Final answer:
Geographical gradients of allele frequencies in killifish are maintained by gene flow in geographically continuous populations, and by natural selection and genetic drift in geographically discontinuous populations, leading to divergence in allele frequencies.
Step-by-step explanation:
Geographical gradients of allele frequencies in killifish on the east coast can be maintained by several processes, including gene flow, natural selection, and genetic drift. Normally, when a species has a geographically continuous population, gene flow allows for a homogeneous mix of alleles along its range. However, when populations become geographically discontinuous, this free flow of alleles is restricted, and over time, these populations can evolve differently.
Environment and natural selection play significant roles. Variations in climate, resources, predators, and competitors can cause natural selection to favor different adaptations in separated populations leading to a divergence in allele frequencies. Likewise, genetic drift can significantly impact smaller, isolated populations, leading to rapid evolutionary changes independent of other populations.