Lab #5 : Trilobites Phylogenetic Tree by Josselin Chambily, Bishoy Galil, Lauryn Newan and Oluseyi Banjo
Blog Assignment #3
1. Post a picture of your tree.
Figure 1: Trilobites' Phylogenetic Tree
In order to realize this tree, we previously created a matrix according to each specie's characteristics. In the matrix, a 0 translates the lack of a the specific characteristic in the specie, a 0.5 means that the trait is somehow present and finally, a 1 represents the presence of the characteristic.
Figure 2: Matrix based on morphological characteristics.
We decided to choose the trilobite specie number #3, Peronopsis interstricta, as our outgroup. Thanks to the matrix, we can clearly see that species number #3, #5 and #18 stand out from the others by their lack of common traits. Therefore, we took away Trimerus dekayi and Trimerus dephinocephalus because Peronopsis interstricta was the most different-looking specie.
2. According to your tree, what is one basal or ancestral characteristic?
We can see that the circular cephalon is a great example of an ancestral characteristic. Indeed, every specie following its apparition on the tree present a circular cephalon.
One derived characteristic?
Complex globella or pleurons are derived characteristics because they evolved in their own branch of the tree, differentiating their respective species from the others.
3. According to your tree, is the rear ''spine'' of species 6 homologous or analogous to that of species 14?
The rear ''spine''; or the ''stinger'' as we called it; of Olenellus clarki is analogous to Dalamnites verrucosus' one. As we can see on the tree, each specie developed this trait on their own, away from the other specie. The presence of the stinger in both of these species can be a proof of convergent evolution.
4. Are there any traits that were lost but then evolved again independently?
Our tree doesn't show any evidence that a characteristic has been lost and developed again later in time. However, few cases of convergent evolution and analogous traits are noticeable. In fact, specie #11 (Albertella helena) and #6 (Olenellus clarki) both share the presence of long pleurons in the middle of their thorax, and specie number #19 (Odontopleura callicera) and the two sisters species #10 (Coronura aspecians) and #14 (Dalamnites verrucosus) all have a rhough textured exosqueleton.
5. Describe one important difference between your tree and another group's tree. Upon reflection, which tree seems better?
This tree comes from the group of Darsi, Tiger, Travis and Solace. We can notice that their tree always mentions which trait is responsible for the apparition the new branches while ours doesn't. For example, our tree misses a derived characteristic when species numbers #16, #1, #4, #7 and #13 separate themselves from the ancestral branch. This error makes our tree less accurate than theirs. However, the accumulation of new traits in their tree tends to create polyphyletic groups while you are supposed to avoid them with phylogenies. Even if their tree seems to be more logical when you follow branches, we believe that ours is better because it respects the phylogeny rule to not create polyphyletic groups.
Hey, great post! I am really surprised by the outcome of your groups tree. We did have similarities like the outgroup, the final group that broke off and 5 &18 and 10 & 14 being a sister taxa. I am surprised that your group also had a spine on the rear as an analogous trait because after doing the questions I felt that numbers 6 and 14 were suppose to be a sister taxa. The difference between our two trees really show that these trees are only hypothesis because besides mainly the outgroup and the final trilobite 16 the trees were really different. I think the only way be can possibly get closer to the real tree, which is unknown, is that we farther study the level of importance of each trait so we know which ones to focus more on.
ReplyDeleteI like how you follow the parsimony to construct your tree. It is hard, especially when you don't know which trait is more important or which trait shows up first. Great post!
ReplyDeleteHey great job guys this post is really nice and detailed. One thing I noticed is that you guys chose a lot of traits for your matrix! My group chose four or five while you guys had eight traits! Kudos to you guys for sorting through all these traits and even specifying between a full presence and a half presence. I wonder if that made the process a lot more complicated for you guys. I also wonder if that created a more accurate tree. Anyways, great work.
ReplyDeleteI really like the way your group organized your tree! It clearly shows species that are very closely related by grouping them in separated sister taxa. I found the way you recorded data interesting; how did you determine whether a trait was somewhat present vs present? I think this way of recording data could be beneficial when putting together a phylogenetic tree because it could be the deciding factor of which species are most closely related, especially in a large group of samples. I may just have to use this technique the next time I am making a phylogenetic tree, so thank you for the idea! Awesome job!
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