California condors have been in danger of extinction for years. For three decades, scientists from the San Diego Zoo Wildlife Alliance have been conducting genetic studies to determine the relationship between chicks and their parents. The surprise came when they discovered that there were two individuals who were each the children of a female condor, but who were not genetically related to any male and, therefore, were biologically orphans of a father. To avoid possible errors, they repeated the genetic test on numerous occasions. The conclusion they reached is that these had been produced by parthenogenesis, a form of asexual reproduction. What is striking is that the mothers of these birds, which were in captivity, lived with males and had previously reproduced sexually. In this way, this discovery, published in Journal of Heredity, is the first case of parthenogenesis in condors and the first of any avian species where the female had access to a male.
Cynthia Steiner, associate director in the conservation genetics laboratory of the San Diego Zoo Wildlife Alliance and co-author of the study, defines parthenogenesis as “asexual reproduction in which females can produce chicks without the contribution of a male. The eggs are not fertilized by sperm. There is a duplication of the genetic material of the female and it is the one that will contribute to producing the chick ”. It is important to distinguish between obligate and facultative parthenogenesis. Obligate parthenogenesis occurs in many species, especially some lizards, in which the development of a new individual occurs exclusively without male contribution. The case of the Californian condors is optional, since they are females that normally reproduce sexually, but which, for reasons unknown to these scientists, on this occasion have been asexual. Jesús Gómez-Zurita, scientist at the Botanical Institute of Barcelona and who previously worked at the Institute of Evolutionary Biology, describes the birth of these individuals as “a biological error that should not happen” and adds that the genetics of the species itself has “mechanisms ”To prevent this from happening.
These two discovered birds, both male, were born in different places and years. SB260 was born at the San Diego Zoo in 2001 and SB517 was born at the Los Angeles Zoo in 2009. Both died at a young age, since the life expectancy of these large vultures in captivity is around 60 years, according to Steiner. The first of them died just before his second birthday, after being released into the wild and not adapting to it; He was of weak physical form, with a body shorter in stature and weight than his kind. SB517 lived to be nearly eight years old, after reaching sexual maturity. He was never released and the veterinarians who were in his charge describe that, in addition to being smaller, he had scoliosis and a more docile behavior, rare among males.
Their progenitors reproduced sexually with a pair of males before the birth of the parthenotes, a name that qualifies the individuals that are born by parthenogenesis. Specifically, the mother of SB260 had 11 chicks by sexual reproduction with the same male and that of SB517 had 23 chicks previously in the same way and then another two.
According to data from the end of 2019, the California condor has a population of 525 individuals, 219 of them in captivity and the rest in the wild. Although they remain in significant danger of extinction, they managed to overcome the bottleneck they went through in 1982 when they were low with only 22 birds. This was achieved by conserving genetic variation by mating low-related individuals. Since this program began in 1988, which has allowed the detection of these parthenotes, more than 1,000 chicks have hatched.
The dangers of parthenogenesis
Parthenogenesis has occurred in more than 80 different species, since it was discovered by Charles Bonnet in the mid-18th century. The conditions that are needed for this to occur are not entirely clear. Enrique Font is a professor at the University of Valencia, where he teaches the subject of herpetology, a branch whose animals are characteristic for this type of reproduction, and explains that forced parthenogenesis is associated with hybridization between a male and a female of different species and that in the result “there are alterations that make the female become parthenogenetic from that single mating and give rise to a clone. With this a species is established in which from that moment there are no more males ”. As for facultative parthenogenesis, which has been documented in four very diverse taxonomic groups such as birds, sharks, lizards and snakes, this scientist explains that it has been suggested that it may be due to an adaptive nature or, coinciding with Gómez-Zurita, by a “ aberration”.
This asexual reproduction process could be considered as an option to help the figures of the populations that are in danger of extinction, but it is very complex because it is a process that occurs naturally, according to these experts, and they do not consider it something feasible. Steiner suggests that it can be a mechanism to start new populations when they migrate to other areas. However, remember that parthenotes are characterized by having a very low genetic variability, since they are two exact copies of the mother’s genes: “It is not completely beneficial for a population that all individuals are produced by parthenogenesis because there is a decrease in genetic variability ”. This genetic variability allows us to have “a cushion of resistance” to be able to face these new changes in the environment. In addition, in some animals, parthenogenetic females only produce males, which would make it even more difficult for the species to spread, since they cannot reproduce alone.
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