Question

Which alternative hypothesis is made far less likely by having three R and K lines, rather than one of each?

Answer 1

Both the populations of Drosophila seem to have the same gene for foraging behavior

Therefore, the alternative hypothesis which is made far less likely by having three R and K lines, rather than one of each is: 

The difference between the R and K lines is the result of environmental differences in the food availability of their habitats.