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Amphibians are animals that have the ability to live in their first life cycle in the aquatic environment, to later finish developing and living in the terrestrial environment, although many generally remain related to humid spaces. Frogs are within this group and taxonomically belong to the class Amphibia, order Anura, considering the vertebrates that possess the greatest diversity of reproductive strategies on Earth, aspect that is linked to processes of natural and sexual selection.
These various forms of reproduction are related to the combination of morphological, physiological and behavioral traits that are expressed in the anurans and that produce reproductive success in this group. In Animal Expert we want to offer you in this opportunity information about how frogs are born, so we present you this interesting article.You may also be interested in: The reproduction of frogs Index
- How do frogs reproduce?
- Life cycle of frogs
- Egg development and birth of frogs
How do frogs reproduce?
Anurans possess a varied reproductive differentiation, which depends on the place where oviposition occurs, the type of larval development and also the type of parental care.
Frogs are oviparous animals that generally have external fertilization, but various studies have shown some cases with internal fertilization, such as the species Ascaphus truei (frog with tail) and Ascaphus montanus. In addition, viviparous species have also been identified, such as the Nectophry occidentalis, which is endemic to West Africa. On the other hand, it has been reported that there are more than 30 reproductive modes in this group, considering the environment where oviposition occurs. In this sense, they can be exclusively aquatic or terrestrial, but there are also some species with intermediate modes of reproduction.
For the reproduction of these animals to occur, the male can make sounds in order to attract the female, and when he is ready, he approaches the male so that the amplexus, which is the positioning of the male on the female to fertilize the eggs. Now, it is common that during the process more than one male can participate to try to fertilize the eggs deposited by the female. Also, if there are few females in the area, the males can be active seekers of them..
External reproduction in frogs
When the reproduction is external, the male is positioned on the female (amplexus), this releases the oocytes, the male the sperm and then fertilization occurs. Between the different types of oviposition that have been identified, we can generally mention the following:
- Aquatic oviposition, including various ways of laying eggs.
- Ovoposition in foam nests on water.
- Arboreal oviposition.
- Terrestrial oviposition, where different ways of larval development can occur.
Stages of the reproductive cycle of frogs
In general, the reproductive cycle of frogs is made up of the next stages:
- Cell maturation.
The whole process is regulated hormonally and by environmental conditions. For more information, see this other AnimalWised article on The reproduction of frogs..
Life cycle of frogs
Once fertilization occurs, the life cycle of frogs begins, and in amphibians this is called complex or biphasic life cycle, because these individuals present different morphological and ecological characteristics before and after metamorphosis occurs. The phases or moments of the life cycle of frogs is made up of the following stages:
Starts once fertilization occurs and ends with the hatching of the egg, from which an individual emerges in a larval state. In embryogenesis, a first phase of repeated cell divisions that are called segmentation occurs, then the egg becomes a hollow mass of cells known as blastula, to give way to gastrulation, in which germ layers are formed so that later, cell differentiation can occur, which leads to the generation of an embryo that will have tissue and organ formation. This phase is determined by temperature. We will talk more about this phase in the next section.
Here the metamorphosis begins, and in this stage the growth, formation, transformation and integration of organs and tissues occurs, resulting in a drastic body transformation. From the beginning the head, body and tail of the larva are distinguished. They have a mouth provided with jaws that allow it to start feeding on vegetation, and behind the mouth there is an adhesive disk that provides it with the ability to attach itself to different places. It also has thickening on the sides of the head, which will later become gills..
During metamorphosis, organ and anatomical transformations or remodeling occur, such as that of visceral arches, digestive system and skin. There are also some organs and anatomical parts that are exclusive to the larval stage, such as internal gills, tail and oral structures formed of keratin. On the other hand, structures will emerge that will be functional once the metamorphosis is complete, among which we have the limbs and the gonads. After the metamorphosis, an individual very similar to the adult will result, which is totally different from the one that hatched from the egg.
Here occurs the individual growth and specific changes. It begins with the culmination of metamorphosis and ends when sexual maturation occurs. In general, at this stage there is a complete development of the rest of the organs and functions, as well as the independence to feed and mobilize.
In some species of anurans, it is not so easy to differentiate a young individual from one that has just become an adult, since sizes, for example, do not vary considerably. The same occurs with some species that manage to reach their highest growth and full development of gonads once metamorphosis is complete..
In this phase the reproductive capacity of the individual is consolidated, so reaches maturity and sexual dimorphism. Here many of the changes have been consolidated, so there is a highly specialized individual for the way of life he leads..
It is important to keep in mind that part of the adulthood process also eventually includes aging frog, which we can consider the final stage of its life cycle. However, with aging and senescence certain changes do not stop occurring, and although there is no depth of studies in this regard, it has been shown that in amphibians that reach this stage, there is an increase in collagen fibers, accumulation of more pigments in the skin and a decrease in metabolism occurs.
Egg development and birth of frogs
Amphibians invest a lot of energy in their reproductive process, mainly in the size of their eggs and their quantity, a relevant aspect from a biological point of view for ensure reproduction in cases of vulnerability such as that which occurs in frogs, since especially when the eggs develop exclusively in the aquatic environment, they are exposed to multiple predators.
¿Where do frog eggs develop??
The development of the eggs generally occurs in the aquatic environment, but it is also possible that it occurs at the terrestrial level, where some males dig burrows to which the females are attracted to lay their eggs and then can be fertilized by the male. In other cases, the process occurs inside plants where water has accumulated. Embryonic development can also occur within the female or even in some species in the skin of this.
Although oviposition can occur in the terrestrial environment, frogs generate egg masses that are grouped in a watery or gelatinous substance, which gives them moisture and protection. There are also cases in which these animals carry water to the place where the eggs are developing, since humidity is a vital factor for their maintenance and later that of the tadpoles.
¿How and when are tadpoles born?
The birth of the tadpoles occurs approximately between 6 and 9 days after fertilization, although it is a variable aspect from one species to another. In addition, the temperature of the medium has an important influence on this process..
¿How long does it take for a tadpole to become a frog??
In the animal world, it is very rare that there are traits or processes that can be defined as absolute, since although general characteristics of one or another group can be described, it is important to keep in mind that within each one there are various species that They are presenting their own peculiarities. Therefore, in the anurans it becomes difficult to set a single parameter regarding the time it takes for a tadpole to transform into a frog.
An example of this can be seen in the case of the leopard frog (Lithobates pipiens) and the bullfrog (Lithobates catesbeianus). The first takes 3 months to metamorphose and the second can take between 2 and 3 years..
Today, frogs are one of the amphibians most endangered, since the alteration of their habitat and the effects of climate change considerably affect their populations because they are very susceptible to changes in humidity and temperature, and especially their reproductive processes depend on these aspects.