Reptiles’ reproductive activities are closely linked to narrow windows of temperature and moisture regimes in spring and summer. Climate change may alter these periods and cause boom-bust cycles of lizard reproduction.
Most reptiles are oviparous (lay eggs). However, some snakes and lizards such as boas are viviparous, giving birth to live young. Males have a penis or hemipene that is s도마뱀분양 eparate from the urinary tract and is used exclusively for reproduction. Secondary sexual characteristics include a longer tail and proportionally larger head in males, and three noticeable horns on the male Jackson’s chameleon.
In a sexual reproduction system, sperm are passed from the male to the female’s reproductive organs during copulation. Fertilization occurs internally in most reptiles, and the fertilized eggs are then released from the female’s body through an opening called the cloaca. In a minority of reptiles, the fertilized eggs are retained inside the mother and may develop through ovovivipary (turtles and some snakes) or vivipary, in which the fertilized eggs are carried around inside the body of the female and fed from the maternal cloaca (boas and some chameleons).
The general understanding is that genotypic and temperature-dependent sex determination mechanisms operate separately, with sex chromosomes having no bearing on the sex of an early embryo until it enters a thermosensitive phase of development. But research suggests that some reptiles experience a combination of both, where sex chromosomes and temperature are involved in determining the sex of a newly hatched embryo.
A lizard genus, Aspidoscelis, is one example where both sex-determining mechanisms are at work. These lizards are oviparous, laying eggs, but they are also ovoviviparous and capable of producing young that are genetically identical to their mothers. According to molecular biologist Peter Baumann, these asexual reproducers, which include about 70 vertebrate species, use all the sex chromosomes they have and solitarily reproduce offspring that are genetic clones. Hence, “if one individual is sick or an environmental change occurs that kills one, it could affect the entire population.”도마뱀분양
Reptiles that lay eggs (oviparous) get embryo nourishment from the yolk alone, or at least partially so (lecithotrophy). All crocodilians, turtles, tuataras, and a majority of snakes and lizards are oviparous.
To reproduce, a male reptile deposits one or two sperm in a female’s cloaca. After a brief courtship, the male inserts his single penis—or, as in lizards, one or two hemipenes—into each ovary through a cloacal opening called the genital papillae. The sperm move up each oviduct to an opening adjacent to an ovary, where they fertilize individual eggs.
Depending on species, the number of eggs produced may be as few as one per clutch or as many as thousands. Often, the number of eggs is influenced by temperature. For example, in the oviparous snake Opheodrys vernalis, egg production peaks in summer when temperatures are high, but it declines after the eggs hatch.
In some cases, a male can complete spermatogenesis and store sperm for years, so it can be used to fertilize subsequent clutches. This is known as parthenogenesis, and it is seen in the diamondback terrapin (Malaclemys terrapin).
In addition to having an unusual reproductive mode, a male lizard or snake’s genital structures are unusually large for its body size. These features help distinguish males from females, and are especially noticeable in chameleons, where male Jackson’s chameleons (Chamaeleo jacobini) have horns on their heads that the females lack.
Oviparous animals lay eggs that develop within the mother. This is the reproductive method used by most fish, amphibians, reptiles, and monotreme mammals (like the platypus).
Some reptiles are oviparous, while others are viviparous, meaning they give birth to live offspring. Viviparous reptiles develop embryonically inside their mothers, which provides them with all of the nutrients they need to mature. This type of reproduction has a number of advantages for females, including the ability to produce more offspring per breeding season. However, vivipary also increases the risk of bacterial infection and exposure to hostile environmental conditions.
Among viviparous reptiles, males may discharge sperm into the female’s cloaca through direct cloacal apposition (e.g., tuataras [Sphenodon]) or through the use of an intromittent organ (e.g., crocodiles and lizards). The penis homologue of the mammalian male organ is present in some reptiles, but is rarely used during copulation; it is instead replaced by a structure called a hemipenis (e.g., turtles and lizards).
Despite these disadvantages, some oviparous reptile species have nongenetically switched back to viviparity. However, studies of the offspring of these species indicate that sex is not a significant source of variation in body size, residual yolk, or fat bodies at birth or hatching. Two oviparous (Deinagkistrodon acutus and Xenochrophis piscator) and six viviparous (Elaphe carinata, Enhydris chinensis, Naja atra, Rhabdophis tigrinus lateralis, and Sinonatrix annularis) species showed sexual dimorphism in SVL at hatching or birth, but in no case was male sex significantly larger than female sex.
Viviparous means that animals give birth to live young, instead of laying eggs. Viviparous animals include birds, reptiles, amphibians, and most fishes. Some shark species are ovoviviparous, meaning they lay eggs but develop inside of the mother’s body. This is also called aplacental vivipary.
In viviparous animals, the fertilized egg is retained and nourished within the mother’s body until it hatches and develops into a young animal, such as a frog or salamander. Embryos in viviparous animals may derive nutrients from the yolk of the egg or from other sources such as the uterus, placenta, or mother’s blood. Embryos are typically protected by the mother’s cloaca and sometimes by a hard shell or membrane.
Viviviparous embryos in a fish or shark may be fed directly by their mother’s gills, which are located in the mouth and throat area of these animals. This is known as oophagy or adelphophagy. Alternatively, some sharks and squid use their oviducts to transport eggs to the cloaca where they can be nourished by maternal nutrient secretions.
Many reptiles are oviparous, but some groups of lizards and snakes have evolved a form of viviparity that is called ovovivipary. Ovoviviparous lizards produce one or more clutches per year, and mature to adulthood at various times after hatching. This reproductive strategy reduces the amount of maternal resources needed for reproduction, and allows oviparous lizards to have larger litter sizes than their viviparous ancestors.