INTRODUCTION OF REPRODUCTION IN AMPHIBIANS

Reproduction is a crucial trait in the life history of any organism and scientists have been intrigued and challenged by this event, and the structures associated with it, ever since the days of Darwin (1871).

Both aquatic and terrestrial vertebrates have evolved an extraordinary diversity of reproductive strategies and morphologies, including varieties of oviparity and viviparity.

Among tetrapods, the diversity of reproductive modes is exceptionally high in amphibians. In this group, we also see multiple trends towards terrestrialization and internal fertilization.

Reproductive modes such as viviparity have evolved in- dependently in all three lineages of modern amphibians.
Internal fertilization is a precondition for viviparity. It is associated with different strategies of sperm transfer, which have evolved within all three amphibian orders, ranging from cloacal apposition in anurans to a true copula via a male intromittent organ in caecilians.

Dioecious:

Amphibians are dioecious i.e. male and female reproductive organs are in separate individual.

Location of ovary and testes:

Ovary and testes are located near the dorsal body wall.

Moist Habitat:

The developing egg lack any resistant covering, due to which development is tied to moist Habitat, usually water. Few anurans have terrestrial nests that are moist by near water.

Caecillians and salamanders have internal fertilization:

Only about 10 of all salamanders have external fertilization. All other produce spermatophores and fertilization is internal. Egg is deposited in soil or water and remain in oviduct during development. All caecillians have internal fertilization and 75 have internal development.

Tadpoles:

Amphibians includes larval stages called tadpoles. Amphibians tadpoles often differ from adults in mode of respiration, Locomotion and diet.

Courtship behavior:

A courtship display is a set of display behaviours in which an animal usually male attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviours often include ritualized movement, vocalizations, mechanical sound production or display of beauty, strength or agonistic ability.

In salamanders:

Salamanders rely on olfactory and visual cues in courtship and mating.

In Anurans:

Male vocalizations and tactile cues are important for anurans. Many species congregate in one location during times of intense breeding activity. Male vocalizations are specie specific and function in the initial attraction and contact between mates. After that, tactile cues become more important.

Amplexus:

The male grasps the female, his forelimbs around her waist so that they are oriented in the same direction and the male is dorsal to the female. This positioning is called amplexus and usually lasts from 1 to 24 hours but may last for days in some species. During amplexus, the male releases sperm as the female releases eggs.

In caecillians:

Little is known of caecillian breeding behaviour. Males have an intromittent organ that is a modification of the cloacal wall, and fertilization is internal.