Photo credit: arstechnica.com
Hybrid animals and plants, once regarded as unusual occurrences in nature with limited evolutionary consequences, are now understood to play a significant role in species formation. Contrary to earlier beliefs, hybridization is a prevalent phenomenon, with around 25 percent of plant species and approximately 10 percent of animal species exhibiting inter-species mating.
Jeremie Fant, a conservation scientist at the Chicago Botanic Garden, highlights the evolutionary significance of hybridization, noting that while these events may seem rare on the surface, they have been integral to evolutionary history. In the realm of plants, for instance, hybrids are commonly found across various lineages, and their emergence can lead to important evolutionary shifts.
Usually, the crossing of two distinct species results in evolutionary dead ends. This can occur when hybrids are infertile or when they are absorbed back into one of the parent species’ populations, resulting in only a few genetic traces remaining. However, there are exceptional cases where hybridization can lead to the development of new populations with unique evolutionary trajectories.
When two closely related species coexist in overlapping geographical areas, they may create what are termed “hybrid zones.” These zones are often observed at the interfaces of differing ecosystems, where a plant species adapted to one soil type may interbreed with a related species suited to another type. The offspring may thrive in intermediate environments, showcasing traits from both parent species.
These hybrid zones can exhibit stability over time, demonstrating minimal genetic interchange with the parent populations. The genes beneficial to organisms within the hybrid zone may not confer advantages to those outside it, limiting their spread.
In some cases, hybridization escalates beyond a simple zone to form what is known as a “hybrid swarm.” This concept first appeared in a 1926 Nature article discussing the flora of New Zealand.
Defining a hybrid swarm can be complex, as even the term “species” is subject to debate within the biological community. Generally, a species is characterized as a group of organisms capable of interbreeding, but this definition can be problematic. For instance, lions and tigers are distinct species yet can mate and produce ligers.
Consequently, the definition of a hybrid swarm is flexible, encompassing scenarios where distinct populations of two or more species merge, or even when subspecies or regional variations intermingle. Essentially, it refers to the processes by which genetically different populations interact, breed, and form new groups, combining genetic material from all involved parent species.
Hybrid swarms often display a varied mixture of genetic and physical traits, reflecting characteristics that fall between those of the parent species. Notably, hybridization can be directional, where initial hybrids can generate offspring by backcrossing with one parent species, potentially leading to better-adapted combinations for shared environments.
However, unlike hybrids found in stable hybrid zones, swarms are inherently unstable. They may either dissipate or flourish to the extent that they outcompete their parent species, sometimes leading to the extinction of those original populations. The formation of successful hybrid swarms is still considered uncommon.
“In many instances, hybrid swarms are not established,” Taylor explained. “While hybrids arise, they often fail to thrive in comparison to either parent species.” Nevertheless, in situations where hybrid swarms do take hold, they can exert significant ecological influence.
Source
arstechnica.com