By Rodney Hsu

In part one, Biological species concept, I brought up the fact that status of a species is not static, it is continuously evolving. How exactly can we determine when a species becomes two distinct species, or whether two species evolved from a common ancestor or not? These questions are extremely complex and hard to answer, yet we can gain some understanding by looking at several examples that have been documented in the past.

Speciations - Factories of species

The term speciation can be defined as the creation of a new species. When one population of a species is separated into two by some sort of physical factor, eventually the two sub-populations will evolve differently and become two distinct species. In this case, speciation has taken place. The most common scenario of speciation takes place when some kind of geographical event has taken place. A barrier is created during these events that prevents two separated populations coming in contact. These barriers may include glacier, fallen rocks, etc. Formation of islands can also isolate populations, resulting in speciation. Lakes are considered as "aquatic islands" because they are completely surrounded by terrestrial barrier that prevents aquatic creatures to move between lakes. New lakes, or islands, can form by rock falls, droughts, and other chance events. Once separated, physical appearance, behaviours will eventually differ between the two populations. When the two populations have evolved and meet once again, if interbreeding does not occur, it can then be concluded that they are two completely different species. Speciation is not an instant event, but an ongoing process that can take up thousands of years.

Story of the deepwater sculpin

The deepwater sculpin (Myoxocephalus thompsoni) can be found in the Great Lakes. In the last several decades, this species has been slowly disappearing as it is very susceptible to toxin. In Lake Ontario, it was last seen in 1972. It's a tiny fish, weighing 15 grams at maximum. It's also the largest freshwater sculpin in North America. It lives primarily in deep, cold water. This tiny species, would normally not raise an angler's eye brows, but it tells a fantastic story that dates back to the last glacial age!

It wasn't until recently that the deepwater sculpin was established as an unique species. Several decades ago, it was thought this particular freshwater sculpin, is just a variety of the fourhorn sculpin found in the Arctic Ocean. The fourhorn sculpin, characterized by the four distinct "horns" on the upper portion of its head, lives in shallow cold water of the Arctic. It is found along the Northern Canadian coast, Alaska, Greenland and parts of Scandinavia. The two "varieties", as they were known, are similar in size, colour and shape. If they are the same species, how does one population inhabit in the cold Arctic Ocean, while the other one ends up in several lakes that are inaccessible from the ocean?

The answer to this mystery, is glaciation. During the last glaciation, the entire Canada and parts of America are completely covered with ice. When this period was over, glaciers began to melt. As they melted, huge glacial lakes are formed due to the large amount of water that accumulated. These large glacial lakes were connected to the ocean as the water drained into it. When this occurred, coastal marine organisms saw it as an opportunity to find new habitat, therefore they moved into the glacial lakes. As the lakes continued to drain, they began to retreat and eventually connections between the lakes and the ocean were cut off. As a result, many of these marine organisms were "trapped" in the lakes, and eventually established new populations.

The fourhorn sculpin was just one of many species that used this opportunity to established new colonies. When the earth began to warm up after glaciation, they moved into deeper portion of the lakes where the temperature is similar to the Arctic ocean. After thousands of years of evolution, despite of only small amount of physical changes, scientists decided that these freshwater fourhorn sculpin should be named as a new species, deepwater sculpin. The deepwater sculpin, is known as a "glacial relict" of the fourhorn sculpin. It lacks the four horns, possibly due to the absence of predators in these deep freshwater lakes. Today, these tiny creatures have a new threat, pollution is slowly exterminating the populations of deepwater sculpin, wiping out a significant evidence of post-glacial evolution.

This is just one of the many prime examples of speciation during glaciation in North America. As the water rose and dropped when ice melted and formed, habitats were created and destroyed, which were colonized by new populations. It takes thousands, or millions of years to form a new species. When thinking in that time scale, it should make you appreciate the salmon, trout, sturgeon and even sculpin that distribute across North America much more.