A team of researchers in the U.K. has observed a female cichlid hybrid fish growing male reproductive organs, impregnating itself and bearing offspring. The strange process, called "selfing," is extremely rare in vertebrates, although it has been observed in other animals in past studies.
During their study, the team examined cichlid fish and, at one point, bred two different species of the fish. After the breeding, several offspring were birthed, one of which was a female that later developed male reproductive organs.
The selfing fish reproduced by mixing sperm and eggs in its mouth. In the case of this study, the hybrid released sperm into the water and then sucked it back into its mouth, where it led to the fertilization of eggs that were present. Shortly after this event, the fish gave birth to several offspring.
The strange process was not a onetime occurrence - the fish fertilized itself numerous times over the course of a year, giving birth to 42 offspring, both male and female, and was both the mother and father of all of them. All offspring showed no signs of unnatural physical characteristics and were able to reproduce normally, with none of them resorting to selfing.
The team noted, however, that the offspring suffered from inbreeding depression, which refers to minimal genetic diversity that can sometimes lead to birth defects and genetic abnormalities in future generations.
Selfing is believed to have evolved as a mechanism for allowing genetic diversity and is seen elsewhere in the animal kingdom. Some other species that participate in the process include mangrove killifish, although they engage in the process only in times when there are no potential mates available, making it an adaptation that evolved out of necessity.
The researchers of the current study believe that the selfing they observed in the cichlid female was the result of its parents having different sex-determining genes and is a behavior that is not likely to happen often in the species. However, they acknowledge that selfing has likely happened before in the species but simply went unreported.
The findings were published in the March 23 issue of the journal The Royal Society Open Science.
