Objectives
Reptiles: Agama Lizard (Agama agama)
Phylum: Chordata
Sub-phylum: Vertebrata
Habitat: Lizards live in desert, grassland, rainforest, around homes, building, trees and rocks.
Agama lizard is sometimes called rainbow lizard because of the colorful displays put on by the adult male. Agama show sexual dimorphism (difference in appearance among male and female). The female possesses brown head with green spots and brown body with yellow patches. The dominant male (adult male) has bright red or yellow head, dark blue body and the tail with different colors.
Structure of Agama Lizard
The body is covered by dry, horny, overlapping scales. It has a triangular head separated from the trunk by a short neck, a long tail and two eyes. Each eye is protected by movable eyelids; a transparent fold of skin called nictitating membrane and a ridge of hard scales. Behind the eyes are well-developed circular ear-drums or tympanum.
It has a terminal mouth with homodont dentition. Above the mouth is a pair of nostrils.
The male possesses a fold of skin called gular fold, below the chin, which is lowered during courtship or frightened. It also has a scaly growth of skin called nuchal crest above the neck. It is raised during fighting.
Two pairs of limbs arise from the trunk. The limbs are shot and stout with five digits which are not webbed. The hind-limbs are longer than the fore-limbs.
The trunk terminates in a long tapering tail. Many lizards can detach their tails to escape from predators, an act called autotomy, but this ability is not shared by all lizards.
Movement in Agama Lizard
Agama lizard can run, climb and cling using strong, clawed digits of it limbs. It run quickly on its hind limb for short distances. The tail helps in balance and movement.
The limbs are unable to support the body clearly of the ground at rest. This is because the limbs extend out horizontally and not directly under the trunk as in mammals.
Feeding in Agama Lizard
Agama lizard is insectivores, which feed on mainly ants, grasshoppers and termites.
It sits in vegetation or in shade and wait until an insect walks by and then chase the prey. It catches the prey using a tongue with a tip covered by mucous glands.
It possesses small teeth for crushing the prey before swallowed.
Respiration in Agama Lizard
Excretion in Agama Lizards
Excretion is performed mainly by two small kidneys. Uric acid is the main nitrogenous waste product excreted by lizards. Reptile kidneys are unable to produce liquid urine; this is because they lack a specialized structure called a loop of Henle.
The nitrogenous waste is excreted as white, solid substance along with the faeces.
The solid uric acid produced is an adaptation of water conservation in lizards.
Reproduction in Lizards
1. Courtship and Mating
The male develops dramatic colorful markings; the head, neck and tail turn bright orange, and the body dark blue.
The male approaches the female from behind and bob the head to attract her.
The female curved her back with the tail and head raised. The male chased, grasps and mount on her. They pair at 90 degrees in order to bring their cloacae together.
The male pushes the base of his tail onto her cloaca, inserting his hemi-penis and introduce sperms into the female. Fertilization is internal.
2. Egg Laying and Hatching
The female lays the fertilized eggs in a hole she digs with her claws and cover the eggs with soil. The eggs are hatch within eight to ten weeks.
The young lizards become active and immediately start eating sand, plants, and insects.
Lizard Territory
A territory consists of one adult male, several adult females and young of both sexes. The dominant male defends his territory.
It displays several behaviors, such challenge, threat and fighting.
The challenge display is shown in a situation where young male showing orange color (or reproductive color) is chased out of the territory.
It challenges or fights if an intruder tries to mate with his females.
The threat is display by rapid up and down movement of the head with the gular fold fully extended. The whole body raises and lowers.
Adaptation of the Lizard to its Environment
1. Presence of lungs for respiration.
2. Clawed digit which allows lizards to climb.
3. It has well developed eye for detecting prey.
4. Long mucous tongue for trapping prey.
5. Dry scaly skin for protection against water loss
6. Long tail for balancing while moving
Features of Evolutionary Advancement of Lizards over Frogs or Toads
1. Presence of strong legs with clawed digit for climbing and running quickly on land.
2. Lizards lay shelled eggs that for prevention of desiccation
3. Lizards are diurnal animals. They are adapted to daylight conditions, with color vision and more advanced visual depth than in amphibians.
4. Respiration in lizards occurs only through the lung but amphibians’ respiration occurs in more primitive structures such as the skin and mouth in addition to the lung.
Difference between male lizard and female lizard
|
Male lizard |
Female lizard |
|
Large in size |
Small in size |
|
More
prominent nuchal crest and gular fold |
Less prominent nuchal
crest and gular fold |
|
Orange head |
Brown head with green spots |
|
Brightly
colored |
Usually, dull colored |
|
Hemi-penis present |
Absence of hemi-penis |
|
Dark
blue trunk and tail with different colors; blue at base, orange in the middle
and black at the tip |
Brown trunk with yellow
spots and brown tail |
Difference between the External Features of Lizard and Toad
|
Lizard |
Toad |
|
Long and narrow trunk |
Short and wide trunk |
|
Dry
scaly skin |
Moist skin without scales |
|
Presences of neck and tail |
Absences of neck and tail |
|
Forelimb
has five digits |
Forelimb has four digits |
|
Presence of teeth |
Absences of teeth |
|
Hind-limbs
are not webbed |
Hind-limbs are webbed |
|
Less prominent tympanum membrane and eyes
are not bulging |
Prominent tympanum membrane and bulging eyes |
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