Download 06 ICA 6 Coevol-Mutualism rubric

ICA 6 COEVOLUTION/MUTUALISMS
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1. Pairwise interspecific interactions Which is: +/-, +/0, +/+, -/-, -/0 ?
Mutualism +/+
Herbivory +/Facilitation Commensalism +/0
Predation +/Amensalism
-/0
Parasitism +/Competition -/Disease +/2. Can the type of interaction change over evolutionary time? Yes Give an example.
A seed predator may become a seed disperser…so changes from +/- to +/+
3. What is coevolution? Traits of 2 or more species change in response to selection by
their mutual interactions controlled by those traits.
What must occur for a change in allele frequency in each species? Traits must have 1)
variation and 2) genetic basis. 3) Traits of each species must affect the fitness of
individuals of the other species (and vice versa).
Are all coevolutionary relationships mutualistic? No Explain. They can be mutualisit
or antagonistic (e.g. competitors or predator/prey interactions can cause coevolution).
4. What is the difference between strict = only 2 species interacting
and diffuse = multiple species interact to affect each other’s traits coevolution?
Which is more common? diffuse
5. Figure 4. In Batesian mimicry, is the model or mimic palatable? mimic
Which must be more common: model or mimic? model Why? predator must
have greater chance of encountering unpalatable model so that it learns to
avoid any organism with this color pattern, including the mimic.
6. Figure 5. How do Batesian and Mullerian mimicry differ? Batesian: one unpalatable
model and one palatable mimic; Mullerian: multiple species unpalatable
How many species are palatable? 0 unpalatable? all in Mullerian mimicry?
How does it deter predators? More species with same morphology/color increases
probability that predator encounters at least 1 prey; all species benefit from that
one species.
7. Use the interaction between a wheat rust (a fungus-causing disease) and wheat to
illustrate the steps involved in an ‘evolutionary arms race. What is the ‘gene-for-gene
concept? Include genes for resistance and virulence.
1. plant has gene for resistance; selection on fungus for matching gene for virulence.
2. fungus gains virulence; selection on plant for new gene for resistance.
3. plant regains resistance; selection on fungus for new gene for virulence.
4. fungus regains virulence; selection on plant for new gene for resistance. etc…
8. Describe the coevolution between Australian rabbits and the myxoma virus; Most rabbits
had no gene for resistance .prior to the introduction of the myxoma virus with a gene for
virulence. High rabbit mortality ensued, but over time the level of mortality declined. Selection
by the virus favored the few rabbits with resistance and they increased in number. Selection
by the death of rabbits favored the few viruses with lower virulence that did not kill their
required living host. Thus over time coevolution occurred as the rabbits gained more
resistance and the virus less virulence.
9. What evidence is used to claim a coevolutionary relationship?
1. inferential e.g. closely related herbivores feed on closely related plants; suggests
long history of each selecting for traits in the other group.
2. experimental e.g. see question 7.
10. Experimental evidence of a coevolved mutualistic relationship: Ants + tree hoppers.
If…treehoppers feed ants and ants protect ‘hoppers from predatory spiders,
then more ‘hoppers will be present when ants present than when ants removed.
Figure 1.What is the independent variable? presence/absence of ants
What is the dependent variable? number of ‘hoppers
Summarize the results. More ‘hoppers were present when ants present than absent.
What is the conclusion? Is this a mutualistic relationship? Yes; the ‘hoppers feed
the ants and the ants protect ‘hoppers from predators.
In year 2, spiders were low in number; predict the difference in treehopper number
in ants vs. no ants. no difference. The relationship has changed from being mutualistic +/+
to one in which the ants provide no benefit to the treehoppers which incur a cost by giving
away free sugar to the ants + /- .
11. What is a trophic mutualism? 2 or more species specialized in complementary
ways to obtain limited energy and nutrients. (trophic = pertaining to food)
A. Figure 2. Describe the mutualism between legumes and Rhizobium bacteria.
Legume provides shelter and food to bacteria that provide nitrogen to legume.
B. Figure 3. between endomycorrhizae and higher plants Plant provides food to
non-photosynthetic fungi that provide ‘soil mining’ of P for plants.
12. What is a defensive mutualism? Species receive food for shelter in return for defense
by other species against natural enemies.
Figure 4. Describe the relationship between eels + cleaning shrimp Shrimp eat eel’s
parasites (= food) while shrimp rid the eel of its enemy (parasites).
Figure 5. between Acacia and ants Plant provides shelter, nest sites, and food to ants
that provide defense against herbivores (and fire and vines).
Figure 6. What is the evidence that Acacia benefit from ants? Survial, shoot weight,
number of leaves and thorns are less for plants without and than with ants.
What is a possible evolutionary response when a plant, but not the ant, invades an
island? Why? The plant evolves without thorns and food. They are costly to make
and provide no benefit to the plant in the absence of the ant. Perhaps they divert
those energies to a new defense such as chemical defense.
(On the mainland, they are mutualists).
13. What are two types of dispersive mutualisms? 1. pollination 2. seed dispersal
Which type is related to gene flow? both
Can seed dispersal involve no mutualism? How? Yes, if seeds are dispersed
by abiotic forces such as wind, water, hydrostatic explosion.
14. What are three reasons that strict mutualisms are rare?
1. So many species are interacting that selection is diffused from any one species.
2. Species don’t consistently co-occur through space or time.
3. Genetic complexities cause the two species to evolve at different rates; or one
species has more potential to evolve than the other.
15. Figure 7. Describe the complex relationship between the Yucca plant and the Yucca
moth. Moth pollinates plant and also lays eggs in some ovules (potential seeds) of
plant that feeds pollen to moth and provides nourishment to its young. Is the
relationship mutualistic? Explain. It’s a strict (obligatory mutualism. Plant must
have moth for pollination and moth must have plant to raise its offspring. Both have
no relationship with other species for pollination or a place to raise offspring.
Figure 8. When did the adaptations arise? Before establishment of mutualism =
preadaptations in earlier lineages.
Do the adaptations occur in close relatives that are not mutualists? yes; sometimes
the moths are predators only and not pollinators.
What’s the main point here? Some mutualisms today that appear to have coevolved
traits that were actually preadaptations that were critical to the development of the
obligate mutualism.