Final answer:
Founder effects in Polynesian field crickets cause genetic bottlenecks, resulting from a small group of individuals establishing a new population with potentially less genetic variation than the original population. The correct option is D.
Step-by-step explanation:
Founder effects in Polynesian field crickets lead to genetic bottlenecks. The founder effect is a type of genetic drift that occurs when a new population is established by a very small number of individuals from a larger population.
This small group may not have the same genetic variation as the original population, which can result in reduced genetic diversity and can magnify certain alleles within the new population, as seen in the case of the Afrikaner population with higher incidences of Huntington's disease and Fanconi anemia.
It is not associated with increasing genetic diversity, leading to random mating, or being a direct result of migration events, but it often stems from such events.