Problem 6 - Campbell Biology

Question

EVOLUTION CONNECTION The fungus-alga symbiosis that makes up a lichen is thought to have evolved multiple times independently in different fungal groups. However, lichens fall into three well-defined growth forms. However, lichens How could you test the following hypotheses? Hypothesis \(1 :\) Crustose, foliose, and fruticose lichens each represent a monophyletic group. Hypothesis \(2 :\) Each lichen growth form represents convergent evolution by taxonomically diverse fungi.

Step-by-Step Solution

Answer

Construct phylogenetic trees from DNA sequences to see if each lichen growth form is monophyletic, supporting Hypothesis 1, or if there's evidence of convergent evolution, supporting Hypothesis 2.

Step 1 - Collect Samples of Lichens

Gather ample samples of crustose, foliose, and fruticose lichens across various geographic locations to ensure a diverse range.

Step 2 - Extract DNA

Extract the DNA from the fungal component of each lichen sample. This step is essential for subsequent genetic analysis.

Step 3 - Sequence the DNA

Perform DNA sequencing on the extracted DNA to obtain genetic information about the fungi involved in the lichens.

Step 4 - Construct Phylogenetic Trees

Using the DNA sequence data, construct phylogenetic trees to visualize the evolutionary relationships between the fungi in the different lichen growth forms.

Step 5 - Analyze Phylogenetic Relationships

Examine the phylogenetic trees to determine if crustose, foliose, and fruticose lichens each form their own monophyletic clades (common ancestor and all its descendants). This will help test Hypothesis 1.

Step 6 - Look for Evidence of Convergent Evolution

If fungi from different taxonomic groups are found within the same lichen growth form but do not form monophyletic clades, this would support Hypothesis 2 by suggesting convergent evolution.

Step 7 - Comparative Morphological Analysis

As a supplementary analysis, compare the morphological traits of the lichens to see if similar forms have evolved independently. This can add further evidence for Hypothesis 2.

Key Concepts

fungus-alga symbiosis

Lichens are interesting organisms made up of a symbiotic relationship between a fungus and an alga (or sometimes a cyanobacterium). In this partnership, the fungus provides the structure and protection, while the alga performs photosynthesis to produce food. This mutualistic relationship allows lichens to survive in various extreme environments, such as deserts and tundras.

monophyletic group

A monophyletic group, also known as a clade, consists of an ancestor and all its descendants. To determine if crustose, foliose, and fruticose lichens are monophyletic, scientists would need to create phylogenetic trees using DNA sequence data. If each growth form forms its own clade, this would suggest that each type evolved from a common ancestor, supporting the hypothesis that they are monophyletic groups.

convergent evolution

Convergent evolution occurs when different species independently evolve similar traits. For lichens, this would mean that crustose, foliose, and fruticose forms evolved similar structures due to similar environmental pressures, not because they share a common ancestor. By examining the DNA sequences, scientists can determine if fungi from different taxonomic groups display similar growth forms, supporting the hypothesis of convergent evolution.

phylogenetic analysis

Phylogenetic analysis involves creating a 'family tree' that shows the evolutionary relationships between species. In the case of lichens, scientists extract DNA from fungal components of different lichen samples, sequence the DNA, and use this information to build phylogenetic trees. These trees help scientists see how closely related different species are and whether certain traits are inherited from a common ancestor or evolved independently.

DNA sequencing

DNA sequencing is the process of determining the exact sequence of nucleotides in a DNA molecule. For studying lichen evolution, scientists extract DNA from the lichens, sequence it to get genetic information, and analyze these sequences. This genetic data is used to construct phylogenetic trees, which help test various hypotheses about how different lichen forms evolved. DNA sequencing is crucial for understanding the genetic relationships and history of organisms.