Amphibians they are vertebrate animals which are characterized by having the bare and permeable skin, without scales.
In this article we will explain all the secrets of these animals, starting with the reproduction of amphibians, the types of amphibians that exist, some examples and others Interesting Facts which I'm sure will be very useful to you.
Reproduction of amphibians
Being oviparous, reproduction of amphibians It is by eggs. Reptiles and mammals reproduce by internal fertilization (within the female) while in most amphibians, especially anurans (frogs and toads), the predominant species is external fertilization.
La Fertilization of amphibians usually occurs in fresh water, because this type of water protects the eggs during their development and compensates for lack a shell and attachments such as the amnion. Therefore, the eggs must remain in humid environments that prevent its drying out, which explains the group's permanent link with water.
Fertilization, being external in anurans, follows a characteristic process: the male holds the female by means of the amplexus and as she releases the eggs, the male He spills his sperm on them to fertilize them. The eggs remain in the water forming clusters or cords, or attached to vegetationAquatic larvae emerge from them.
Both in fish and amphibians, in which external fertilization predominates, The eggs have a thin, gelatinous covering to allow the passage of sperm. Therefore, they usually settle in the water, sticking together and forming voluminous bunches or cords, depending on the species.
Amphibians are born as a aquatic larva that moves with a tail and breathes through gillsWhen the larva, called a tadpole, has grown enough, it undergoes a process of metamorphosis deep. Except for some species of frogs from tropical rainforests that have direct development, these larval characteristics disappear and develop lungs and limbs as the tadpoles grow.
This class of vertebrate amphibians is made up of frogs, toads, salamanders and caeciliansThey have the ability to live both in and out of water, although they need humid environments, since its skin plays an essential role in respiration and water balance.
External fertilization, internal fertilization and amplexuses
In anurans, the general rule is external fertilization with amplexus, but in urodeles (newts and salamanders) it is common internal fertilization through a spermatophore that the male deposits and the female collects with her cloaca. The amplexus also varies between species: it can be axillary (the male holds it behind the front legs), inguinal (at hip level) or cephalicThis diversity of behaviors improves the reproductive efficiency in different habitats.
Why is water essential for reproduction?
Amphibian eggs they have no shell waterproof like those of reptiles and birds; its casing is gelatinous and permeable, so they lose water easily. The aquatic environment or environments with constant humidity are essential to prevent drying out. In addition, water provides dissolved oxygen and cushions sudden temperature variations during embryonic development.
Many species have evolved strategies to minimize risks as predation or desiccation: put into foam nests or bubbles, eggs on hanging leaves that fall into the water when they hatch, underwater chambers excavated by the parents, or even the choice of microhabitats like bromeliads that accumulate water in their leaves.
Diversity of reproductive modes in amphibians
The reproduction of amphibians is extraordinarily variedRecent research has proposed classification systems that include dozens of reproductive modes depending on features such as the laying site (running water, ponds, bromeliads, moist soil), the presence or absence of metamorphosis before or after hatching, or the existence of structures such as foam nests. Overall, more than 100,000 have been described. seventy variants between the different orders.
Some illustrative examples: in certain frogs of the family Pipidae, the females They carry their eggs on their backs until hatching; in tree frogs of humid forests, the eggs are laid in bromeliads or cavities of bamboo, where the larvae complete their development; there are species that build underwater cameras to deposit and protect the eggs; others present direct development (the young are born as miniature adults), common in some leaf frogsEven in caecilians, unique maternity wards have been observed in which the young they feed on the skin from the mother, rich in nutrients.
This diversity also includes plasticity within the same species: there are frogs capable of choosing between different laying places (pond, moist soil or bromeliads) depending on local conditions. Such strategies increase the chances of success in the face of environmental changes, while other species are strictly dependent on a single mode.
In urodeles, in addition to the internal fertilizationSome salamanders retain their eggs in the oviduct until they give birth. live young fully formed, and in a number of tropical amphibians reproduction occurs on land with parental care prolonged to maintain humidity and avoid predators.
Amphibian animals, what are they?
In Latin the word amphibian has a peculiar meaning, it literally refers to “two lives”. And this is a distinguished peculiarity of these animals, capable of adapting and carrying out their biological functions in two different ecosystems: land surface and water areas. However, we are going to delve a little more into the meaning of amphibian.
Amphibians are part of that great family of living beings classified as vertebrates (they have an internal skeleton), anamniotes (its embryo develops without amnion or allantois, so they need humidity external), tetrapods (with four limbs, ambulatory or manipulative) and ectothermic (their body temperature depends on the environment).
