Explain Reproduction in Reptiles


Reptiles:

Reptiles are the tetrapod animals that include today’s snakes, crocodiles, lizards, turtles and tuataras.

Habitat:

    Today, reptiles live in a wide range of habitats. They can be found on every continent except Antarctica. Many turtles live in the ocean, while others live in freshwater or on land. Lizards are all terrestrial, but their habitats may range from deserts to rainforests, and from underground burrows to the tops of the trees.

Sex Differentiation and Genitalia:

Both male and female reptiles possess internal sexual organs that can be difficult to detect externally. The testes of male reptiles are housed in the body. Males can either have a single penis such as in Turtles and Crocodiles or may have two hemipodes as in Lizards and Snakes that can be detected externally by pair of bulges behind the cloaca. The cloaca is present near the animal’s tail. The genitalia of male animals is purely reproductive, and they are separated from the urinary tract. The male and female reptiles are also categorized on the basis of secondary sexual characteristics such as size, proportions, horns, and coloring.

Reproductive Behaviors:

The reproductive methods or the behavior of reptiles differ in a great way from mammals. While, some reptiles lay eggs like that of birds but, there are still some livebearer reptiles. Most of the reptiles are oviparous, meaning that they lay eggs that hatch outside the female’s body. However, several snakes and lizards are in fact ovoviviparous. This shows that they give birth to live young ones. The eggs of such reptiles are housed inside and also hatched inside the reptilian body.

Courtship Behaviors:

Reptiles offend display different courtship behavior to attract their opposite sex animal for mating. For example, many Chameleons change the color while attracting the female. Male turtles will often bob their heads up and down to attract the female partners. The red-sided garter snake often gathers in groups of up to 30,000 which is called as a mating ball. Many of the lizards and snakes also release pheromones, chemical scents biologically designed to attract the opposite sex.

Breeding Methods:

A A. Sexual Reproduction:

Fertilization must occur in the reproductive tract of the female before protective egg membranes are laid down around an egg. In males, a pair of ducts deliver sperm to the cloaca. Fertilization occurs in the upper regions of the oviduct, which leads from the ovary to the cloaca.  The male does this by inserting his penis or hemipodes into the female cloaca. After copulation, sperm may be stored in a seminal receptacle in the female reproductive tract. Secretions of the seminal receptacle nourish the sperm and arrest their activity. Sperm may be stored for up to four years in some turtles, and up to six years in some snakes. In many species, this sperm can remain intact for years so the female can produce additional offspring without any other male contact. Interestingly, some species of lizards produce offspring without males in a process known as parthenogenesis.

B. Asexual Reproduction:

Parthenogenesis has been described in six families of lizards and one species of snakes. In these species, no males have been found. Populations of parthenogenetic females have higher reproductive potential than bisexual populations. A population that suffers high mortality over a cold winter can repopulate its habitat rapidly because all surviving individuals can produce offspring. This apparently offsets the disadvantages of genetic uniformity resulting from parthenogenesis. Asexual reproduction has been identified in squamates in six families of lizards and one snake. In some species of squamates, a population of females is able to produce a unisexual diploid clone of the mother. This form of asexual reproduction, called parthenogenesis, occurs in several species of gecko and is particularly widespread in the teiids (especially Apiocerids) and lacertids (Lacerta). In captivity, Komodo dragons (Araneidae) have reproduced by parthenogenesis.

Reptilian Eggs:

Unlike amphibians, reptiles produce amniotic eggs. The shell, membranes, and other structures of an amniotic egg protect and nourish the embryo. These eggs are often supplied with large quantities of yolk for long developmental periods. They keep the embryo moist and safe while it grows and develops. They also provide it with a rich, fatty food source (the yolk). Most reptiles lay amniotic eggs covered with leathery or calcareous shells. An amnion, chorion, and allantois are present during embryonic life.

The eggshell :

Ø  i. protects the crocodile embryo

a and keeps it from drying out, but it is flexible to allow gas exchange.

Ø  The chorion aids in gas exchange between the inside and outside of the egg.

Ø  It allows carbon dioxide to exit the egg and oxygen gas to enter the egg.

Ø  The albumin further protects the embryo and serves as a reservoir for water and protein. The allantois is a sac that collects the metabolic waste produced by the embryo.

Ø  The amniotic sac contains amniotic fluid  which protects and cushions the embryo.

Ø  The amnion aids in osmoregulation and serves as a saltwater reservoir.

Ø  The yolk sac surrounding the yolk contains protein and fat-rich nutrients that are absorbed by the embryo via vessels that allow the embryo to grow and metabolize. 

Care of Young ones:

Most reptile species do not care for their young, who are left to fend for themselves from birth. Usually, reptiles will hide their eggs in a hollow log or hole in the ground to protect them from hungry predators. Some snake species, however, including pythons and mud snakes, protect their young by wrapping their tales around the eggs. Alligators place their babies gently in their mouths and carry them to water. The number of eggs a reptile produces varies a lot from species to species. Sea turtles lay up to 150 eggs each season, while African tortoises lay just one or two.

About 100 species of reptiles have some degree of parental care of eggs. One example is the American alligator  Mississippians. The female builds a mound of mud and vegetation about 1 m high and 2 m in diameter. She hollows out the center of the mound, partially fills it with mud and debris, deposits her eggs in the cavity, and then covers the eggs. Young feed on scraps of food the female drops when she feeds and on small vertebrates and invertebrates that they catch on their own.

Temperature-dependent sex determination (TDSD):


Some reptiles exhibit temperature-dependent sex determination (TDSD), in which the incubation temperature determines whether a particular egg hatches as male or female. TDSD is most common in turtles and crocodiles but also occurs in lizards and tuatara. To date, there has been no confirmation of whether TDSD occurs in snakes. Temperatures between 32.5 and 33°C result in male offspring. Temperatures around 32°C result in both male and female offspring.