Final answer:
The type of selection happening with platypuses is not specified, but the concepts of frequency-dependent, diversifying, stabilizing, and directional selection are all potential types that could influence the platypus population depending on environmental factors and phenotypic advantages.
Step-by-step explanation:
The type of selection that could be occurring in the population of platypuses is not mentioned specifically in the provided text, but we can discuss the general concepts of natural selection that might apply. In frequency-dependent selection, phenotypes can be favored either because they are common (positive frequency-dependent selection) or rare (negative frequency-dependent selection). We also have diversifying selection, where two or more distinct phenotypes have distinct advantages, while intermediate phenotypes are selected against. An example included is of mice with different coat colors on a beach with different environmental backgrounds. Stabilizing selection occurs when an average phenotype is favored and genetic variance decreases as a result. Lastly, directional selection may take place when an environmental change causes phenotypes at one end of the spectrum to be selected for, as seen with the peppered moth during the Industrial Revolution.