By: William E. Schlosser, Ph.D.
Speciation of Elk (Cervus canadensis) has been through many paths to reveal genetic variations within this genome. We see elk around the northern hemisphere, but the genetic differences between sub populations are significant. It is so significant that cross breeding between groups does not generally produce viable offspring.
That is to say, the offspring cannot themselves mate to produce viable offspring. When this is marked, we know a speciation event has occurred!
Cervus canadensis Var. nelsonii on Kamiak Butte south facing aspect.
Cervus canadensis Var. nelsonii on western side of Kamiak Butte
Elk heard leaving Kamiak Butte, December 2020 to start their annual migration trek.
Cervus canadensis Var. nelsonii yearlings getting for herd migration December 2020.
Allopatric Speciation
The geologic conditions confirming the current Ice Age we are still exiting from was seen only about 11,700 years ago: the current ice age was at its chilling crescendo. Surface waters were mostly frozen, locked in terrestrial glaciers and sea-ice. This meant there was less water resting in the oceans, sea level stood 120 meters, 400 feet lower than it does today. That means the Bering Straights were open fields and boreal forests, connecting these two continents.
This territory was an easily traversed path between these two continents. Species of all types were connected along this connection linking current day Alaska with the Russian Far East. The connective tissue now under the North Sea, was about the size of today’s country of Mexico. At that time, 21,000 years ago, the world was in the apex of the ice age and the elk species were connected as a series of populations along this continental connection zone. Genetic materials were still shared between populations.
Allopatric speciation is based on the extent to which associated populations are isolated from one another: the 400-foot-deep Beringia ocean is a significant barrier for elk to pass. The Allopatric speciation event separated C.c. canadensis into separate populations. In North America the species continued to evolve, with each sub-population experiencing random mutations which revealed through adaptive responses. Random selection favored genetic traits which were strengthened within each restrictive environment. Across North America, many variations of restrictive environments are found.
Kamiak Butte, Washington, is home to North American Elk (C.c.nelsonii) populations. This variant of elk is similar, but not genetically identical to Roosevelt elk (C.c.roosevelti) which are found about 300 miles to the west in the temperature rainforests of Washington’s Olympic Peninsula.
Parapatric Speciation of Elk
Subpopulations of a species evolving in reproductive isolation from one another, while continuing to exchange genes. This mode of speciation has three distinguishing characteristics:
- Mating occurs non-randomly
- Gene flow occurs unequally
- Populations exist in either continuous or discontinuous geographic ranges.
This distribution pattern may be the result of unequal dispersal, incomplete geographical barriers, or divergent expressions of behavior, among other things. Parapatric speciation predicts that hybrid zones will often exist at the junction between the two new populations.
Due to the continuous nature of a parapatric population distribution, population niches will often overlap, producing a continuum in the species’ ecological role across an environmental gradient. Reduced gene flow of parapatric speciation often produces a cline in which a variation in evolutionary pressures causes a change to occur in allele frequencies within the gene pool of each differentiating population. This is enabled through environmental gradients that ultimately results in genetically distinct sister species. This is parapatric speciation.
Rocky Mountain elk (C.c.nelsonii) in Yellowstone National Park live in the temperate coniferous and hardwood forests and rangelands. Big antlers are not a liability to be hung up in the understory brush or in low hanging tree branches. But they sure serve a purpose when being attacked by a pack of wolves!
Rocky Mountain elk (C.c.nelsonii) and Roosevelt elk (C.c.roosevelti) are two genetically unique varieties of elk and are in the first and second stage of speciation. They have demonstrated ample evidence of speciation adaptations to different environmental restrictions; (C.c.roosevelti) are genetically different from (C.c.nelsoni). They have responded to different restrictive environments.
Trails of the elk herd leaving Kamiak Butte in December 2020 as part of their annual migration.