Arxiu d'etiquetes: monotreme

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

Anuncis

Danger, poisonous mammals!

We usually associate snakes, spiders, jellyfish, etc. as venomous animals par excellence, but did you know that there are poisonous mammals? In this article we will discover who are they and the nature and use of their poisons.

THE PLATYPUS

The platypus (Ornithorhynchus anatinus) is the most famous among the poisonous mammals, and not just for this feature. With a peak like a duck and oviparous (laying eggs), when it was discovered some scientists thought it was a fraud.

platypus ornitorrinco ornitorinc
Platypus (Ornithorhynchus anatinus). Photo by Jonathan Munro

They belong to the order monotremes, which means “one hole” in reference to the cloaca, the end of the digestive and reproductive systems. Some evolutionary biologists refer to them as the “missing linkbetween reptiles and mammals, as they have characteristics of both groups. Monotremes are the only mammals that lay eggs, but his body is covered with hair and the young are fed with breast milk. They are distributed by Australia, Tasmania and New Guinea.

Platypuses have a spur on the hind legs, which only in the case of males, release poison produced by femoral glands (located in the leg). The male uses it mainly to defend their territory and establish their dominance during the mating season, although if it is bothered also uses it as a defense. This poison can kill small animals, including dogs, and cause severe pain and swelling in humans. This pain can last days or months.

Platypus spur, espolón ornitorrinco
Spur on the hind leg of a platypus. Photo by E. Lonnon

Toxins are four proteins, three of which are unique to the platypus. They are like the defensins (DLP, defensin-like proteins). These are globular proteins, small and compacted, involved in the activation of pain receptors. Understanding how these toxins act it has special interest because they cause a lasting and severe pain; it may open new chances in the synthesis of analgesic drugs.

short-beaked echidna, equidna de nariz corta, equidna de nas curt
Short-beake echidna (Tachyglossus aculeatus). Photo de Tony Britt-Lewis

Echidnas (family Tachyglossidae) complete the order of monotremes with the platypus; consequently they are also oviparous. The family consists of four species, with the common characteristic of having the body covered with dense hair and spines. They are mainly insectivores specializing in ants and termites.

Like the platypus, they also have spurs behind the knees, but their secretions are not poisonous. The substances are used to mark their territory, according to the recent studies.

SLOW LORIS

As we saw in a previous post, lorises are primates in the prosimians suborder. They are nocturnal, arboreal and feed primarily on insects, vegetables and fruits. The slow lorises (Nycticebus) living in Southeast Asia, are the only poisonous primate. They possess poison glands on the elbows (brachial gland), and poison their body with arms and tongue, which can also join saliva and be transmitted by bitting.

lori pigmeo, nycticebus pigmaeus,
Pygmy slow loris (Nycticebus pigmaeus). Photo by Ch’ien C. Lee

In this case the poison is used as a defense against predators, causing them pain, inflammation, necrosis (cell death) in the area of the bite, hematuria (blood in urine) or in some cases anaphylactic shock (allergic reaction) which can lead to death, even in humans (some are threatened by the illegal pet trade and traditional Chinese medicine). The poison also serves as protection for the young, they are licked by their parents and the poisonous secretion is distributed throughout the coat. Being poisonous, unusual among primates, can help counteract the disadvantages of its slow movements. Exudate from glands, as in echidnas, can also give olfactory information of range and territory between individuals of loris (Hagey et al., 2007).

Loris de Kayan (Nycticebus kayan). foto de Ch'ien C. Lee
Kayan loris (Nycticebus kayan). Photo by Ch’ien C. Lee

Toxins are polypeptides (generated when glandular secretion is mixed with saliva) and an unidentified steroid. Secretion is similar to the allergen Fel d 1 which is in the domestic cat and cause allergies in humans (Hagey et al., 2006; Krane et al., 2003).

It is believed that slow lorises even have converged evolutionarily with cobras, for his defensive behavior when threatened, whistling and raising his arms around his head. (Nekaris et. al, 2003).

Loris, cobras, evolucion, convergencia
Mimicry between loris and cobras. 1. Javan slow loris, 2 y 3. Spectacled cobra, 4. Bengal slow loris. Photo by Nekaris et. al.