They have a period called metamorphosis (transformation that they experience during their development and that affects the morphology, functions and lifestyle). Among the notable changes is the passage from gills to lungs, as well as the development of limbs and the resorption of the tail in most anurans.
Types of amphibians
Triton
Within this great family that amphibians make up, we can make a small classification based on three orders: anurans, caudates o urodeles y apodal o gymnophiona.
The anurans They group together all those amphibians that we popularly know as frogs and toads. Be careful: frog and toad are not the same species. They are grouped together due to their morphological and behavioral similarities, but they present a great diversity internal. They usually lack a tail in adulthood, they have hind legs powerful for jumping and usually external fertilization.
The urodeles They are distinguished by presenting a long tail and an elongated trunk. Their eyes are not excessively developed and may be covered by a thin skin. Here we find the newts, salamanders, protea y mermaidsIn many cases they exhibit internal fertilization and locomotion based on undulations and quadrupedal gait.
Finally, there are the types of apodal amphibians, which are the most peculiar of all due to their appearance. They resemble a worm or earthworm for lacking limbs and having a cylindrical and elongated body. Most lead a life underground and have senses adapted to this environment.
Amphibian characteristics
As we said, amphibians are vertebrate animals and have the “privilege” of being the most primitive among tetrapods that inhabit the Earth, with a lineage that dates back to hundreds of millions of years.
They have four limbs: two front and two back. These limbs are known as chiridio, with a morphology similar to the human hand: four fingers on the front feet and five on the back, although there are variations depending on the group. Many amphibians also have a functional tail (especially urodeles).
Being from cold blood (ectotherms), their body temperature depends on the environment, since they cannot self-regulate heatThis condition drives its activity in humid hours or nocturnal and their close connection with bodies of water.
Its oviparous, since they are born from eggs. The female is responsible for laying them and always does so in an aquatic or very humid environment. Therefore, young specimens have gill breathing and, in the case of anurans, they go through an aquatic larval phase.
The skin is permeable and can be crossed by molecules and gases. Many species secrete toxic substances as a defense, and the skin actively participates in the skin respiration and water balance. Its character moist and flake-free allows them to absorb water and oxygen, but also makes them vulnerable to dehydration when the ambient humidity is low.
The circulatory system has a tricameral heart composed of two atria and one ventricle, with circulation closed, double and incompleteThis design allows for partial separation of oxygenated blood from non-oxygenated blood.
The eyes are usually bulky and bulging, providing a large field of view ideal for hunting. Although it may not seem so, many amphibians they do have teeth (especially small ones and in the jaws), useful for holding prey. Their sticky tongue, especially in anurans, is a key tool for capture. The digestive system includes a tubular stomach, intestine, two kidneys and urinary bladder.
Skin, chromatophores and poisons
The skin of amphibians contains mucous and even granular glands that secrete defensive substances. chromatophores (pigment cells) generate colorations for camouflage or warning (aposematism). Toxic skin compounds help prevent predators and can inhibit fungi and bacteria harmful to the skin.
Differences between amphibians and reptiles
- Eggs: in reptiles they have a waterproof shell; in amphibians they are soft and gelatinous.
- Hatchlings: Reptiles are born in the form of adult miniatures; in amphibians there are metamorphosis from larva to adult.
- Fertilization: reptiles, intern; amphibians, generally external in anurans and intern in urodeles.
- Skin: amphibians, moist and permeable; reptiles, dry and waterproof, covered in scales.
- Breathing: reptiles, pulmonary; amphibians, branchial, pulmonary and cutaneous according to phase.
- Activity: amphibians often nocturnal and dependent on humidity; many reptiles, more daytime.
Examples of amphibians
Salamander
At present, there are catalogued around 3.500 species of amphibiansHowever, scientists estimate that the total number may be around 6.400 or more, given the continued description of new species.
When thinking of amphibians, a species usually comes to mind. frog or toad, but we also find newts y salamanders, as well as the discreet ones caecilians.
These are just a few examples of amphibians, although, logically, there are many more:
Anderson salamander (Ambystoma andersoni)
This type of salamander is also known as the Purépecha axolotl or achoque. It is an endemic species, meaning it only exists in a specific location. In this case, it only lives in Laguna de Zacapu, located in the state of Michoacán (Mexico). It is characterized by a strong, short tail and external gills. Its color orange or red, added to black spots along the body, making it unmistakable.
Marbled Newt (Triturus marmoratus)
It is found mainly in European territory, in the northern part of Spain and eastern France. It has a mottled greenish very striking and a dorsal line reddish that runs along the back, a characteristic feature of the group.
