Based on the data provided in part A of the passage, there are parasite load decreases followed by increases. Justify how trypanosome biology and features of the immune system could interact to result in this varying parasite load. A. As one glycoprotein variant becomes recognized and attacked by the adaptive immune system, another glycoprotein that is not yet recognized is able to persist. B. The longer the glycoprotein variants persist in the body, they attack and impair the immune system over time. C. As both glycoprotein variants become recognized by the innate immune system, the parasite load levels fall until the immune system can no longer detect the parasite, which allows the trypanosome to thrive. D. As antibody levels increase, the parasites with the associated glycoprotein variant are able to evade detection by the adaptive immune system.

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.