In the following video a lazy lori is disturbed and hisses like a snake while trying to bite:

SOLENODON OR ALMIQUI

They are small and nocturnal mammals, basically insectivores, that live in the West Indies. The Hispaniolan solenodon (Solenodon paradoxus), also known as the Dominican solenodon, Haitian solenodon or agouta, lives on the island de La Española (Dominican Republic and Haiti) while The Cuban solenodon or almiqui (Solenodon cubanus) is distributed throughout Cuba. They are considered living fossils because they have similar characteristics to primitive mammals of the end of the Mesozoic Era (kingdom of the dinosaurs).

solenodonte de La Española (Solenodon paradoxus
Hispaniolan solenodon (Solenodon paradoxus). Photo by Eladio M. Fernández.

Unlike other poisonous mammals, toxic saliva is produced under the jaw (submandibular glands), which is transported by pipes to the front of the mouth. The second incisor teeth have a groove where toxic saliva accumulates to promote their entry into the wounds. They are the only mammals that inject venom through its teeth, similar to the way snakes do.

diente, solenodon, teeth, surco
Paradoxus Solenodon lower jaw incisor showing the groove. Photo by Phil Myers

The main function of this venom is to immobilize prey, as well as insects they can hunt small vertebrates such as reptiles, amphibians and birds.

Almiquí, Cuba, Solenodon, cubanus, Cuban giant shrew
Cuban solenodon (Solenodon cubanus). Photo by Julio Genaro.

This poison may have been developed to keep alive but immobilized prey during times of shortage, to aid in digestion, minimize energy expenditure in the struggle for hunting and face prey even twice as big as them. This venom is not deadly to humans.

SHREWS

The northern short-tailed shrew (Blarina brevicauda), the Eurasian water shrew (Neomys fodiens) and the Mediterranean water shrew (Neomys anomalus) also have submandibular glands similar to solenodons. They are distributed by North America (northern short-tailed shrew) and Europe and Asia (water shrews), including the Iberian Peninsula.

Musaraña colicorta americana (Blarina brevicauda). Foto de Gilles Gonthier.
The northern short-tailed shrew (Blarina brevicauda). Photo by Gilles Gonthier.

The short-tailed shrew can consume up to three times its weight in food per day. Their saliva is the most poisonous and uses it to paralyze their prey, to eat them or keep them alive in times of shortage. The water shrews also store its immobilized prey under rocks.

Musgaño (Neomys anomalus). Foto de rollin Verlinde.
Mediterranean water shrew (Neomys anomalus). Photo by Rollin Verlinde.

These animals attack from behind and bite the neck of its prey so that the poison acts more quickly, affecting the central nervous system (neurotoxins). The respiratory and vascular system is also affected and causes seizures, incoordination, paralysis and even death of small vertebrates.

Musgaño patiblanco-Neomys_fodiens, Wasserspitzmaus
Eurasian water shrew (Neomys fodiens). Photo by R. Altenkamp.

Its teeth don’t have grooves as the solenodons do, but a concave surface to store the toxic saliva.

neomys, anomalus, mandibula, dientes, veneno
Lower jaw of Neomys anomalus. Photo by António Pena.

It is suspected that other mammals also produce toxic saliva similarly, as the European mole (Talpa europaea) and other species of shrew, but there are no conclusive studies.

MANED RAT

The maned rat or crested rat (Lophiomys imhausi), lives in Africa and  uses his poisoned hair to protect themself from predators.

Rata crestada Lophiomys_imhausi, rata de crin, maned rat
Maned rat (Lophiomys imhausi). Photo by Kevin Deacon

Unlike other mammals that produce their own poison, the crested rat gets toxin (called ouabain) from the bark and roots of a tree (Acokanthera schimperi). Chews the bark and the mixture of saliva and toxins are distributed on the body. Their hairs are cylindrical whith a perforated microscopic structure, which favors the absorption of venom. In case of danger, it bristles and shows his brown coat with white stripes, warning of its potential danger. This strategy of persuasion based on brightly colored warning is known as aposematism present in many animals, such as bees.

In this BBC video you can see a crested rat and a hair under the microscope absorbing ink, showing its porous structure:

It is unknown how it is immune to the toxin, since it is the same substance used by some African tribes for hunting such large animals like elephants.

Ouabain is a glycoside which controls the heartbeat, causing infarcts if absorbed in large quantities. The study of the mechanisms that protect the crested rat of a substance that regulates the heartbeat, can help develop treatments for heart problems.

European hedgehogs (Erinaceus europaeus) have similar behavior (smearing the body with foreign poison), but it is not established whether the objective is defensive because it does not scare away predators.

In conclusion, strategies, practices and nature of the poison in mammals are varied and their study may have important medical implications for drug development and increase awareness of the evolutionary relationships between different groups of living animals (reptiles-mammals) and their ancestors.

REFERENCIAS

MIREIA QUEROL ALL YOU NEED IS BIOLOGY