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Ch. 25 - Phylogenies and the History of Life
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoFreeman 8th EditionCh. 25 - Phylogenies and the History of LifeProblema 5
Capitolo 25, Problema 5

What important assumption does parsimony make when assessing which phylogenetic tree is most accurate? Why was parsimony misleading in the case of the astragalus during the evolution of artiodactyls?

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Parsimony assumes that the phylogenetic tree that requires the fewest evolutionary changes is the most likely to be accurate. This principle is based on the idea that simpler explanations, requiring fewer changes, are preferable.
The assumption of parsimony can be misleading if convergent evolution or evolutionary reversals occur. These phenomena can lead to similar traits evolving independently in different lineages, which can be misinterpreted as shared ancestry.
In the case of the astragalus bone during the evolution of artiodactyls, parsimony was misleading because it failed to account for convergent evolution. The astragalus bone evolved similar morphological traits in different groups of artiodactyls independently.
The misleading result from using parsimony in this case led to incorrect assumptions about the relationships between different artiodactyl groups. It suggested a closer relationship between groups that independently evolved similar astragalus traits, rather than their true evolutionary relationships.
To avoid such issues, other methods like maximum likelihood or Bayesian inference, which consider the probability of evolutionary changes and can incorporate more complex models of evolution, are often used alongside or instead of parsimony.

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Parsimony Principle

The parsimony principle in phylogenetics assumes that the simplest explanation, or the tree with the least number of evolutionary changes, is the most likely to be correct. This approach minimizes the complexity of evolutionary pathways by favoring trees that require fewer character state changes, thus providing a straightforward method for inferring relationships among species.
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Parsimony

Phylogenetic Trees

Phylogenetic trees are graphical representations that depict the evolutionary relationships among various biological species based on their genetic or phenotypic characteristics. These trees illustrate how species diverged from common ancestors over time, allowing researchers to visualize and analyze evolutionary history and lineage.
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Building Phylogenetic Trees Example 2

Convergent Evolution

Convergent evolution occurs when unrelated species evolve similar traits or adaptations in response to similar environmental pressures, rather than from a common ancestor. This phenomenon can mislead phylogenetic analyses, such as in the case of the astragalus in artiodactyls, where similar adaptations may be incorrectly interpreted as evidence of close evolutionary relationships.
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Convergent and Divergent Evolution
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Which of the following best characterizes an adaptive radiation?

a. Descendant species occupy a large geographic area.

b. A single lineage diversifies rapidly, and descendant species occupy many habitats and ecological roles.

c. Natural selection is particularly intense, because disruptive selection occurs.

d. Species recover after a mass extinction.

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Use the fossil evidence shown in Figure 25.6 to determine whether flight evolved earlier in insects or in birds. Is flight an example of homology or convergent evolution? Explain.

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Which of the following is an example of homoplasy?

a. Hair in humans and fur in mice

b. Astragalus ankle bones in hippos and deer

c. Hox genes in humans and flies

d. Streamlined bodies in dolphins and ichthyosaurs

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Critique the following statement: The absence of a trait cannot be used as a synapomorphy in phylogenetic analysis; only shared derived traits that are present in the clade can be used.

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You can use a 'one-snip test' to identify monophyletic groups—meaning that if you 'cut' any branch on a tree, everything that 'falls off' is a monophyletic group. Why is this valid?

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