Explain Why Scientists Use Shared Characteristics to Make Cladograms

Cladogram Definition

A cladogram is a diagram used to represent a hypothetical relationship betwixt groups of animals, called a
phylogeny. A cladogram is used by a scientist studying
phylogenetic systematics
to visualize the groups of organisms beingness compared, how they are related, and their near common ancestors. A cladogram can be elementary, comparing only two or three groups of organisms, or it can be enormously circuitous and comprise all the known forms of life.

Cladogram design is universal, although unproblematic. A cladogram consists of the organisms existence studied, lines, and nodes where those lines cantankerous. The lines represent evolutionary fourth dimension, or a serial of organisms that pb to the population information technology connects to. Nodes represent common ancestors between species. At some signal in the past a population of mutual antecedent organisms was divided, giving rise to the different organisms existence studied. Some cladograms show evolutionary time through the calibration of the lines, longer lines significant more fourth dimension. Some cladograms chose to show extinct species, while others omit them. Any particular cladogram is formulated specifically for the use information technology is needed.

A cladogram gets its name from the
clades, or groups of organisms that are displayed. A clade is a grouping of living organisms and the common ancestor they are derived from. Scientist utilise
synapomophies, or shared derived characters, to define these groups. For example, mammary glands are a shared feature of mammals. All mammals and their oldest mutual antecedent, had or have mammary glands. Thus, if we are looking at an unidentified animal and trying to place information technology in a cladogram, if information technology has mammary glands we know it belongs in that branch.
Symplesiomorphies, by contrast, are characters that all organisms in the cladogram take. If the cladogram including the mammals was of all vertebrates, then the presence of vertebrae in our unknown brute would be a symplesiomorphy. Symplesiomorphies do non tell us anything about the relatedness of dissimilar groups in a cladogram, considering all the organisms take (or had), that feature. A very simple cladogram of the vertebrates tin be seen below.

Scientists use cladograms to propose and ask questions near the evolutionary relationships betwixt different species. Past giving weigh to derived characters and recognizing ancestral characteristics, scientists can compare different phylogenies of the same groups of organisms. Some will exist very complex, as characters will have to independently ascend in multiple lines. Others volition be simple, or
parsimonious, and volition contain fewer changes between groups. Any set of characters can be used to create a cladogram. DNA is the preferred method, as it is incredibly authentic. However, before the days of DNA, scientists created accurate cladograms using a diverseness of other traits. While the evolutionary relationships between organisms cannot exist determined on whatsoever 1 trait, combining the parsimonious results of many dissimilar traits will atomic number 82 to the most probably phylogeny. The cladogram that describes this phylogeny will likely be the most simple and accept the fewest nodes.

Examples of Cladogram

Primates

In the above cladogram of Primates, the various groups of primates being compared are listed on the peak. The various nodes on the diagram represent the various common ancestors between the groups. The Apes, the group containing humans, and all the common ancestors (nodes) downwardly to the lowest ape are considered a clade, or grouping of organisms with similar characters due to mutual descent. The clade could be extended to include everything except the Lemurs, Lorises, and the lowest node. If this were the case, the line leading to lemurs would be considered the
outgroup, while the remainder of the primates would exist considered the
ingroup. These terms are only used to describe different groups when discussing them in scientific writing.

Whales and Related Animals

Below is a much more than complicated cladogram of whales and the animals they are related to. Many more groups are represented, down to genus and species in some cases. In this cladogram, bold lines stand for living species, while narrow lines stand for extinct species from the fossil record. The numbers above each line represent the number of evolutionary changes that had to occur in that branch from the ancestral form.

Looking at the height box of
Cetaceamorpha, this branch represent
Cetaceans
(whales and dolphins) and their related ancestors. Until the discovery of the various fossils that bridge the gap between hippos and whales, the phylogeny of this tree was in question. Withal, these fossils have started to shut the gap between hippos and cetaceans, forming a series of small steps. Near the height of the diagram, the number of evolutionary changes jumps from 1 or 2 to 9 or 10 in each pace. This represents an evolutionary gap that is all the same not understood. The ancestral forms of whales and dolphins presented on this cladogram would take been shallow-h2o animals, as seen by their functional limbs. Every bit the ancestors of whales moved further out to sea, it becomes less and less probable that their fossilized remains volition be found.

Many characteristics were considered in the creation of this cladogram. For example, the outgroup Ferae is the only group that does not have some sort of hoof or big toes. In add-on, the Ferae have specialized cannibal teeth. The rest of the groups go distinguished on different derived characters, such as humps in the camels, the presence of a rumen in the Ruminantiaphorpha, and others. Whales are a particularly difficult grouping to hypothesize about, due to the lack of fossil evidence and the vast physiological divergence betwixt whales and their closest relatives. Without limbs, for instance, it is impossible to know that whale are related to animals with limbs unless some evidence is found to that consequence. Luckily for systematics, new methods of DNA analysis let scientist to compare Deoxyribonucleic acid direct, leading to a better agreement of how organisms are related and how changes happen between populations.

Interpreting Cladograms

In the post-obit cladograms, it appears equally if two different phylogenies are being presented. In the cladogram on the right, it appears that A is more closely related to C than in the cladogram on the left. This is only a play tricks of presentation, but represents no meaning in terms of relatedness. These two cladograms exercise, in fact, represent a single phylogeny.

When creating or reading cladogram, it is important to remember that the just of import features of the cladogram are the lines and the nodes. In these two cladograms, the lengths of the lines are roughly the aforementioned and more importantly, the nodes are in the same places. In both diagrams, A and B share a node that is further away from the origin of the line in the diagram. This tells united states that A and B are more closely related than C is to either group. The order of A and B, too equally the orientation of the lines, does non thing. A cladogram may exist drawn left to right, right to left, top to bottom, or lesser to top. Some large cladograms are fifty-fifty fashioned in a circle to include all the groups they represent. In some cladograms, evolutionary fourth dimension in millions of years is represented to give an approximation from the lengths of the lines.

• Phylogeny
  – A hypothetical relationship between organisms, represented by a cladogram.
• Symplesiomorphy
  – A characteristic that all organisms on a cladogram possess.
• Synapomorphy
  – A characteristic that but a specific group, descended from a common ancestor, possess.
• Homoplasy
  – A shared graphic symbol that is shared through convergent evolution, non mutual decent.

Quiz

1. In the post-obit cladogram, which groups are nearly closely related?



A.
Beetles and Ants
B.
Flies and Beetles
C.
Moths and Flies

2. You are making a cladogram of fruit. You have 4 fruits: a assistant, and orange, a red apple, and a light-green apple. On appearance alone, which of these is an outgroup, and which ii belong on the node furthest from the start of the diagram?

A.
Orangish; Banana and Red Apple
B.
Banana; Orange and Red Apple
C.
Banana; Red Apple tree and Green Apple tree

3. Look at the cladogram referenced in question #i. Which of the following characteristics is a symplesiomorphy of the cladogram?

A.
Wings
B.
A natural language to get together nectar
C.
Wings that fold under a difficult beat out