Parental Care of Amphibia
The class Amphibia belongs to the subphylum Vertebrata of phylum chordata. All the representatives of Clssa Amphibia are ectothermic, tetrapod vertebrate animals which inhabit a wide variety of habitats including terrestrial, arboreal, fossorial, or freshwater aquatic ecosystems. The name amphibian is derived from Greek word "amphibious" which means “living a double life”. Because some species are permanent land dwellers, while other species show an entirely aquatic mode of life.
There are about 8100 known living amphibians, of which nearly 90% are frogs. Amphibians first appeared about 340 MYA (million Years Ago) ago during the Middle Mississippian Epoch of the Paleozoic Era. The representatives of modern amphibians are frogs, toads, newts, salamanders and caecilians, show several unique characteristic features.
Parental Care of Amphibia
Parental care is one type of activities to protect and maintain of its own offspring from the predators. Actually, it is the care of eggs and the young by the parents until they become able to protect themselves from the enemies.
Building nests in suitable places before laying eggs, making incubation after laying eggs, carrying eggs if necessary, taking care of larvae, taking care of eggs and larvae are all innate instincts of animals. Although this instinct is improved in mammals, but lower class animals also show more or less parental care for their eggs and young. Parental care is the maintenance and upbringing of parents to protect eggs and young from hostile environments and enemies.
Amphibians face many problems as they move from aquatic life to terrestrial life. They use several methods to solve these problems. Different amphibians care for eggs and offspring in different ways, especially for breeding and for protecting its own clan. The process of parental care of different amphibians is discussed below.
Some frogs and toads take care of their eggs by selecting suitable places. Zhangixalus schlegelii (=Rachophorus schlegelii) dig holes in the muddy banks of rivers or ponds at the beginning of breeding. During sexual intercourse, both male and female enter the hole and close the mouth of the hole. Firstly, the female frog makes foam with its cloacal secretion. In this foam, female frogs lay eggs and then male frogs release sperm on eggs. The resulting foam protects the eggs from dryness. Then both the male and the female cut a tunnel through the bottom of the hole and went into the water of the pond. When the larvae hatch from the eggs, the foam becomes liquid and rolls into the pond water.
Many amphibians build nests before laying eggs and raise their young. Nests can be of several types-
A female frog named Hyla faber builds a small nest on the edge of a muddy pond before breeding. Male frogs make this kind of nest by circling on soft mud. This type of nest is usually about 30 cm in diameter and its edges are slightly above the water level. As a result, eggs and larvae are protected from the predators of the pond.
Nest Made By Leaf
Phyllomedusa, a South American frog, uses the adhesive juice extracted from cloaca to attach to the edges of leaves. Such leafy nests are usually found on the hanging branches of plants near water bodies. When the nest is filled with rain water, the larvae hatched from the eggs fall on the water.
Nest Made by Wax
Hyla resinfictrix is a type of tree frog that collects wax from bee nests and builds earthen-like nests on tree trunks. When the nest is full of rain water, they lay their eggs there.
Nest Made by Shoot
An amphibian called Triton builds a nest by attaching the young tip of the tree together and the female frog lays eggs there.
Parental Care Through Foam Creating by Water
After laying eggs in the water, both males and females members of Rachophorus maculatus, move their hind arms to produce foam in the water. As a result, the eggs are protected from dryness and remain invisible to the predators.
Carrying of Egg in the Body
In case of Brazilian tree-frog (Hyla goeldii), the female frogs lay eggs in the primary brood pouch. The skin of the frog's back is folded to form a brood pouch. The eggs remain in the brood pouch until completion of metamorphosis.
Espada's marsupial frog (Gastrotheca testudinea) keeps the eggs in a single large brood pouch over the back which is covered by the skin and they are opened posteriorly in front of cloacal aperture.
In case of Obstetric toad of Europe (Alytes obstetricans), the male winds the cords of eggs laid by the female is attached to his body and hindlegs by gelatinuous adhesive substance. Here, they takes care of the eggs until they hatch from the eggs.
In the case of female member of the Duski salamander (Desmognathus fuscus(urodele), the eggs are laid in the form of rosary-like strings. The string is bound around her neck and they care them at a comparatively dry spot. Salamandra salamandra retains some eggs for 10-20 months and develops fully in water after larvae are born.
In case of a Sri Lankan tree frog (Rhacophorus reticulatus), the female member carries the eggs glued to her belly.
Pipa americana (Surinam toad) and Pipa dorsigera species show more improved parental care to their offspring. During the breeding season, the skin on the back of the female become soft and spongy. When the fertilized egg is implanted in the back of the female, a hole is gradually formed in the skin. The hole is covered by a lid. Ovulation is complete in this hole. The developing larvae have a blood vessel-rich tail. These larvae have a close connection with the mother body. After about 80 days, the larvae are detached from the mother body.
Carrying Tadpole Larvae in the Body of the Phyllobates
In this species, their tadpoles are carried on their backs and transferred from one reservoir to another. Similarly, Arthroleptis carries larvae. But Denarobates carry larvae in the beak like suckers. Their goal is to transport larvae to protect themselves from adverse environments.
Parental Care Using the Mouth or Gular Pouch
In small South American frog, called Rhinoderma darwini, the eggs are carried by the male to the comparatively massive vocal sacs that expand over its ventral surface. In this massive vocal sacs, the eggs develop.
The female West African tree-frog, called Hylambates breviceps transported the eggs using her mouth while the female Australian frog called Rheobatrachus silus use her stomach to keep her eggs. The tadpole larvas are ejected through mouth after completing metamorphosis.
Parental Care By Coiling the Body Around Eggs
In red-backed salamander (Plethodon cinereus-urodele), the female members lay eggs beneath the stones or in the hollow of rotten log and the mother coils surround the eggs. In case of Japanese giant salamander (Andrias japonicus) (urodele), the male coils surround the eggs.
The two-toed amphiuma (Amphiuma means- Congo eel) and the female member of the Ichthyophis glutinosa surround the eggs and guard them like snakes so that the eggs are not damaged by the enemy. In this case, they lay eggs in burrows in damp soil. Hypogeophis also coils surround the eggs until they hatch
Some amphibians give birth instead of laying eggs. In fact, the eggs are still in the fallopian tubes and hatch there. As a result, the female member gives birth child like uterine rupture. Such a condition is observed in African frogs called Nectophrynoides and Pseudophryne. Their larvae have long blood vessel-rich tails that maintain contact with the mother body and absorb food from the mother body.
A more advanced condition is seen in the case of the European salamanders, Salamandra salamandra and Salamandra atra. In this case, the eggs are implanted in the uterine cavity and here, a full metamorphosis of the tadpoles occur. The viviparity in the class Gymnophiona is clearly noticeable.