In phylogenetics, we use the terms monophyletic, polyphyletic, and paraphyletic. What do each of these terms mean? How might the concept of shared, derived traits fit with these terms?
I know what each of the terms mean. I am not sure about the second question.
In phylogenetics, the terms monophyletic, polyphyletic, and paraphyletic help us understand the relationships between different groups of organisms. Let's take a closer look at each term and how the concept of shared, derived traits fits with them:
1. Monophyletic: A monophyletic group, also known as a clade, consists of an ancestor and all of its descendants. In other words, it includes all the organisms that share a common ancestor. For example, if we consider the group of mammals, it would be monophyletic because it includes all mammals and only mammals. Shared, derived traits, also called synapomorphies, play a crucial role in defining monophyletic groups. These traits are characteristics that are shared by all members of a group and have originated in their most recent common ancestor.
2. Polyphyletic: A polyphyletic group consists of organisms that do not share a recent common ancestor. Instead, they have converged or evolved independently to exhibit similar traits. This means that the similarities between members of a polyphyletic group are not due to a shared evolutionary history. An example of a polyphyletic group would be the selection of flying animals, which includes birds, bats, and insects. Although they all possess the ability to fly, they evolved flight independently, and their common ancestor did not possess this trait.
3. Paraphyletic: A paraphyletic group comprises an ancestor and some, but not all, of its descendants. In other words, a paraphyletic group excludes certain descendants that have branched off from the common ancestor. This exclusion is typically based on the absence of a specific trait. For instance, if we consider the group of reptiles without including birds (which are descended from reptiles), it would be paraphyletic because it does not contain all descendants of the common reptile ancestor. In this case, the trait distinguishing birds from reptiles (the ability to fly) leads to the paraphyletic nature of the reptile group.
In summary, the concept of shared, derived traits is closely related to the terms monophyletic, polyphyletic, and paraphyletic. Shared, derived traits are used to define monophyletic groups, as these traits are inherited from a common ancestor. On the other hand, polyphyletic groups exhibit similar traits that have evolved independently, not being shared due to a common ancestor. Finally, paraphyletic groups arise when a specific trait leads to the exclusion of certain descendants from a common ancestor, resulting in an incomplete group.