15. Which of the following scenarios best illustrates commensalism between two organisms? (A) Clownfish live among the tentacles of sea anemones, gaining protection from predators while the anemones benefit from increased nutrient input. (B) Cattle egrets forage near grazing rhinoceroses, catching insects disturbed by the rhinos' movement, without affecting the rhinos. (C) A harmless hoverfly evolves yellow-and-black stripes resembling those of stinging wasps, deterring predators. (D) Mycorrhizal fungi form associations with plant roots, providing nutrients to the plant in exchange for sugars produced by photosynthesis. (E) Orchids of the genus Anguloa produce flowers that mimic the scent and shape of female Euglossine bees, attracting male bees that attempt to mate and inadvertently pollinate the flowers.

4. Which of the following descriptions is incorrect for a recognized type of natural selection? (A) Directional selection: A mode of natural selection in which individuals with phenotypes at one extreme of a trait distribution have higher fitness than those with intermediate or opposite extreme phenotypes. (B) Stabilizing selection: A mode of natural selection that favors both phenotypic extremes over intermediates, potentially increasing variation and leading to a bimodal distribution or speciation. (C) Balancing selection: A mode of natural selection that maintains genetic diversity in a population by favoring multiple alleles, often through mechanisms like heterozygote advantage or varying selection pressures across environments. (D) Purifying selection: A mode of selection that removes deleterious mutations or alleles, preserving functional genetic sequences and reducing genetic variation at conserved loci. (E) Frequency-dependent selection: A mode of selection where a phenotype's fitness depends on its frequency in the population—often, rare phenotypes have higher fitness.

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