Self-study
P1
A lichen consists of a fungus living in symbiosis (i.e., a mutually beneficial relationship) with an alga. ████████ ████ ████████ ██ ███ ███████ ████████████ ██████ ████ ██ █████ ████ ████ ████ ████████████ ███ ████████████ ███████ ██ ██████████████ █████ ████ ████ █ ████████ ███
Intro topic / phenomenon ·
What's the evolutionary origin of lichen?
Lichen is a fungus living in a mutually beneficial relationship with an alga.
Hypothesis ·
New study shows lichen are close relatives of certain common fungi
That's why some lichen look like mushrooms.
P2
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Why lichen was hard to classify ·
Hard to study their DNA
Fungi are usually in a parasitic or symbiotic relationship with another organism. Hard to tell DNA apart. Lichen in particular are hard to isolate from their associated organism.
Old classification ·
Lichen were considered separate from other fungi with unknown origin
New classification ·
Some lichen belong to fungus family tree
New tools allowed us to isolate lichen-fungi DNA from their associated organisms. Researchers think we'll find that more types of lichen belong to additional branches of the fungus family tree.
P3
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Implication ·
Provides evidence that parasitic interactions don't always evolve over time to help host organisms
Fungi that are both harmful and helpful to the host organism are found throughout fungus evolutionary history. We know this because lichen, which are beneficial to their host organism, are found in different positions throughout the family tree. (So there's some kind of back and forth harmful-to-host, helpful-to-host, harmful-to-host development in the fungus family tree.)
Passage Style
Phenomenon-hypothesis (RC)
Single position
19.
Which one of the following, ██ █████ ████ ███████ ███ ████████ █████████ ██ ███ ██████████ ████ █████████ ████████████ █████████ ██████ ██████ ██████████
a
Evolutionary theorists now █████████ ████ █████████ ████████████ █████████ ██████ ██████ ███████ ███████████ ██████ ████ ████ ██████
If anything, this supports the author’s criticism. The author believes parasitic relationships do not inevitably evolve toward symbiosis. So if symbiotic relationships evolve toward parasitism, that helps the author’s view.
b
The evolutionary tree ██ █████ ██ ████████ ████ ███████ ████ ████ ██ █████████ █████████ ██ █████████ ██████████
Greater complexity doesn’t have any clear impact on what we can glean from fungus evolutionary history. Does the greater complexity suggest symbiotic fungi do not evolve toward parasitism? We don’t know.
c
The DNA of █████ ████████ ██ █████████ ████████████ ██ ███ ████ █████████ ██ ███████ ████ ████ ██ █████ ████████ ██ █████████ █████████████
We’ve already dealt with the isolation problem. DNA research figured out the evolutionary origin of lichen-forming fungi. Whether one kind of fungi is more or less difficult to isolate from its host than another doesn’t provide evidence for or against the view that parasitic relationships evolve toward symbiotic ones.
d
The placement of ██████████████ █████ ██ █ ████████ █████ ██ ███ ██████ ██████ ████ ██████ ███ ████ ████ █████████ █████ █████████ ███████ ████ █████ ████ █████████ █████
We already know that there are examples of parasitic fungi later in evolutionary history than symbiotic ones. This is part of the author’s support. So it doesn’t weaken the author’s argument.
e
Branches of the ██████ ██████ ████ ████ ████ ███████ ████ █████████ ██ ██████████ ███████ ███ ███ ███████ ███████████
The symbiotic fungi that evolved to parasitism die out shortly after this evolution – this provides evidence that evolution toward parasitism isn’t viable in the long run. So, the view that the author is criticizing – that parasitic interactions evolve over time “eventually to symbiosis” can still be true, despite the existence of some instances of symbiotic fungi becoming parasitic. Those symbiotic-to-parasitic fungi die out. Only the parasitic-to-symbiotic continue.