Tickleback evolution lab final quiz 1. how did some ancestral sea-run stickleback populations come to live exclusively in fresh water? these populations swam to freshwater lakes to spawn and then never returned to the ocean because there were fewer predators in lakes. they became trapped in lakes that formed at the end of the last ice age. they don't actually live exclusively in fresh water; they only live in fresh water at certain stages in their lives. they developed traits that made them better adapted to fresh water and, as a result, had to move to a freshwater environment to survive.

The correct answer is "some stickleback populations come to live exclusively in fresh water they became trapped in lakes that formed at the end of the last ice age".

Explanation:

There are different types of speciation. Allopatric speciation consists of the geographic separation of a continuous genetic background so that it can give place to two or more new geographically isolated populations. Some barriers might impede the genetic interchange or genetic flux, making a place to two new populations that are separated and can not get together to mate anymore. Glaciation is one of the most important drivers of speciation and production of different phylogeographic structures by vicariance. Glacials originate isolated gene-pools that accumulate differences that end in reproductive isolation. Melting of the ice also generated divergence and speciation, as land appearance acted as a barrier for some populations.  

During the last glaciation, stickleback fishes were able to reach certain new places or areas that provided better conditions to inhabit. There were fewer predators and more available food sources that made these new areas to be a better choice. These new grounds were lakes and were the product of ice melting. But at a certain point, as ice melting increased, the land started to show up again and became a barrier for this species. Animals that were living in lakes could not go back to the sea, they were trapped so they had to adapt to living exclusively in lakes. This species diverged and suffered speciation.