Reproduction in Frogs

Introduction to Reproduction in Frogs

Reproduction is a process where organisms create new individuals and enable their species to continue. Frogs are unisexual and show sexual dimorphism. The male frog is slightly smaller than the female frog. During breeding season male frogs produce croaking sound by the help of vocal cords. The croaking is an invitation for copulation.

In a context relative to frog reproduction, understanding of the life cycle as it is an alternating aquatic and terrestrial period. Research done on frog reproduction results in the conservation of the species. Most are indicators of environmental health about the evolutionary adaptations in amphibians.

General Reproductive Behaviour of Frogs

An overview of frog reproduction is given below-

External Fertilisation and Mating Calls

Frogs exhibit numerous reproductive behaviours that are primarily elicited by the surrounding ecological conditions, such as temperature, moisture, and others. A majority of the frogs reproduce by external fertilisation, where males release sperm through the eggs as the female lays them. External fertilisation usually includes particular mating calls used by the males to alert the females during the reproductive season.

Differences Between Male and Female Frogs

Male frogs are generally small-sized with inflated vocal sacs, which they inflate to make mating calls. In many species, they develop nuptial pads on the forelimbs during their reproductive season that help them grasp the female while in amplexus. Female frogs are usually bigger, with more developed ovaries for laying eggs.

Anatomy of Frog Reproductive System

The anatomy of frog reproduction is given below-

Male Reproductive System (Testes, Vasa deferentia, Cloaca)

The reproductive system in male frogs consists of paired testes, which produce sperm, and vasa deferentia, which carry the sperm to the cloaca. The cloaca is a common chamber into which both the digestive and the urogenital systems open and that carries or stores up the sperm during mating.

Female Reproductive System (Ovaries, Oviducts, Cloaca)

The female frog also possesses an immature pair of ovaries, which are egg-producing. The oviduct conveys the egg to the cloaca and then are finally expelled out during the process of laying. In line with males, the female cloaca also serves the function of being the opening for the reproductive, digestive, and excretory systems.

Breeding Season and Mating Behavior

The breeding and mating behaviour is given below-

Environmental Triggers

They mostly breed when the environment is right, for instance, when it is warm and humid it is a signal that shortly it will rain which would mean appropriate breeding grounds for laying eggs and tadpoles development.

Courtship and Mating Calls

Male frogs possess vocalisation to attract females. Advertisement calls are very distinctive to every species. They vary in pitch, duration, and frequency. Females answer these calls approaching the male to show their readiness to mate.

Courtship Rituals

Frog courtship frequently involves extensive physical contact between the male and female and terminates in amplexus. The male positions himself on the back of the receptive female.

Amplexus – Definition and Types (Axillary, Inguinal)

Amplexus is a form of mating in which a male grabs a female. This phenomenon is noted when the male grasps the female so tightly that he holds her in amplexus, which holds her limbs out of the way and ensures that sperm encounter eggs as they are released by the female.

There are two common forms of amplexus: axillary (male grasps the female under her forelimbs) and inguinal (male grasps the female around the waist near the hindlimbs).

Fertilisation and Egg-Laying in Frogs

The fertilisation and egg-laying are given below-

External Fertilisation Process

The female deposits the eggs in a more or less suitable area, usually aquatic ecosystem, and the male deposits the sperm over the eggs. This process heavily depends on the time and environmental factors.

Egg Deposition Sites (Water, Leaves)

Eggs are typically laid in a soft mass. The eggs become engulfed in a jelly-like substance that absorbs water and becomes hard in water. Many species lay their eggs in water bodies such as ponds or streams.

Some species lay their eggs on leaves overhanging water bodies, and when the froglets hatch, they drop into the water. The ability of the eggs to develop and hatch depends on the site on which they are laid or deposited.

Types of Egg Masses (Clusters, Strings, Foamy Masses)

The frog eggs are usually deposited in clusters, strings, or foamy masses, depending on the species. However, the variation and difference between all these are the level of protection from predators or environmental conditions offered by such forms of egg masses.

Developmental Stages in Frogs

The developmental stages are given below-

Embryo Development (Blastula, Gastrula, Neurula)

Previously fertilised frog eggs develop from a one-celled zygote to the multicellular stage of frog embryos, very rapidly. There exist five major stages of development, that is; the blastula, the gastrula, and the neurula. All these stages result in the formation of a tadpole.

Tadpole Development and Metamorphosis

The tadpoles are aquatic larval forms of the frog and with increasing age. The tadpoles undergo metamorphosis to become terrestrial adult frogs. Their respiratory organ changes to lungs, the tail is reabsorbed, and they develop their appendicular limbs.

Parental Care in Frogs

The parental care is given below-

Species-Specific Care Behaviour

Parental care in frogs displays a great diversity among species, with many guarding eggs from predators, some carrying tadpoles on the back, and others in special pouches. These kinds of behaviour enhance the possibility of better offspring survival in harsh environments.

Examples (Poison Dart Frog, Surinam Toad)

Some species, however, are extreme in parental care, with the poison dart frog being one such case. Either the male or the female is usually left to guard the eggs. In some cases, tadpoles may even be carried to sites with available water. In sharp contrast, the Surinam toad carries eggs embedded in its back until the hatching stage.

Reproduction in Frogs NEET MCQs (With Answers & Explanations)

This topic carries a significant weightage in NEET exam. Important topics to be covered are:

• Reproductive Behavior

• Male and Female Reproductive Systems

• Metamorphosis

Practice Questions for NEET

Q1. Bidder's canal in frog is found in

1. Liver

2. Testis

3. Ovary

4. Kidney

Correct answer: 4) Kidney

Explanation:

Bidder’s canal is present in the kidney of male frogs. It is helpful in the transfer of sperm from the vasa efferentia to water. Bidder’s canal is found in the kidneys of male frogs and plays a crucial role in transferring sperm from the vasa efferentia to the external environment. It helps channel sperm to the urogenital opening, allowing for external fertilization in water. Additionally, it functions as part of the excretory system, assisting in removing waste and excess water. This dual function is essential for efficient reproduction and excretion in amphibians.

Hence, the correct answer is option 4) Kidney.

Q2. Iodine deficiency in frog tadpole will lead to

1. Accelerated metamorphosis

2. Development of a giant frog

3. Inhibition of metamorphosis

4. Development of a miniature frog

Correct answer: 3) Inhibition of metamorphosis

Explanation:

Thyroxine, which is derived from iodine and the amino acid tyrosine, plays a crucial role in the metamorphosis of amphibian tadpoles. A deficiency in thyroxine slows down metamorphosis, resulting in the continuation of larval life.

Hence, the correct answer is option 3) Inhibition of metamorphosis.

Q3. What is the process of fertilization called in frogs?

1. Copulation

2. Spawning

3. Budding

4. Syngamy

Correct answer: 4) Syngamy

Explanation:

Syngamy is the process of fertilization in frogs, where the male's sperm unites with the female's egg to form a zygote.

Syngamy is the fusion of two gametes, resulting in the formation of a zygote. In frogs, fertilization is external, and the female releases her eggs into the water, where the male's sperm fertilizes them.

Copulation is a process of sexual intercourse where the male and female gametes are transferred through the cloacal openings in frogs. Spawning is the process of releasing a large number of eggs and sperm into the water, where fertilization occurs externally in frogs. Budding is a form of asexual reproduction in which new individuals develop as outgrowths from the parent organism, commonly seen in hydra and some other invertebrates.

Hence, the correct answer is option 4) Syngamy.

Also read:

• MCQs on Reproduction and Development in Frogs

• Connective Tissues

• Digestive System of Frog

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