specimen and in 1933 arrived at Hobart Zoo the nicknamed Benjamin. In 1936, he was forgotten outside his cage and did not survive the freezing temperatures at night. 59 days before, it had been approved officially the protection of the species.

Only 128 years after his “discovery” the last thylacine died. Photo by David Fleay colored by Neitshade

After the 50 years required by the scientific community without any sightings or evidence of its existence, the thylacine was officially declared extinct by IUCN in 1986. Many claim to have seen the thylacine and even filmed one in the wild, but there are no no definitive evidence.

CURRENT RESEARCH

The International Thylacine Specimen Database is an international database that compiles all existing records of the Tasmanian wolf (museum specimens, bones, photos, videos…). Since 1999, there have been attempts to bring the thylacine back to life by cloning techniques, which have been unsuccessful. In 2008, Australian scientists were able to extract DNA from specimens preserved in alcohol and activate a gene implanting it in a mouse embryo and in 2009 the complete sequencing of mitochondrial DNA was published. The elusive goal is to activate the complete genome of thylacine, to have a real possibility of cloning. But if that happens, what are the ethical, economic and scientific implications of the reappearance of an extinct species? The debate is still open.

*Thylacinus cynocephalus from greek θύλακος (thylakos, “pouch”) and κυνοκἐφαλος (kinokefalos, “dog-headed”).

REFERENCES

• Animal. Clutton-Brock, Juliet et al.  2002. Animal. Pearson Educación
• ¿Qué era en realidad el tilacino?
• The thylacine museum
• El último tilacino
• El misterio del último lobo marsupial
• Tasmanian tiger’s jaws were too weak to kill sheep
• Extinct Tasmanian tiger could roar back into life after DNA is implanted into a mouse
• Resurrection of DNA Function In Vivo from an Extinct Genome
• Imagen de portada por Robb Kendrick