Parthenogenesis

The lizard Cnemidophorus neomexicanus (center) has only females that reproduce by partenogenesis. Two species with asexual reproduction are C. inornatus (left) and C. tigris (right). These are hybridized and produce asexual form C. neomexicanus.

Parthenogenesis is a form of reproduction based on the development of unfertilized female sex cells (ovules), which occurs with some frequency in flatworms, rotifers, tardigrades, crustaceans, insects, amphibians, and reptiles, more rarely in some fish and, exceptionally, in birds. Parthenogenesis was discovered by Charles Bonnet. Jan Dzierżon was the first to discover the parthenogenetic origin of bee drones.

It consists of the segmentation of the ovule without fertilization, triggered by environmental factors, chemicals, electric shocks, etc. In some cases (fish), which we refer to as geitonogamy, contact or fusion with a male gamete is required, but fertilization is not completed, the male cell not contributing its genes. In some animals and under certain specific conditions, an egg can develop into a new being without having been fertilized by a sperm.

The product, called a partenote, will not be able to carry male-specific chromosomes. Depending on the modality of sex determination, this can limit the offspring to only one of them, as occurs in bees and other hymenopteran insects, where females are diploid, coming from fertilized eggs, and haploid males, parthenogenetic.

Although the procedure has also been tried with male gametes, embryo development has not yet been achieved, because male cells are generally reduced to the sole function of fertilizing, while female cells are characteristically totipotent.

Types of parthenogenesis

Depending on whether or not meiosis exists, the following can be distinguished:

• AmeIotic mid-genesis or diploid: There is no meiosis and the egg is formed by mitosis and therefore diploid. It can be considered as asexual reproduction, as there are no haploid cells. This guy is known in some silverlminths, rotmals, crustaceans, insects and amphibians.
• Meiotic partogenesis or haploid: a haploid egg is formed by meiosis that develops without being fertilized. It is given in some silverlminths, rotmals, anelids, insects (bees, wasps, insects stick and ants), fish, amphibians and reptiles. Although there is no syngamy, meiosis occurs, and therefore recombination, so it can be considered a means of sexual reproduction. At times, the individual remains, albeit recombinant, haploid; at other times, the diploid condition is recovered by duplication of the chromosomes; such is the case of some insects, in which the resulting "n" egg, recombine with its own polar corpuscle, also "n", forming a diploid cell, from which a diploid adult will emerge.

In the latter, while a female haploid gamete produces an individual in all cases, we can divide it into three types:

• Arrenotoquia: type of partenogenesis in which male progeny is partogenetic and female is by sexual reproduction. It is given in the vast majority of Hymenoptera. It's the case of all subspecies. Apis melliferaexcept Apis mellifera capensisand other members of the Apidae family, Formicidae, etc.
• Telitoquia: type of partenogenesis in which the progenie is feminine. Case of parasiticism Apis mellifera capensis on Apis mellifera scutellata, or other groups such as a few inches or stick insects.
• Anfitoquia o deuterotoquia: type of partogenesis by which the offspring is constituted by individuals of both sexes. It occurs in some Coccoidea, Aphididae and Cladocera among other groups.

Parthenogenesis in rotifers

Matthew Meselson received the 2004 Lasker Prize. He and his students are investigating why sex is necessary for evolution. Some small aquatic animals, bdelloid rotifers, are parthenogenetic and have survived for millions of years without sex. They serve as an experimental model system. Meselson assumes that the advantage of sex may lie in its ability to reduce what he calls the "genetic parasites" (the transferable items). These are the pieces of DNA that multiply themselves and can cause genetic damage. Bdelloid rotifers do not appear to have such parasites.

Parthenogenesis in snails

Some species of parthenogenetic gastropods have been studied, especially regarding their status as invasive species. Some species including Potamopyrgus antipodarum, Melanoides tuberculata, and Tarebia granifera.

Parthenogenesis in insects

Pulgons are reproduced partenogenetically when the conditions are favorable.

Examples of parthenogenesis are those that occur in many insects, mainly in Hymenoptera, such as ants and bees, and also in other orders, such as the Phasmatodea, where there are even known species that only reproduce parthenogenetically, as occurs with the odonato Ishnura hastata. In Hymenoptera the egg develops whether or not it has been fertilized. If it develops parthenogenetically, it gives birth exclusively to haploid individuals that are then male; if it is fertilized, females (diploid) are born. (The females of social insects, such as the bee, depending on the food the larva receives, can become workers or queens).

In other species, parthenogenetic reproduction occurs under the influence of external conditions. For example, aphids, plant parasites, reproduce parthenogenetically when conditions are favorable and there is abundant food. Otherwise, such as in late summer and fall, they produce sexually reproducing males and females.

