Hello, welcome back to another week of Great White Shark topics. The previous blog focused on the fuel economy of sharks, their metabolic rates, and how it helps them adapt to their environment. This week we will be talking about phylogenetic trees and how the Great white shark fits into them. Phylogenetic trees are diagrams that represent evolutionary relationships amongst organisms. Today we will be looking at a few phylogenetic trees and discussing their relationships with the Great White Shark and the trait of focus for the tree. The first tree we will be analyzing is: 

 

Phylogenetic Tree 1 

From: de Bellard, Maria. (2016). Myelin in Cartilaginous Fish. Brain Research. 1641. 10.1016/j.brainres.2016.01.013.  https://www.researchgate.net/figure/Phylogeny-of-myelin-from-chondrichthyes-perspective-The-phylogenetic-tree-summarizes-the_fig4_290624062

 

This phylogenetic tree is first broken into two main categories, Gnathostomes, and Agnathans. Agnathans are jawless organisms while Gnathostomes are organisms with jaws. The two categories are further divided into Cyclostomes (Agnatha),  Chondrichthyans, Actinopterygians, and  Sarcopterygians, which are all Gnathostomes. If we look for sharks on the tree, we will see that they are under the category of Chondrichythians. The name Chondrichthyans means cartilaginous fish. Sharks are not the only members of the class Chondrichthyans, chimera, rays, and skates also fall under the same class. However sharks, skates and rays belong under Elasmobranches, while chimeras belong to the subclass Holoesteans. One of the differences between the subclasses is that Elasmobranches, do not have an operculum, gill covering, while Holeseans do, to be put simply. Both subclasses also have a different amount of gills and their embryonic development is different. 

Now that you have a bit of backstory to Class and subclasses, let’s focus on the intended topic of the phylogenetic tree. The tree talks about the evolution of myelin proteins. Myelin proteins help with lining the axons of nerves in order for propagated signals to travel faster and main the same strength of the original signal. Understanding how these proteins evolved in these classes can further help scientists understand the nervous systems in them and how their sensory systems work.

 

The second phylogenetic tree we will be looking at is: 

 

Phylogenetic Tree 2 

From: Nicholas J. Marra, Michael J. Stanhope, Nathaniel K. Jue, Minghui Wang, Qi Sun, Paulina Pavinski Bitar, Vincent P. Richards, Aleksey Komissarov, Mike Rayko, Sergey Kliver, Bryce J. Stanhope, Chuck Winkler, Stephen J. O’Brien, Agostinho Antunes, Salvador Jorgensen, Mahmood S. Shivji

This phylogenetic tree in comparison to the first phylogenetic tree focuses on elasmobranch adaptations that help with wound healing. For more context I will be adding the graph shown below:

 

 

Graph 1 

From: Nicholas J. Marra, Michael J. Stanhope, Nathaniel K. Jue, Minghui Wang, Qi Sun, Paulina Pavinski Bitar, Vincent P. Richards, Aleksey Komissarov, Mike Rayko, Sergey Kliver, Bryce J. Stanhope, Chuck Winkler, Stephen J. O’Brien, Agostinho Antunes, Salvador Jorgensen, Mahmood S. Shivji

Proceedings of the National Academy of Sciences Mar 2019, 116 (10) 4446-4455; DOI: 10.1073/pnas.1819778116. https://www.pnas.org/content/116/10/4446/tab-figures-data

 

 

Phylogeny tree 1 and Phylogeny tree 2 are different in the sense that tree 2 did not start from a broad class and work its way into subclasses, it more so shows different Elasmobranchii, while tree one shows the relationships all the way from jaws to how they have different embryonic development. Phylogenetic tree 2 is more finely focus on different Elasmobranchii as opposed to tree 1 which shows broad relationships between different classes and how they deviated in time. Looking at evolutionary changes in animals not only from a physical sense, but a molecular sense could potentially lead to even more understanding of these animals and maybe one day even greater scientific discovery that humans could use to adapt for our benefit.

 

Thank you once again for showing up and engaging with this weeks’ topic. Can you think of any other traits that phylogenetic trees, can and should focus on? Thank you for reading and see you on the next blog.