Question

Over 20 species of fish have descended from a single common ancestral species. Fossil evidence shows that each of these species evolved when fluctuating water levels totally isolated small sub-populations of the original ancestral species into several different small lakes and prevented interbreeding. Today they are all completely sympatric (all live in the same large lake.) We can identify them all accurately by their morphology. With this evidence, how best can we hypothesize what type of speciation was involved ?

A) Sympatric speciation

B) Allopatric speciation

C) Phylogenetic speciation

D) Phenetic speciation

Answer 1

From the given evidence, it can be hypothesized that "allopatric speciation" was involved.

This is because the fishes had a common ancestor but were separated by a geographical barrier provided by fluctuating water levels which is the key of allopatric speciation. Due to this geographical barrier, the species gradually got modified and became reproductively isolated. That is why interbreeding was prevented.

Also, they have different morphological features due to adaptation to different type of environment which makes it easy to identify the different species accurately.