Amphibians are animals that have the ability to live in their first cycle of life in the aquatic environment, and then finish developing and live in the terrestrial environment, although many generally remain related to humid spaces. Frogs are within this group and taxonomically they 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 anurans and that produce reproductive success in this group. On our site we want to offer you this time information on how frogs are born, so we present you with this interesting article.
How do frogs reproduce?
Anurans have 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 present external fertilization, but various studies have shown some cases with internal fertilization, such as Ascaphus species truei (tailed frog) and Ascaphus montanus. Additionally, 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 medium 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 emit sounds in order to attract the female, and when ready, he approaches the male so that theoccurs 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. female. Also, in cases where there are few females in the area, the males can be active seekers of them.
External reproduction in frogs
When reproduction is external, the male positions himself on the female (amplexus), she releases the oocytes, the male the sperm and then fertilization occurs. Among the different types of oviposition that have been identified, we can generally mention the following:
- Aquatic oviposition, which includes various ways of laying eggs.
- Oviposition 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 terms, the reproductive cycle of frogs is made up of the following stages:
- Oogenesis.
- Spermatogenesis.
- Cell maturation.
- Vitellogenesis.
- Courtship.
- Fertilization.
The entire process is regulated hormonally and by environmental conditions. For more information, check out this other article on our site about Frog Reproduction.
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 have different morphological and ecological characteristics before and after metamorphosis occurs. The phases or moments of the life cycle of frogs are made up of the following stages:
Embryogenesis
Begins 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 occurs, which is called segmentation, then the egg becomes a hollow mass of cells known as a blastula, to give way to gastrulation, in which the germ layers are formed so that subsequently, cell differentiation can occur, which leads to the generation of an embryo that will have the formation of tissues and organs. This phase is determined by temperature We will talk more about this phase in the next section.
Larval phase
Metamorphosis begins here, and in this stage the growth, formation, transformation and integration of organs and tissues occur, resulting in a drastic body transformationFrom the beginning the head, body and tail of the larva can be distinguished. They have mouths equipped with jaws that allow them to start feeding on vegetation, and behind the mouth there is an adhesive disc that gives them the ability to attach to different places. It also has thickenings on the sides of its head, which will later become gills.
During metamorphosis, anatomical and organ transformations or remodeling occur, such as visceral arches, the digestive system and skin Also there are some organs and anatomical parts that are exclusive to the larval stage, such as internal gills, tail, and oral structures made of keratin. On the other hand, structures will emerge that will be functional once the metamorphosis is over, among which we have the limbs and the gonads. Once the metamorphosis is finished, the result will be an individual very similar to the adult, which is totally different from the one that hatched from the egg.
Youth
Here occurs the growth of the individual and specific changes It begins with the culmination of metamorphosis and ends when sexual maturation occurs. In general, in this stage there is a complete development of the rest of the organs and functions, as well as the independence to eat and move around.
In some species of anurans, it is not so easy to differentiate a young individual from one that has just become an adult, since the sizes, for example, do not vary considerably. The same happens with some species that manage to reach their greatest growth and total development of gonads once the metamorphosis is complete.
Adulthood
In this phase the reproductive capacity of the individual is consolidated, so it reaches maturity and sexual dimorphism. Many of the changes have been consolidated here, so you have a highly specialized individual for the way of life you lead.
It is important to keep in mind that part of the process of adulthood also ultimately includes the aging of the frog, which we can consider the stage end of its life cycle. However, with aging and senescence certain changes do not cease to occur, and although there is no depth of study 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.
Development of the egg 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 guarantee 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?
Egg development generally occurs in the aquatic environment, but it may also occur on land, where some males dig burrows to which the females are attracted so that they deposit their eggs and then they can be fertilized by the male. In other cases, the process occurs inside plants where water has accumulated. Embryonic development can also occur inside the female or even in some species on the skin of the female.
Although oviposition can occur in the terrestrial environment, frogs generate masses of eggs 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 moisture is a vital factor for their maintenance and later the of the tadpoles.
How and when do tadpoles hatch?
The birth of tadpoles occurs approximately 6 to 9 days after fertilization, although this varies from species to species. other. In addition, the temperature of the medium has an important influence on this process.
How long does it take for a tadpole to turn into 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 group or another can be described, it is important to bear in mind that Within each one there are different species that present their own particularities. Therefore, in anurans it is difficult to establish a single parameter regarding the time it takes for a tadpole to transform into a frog.
Examples of this can be seen in the case of the leopard frog (Lithobates pipiens) and the bullfrog (Lithobates catesbeianus). The first takes 3 months in the process of metamorphosis and the second can do it between 2 and 3 years.
Currently, frogs are one of the amphibians in greatest danger of extinction, 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.
