AP Biology: Mutualism and Coevolution Practice Questions
Practice mutualism and coevolution reasoning with original AP Biology multiple-choice questions. These items emphasize fitness costs and benefits, mechanisms that stabilize cooperation, experimental design, and cautious interpretation of evolutionary evidence.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
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Answer the questions below — you get instant feedback and a full explanation for each.
1. A flowering plant receives more successful pollen transfer when visited by a moth, while the moth obtains nectar that increases its reproductive output. Which interaction is most directly described?
Explanation. The interaction is mutualistic when both partners gain a fitness benefit: the plant gains pollen transfer and the moth gains food that improves reproduction. The outcome should be evaluated by effects on fitness, not simply by whether resources are exchanged.
2. Legume plants reduce resources supplied to root nodules that fix little nitrogen. How can this response help stabilize the plant-bacterium mutualism?
Explanation. Reducing resources to poorly performing nodules acts as a sanction. It makes low-cooperation strategies less rewarding and can favor bacterial variants that provide more nitrogen to the plant.
3. Female insects can detect chemical differences among potential microbial partners and preferentially associate with strains that provide an essential nutrient. Which mechanism is illustrated?
Explanation. Partner choice allows a host to associate preferentially with partners that provide greater benefits. This can increase the reproductive success of cooperative symbiont strains relative to less beneficial strains.
4. Two mutualistic species have similar branching patterns in their phylogenetic trees. Which conclusion is most scientifically appropriate?
Explanation. Matching phylogenies can support a cospeciation hypothesis, but the pattern alone is not proof. Divergence dates and alternatives such as partner switching, extinction, and incomplete sampling must also be evaluated.
5. A plant species is pollinated by several insect species, and each insect also visits many plant species. Selection on flower shape differs among locations because the local visitor community differs. This pattern best illustrates which concept?
Explanation. Diffuse coevolution occurs when selection on a species is shaped by a set of interacting species rather than one exclusive partner. Geographic differences in the interaction network can therefore produce different selective pressures.
6. A coral-algal association benefits both partners in clear, nutrient-poor water, but unusually warm water disrupts the association and reduces coral survival. What does this observation show?
Explanation. The costs and benefits of an interaction can change with temperature, nutrients, or other conditions. A mutualism is defined by a net benefit under the conditions measured, not by a permanently fixed outcome.
7. A plant lineage depends entirely on one pollinator species, whereas a related plant can reproduce with several pollinators. Which statement best distinguishes the interactions?
Explanation. An obligate mutualism is required for a partner's survival or reproduction, while a facultative mutualism is beneficial but not strictly required. Dependence can also differ between the two partners.
8. Researchers propose that long-tubed flowers and long-tongued pollinators evolved through reciprocal selection. Which study would best test this proposal?
Explanation. Evidence for reciprocal selection requires showing that heritable traits in each species affect fitness through the interaction. Measurements across populations or generations help distinguish coevolution from resemblance produced by other causes.
9. Scientists want to test whether a mycorrhizal fungus increases plant phosphorus uptake when soil phosphorus is scarce. Which design provides the strongest causal evidence?
Explanation. A replicated factorial experiment separates the effect of fungal inoculation from the effect of phosphorus availability and tests whether the fungal benefit changes with nutrient context. Random assignment reduces systematic bias.
10. A grazing animal removes old leaf tissue and incidentally stimulates new plant growth, but the animal trait evolved only because grazing supplies food. Why is this not sufficient evidence of coevolution?
Explanation. One species can benefit another as a side effect of a trait selected for another reason. Coevolution requires evidence that each species has imposed selection leading to evolutionary change in the other.
11. A beneficial bacterial symbiont is transmitted from a female insect directly to nearly all of her offspring. Why can this transmission mode favor cooperation by the symbiont?
Explanation. With reliable vertical transmission, symbionts often reach future hosts through the current host's offspring. Traits that preserve or improve host reproduction can therefore also improve symbiont transmission, aligning fitness interests.
12. In one region, plants obtain large benefits from an ant defender and invest heavily in nectar rewards. In another region, ant defense is weak and plants invest less. Which additional evidence would most strongly support a geographic mosaic of coevolution?
Explanation. A geographic mosaic involves spatial variation in reciprocal selection, often combined with movement of alleles among populations. Demonstrating heritable traits and location-specific fitness effects would connect the observed pattern to coevolution.
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FAQ
What is mutualistic coevolution?
It is reciprocal evolutionary change in which each partner's heritable traits affect selection on the other while both receive a net fitness benefit from the interaction.
How can mutualisms remain stable when cheating is possible?
Partner choice, sanctions, repeated association, spatial structure, and aligned transmission can reduce the relative fitness advantage of partners that take benefits without providing enough in return.
Does a matching pair of traits prove coevolution?
No. Matching traits are consistent with coevolution, but researchers also need evidence of heritable variation, reciprocal selection, evolutionary change, and plausible alternatives.