Asexual reproduction

[2] While all prokaryotes reproduce without the formation and fusion of gametes, mechanisms for lateral gene transfer such as conjugation, transformation and transduction can be likened to sexual reproduction in the sense of genetic recombination in meiosis.

Eukaryotes (such as protists and unicellular fungi) may reproduce in a functionally similar manner by mitosis; most of these are also capable of sexual reproduction.

Vegetative propagation is a type of asexual reproduction found in plants where new individuals are formed without the production of seeds or spores and thus without syngamy or meiosis.

[13] Many multicellular organisms produce spores during their biological life cycle in a process called sporogenesis.

However, both events (spore formation and fertilization) are necessary to complete sexual reproduction in the plant life cycle.

Fungi and some algae can also utilize true asexual spore formation, which involves mitosis giving rise to reproductive cells called mitospores that develop into a new organism after dispersal.

This method of reproduction is found for example in conidial fungi and the red algae Polysiphonia, and involves sporogenesis without meiosis.

Most lichens, which are a symbiotic union of a fungus and photosynthetic algae or cyanobacteria, reproduce through fragmentation to ensure that new individuals contain both symbionts.

These fragments can take the form of soredia, dust-like particles consisting of fungal hyphae wrapped around photobiont cells.

[20] Parthenogenesis occurs in the wild in many invertebrates (e.g. water fleas, rotifers, aphids, stick insects, some ants, bees and parasitic wasps) and vertebrates (mostly reptiles, amphibians, and fish).

For example, female zebra sharks will reproduce asexually if they are unable to find a mate in their ocean habitats.

Today, the largest species that has been documented reproducing parthenogenically is the Komodo dragon at 10 feet long and over 300 pounds.

In flowering plants, the term "apomixis" is now most often used for agamospermy, the formation of seeds without fertilization, but was once used to include vegetative reproduction.

Male apomixis can occur in rare cases, such as in the Saharan Cypress Cupressus dupreziana, where the genetic material of the embryo is derived entirely from pollen.

[33] The offspring produced in androgenesis will still have maternally inherited mitochondria, as is the case with most sexually reproducing species.

Androgenesis occurs in nature in many invertebrates (for example, clams,[34] stick insects,[35] some ants,[36] bees,[37] flies[38] and parasitic wasps[37]) and vertebrates (mainly amphibians[39] and fish[37][40]).

[42][43][44] This has been noted in many plants like Nicotiana, Capsicum frutescens, Cicer arietinum, Poa arachnifera, Solanum verrucosum, Phaeophyceae,[45] Pripsacum dactyloides, Zea mays,[37] and occurs as the regular reproductive method in Cupressus dupreziana.

There are also clonal species that reproduce through vegetative reproduction like Lomatia tasmanica[46][47] and Pando,[48] where the genetic material is exclusively male.

Other species where androgenesis has been observed naturally are the stick insects Bacillus rossius and Bassillus Grandii,[35] the little fire ant Wasmannia auropunctata,[36] Vollenhovia emeryi,[37] Paratrechina longicornis,[37] occasionally in Apis mellifera,[37] the Hypseleotris carp gudgeons,[37] the parasitoid Venturia canescens,[37] and occasionally in fruit flies Drosophila melanogaster carrying a specific mutant allele.

This method of reproduction has been found in several species of the clam genus Corbicula,[34] many plants like, Cupressus dupreziana,[50] Lomatia tasmanica,[46][47] Pando[48] and recently in the fish Squalius alburnoides.

[40] Other species where androgenesis has been observed naturally are the stick insects Bacillus rossius and Bassillus Grandii,[35] the little fire ant Wasmannia auropunctata,[36] Vollenhovia emeryi,[37] Paratrechina longicornis,[37] occasionally in Apis mellifera,[37] the Hypseleotris carp gudgeons,[37] the parasitoid Venturia canescens,[37] and occasionally in fruit flies Drosophila melanogaster carrying a specific mutant allele.

This dynamic reproductive cycle allows them to produce specialized offspring with polyphenism, a type of polymorphism where different phenotypes have evolved to carry out specific tasks.

The freshwater crustacean Daphnia reproduces by parthenogenesis in the spring to rapidly populate ponds, then switches to sexual reproduction as the intensity of competition and predation increases.

The slime mold Dictyostelium undergoes binary fission (mitosis) as single-celled amoebae under favorable conditions.

[54][55] Inheritance of asexual reproduction by a single recessive locus has also been found in the parasitoid wasp Lysiphlebus fabarum.

[62] Bdelloid rotifers are extraordinarily resistant to damage from ionizing radiation due to the same DNA-preserving adaptations used to survive dormancy.

[66] Similar findings suggest that the mite species Oppiella nova may have reproduced entirely asexually for millions of years.

Current hypotheses[69] suggest that asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments.

Developmental constraints[70] may underlie why few animals have relinquished sexual reproduction completely in their life-cycles.

[71] Facultatively apomictic plants increase frequencies of sexuality relative to apomixis after abiotic stress.