In some insects, parthenogenesis is frequently related to the reduction or complete atrophy of the wings, so that their ability to move is little or absent. Winglessness is a disadvantage for sexually reproducing insects, as they must travel to meet the opposite sex, but is not a problem for parthenogenetic species. The correlation between parthenogenesis and winglessness is observed in many insects. of parasitic life, such as lice and fleas, and in some free-living species that inhabit environments where the energy cost of flight is high, for example, weevils that inhabit deserts, oceanic coasts, or high mountain areas. In environments with greater biotic complexity, such as forests and jungles, there is a lower proportion of wingless insects and parthenogenesis is less frequent.

Another feature often associated with parthenogenesis is polyploidy (an increase in an organism's complete set of chromosomes). Since polyploid females produce non-viable gametes, since meiosis gives rise to an irregular number of chromosomes in each cell nucleus, parthenogenesis becomes the only way to escape sterility.

A superiority of parthenogenetic insects has been suggested to colonize environments with harsh climates or with a high degree of disturbance, since they would be better adapted than the sexual forms to face adverse conditions outside their original distribution area. For this reason, many phytophagous insects that reproduce by parthenogenesis, such as certain species of weevils (Coleoptera: Curculionidae) are detrimental to crops established in marginal areas. In such environments, parthenogenetic females often act as opportunists and become pests.

Parthenogenesis in fish

Some rare species of tropical fish can alternate sexual reproduction with parthenogenesis, usually parthenogenesis occurs when males are scarce, this has been observed in at least two species of sharks, the hammerhead shark (Sphyrna mokarran) and the zebra shark (Stegostoma fasciatum).

Parthenogenesis in amphibians and reptiles

The parthenogenesis of these groups is different from that of insects, there are always populations of females that reproduce without the need to be fertilized by males. It is a process of asexual reproduction. We would be in the presence of genetic clones, which would not have the possibility of genetic variation achieved in sexual reproduction, therefore they should be unable to adapt genetically to environmental changes except for the effect of mutations.

The status of these "species" It is possible that they have phases of sexual reproduction at some historical moment, while in another they reproduce by parthenogenesis. This alternation is common in aphids and some other arthropods, such as water fleas and recently the dust mite (Crotoniidae). the formation of the ovules by the queen, but by the plurality of males (polygamy), even though each one of them, haploid, is limited to producing genetically identical spermatozoa.

In reptiles and amphibians, the color patterns and mimetic drawings are similar for all individuals of the clone.

Some authors have outlined hypotheses about the advantage that these "species" parthenogenetic in very stable environments, which would be worth as an explanation for the biological evolution of these species, which we will call fixists, due to their scarce flexibility in the face of the process of natural selection.

Parthenogenesis occurs quite frequently in some gecko species such as Heteronotia binoei; Cases of parthenogenesis are known in snakes such as Ramphotyphlops braminus. Exceptionally in monitor lizards such as the Varanus komodoensis.

Parthenogenesis in birds

Of current birds, cases of parthenogenesis have been recorded in specimens of Meleagris gallopavo, Gallus gallus and some species of quail. 2 cases of California condors were recently discovered.

Parthenogenesis in Mammals

In 1936 Gregory Goodwin Pincus reported that he had successfully induced parthenogenesis in a rabbit. In April 2004, scientists at the Tokyo University of Agriculture used parthenogenesis to create a fatherless mouse. Using gene targeting, they were able to manipulate two H19/IGF2 and DLK1/MEG3 loci to produce a bimaternal mouse and subsequently show that fatherless mice had greater longevity.

Induced parthenogenesis in mice and monkeys often results in abnormal development. This is because mammals possess regions of genetic imprinting, where either the maternal or paternal chromosome is inactivated in the progeny for development to proceed normally. A mammal created by parthenogenesis would have twice the dose of maternally imprinted genes, and lack the paternally imprinted, leading to developmental abnormalities. It has been suggested in the folding of the placenta or in the interdigestion, which are some of the causes of the abortive development of porcine parthenotes. As a consequence, research in human parthenogenesis focuses on the production of stem cells for use in medical treatments, and not as a reproductive strategy.

Causes of parthenogenesis

Determining how parthenogenesis appeared in living things is challenging, but scientific research is slowly unraveling this mystery. A causative agent of parthenogenesis is a bacterium belonging to the order Rickettsiales called Wolbachia that induces the endogenesis of arthropods and nematodes; It is speculated that this bacterium entered the DNA (deoxyribonucleic acid) of these animals, mitigating it. Species that carry Wolbachia, such as Apis mellifera, owe this bacterium the ability to develop unfertilized eggs.

The aporisma is a reproductive process comparable to an endogenesis that occurs in some plants.