Aphid. Aphids, tiny insects found the world over, are “essentially born pregnant,” says Ed Spevak, curator of invertebrates at the St. Louis Zoo.
In other words, aphids are frequently born pregnant. According to scientists, this process tends to repeat itself for about 10 to 30 generations before a new cohort of sexual, egg-laying aphids is born as the weather cools down. Environmental cues determine if a gestating aphid will forgo sex or not.
The swamp wallaby is the only mammal that is permanently pregnant throughout its life according to new research about the reproductive habits of marsupials.
Most aphids are born pregnant and beget females without wastrel males. These parthenogenetic oocytes result from a modified meiosis that skips the reduction division, maintaining diploidy and heterozygosity. Embryos complete development within the mother's ovary one after another, in assembly line fashion.
Seahorses and their close relatives, sea dragons, are the only species in which the male gets pregnant and gives birth.
Most animals that procreate through parthenogenesis are small invertebrates such as bees, wasps, ants, and aphids, which can alternate between sexual and asexual reproduction. Parthenogenesis has been observed in more than 80 vertebrate species, about half of which are fish or lizards.
Many species of fish, like the kobudai, are known as “sequential hermaphrodites”: they can switch sex permanently at a specific point in their lives. The majority of “sequential hermaphrodites” are known as “protogynous” (Greek for “female first”): they switch from female to male.
The shortest known gestation is that of the Virginian opossum, about 12 days, and the longest that of the Indian elephant, about 22 months. In the course of evolution the duration of gestation has become adapted to the needs of the species.
Most insects produce eggs but some, such as aphids, are viviparous and give birth to live young. The female aphids reproduce by means of parthenogenesis. In species where viviparity gives rise to larvae the species can be termed larviparous.
Fastest Procreators:
The aphid might be small, but it makes up in multiplication. Assume you had one female aphid and that no predators will disrupt your numbers. One female can produce 41 offspring. In one season that same female can produce 41 offspring, 16 times.
Mammals. Large mammals, such as primates, cattle, horses, some antelopes, giraffes, hippopotamuses, rhinoceroses, elephants, seals, whales, dolphins, and porpoises, generally are pregnant with one offspring at a time, although they may have twin or multiple births on occasion.
Elephants have the longest pregnancy period of any living mammal. If you – or someone you know – has experienced a pregnancy that seemed to go on forever, spare a thought for the elephant.
The Australian three-toed skink (Saiphos equalis) is doubly remarkable: Not only can it both lay eggs and bear live young, but it can do both within a single litter of offspring.
The First Animals
Sponges were among the earliest animals. While chemical compounds from sponges are preserved in rocks as old as 700 million years, molecular evidence points to sponges developing even earlier.
Seahorses are one of only a few examples in the animal kingdom where the male rather than the female gives birth.
Cockroaches don't technically get pregnant because most species (see above) don't give birth to live young. But when they do get “pregnant”, they form the egg sac that will hold their eggs until they hatch. Some species only mate once; they'll keep reproducing from that first mating for the rest of their lives.
Ants have complete metamorphosis. Queen ants lay eggs. The baby ant that hatches from the egg is a larva, with no legs, just a soft white body like a worm and a small head.
Eggs and egg sacs. Female spiders produce either one egg sac containing several to a thousand eggs or several egg sacs each with successively fewer eggs. Females of many species die after producing the last egg sac. Others provide care for the young for some period of time; these females live one or, at most, two years ...
Female lions, lionesses, are able to give birth to cubs all year round, usually from the age of about three or four years old. Pregnancy lasts for around 110 to 120 days.
A cow is pregnant for around nine months (or 279 to 292 days). The gestation length varies depending on several factors, such as the breed of the cow and the sex of the calf.
Pregnancy lasts for about 280 days or 40 weeks.
Hermaphroditic animals—mostly invertebrates such as worms, bryozoans (moss animals), trematodes (flukes), snails, slugs, and barnacles—are usually parasitic, slow-moving, or permanently attached to another animal or plant.
But perhaps the most surprising thing about Auanema sp. is that it's found in three sexes – male, female and hermaphroditic. While hermaphroditism is relatively common in the world of invertebrates, this new worm species does things a little differently.
In the great majority of tunicates, mollusks, and earthworms, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the female or male. Hermaphroditism is also found in some fish species, but is rare or absent in other vertebrate groups.