Snail Evolution

How did the Banff Springs Snail Evolve?

Given the glacial history of the area near the town of Banff, the following simple theory was published in the scientific literature in 2001.

About 10,000 to 12,000 years ago, the last glaciers from the Wisconsin glaciation retreated from the area around the town of Banff. Left behind was a large glacial Lake Vermilion. Snails of the Family Physidae seem to like warm water. For example, near Edmonton, Alberta, the Common Tadpole Snail (Physella gyrina) can reproduce year-round in warm water produced from a coal-powered electrical generation plant. Within this ancient glacial lake lived the ancestors of the Banff Springs Snail, probably Physella gyrina. Some of these Tadpole Snails liked living in the warm water produced by the Cave and Basin thermal springs, which flowed into the ancient lake. The shoreline of the ancient lake was at approximately the same elevation as the Cave and Basin Springs. Over time, as the lake level dropped, the snails became reproductively isolated from their ancestors and a new species – the Banff Springs Snail – evolved.

This theory will have to be slightly modified. More recent studies have shown that the tufa rock that forms the Cave Spring is only between 3,200 and 5,300 years old. Consequently, the Banff Springs Snail did not arise from its ancestors 10,000 to 12,000 years ago, but much more recently. A similar age has been determined for the Miette Springs in Jasper National Park. They are believed to have begun flowing and started depositing tufa about 4,500 years ago, under cool and moist habitat conditions coincident with higher ground-water levels of the Neoglacial period. This period followed the Hypsithermal, a multiphased warm period between 9,000 and 5,000 years ago, when the climate was warmer and dryer than average and immediately followed the retreat of the glaciers. It is feasible that the thermal springs on Sulphur Mountain had little or no flow during the prolonged dry period of the mid-Holocene Hypsithermal.

Re-examining the glacial history near the town of Banff reveals the following details:

About 13,000 years ago, the glaciers had retreated back into the mountains. However, a glacier still plugged the Bow Valley and lay overtop the current townsite of Banff, although the top of Tunnel Mountain was now exposed. Glacial Lake Vermilion, at 1432 m elevation, extended northwards from the eastern extent of the glacier and up the Cascade River. Water may have flowed out the Glacial Lake through the current path of the Cascade River. Between 13,000 and 11,000 years ago, the glacier continued to retreat westward up the Bow Valley. The toe of the glacier was about halfway between the western edge of Third Vermilion Lake and the Highway 1A turnoff. To the east of the glacier lay Proglacial Lake Vermilion at 1395 m elevation (proglacial means near-glacial). This water body extended to Bow Falls on the Bow River to the southeast and towards Cascade Ponds to the northeast. It may have drained both through the Cascade and Bow rivers. Sometime between 10,000 and 8,000 years ago, the lake shrank some more and was now at an elevation of 1383 m, draining only through the Bow River over Bow Falls (currently, the cool springs at Third Vermilion Lake sit at an elevation of 1381 m). The waterbody was now called Holocene Lake Vermilion. The northeastern edge of the lake was somewhere near the road to the Banff Industrial Compound and trailer drop-off. By about 6,600 years ago, the lake continued to shrink and its eastern edge was somewhere near the Banff C.P.R. train station. But, the Hypsithermal period was coming to a close.

As Holocene Lake Vermilion continued to shrink and then was slowly in-filled by sediments deposited by the Bow River and alluvial fans of tributaries, the thermal springs along the flank of Sulphur Mountain sprang to life during the cool and moist conditions following the Hypsithermal. The ancestors of the Banff Springs Snail congregated near the warm water inflows flowing from the Cave and Basin Springs into the Cave and Basin Marsh and Bow River. Over time, perhaps as they slowly made their way upstream, they became reproductively isolated. We do currently see Banff Springs Snails actively crawling upstream to get closer to the thermal spring origin pools.

Alternatively, perhaps a bird transported an ancestral snail directly into the Basin Spring pool. Ducks and other shorebirds have occasionally been observed in the Basin Spring and this mode of transport has been documented in the scientific literature. Adding additional credence to the bird transport theory and in contrast to the snail-crawling upstream theory is that while one can easily observe the Common Tadpole Snail off the fish observation platform at the Cave and Basin Marsh, the middle sections of the thermal spring outflow streams at the Cave and Basin are devoid of physid snails.

It seems that bird transport may be a better theory and would also need to be invoked to explain the snail’s historic and current distribution.

BSimg_0431

The Common Tadpole Snail, Physella gyrina, at the Fish Observation Platform of the Cave and Basin. The long, thin tentacles can bee seen.

Next Page – How does the Banff Springs Snail Reproduce?