The graph below represents a hypothetical two-dimensional environment, temperature along the x-axis and moisture along the y-axis. The A locus affects fitness with respect to temperature, the B locus affects fitness with respect to moisture. The two-locus genotype shown in each quadrant represents the combination with highest fitness.

a) Suppose the environment fluctuates consistently, such that some years are hot and dry and other years are cold and wet. (i) Will natural selection favor or disfavor sexual reproduction? (ii) If selection gets its way, will the resulting linkage (dis)equilibrium be coupling, repulsion, zero, or “can’t say”? Explain, in no more than two sentences.

b) Suppose the environment fluctuates randomly, such that there is an equal chance that any given year falls into any of the four quadrants. (i) Will natural selection favor or disfavor sexual reproduction? (ii) If selection gets its way, will the resulting linkage (dis)equilibrium be coupling, repulsion, zero, or “can’t say”? Explain, in no more than two sentences.

c) Suppose the two environmental variables fluctuate but they are out of phase, such that hot/dry tends to be soon followed by hot/wet and cold/wet tends to be soon followed by cold/dry, etc. (i) Will natural selection favor or disfavor sexual reproduction? (i) Will natural selection favor or disfavor sexual reproduction? (ii) If selection gets its way, will the resulting linkage (dis)equilibrium be coupling, repulsion, zero, or “can’t say”? Explain, in no more than two sentences.