by Piter Kehoma Boll
Hybrids, as you probably know, are organisms that arise from the mating of two individuals of different species. A mule, for example, is a well known hybrid between a horse and a donkey. Hybrids are usually sterile, although not all of them are, and some of them have a very peculiar way to continue to exist by using a process called hybridogenesis.
Hybrids that rely on hybridogenesis function in the following way: there are two original species, let’s call them A and B. When they copulate with each other, they produce a hybrid offspring, AB, which has half of the genes from one parent and half from the other. In “normal” hybrids, such creatures are completely sterile, unable to produce viable gametes, or can give rise to a new hybrid species by producing mixed gametes. However, in this peculiar kind of hybrids, called kleptons, things work differently.
Pelophylax kl. hispanicus, the holder of a treasure. Photo by Andreas Thomsen.*
When kleptons are producing gametes, they never recombine the genomes of the two parents, but rather exclude the genome of one of them and produce gametes that contain the genome of the other parent. For example, the hybrid AB produces only A gametes, while the B genome is excluded. This means that if AB mates with a partner of the species A, the offspring will be formed by pure A individuals. If mating with B, the offspring will contain only new AB hybrids.
The edible frog Pelophylax kl. esculentus is a klepton formed by breeding P. lessonae and P. ridibundus. The klepton only produces gametes of P. ridibundus, eliminating the genome of P. lessonae during meiosis. (Photo by Wikimedia user Darekk2).**
This mode of reproduction is very common in frogs of the genus Pelophylax, as the example seen in the picture above. Another interesting point about kleptons is that they are usually unable to mate with another klepton. They rely one the parent species to reproduce, therefore “parasitizing” them.
A recently published paper on Pelophylax frogs reports a peculiar case in which one of the parent species is extinct. The klepton, known as Pelophylax kl. hispanicus, is the result of P. bergeri crossing with a now extinct species of Pelophylax. The case is that the gametes that P. kl. hispanicus produce are of the extinct species, but they can only fertilize gametes of P. bergeri. In other words, we could say that the extinct species is still alive inside the klepton, relying on P. bergeri to pass to the next generations.
Pelophylax kl. hispanicus is a klepton that maintains the genome of an extinct species alive. Image extracted from Dubey & Dufresnes (2017).**
The authors suggest that perhaps we could find a way to bring the extinct species back, separated from P. bergeri. Although the result of crossing two P. kl. hispanicus is an sterile offspring, they think that continuous trials may end up revealing an eventual fertile offspring. Is it worth trying? Perhaps. But anyway, this is one more astonishing feature of nature, don’t you agree?
How many more extinct species may be living in a similar way, trapped in a hybrid?
– – –
Like us on Facebook!
– – –
Wikipedia. Hybridogenesis in water frogs. Available at <https://en.wikipedia.org/wiki/Hybridogenesis_in_water_frogs>. Access on October 12, 2017.
Dubey, S.; Dufresnes, C. (2017) An extinct vertebrate preserved by its living hybridogenetic descendant. Scientific Reports 7: 12768. https://dx.doi.org/10.1038/s41598-017-12942-y
– – –
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
This work is licensed under a Creative Commons Attribution 4.0 International License.