Imagine two populations of snails that are polymorphic for sexual reproduction. In each of the two popula-tions, several asexual lineages and a panmictic, sexually reproducing subpopulation of snails are living in the same environment

Question

Several years ago, a new pathogen was detected in the first population. This pathogen is predominantly transmitted between parents and their offspring, but on occasion it is also transmitted horizontally between unrelated individuals. The pathogen is now infecting both sexual and asexual individuals. Since the introduc-tion of the pathogen, the formerly stable ratio of sexual vs. asexual snails has shifted significantly in favor of the sexually reproducing individuals. The second population became at the same time infected with a patho-gen that is almost always transmitted horizontally. In the second population, no shift in the ratio of sexuals vs. asexuals has been observed. Speculate on why the difference in transmission between the two pathogens may have shifted the proportion of sexual reproduction in the first but not in the second population. Limit your answer to one to two sentences.
What will be an ideal response?

Answer 1

ANS:
Vertically transmitted pathogens are expected to adapt to their genetically identical lineage of asexual hosts. Sexual reproduction makes such adaptation more difficult.