Within the different animal reproductive systems, the Ovoviviparous stands out for its curious double role in the development of the embryo. Ovoviviparous Animals show traits of oviparous animals mixed with those of viviparous animals, quite a feat of nature. You will be able to know much more about these rare natural wonders by continuing reading.
What are Ovoviviparous Animals?
Ovoviviparous animals are known as those that have particularities of the development of the viviparous embryo as well as those of oviparous. In nature, varieties of invertebrates and vertebrates are found with this reproductive system. Different kinds of embryonic development have been present in our natural environment: oviparous, viviparous and ovoviviparous.
Development
The development of ovoviviparous animals occurs inside an egg before its birth. What is distinctive about ovoviviparous is that the egg remains inside the mother until the development of the embryo is complete. Therefore the creature emerges from the egg immediately as soon as the egg is laid. It can even emerge from the egg inside the mother's body and that later is when the birth takes place.
A broader definition of an ovoviviparous animal would be: “that reproductive system in which the eggs develop within the mother without any nutrition from her; the hatching of it takes place inside it or as soon as they are released, in such a way that the young are born alive ». The origin of the term ovoviviparous comes from Latin and is the conjunction of: ovo or 'egg', vivus or 'alive' and parere or 'to give birth'.
It is important to differentiate ovoviviparous from other species whose embryonic development takes place inside eggs, which are called oviparous. The latter lay their eggs outside at the beginning of embryonic development, that is, the embryos develop outside the mother's body. They must also be differentiated from viviparous animals, whose embryo develops inside the mother's body, such as mammals.
In contrast to the viviparous whose embryo also develops inside the mother, the embryo of the ovoviviparous differs in that it is covered by a shell that prevents its mother from feeding it directly.
In short, we can conclude that these are the similarities and differences between the three systems of embryonic development:
- Common point between ovoviviparous and oviparous: The embryo is protected by a shell.
- Common point between ovoviviparous and viviparous: Fertilization takes place inside the mother's body, where the embryo also develops.
Features
For all of the above, ovoviviparity is that the female conceives eggs, but these remain inside her. Whenever the embryo reaches its development, there are two alternatives:
- The female lays the eggs, which hatch as soon as they are released.
- Hatching takes place prior to delivery, with which the young emerge directly from the mother.
It can be pointed out from this that the animals that have this kind of embryonic development carry out an intermediate process to the other two modes of reproduction. Thus, ovoviviparism is a combination of viviparity and oviparity. The characteristics that distinguish ovoviviparity are the following:
- If there is internal fertilization.
- The young, at birth, are alive and fully developed.
- There is no placental link between the mother and the young.
- In certain cases, the nutritional contribution of the embryos can come only from the yolk sac of the egg (usually), while in other cases it does not.
Embryo Subsistence
As part of ovoviviparism, two groups are distinguished according to the nutrition obtained by the embryos. Aplacental viviparism is the way ovoviviparous animals are defined. This consists in that the embryos are kept in the mother's uterus but they do not obtain any nutritional contribution nor do they have a placental nexus with the mother.
Two different forms of embryonic development have been defined: matrotrophy or lecytotrophy. Matrotrophic species are those that quickly deplete the nutritional supply and, to continue their development, get the nutrients from various sources that the mother must provide.
They can get it from other eggs (oophagia), from other embryos (intrauterine cannibalism) or they can present a specialization similar to that of the placenta. Lecithotrophy is defined as the practice used by the larvae of numerous creatures to feed in which they do not seek their food abroad but use the yolk reserves (from their yolk sac) that they carry with them since they were born. AND
In most of these cases, the larval stage is short-lived and the metamorphosis to the juvenile stage is rapid in order to start feeding.
Ovoviviparous Animal Classes
Four main categories have been determined in which most of the ovoviviparous animals are grouped:
invertebrates
As part of the invertebrates, different ovoviviparous varieties are obtained. One of the animal examples par excellence in scientific laboratories is the genus Drosophila, in the fruit fly. Drosophila sechellia exemplifies an ovoviviparous invertebrate of the order Diptera. Another group of invertebrates in which ovoviviparity can be achieved are the gastropods.
Fish: Seahorses
Seahorses are a vertebrate species of the ovoviviparous sea. Specifically, they are fish that belong to the genus Hippocampus. These monogamous animals are recognized because the males are in charge of carrying the fertilized eggs. The gestation period can last between ten days and six weeks according to the species. Every time it culminates, the male releases around 200 or 300 offspring over several hours.
