Phylogenetic tree - Wikipedia
Cladograms are tree diagrams that show the most probable sequence of divergence Cladograms can show evolutionary relationships and demonstrate how. This same idea of relationships can be used in science. Biologists use cladograms and phylogenetic trees to illustrate relationships among. U5 Cladograms are tree diagrams that show the most probable sequence of Analyze a cladogram to explain the evolutionary relationship between species.
The bird and bat wings are homologous structures. However, the honey bee wing has a different structure it is made of a chitinous exoskeleton, not a boney endoskeleton and embryonic origin. The bee and bird or bat wing types illustrate an analogy—similar structures that do not share an evolutionary history.
New analysis of molecular characters not only confirms many earlier classifications, but also uncovers previously made errors. Molecular characters can include differences in the amino-acid sequence of a protein, differences in the individual nucleotide sequence of a gene, or differences in the arrangements of genes.
Phylogenies based on molecular characters assume that the more similar the sequences are in two organisms, the more closely related they are. Different genes change evolutionarily at different rates and this affects the level at which they are useful at identifying relationships. Rapidly evolving sequences are useful for determining the relationships among closely related species. More slowly evolving sequences are useful for determining the relationships between distantly related species.
To determine the relationships between very different species such as Eukarya and Archaea, the genes used must be very ancient, slowly evolving genes that are present in both groups, such as the genes for ribosomal RNA. Comparing phylogenetic trees using different sequences and finding them similar helps to build confidence in the inferred relationships.
Sometimes two segments of DNA in distantly related organisms randomly share a high percentage of bases in the same locations, causing these organisms to appear closely related when they are not. For example, the fruit fly shares 60 percent of its DNA with humans. Why Does Phylogeny Matter? In addition to enhancing our understanding of the evolutionary history of species, our own included, phylogenetic analysis has numerous practical applications.
Two of those applications include understanding the evolution and transmission of disease and making decisions about conservation efforts. The study uncovered the timing and patterns in which the resistant strain moved from its point of origin in Europe to centers of infection and evolution in South America, Asia, North America, and Australasia. The study suggested that introductions of the bacteria to new populations occurred very few times, perhaps only once, and then spread from that limited number of individuals.
This is in contrast to the possibility that many individuals had carried the bacteria from one place to another. This result suggests that public health officials should concentrate on quickly identifying the contacts of individuals infected with a new strain of bacteria to control its spread. A second area of usefulness for phylogenetic analysis is in conservation. Biologists have argued that it is important to protect species throughout a phylogenetic tree rather than just those from one branch of the tree.
Doing this will preserve more of the variation produced by evolution. For example, conservation efforts should focus on a single species without sister species rather than another species that has a cluster of close sister species that recently evolved. If the single evolutionarily distinct species goes extinct a disproportionate amount of variation from the tree will be lost compared to one species in the cluster of closely related species.
The study found that their recommendations differed from priorities based on simply the level of extinction threat to the species. The study recommended protecting some threatened and valued large mammals such as the orangutans, the giant and lesser pandas, and the African and Asian elephants. But they also found that some much lesser known species should be protected based on how evolutionary distinct they are. These include a number of rodents, bats, shrews and hedgehogs.
In addition there are some critically endangered species that did not rate as very important in evolutionary distinctiveness including species of deer mice and gerbils. While many criteria affect conservation decisions, preserving phylogenetic diversity provides an objective way to protect the full range of diversity generated by evolution. Building Phylogenetic Trees How do scientists construct phylogenetic trees?
- Phylogenetic trees
For example, in Figure Clades must include the ancestral species and all of the descendants from a branch point. Thus, lizards, rabbits, and humans all belong to the clade Amniota.
Cladogram - Wikipedia
Vertebrata is a larger clade that also includes fish and lamprey. Which animals in this figure belong to a clade that includes animals with hair? Clades can vary in size depending on which branch point is being referenced. The important factor is that all of the organisms in the clade or monophyletic group stem from a single point on the tree. Shared Characteristics Cladistics rests on three assumptions.
The first is that living things are related by descent from a common ancestor, which is a general assumption of evolution.
12.2: Determining Evolutionary Relationships
The second is that speciation occurs by splits of one species into two, never more than two at a time, and essentially at one point in time. This is somewhat controversial, but is acceptable to most biologists as a simplification. The third assumption is that traits change enough over time to be considered to be in a different state.
It is also assumed that one can identify the actual direction of change for a state.
In other words, we assume that an amniotic egg is a later character state than non-amniotic eggs. This is called the polarity of the character change. We know this by reference to a group outside the clade: Cladistics compares ingroups and outgroups.
An ingroup lizard, rabbit and human in our example is the group of taxa being analyzed. DNA is the preferred method, as it is incredibly accurate.
However, before the days of DNA, scientists created accurate cladograms using a variety of other traits. While the evolutionary relationships between organisms cannot be determined on any one trait, combining the parsimonious results of many different traits will lead to the most probably phylogeny. The cladogram that describes this phylogeny will likely be the most simple and have the fewest nodes.
Examples of Cladogram Primates In the above cladogram of Primates, the various groups of primates being compared are listed on the top. 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 down to the lowest ape are considered a clade, or group of organisms with similar characters due to common 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 rest of the primates would be considered the ingroup.
These terms are simply used to describe different groups when discussing them in scientific writing. Whales and Related Animals Below is a much more 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 represent living species, while narrow lines represent 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 top 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.
However, these fossils have started to close the gap between hippos and cetaceans, forming a series of small steps. Near the top of the diagram, the number of evolutionary changes jumps from 1 or 2 to 9 or 10 in each step.
This represents an evolutionary gap that is still not understood. The ancestral forms of whales and dolphins presented on this cladogram would have been shallow-water animals, as seen by their functional limbs. As the ancestors of whales moved further out to sea, it becomes less and less likely that their fossilized remains will 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 large toes. In addition, the Ferae have specialized carnivorous teeth. The rest of the groups become 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 hard group to hypothesize about, due to the lack of fossil evidence and the vast physiological difference between 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 effect.
Luckily for systematics, new methods of DNA analysis allow scientist to compare DNA directly, leading to a better understanding of how organisms are related and how changes happen between populations. Interpreting Cladograms In the following cladograms, it appears as 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 simply a trick of presentation, but represents no meaning in terms of relatedness.
These two cladograms do, in fact, represent a single phylogeny. When creating or reading cladogram, it is important to remember that the only important features of the cladogram are the lines and the nodes. In these two cladograms, the lengths of the lines are roughly the same 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 us that A and B are more closely related than C is to either group. The order of A and B, as well as the orientation of the lines, does not matter. A cladogram may be drawn left to right, right to left, top to bottom, or bottom to top. Some large cladograms are even fashioned in a circle to include all the groups they represent. In some cladograms, evolutionary time in millions of years is represented to give an approximation from the lengths of the lines.
Related Biology Terms Phylogeny — A hypothetical relationship between organisms, represented by a cladogram. Symplesiomorphy — A characteristic that all organisms on a cladogram possess. Synapomorphy — A characteristic that only a specific group, descended from a common ancestor, possess. Homoplasy — A shared character that is shared through convergent evolutionnot common decent. In the following cladogram, which groups are most closely related?
Beetles and Ants C. Moths and Flies Answer to Question 1 C is correct. Of these choices, moths and flies are the most related organisms according to this cladogram.