Ascientist finds what she thinks is a new species of rodent on a small pacific island. however, some similar-looking rodents inhabit some nearby islands. she mates the new rodent with the nearby rodents and gets viable but infertile offspring. why?
question 15 options:

the old and new rodents underwent vicariance, and their hybrid offspring were sterilized by adaptive radiation.

the new rodents probably derive from fairly recent ancestors that experienced dispersive allopatric speciation.*

the new and old rodents are both allopolyploid after undergoing sympatric speciation.

Option B

Explanation:

Dispersive allopatric speciation,  geographically move apart the population of any species  thereby restricting gene flow between the sub-populations  

These genetic difference accumulate and with time and cause genetic drift and variable selection pressures on the subpopulations.

This causes the separation up to an extent that even if the organisms from these two sub-populations are some how brought close to each other , they will yet not interact with each other and would remain two genetically distinct populations. The differences in mating preference and hybrid inferiority keep these sub-population separate from each other.  

Hence, option B is correct

they fuse to form they have half as many chromosomes as a somatic cell of the same individual. b