Teleosts: Sharks
Certain varieties of sharks, such as the bull shark (Carcharias taurus), are ovoviviparous species. Although the lecithotrophic strategy is the one that has been seen mostly in sharks, the bull shark is a rarity. The bull shark is one of the three most dangerous varieties of shark, together with the tiger shark and the great white shark. And it is that all of these are estimated as the animals with the greatest possibility of attacking humans.
Bull shark pups carry out intrauterine cannibalism, which is why it is considered a matrotrophic variety. Inside the womb, the largest embryo engulfs all its siblings and leaves only one alive, so in the end they only conceive two offspring.
reptiles
As part of the reptiles, ovoviviparism is expressed in different groups. Certain varieties of vipers and snakes, such as the anaconda, the chameleon or the Surinam toad, as well as the solitary species of toads. Only some varieties of the Chamaeleonidae family are ovoviviparous. Among them, the helmeted chameleon (Trioceros hoehnelii), the Trioceros jacksonii chameleon and the Trioceros hoehnelii chameleon are found.
Examples of Ovoviviparous Animals
Most of the animals that are classified as ovoviviparous are of the invertebrate type. However, certain species of vertebrates such as reptiles, fish or sharks also present this category of embryonic development.
White shark
A class of shark of enormous size and robustness, with a bow-like mouth. They have to swim without stopping (they cannot stay still) in order to continue breathing and to stay afloat, since they do not have a swim bladder. The embryos are nourished by means of the vitellium. This shark does not release eggs but the young hatch inside the mother to emerge later developed.
Boa constrictor
Reptile whose length varies from 0,5 to 4 meters, according to the subspecies. Additionally, the females are larger than the males and have a reddish and white, or reddish and brown color, which can also vary depending on the subspecies. Mating takes place in the rainy season. Its gestation lasts for several months. The hatching of the eggs takes place inside the mother's body, from which already developed offspring are born.
dogfish
A kind of small shark, reaching up to a little over a meter in length. It is recognized by its poisonous spines on the body surface. It is the most abundant variety of shark but with a limited distribution. The litter that reproduces will depend on the size of the female, since the usual one consists of 1 to 20 embryos per gestation, but larger females can have larger litters, which are born out of the egg.
Manta Ray (Giant Manta)
It differs from other species because it does not have a poisonous stinger in its tail and also because of its enormous size. It lives in temperate seas and can jump out of the water at the time of reproduction, there are several males that court a female.
In order for one to achieve copulation, they must annihilate their rivals. It is considered that the time that the eggs last inside the female can exceed twelve months. They have one or two pups per litter.
Anaconda
A genus of snake that kills by strangulation. It can reach ten meters in length. Although they do not live in a group but solitary, when the female wants to reproduce, she usually attracts the male by releasing pheromones. From each litter, between 20 and 60 pups of about XNUMX centimeters in length arise.
Surinam Toad
Amphibian that inhabits tropical and subtropical regions, which is characterized by its flattened body and flat, triangle-shaped head. Its coloration is gray slightly green. It is a special class of ovoviviparous animal, since fertilization takes place outside the mother's body. Once fertilized, the female puts the eggs back inside her body.
Unlike other amphibians, which emerge as larvae and then undergo metamorphosis, this toad carries out its larval development inside the egg, and the specimens that hatch already have their final shape.
Platypus
It is considered as a mammal, but releases eggs, so it can also be classified as ovoviviparous. It is a semiaquatic creature that lives in eastern Australia and Tasmania. It is recognized by its peculiar appearance, with a snout that looks like a duck's beak, a tail similar to that of a beaver and legs similar to those of an otter. It is poisonous.
Jackson's Trioceros
Variety of ovoviviparous chameleon. It has three horns, which is why it is called "trioceros". It lives in East Africa. The breeds have their birth in litters of 8 to 30 copies, with a gestation of up to one semester.
Hippocampus (Seahorse)
It is a unique class of ovoviviparous, since the eggs do not mature inside the body of the female but in the body of the male. Fertilization takes place as the female moves the eggs into the male's sac. The sac is similar to that of marsupials, which means that it is external and ventral.
Lution (Crystal Shingles)
Very peculiar species, since it is a lizard without legs. This is that in appearance it is identical to a snake. However, it is known that it is a lizard because there are traces of its skeleton in its body that has the features of lizards. Added to this, it has movable eyelids, in contrast to snakes. It is a reptile that lives in Europe and its length can reach 40 centimeters and females 50. Reproduction takes place in spring. After 3 to 5 months of gestation, the female releases the eggs with the mature young inside her, and hatching occurs immediately.
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