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Another form of sexual parasitism is hybridogenesis, where the reproductive effort of another species is exploited. One such example is a species in the genus Poeciliopsis. This fish consist only of females that mates with males from a closely related species. All the paternal chromosomes are discarded during the production of eggs.
Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. [6] [7] Sexual reproduction also occurs in some unicellular eukaryotes. [2] [8] Sexual reproduction does not occur in prokaryotes, unicellular organisms without cell nuclei, such as bacteria and archaea.
[9] [10] [11] This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice. [ 12 ] [ 13 ] Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers ), while others can switch between sexual reproduction and parthenogenesis.
A pregnant Southern platyfish. Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after the egg-sperm union. [1] Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, scientific articles on fish.
[citation needed] Internal fertilization with many vertebrates (such as all reptiles, some fish, and most birds) occurs via cloacal copulation, known as cloacal kiss (see also hemipenis), while most mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization.
Some anglerfish are notable for extreme sexual dimorphism and sexual symbiosis of the small male with the much larger female, seen in the suborder Ceratioidei, the deep sea anglerfish. In these species, males may be several orders of magnitude smaller than females. [4] Anglerfish occur worldwide.
Most species that reproduce by sexual reproduction are heterogamous—females producing larger gametes and males producing smaller gametes . In nearly all animal species, offspring are carried by the female until birth, but in fish of the family Syngnathidae (pipefish, seahorses and the leafy seadragon), males perform that function. [1]
Therefore, the Amazon molly can only live in habitats that are also occupied by a species of male that will reproduce with them. [24] The Amazon molly reaches sexual maturity one to six months after birth, and typically has a brood between 60 and 100 fry (young) being delivered every 30–40 days.