Common toad (Bufo bufo)
Common in much of Europe and Asia. It prefers habitats with stagnant water, irrigation areas, etc. Its resistance to water poor in quality has favored its expansion. It has coloration brown and skin with Warts notorious.
Vermilion frog (Rana temporaria)
Widespread throughout Europe and Asia. Although it prefers places damp, spends much of its time on land. It presents variation in the color pattern, with a tendency towards brown tones and spots, and a pointed snout very characteristic.
Other interesting examples
- Midwife toad (Alytes spp.): the male carries the laying coiled around its hind legs until it is released into the water when the embryos are ready.
- Saint Anthony's Frog (Hyla spp.): arboreal, with adhesive discs on the fingers and high-pitched edge; typical of temporary ponds.
- Axolotl (Ambystoma mexicanum): example of neoteny, maintains larval features (external gills) in the adult state.
- Proteus (Proteus anguinus): European cave-dwelling urodele, underground life completely aquatic and vestigial eyes.
- cecilias (gymnophiona): legless amphibians of life fossil, often with reproduction Earth and parental care.
Metamorphosis and the life cycle
La metamorphosis It is a key biological process in the life history of amphibians. The typical cycle comprises three stages: embryonic (egg), larval (tadpole or gill larva), and adult. The duration and characteristics vary between species and environments.
- Egg: After fertilization, the embryo grows inside a gelatinous casing permeable, absorbing water and swells, agglutinating the eggs into masses or cords.
- Larva: feeds, grows and breathes by gillsIn anurans, it develops hind legs, then anterior legs, reduces the tail and restructures its digestive system towards a carnivorous diet.
- Adult: breathe for lungs and skin, disperses, looks for a mate and repeats the cycle. In urodeles, metamorphosis can be incomplete or even absent (neoteny) if the aquatic environment is stable and favorable.
There are species with direct development in which there is no external aquatic larval phase: the embryos complete development inside the egg and the young are born as miniature adults, a strategy that reduces dependence on open bodies of water.
The song of the amphibians
In anurans, the singing It is an essential communication tool. Males emit vocalizations to attract females, point out your territorio and coordinate reproduction. Each species has a acoustic pattern own that facilitates specific recognition, and in many frogs a vocal sac acts as a resonator.
Females are usually located in the periphery of the ponds listening to the males and choosing the mate by the singing quality (rhythm, intensity, frequency), a trait linked to physical condition and the ability to defend the territory.
Feeding of amphibians
Adult amphibians are predominantly carnivoresThey consume live prey such as arthropods (insects, arachnids), earthworms, snails and small vertebrates if size permits. The protractile and sticky tongue of many frogs and toads allows for lightning captures.
Amphibian larvae show diverse diets: some are herbivorous or filter-feeding detritivores, while others are carnivorousIt is not uncommon to observe cannibalism among tadpoles, especially when there is a shortage of resources or high density.
Conservation status and threats
Amphibians are one of the groups most threatened of the planet; the bullfrog threat is an example of how a species can alter ecosystems and affect the reproduction of other populations. The loss and fragmentation of the habitat, water pollution, the climate change and emerging diseases (such as chytrid mycoses) have triggered population declines in multiple regions.
Many reproductive modes depend on very specific microhabitats (temporary ponds, bromeliads, shaded streams). The disappearance of a pond or the decrease in local humidity can pause playback of entire populations. Species with plasticity In their reproduction they can adapt better, choosing different laying sites according to the conditions, while specialists are more vulnerable.
Conservation actions include protection of wetlands, pond restoration, invasive species control, health monitoring and breeding programs and reintroduction for critical species. Environmental education and citizen science are also fundamental to detect and mitigate threats in time.
Origin and evolution of amphibians
The amphibian lineage originated from de peces freshwater with fins lobed, capable of supporting their weight and moving on shallow substrates. Over time, these fins gave rise to limbs with fingers, paving the way for the colonization of subaerial environments. Among the earliest tetrapods, forms such as Acanthostega o ichthyostega They show intermediate features between aquatic and terrestrial life.
The transition from water to land is related to the exploration of new resources and the response to variable environmental scenarios (droughts, variations in water bodies). The skin and cutaneous respiration, metamorphosis and ectothermic physiology were key to expanding the presence of amphibians in much of the planet, except in extremely cold or arid regions.
After knowing how they reproduce, what types exist and what their most important characteristics are, it is understood why amphibians are such a group versatile and fascinating: its double link with water and land, the diversity of reproductive strategies, the metamorphosis and sensitivity of their skin make them early indicators of ecosystem health and indispensable players in global biodiversity.