Parthenogenesis: Biological Mechanisms and Types Explained
Natural Parthenogenesis
Parthenogenesis is the embryonic development of a gamete without fertilization by the opposite sex. While male gamete development is rare (observed in some algae), female gamete development is common in nature.
First described by Charles Bonnet in 1740 through his observations of aphids, this process is prevalent in grasshoppers, wasps, and worms. Depending on the species, it can produce males, females, or both:
- Arrhenotoky: Produces males.
- Thelytoky: Produces females.
- Amphitoky (or Deuterotoky): Produces both sexes.
Types of Parthenogenesis
- Cyclical Parthenogenesis: Found in crustaceans and aphids. It involves an alternation between sexual reproduction and parthenogenesis. Telitóquica parthenogenesis predominates in spring and summer, followed by amphitoky, which leads to sexual reproduction.
- Optional Parthenogenesis: Typical of bees. If the egg is fertilized, it develops into a diploid female. If the egg remains unfertilized, it develops parthenogenetically into a haploid male.
- Geographic Parthenogenesis: Common in invertebrates. Related species or populations may reproduce via parthenogenesis in northern regions and sexually in warmer southern regions.
- Accidental Parthenogenesis: Occurs in invertebrates that normally reproduce sexually. Occasionally, unfertilized eggs develop parthenogenetically, resulting in haploid (n) individuals.
- Rudimentary Parthenogenesis: Observed in poultry (turkeys) and mammals (including humans), where it is considered pathological. The development of parthenogenetic oocytes in testicles, ovaries, or the chest results in tumors such as benign teratomas or teratocarcinomas, which contain various tissues but do not form functional organs.
- Paedogenesis: Occurs during the larval stage. Described by Wagner in 1862 in fly larvae, this process involves the development of new larvae within the parent larva, which are released upon the breakdown of larval tissue. This has also been observed in other dipterans.