Have you ever heard about such a beasts as a liger? Mule? Hinny? Or even a Grolar bear?
Do not worry they are not fictional characters from eight Harry Potter movie. These animals are the result of mating between different species of animals and they are called hybrids.
Should we be concerned about this kind of perversion in the animal kingdom? What are consequences of inter-species breeding?
There is no unambiguous answer to these questions. On a bright side hybridization lead to a wonderful event – speciation (rise of new species). On the other hand it can cause loss of native genetic diversity as well as a unique species or population features. Hybridization can prevent some species from extinction if they original genes are unadaptable and useless in a changing environment. On the contrary it can become the reason of occurrence of dangerous and basically indestructible hybrids. In this article I will introduce you with examples of hybridization as well as consequences of the appearance of hybrids in natural ecosystems.
Firstly we should find out what hybridization is?
Naturally individuals of different species do not breed with each other. Mechanisms which prevents species from interspecific breeding is called hybridization barriers. There are different types of these barriers however all of them prevent species from producing viable offspring. Hybridization barriers can be pre-zygotic (it means they occurs before the fertilization) and post-zygotic (it occurs after the zygote is formed).
Pre-zygotic barriers include: temporal isolation (species are ready to breed at different seasons), habitat isolation (they do not live in same habitat), behavioral isolation (they behavior is so different that they do not get when other species is ready to reproduce), mechanical isolation (even when there is an attraction genitals are just incompatible) and gametic isolation (egg and sperm do not recognize each other as a result there is no formation of zygote). Post-zygotic hybridization barriers are quite messy: zygotic mortality (even if the egg is conceived zygote is nor viable), hybrid unviability (offspring can die in each stage of development) or sterility (hybrids are infertile).
However sometimes these barriers do not work at all and breeding between different species leads to viable and fertile offspring. This mechanism is called hybridization.
Hybrids? What’s next?
Usually individuals of different species do not show any preference to breed with individuals of another species. However sometimes it occurs especially if choice of partners in original population is poor or species cannot control movement of their gametes.
In most cases even hybrids tend to mate with one of the species they originated from. As a result a phenomena called introgressive hybridization happens: some genes from one species moves to another species gene pool by the repeated backcrossing of interspecific hybrid with one of its parents. That is a result how we got some genes from noble extinct species of Homo neanderthalensis.
However sometimes features of hybrids are so superior that it can lead to rise of completely new species such as coywolves or grolar bears (grizzly and polar bear hybrids) which are not only superior predators and a threat for North America ecosystems but also a threat for humans (polar bears do not fear humans at all as well as grolar bears).
In some cases it can prevent species which are lacking genetic diversity and adaptable features from extinction. For example California tiger salamander is nearly extinct amphibian species which interbreed with other salamander species. As a result only 8% of California tiger salamanders found are not hybrids with other species. So there is basically no individuals of original species left. However populations of salamanders had increased so some of the genes survived to other generation and their ecological role is protected.
To sum up we need to remember that hybridization naturally occurs in the nature in some cases even though it is prevented by variety of barriers. Occurrence of hybrids can lead to rise of new species, prevent species from extinction or genetic depression. However, hybrids can overwhelm original species and lead to the extinction of them as well as become superior and threaten ecosystems or even humans. Despite what kind of hybrids appear it is always interesting to see how they look.
It would be interesting to read what kind of hybrids you are familiar with. What do you think about the occurrence of them? Is it beneficial or harmful for nature? Please share your thoughts in the comments.