Final answer:
Low heterozygosity in a population of frogs, despite a sizeable effective population size, likely indicates that the population is not in Hardy-Weinberg equilibrium, and could be subject to evolutionary forces such as genetic drift, selection, or the founder effect.
Step-by-step explanation:
If you estimated the effective population size for a group of frogs and found that heterozygosity levels are lower than expected, it might indicate that the population is not in Hardy-Weinberg equilibrium. The Hardy-Weinberg principle assumes that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. However, genetic drift, selection, mutation, and migration can all cause deviations from this equilibrium.
Considering that heterozygosity is reduced, it's likely that the population is undergoing some form of selection or drift that is reducing genetic variability. Other forces such as the founder effect or bottlenecks could also play a role if the population has undergone recent reductions in size or was established by a small group of individuals. Environmental factors like pesticide exposure could also contribute to reduced heterozygosity by imposing selective pressures on the population.