Answer:
The correct answer is - polyploidy.
Step-by-step explanation:
Speciation can be two types allopatric and sympatric speciation. Sympatric speciation is the process of speciation is developing the new species that diverged from the common ancestral species while the ancestral and developed species both can share the same place or geological area. The main cause of such speciation is due to the change in their genetic level more than environmental conditions.
In this case, the frog's species show differences in their ploidy level as well as their mating call but polyploidy is the most likely the difference that evolved first rather than females call for mating.
Thus, the correct answer is - polyploidy.