Two species of fish have been found together in five different lakes. The larger, bottom-dwelling species feeds on large prey close to shore. A surface-dwelling species feeds on small plankton in open water. DNA analysis shows that the two species in each lake are more closely related to each other than they are to any of the other fish species in the lakes. However, they are reproductively isolated. These two species are likely to have arisen due to
a. allopatric speciation.
b. allopolyploidy.
c. sympatric speciation.
d. polyploidy.
e. autopolyploidy.