Does geographic distance between salamander populations increase their reproductive isolation? To answer this question, researchers studied populations of the dusky salamander (Desmognathus ochrophaeus) living on different mountain ranges in the southern Appalachian Mountains.

Question: Does geographic distance between salamander populations increase their reproductive isolation? To answer this question, researchers studied populations of the dusky salamander (Desmognathus ochrophaeus) living on different mountain ranges in the southern Appalachian Mountains. The researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. Four mating combinations were tested for each pair of populations (A and B) - two within the same population (female A with male A and female B with male B) and two between populations (female A with male B and female B with male A). The proportion of successful matings for each mating combination was measured. For example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. Then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). The reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (AA + BB) minus the sum of the proportion of successful matings of each type between populations (AB + BA).

The table (Figure 1) provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.

Part A - Understanding experimental design

What hypothesis did the researchers test in this study?

Answer:

"Reproductive isolation increases with geographic distance between dusky salamander populations"

Explanation:

The mechanisms of reproductive isolation are a assemblage of evolutionary mechanisms, behaviors and physiological procedures dangerous for speciation. They avert followers of dissimilar types from manufacturing offspring, or confirm that any offspring are germ-free. While in allopatric speciation the reproductive isolation is resolute superficially by the spatial isolation of populations, during sympatric speciation specific groups of persons create distinct mating organizations with self-like persons while distribution the similar home with the rest of the unique inhabitants.