Final answer:
Speciation will not occur if there is gene flow between the two subgroups, new traits resulting from mutation will not flow between the subgroups, the two subgroups will be reproductively isolated, and speciation will not speed up due to increased competition between the subgroups.
Step-by-step explanation:
In this scenario, two subgroups of a population by a river are joined when a drought causes the river to run dry. Assuming that speciation has not yet occurred, we can conclude the following:
- Speciation will not occur if gene flow between the two subgroups can increase. Gene flow refers to the movement of genes from one population to another through mating or dispersal. If there is gene flow between the subgroups, individuals can continue to mix their genetic material, preventing speciation.
- New traits resulting from mutation will not flow between the subgroups. Mutations are random changes in an organism's DNA. If the subgroups are unable to exchange genetic material, new traits resulting from mutation will not be shared between them.
- The two subgroups will be reproductively isolated and unable to mate. Reproductive isolation occurs when two groups can no longer mate and produce fertile offspring. In this case, the drought separating the subgroups may have led to physical barriers preventing interbreeding, such as changes in the river course.
- Speciation will not speed up since there will be more competition between the subgroups. Speciation is a gradual process that occurs over long periods of time. Increased competition between the subgroups may shape natural selection, but it does not directly speed up speciation.