Hybrid speciation and its relation to network structures
As a plant science major, I often find myself fascinated by evolution. It is the driving force of the incredible complexity that we see in the natural world around us. This complexity is due to the natural process of life filling every possible environmental niche possible. This pervasive process is known as speciation. However, the very definition of a species is inherently flawed, common knowledge suggests that two different organisms become independant species when they can longer create viable offspring with each other. However, this is false. There are many examples of separate species creating fertile hybrid offspring. One such case is with the species of the Nepenthes genus, the genus is comprised of more than 165 examples of what scientists consider unique species. Each type displays a unique floral and/or foliar morphology, lives in a unique ecosystem and is geographically isolated from the others. However, there is a catch, every species of Nepenthes is able to hybridize and create fertile offspring with every other species of Nepenthes. Technically, according to the official definition of a species, every single one of these 165 morphologically and geographically unique species is actually only one!
This process of hybridization between plant species is common in the wild and brings an entirely new factor in the evolutionary process that occurs when a new species evolves. The contemporary idea is that a new species is formed when some common ancestor splits into two markedly different organisms. However, the paper I have chosen for my blog shows that species can also be formed through the process of hybridization. If two species are genetically similar enough and geographically close enough, they can eventually merge into one entirely new species through hybridization. This concept seems bizarre and counterintuitive to the process of evolution, but it has been observed time and time again all over the world. This implication also suggests that the networks between species in a genus are actually much more complex and dynamic than we think. Speciation can easily be visualized as a simple network, with new “nodes” forming from the connections of a common ancestor. But the concept of hybrid speciation now shows that formerly two nodes can merge into one as well. In such a network, species that hybridize readily and are genetically similar have a strong connection, while those that do not hybridize readily or are not genetically similar have a weak connection. Those nodes that have a strong connection will have a tendency to merge together while the nodes with a weak tie will tend to drift further and further apart.
Such concepts are incredibly useful for scientists wanting to conduct population studies of a genus. One could also visualize each species as a graph, with independent specimens being nodes, doing so would allow a taxonomist to better visualize the occurrence of speciation or hybrid speciation in populations of two species. Speciation occurs when certain specimens start to breed in separate groups. As time goes on the divide becomes more apparent, until there are no common edges. Each species has its own network of specimens creating new nodes and edges among themselves but not ever sharing an edge with a specimen from the other species. This is analogous to the famous karate club story which represents the division of a network, with the people in a karate club due to a difference in philosophical viewpoints. Hybrid speciation is the complete opposite, it begins with two isolated species populations, or networks, that suddenly hybridize, or a form a bridge, due to some environmental circumstance. As time goes on more nodes and edges are formed between the two networks until they fully merge into one new network.
In summary, evolutionary biologists and taxonomists rely heavily on networks to visualize population dynamics and the movement of evolution. Hybrid speciation is one aspect that is incredibly important in structuring these networks because it implies that such networks can be much more complex and dynamic than when you just take conventional speciation into account.
Source:
http://faculty.fortlewis.edu/mccauley_r/quercus_seminar/Hybrid%20speciation%20review%20paper.pdf