September 26, 2021

Reproduction in amphibians

5 min read

Reproduction in amphibians

In this article, we shall study and understand reproduction in amphibians. Basically amphibians concern with the second class of kingdom Animalia. The name amphibian means “double life”’, and this is because the members of this group for the double life that they lead. Their larva spends their initial life period in water, while adult amphibians usually live on land, their soft eggs must be laid in water. Examples of amphibians are frogs, toads, newts, and salamander. Now we shall come to our topic, reproduction in amphibians.

LISSAMPHIBIANS AND AMPHIBIANS

The term “Lissamphibians”  is used to name the recent amphibians and it’s useful to tell them apart from the rest of fossil amphibians, on the other hand, the term “Amphibia” (referring to the aquatic larval stage of most species) is used to name all tetrapods except the amniotes (reptiles, birds, and mammals).

 

How do amphibians reproduce?

Amphibians generally reproduce by means of sexual reproduction. Fertilization is usually external, while internal for caecilian and salamander. They lay a very large number of eggs at one time, and they often do so in groups, all depositing their soft eggs at the same place at the same time. Salamander and caecilians, unlike frogs, do not have a larynx.  They have the ability to produce a few grunt-like sounds, but these are not beneficial for reproductive purposes. Most salamanders normally use their sense of smell to find a mate. The males have the capability to release an odor that attracts females. Males also use posture and color to impress the opposite sex. It should be kept in mind that all the animals, whether reptiles or mammals reproduce sexually (meaning that the species mainly consist of males and females and mating involves the fertilization of gametes, (eggs and sperms). Reptiles and mammals reproduce through internal fertilization, (inside females) while amphibians practice external fertilization. Although some species of frog use internal fertilization. Scientists discovered from their observation that fanged frog uses internal fertilization.

External Fertilization in Amphibians

Most external fertilization in amphibians takes place during the process of spawning where many males and females release their sperms and eggs in the same area, at the same time. The discharge of material may be triggered by temperature, water, or the length of the day.

Sexual Selection in Amphibians

Sexual selection in amphibians means sexual selection processes in frogs, salamanders, toads, and newts, etc. Among the majority of frog species, have breeding seasons at regular intervals where the male-male competition takes place with arriving at the water edge first in large number and producing a wide range of vocalization and some other complex behaviors to attract mates.

 

Can amphibians reproduce asexually?

There are a few species of amphibians, for example, silvery salamander, that can undergo a famous type of asexual reproduction termed parthenogenesis. In this type of asexual reproduction, the sperm needed to stimulate the process must come from males of other salamander species.

 

Reproductive strategies in amphibians

Reproductive success for amphibians requires spermiation, ovulation,  fertilization, oviposition, embryonic development, and metamorphosis are accomplished. Amphibians play roles as keystone species in their environments, evolutionary biology,  model systems for developmental, molecular, and environmental sensors of the manifold habitats where they reside. As described earlier, amphibians reproduce sexually with either external or internal fertilization. They may attract mates with scents or calls. Amphibians produce an-amniotic eggs, so they must be reproduced in water. As mentioned earlier, that amphibians lay their eggs in water, but most caecilians do not require a real standing body of water and may lay their eggs in mud or some other moist substrate. Amphibian larvae undergo metamorphosis to the adult form. Their larval stage is very different from the adult form. After hatching the larvae immediately develop gills in order to survive their aquatic environment. Amphibian larvae bear a strong resemblance to fish, during their early stage. For example, they have a long tail which is used for swimming, gills used for breathing, and they do not still produce limbs.

Amphibian eggs

Unlike tetrapod vertebrates (reptiles, birds, and mammals) amphibians do no produce amniotic eggs. They must lay their eggs in water so that they may not become dry. Amphibian eggs covered in a jelly-like substance. The jelly assists to keep the egg moist and offers protection from predators.

 

Metamorphosis in amphibians

Metamorphosis is the transformation of the larva to a miniature adult and generally from an aquatic to a terrestrial or semi-terrestrial environment. Metamorphosis is initiated and controlled by the hormone thyroxin (TH), and the process is obligatory. In amphibians, there are three stages of metamorphosis, (1) egg (2) larva, and (3) adult.

Paedomorphosis in amphibians

It is a biological process in which the adults of a species retain characters found in the larvae of their parents. This can happen, when the rate of development is very slow, giving rise to a sexually mature juvenile  — neoteny

 

Reproductive Cycles

Age of Sexual Maturity and Breeding Condition

Before attempting to breed amphibians, and especially in the case of hormonal induction of ovulation, it is necessary to confirm that females are of breeding age and in good condition. The age of sexual maturity in amphibians is generally higher in females than in males. It is estimated that males of some species regularly mature in less than 4 months, while females often first spawn in their second year to maximize reproductive investment during risky spawning activity when the rates of predation are very high. In species that live in environments with regular seasonal breeding opportunities, reproduction from each female can take place once yearly (semilparous). Mississippi gopher frog (R. servosa) is the best example of a semilparous species. Females of the Mississippi gopher frog (R. servosa) do not reproduce on every spawning event and sometimes not for several years.

 

Sexing

Sexual dimorphism is present in almost all species from all orders of amphibians, although it is absent in caecilians. The most common way used to sex anurans is to recognize differences between sexes in nuptial pads,  throat and body color,  tympanum size and color, and vocalization.

 

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