Reptile Reproduction

파충류샵 Reptiles lay hard-shelled eggs in a nest that they build. The eggs contain albumen, a fibrous shell membrane and a calcareous layer.

파충류샵

Most reptiles are oviparous (lay eggs) but some species are viviparous, giving birth to live young. Male reptiles have a single or pair of penis-like organs that they use to fertilize eggs.

Fertilization

In reptiles that reproduce sexually, the male organism’s sperm fertilizes a female organism’s egg outside of the body, called external fertilization. Species that produce offspring by this means often are motile, which allows them to travel to spawning locations and avoid environmental factors that deplete their numbers. Externally fertilized eggs are more likely to be washed away, eaten or damaged than those that are fertilized internally.

The rate of sperm head, midpiece and flagellum length evolution varied by fertilization mode both within and across vertebrate clades. In internal fertilizing species, midpiece length evolved faster than flagellum length, while sperm head length did not differ between the two. Within Osteichthyes and Amphibia, analyses were more ambiguous and supported different patterns of sperm component length evolution depending on fertilization mode.

For example, a study found that sex determination in most snake and lizard species is determined by the temperature at which eggs are hatched after fertilization rather than by genetics or other factors. However, a study found that the sex of crocodile and alligator embryos is determined by the temperature at which eggs are fertilized. These findings are consistent with the hypothesis that sex determination is a function of temperature and that environmental influences can cause the emergence of alternative modes of fertilization. This suggests that reptiles’ environmental conditions influence how their sex is determined, which also may affect fertility and other reproductive outcomes.

Egg Laying파충류샵

Over millennia of evolution, nature came up with only two ways for a new animal to come into the world—be born from its mother as a squirming newborn or lay eggs that will grow and develop within them until favorable conditions for hatching arise [1]. The latter approach facilitated terrestrial exploitation by eliminating the need for vertebrates to reproduce in water. However, development of the amniotic egg also introduced potential complications such as variable environmental conditions during embryonic residence in the fertilized state. To overcome this, reptile lineages developed the ability to delay embryonic development within the egg through developmental arrest or aestivation.

Embryonic arrest is achieved through a downregulation or cessation of active cell division and metabolic activity, and is most commonly accomplished by entering a cold torpor that typically persists for several days in avian species but can last weeks in reptile embryos. Depending on the species and its geographic location, developmental arrest may occur both before and after oviposition, enabling synchronization of laying with the emergence of the entire clutch.

Studies of egg turning in reptiles are rare and, when conducted, use different experimental designs and testing methods. For example, one study showed that a treatment of turning the eggs of a corn snake Pantherophis guttatus did not affect emergence time, hatching success or hatchling body size. Nevertheless, post-birth mortality was higher in turned embryos (37.5%) than in unturned embryos (4.5%). A multiple regression analysis using the mother’s snout vent length (SVL) as a continuous predictor and egg position as a dependent variable yielded a significant effect of egg turn.

Parental Care

Parental care is a form of behavior that increases the fitness of offspring by reducing risk. It has evolved dozens of times independently in reptiles and many other animal lineages. It includes protection of eggs from predators, guarding and brooding of hatchlings and young, nest construction, and active feeding. It is most common in females, but males provide parental care in a few species.

Egg-laying reptiles typically have a mechanism that delays development in the oviduct after fertilization. This is thought to allow the eggs time to reach a gastrula stage that is capable of developing into a new embryo. Then the embryo develops in the uterus until the hatchling is born.

In most species that provide parental care, the female bears a great deal of the cost. This may include building and defending nests, creating and guarding egg cases, incubating and brooding eggs or young, carrying young (gestation), and nursing (lactation). In the reptile order Strepsirrhine, maternal care is reduced by the fact that females only breed once a year.

Males rarely provide parental care, but there are a few examples of this in the world’s reptiles. These are primarily in crocodylians, and include a male retaining eggs in his mouth for incubation, or in some species, the laying of multiple fertilized eggs on the body surface. In other reptiles, such as frogs and snakes, males may be involved in building nests, aerating eggs by fanning, or guarding young.

Breeding

Reptiles do not have a larval stage and are born fully formed. This makes them more vulnerable to predators and other threats while also limiting the amount of care they need from their parents. But many reptile parents, such as crocodiles and alligators, will protect their nests from predators and help the hatchlings reach the water after they are born.

Most reptiles have a low metabolic rate and need to conserve energy as they lay eggs and broods of young. To do this, they often find or create incubation conditions that are warmer than the surrounding environment. European grass snakes (Natrix natrix) search for rotting manure piles to lay their eggs in, while Galapagos land iguanas (Conolophus subcristatus) climb up the sides of volcanic craters to deposit their clutches of eggs on geothermally heated soil. Female pythons will even shiver when they lay their eggs to generate body heat and keep them warm.

The sex of most snakes and lizards is determined by the sex chromosomes they have at fertilization, but the sex of most turtle and all crocodilian species is decided by the ambient temperature in which they are laid and incubated. In this temperature-dependent sex determination (TDSD) system, high temperatures select for males while lower temperatures favor females.

A recent study showed that TDSD maximizes offspring fitness in the agamid reptile (Neoplaton ocellatus). Warm incubation temperatures increase embryonic development and promote early sexual maturation, which allows younger females to produce more offspring before they become preyed upon by older males.