Lasenby and Langford 1972

Lasenby DC, Langford RR. 1972. Growth, life history, and respiration of Mysis relicta in an arctic and temperate lake. Journal of the Fisheries Research Board of Canada 29: 1701-1708.

These authors studied the small “glacial relict” freshwater crustacean Mysis relicta from Char Lake, NWT (now Nunavut) and from Stony Lake, southern Ontario, two populations separated by about 30 degrees of latitude. They were attempting to test the hypothesis that poikilotherms show metabolic compensation for changes in environmental temperatures.

This study did not find evidence of such metabolic compensation; if they were compensating for temperature, similar activity levels would be expected in different populations, but the Char Lake animals were “more lethargic” and consumed significantly less oxygen than the Stony Lake animals. Char Lake mysids did not migrate vertically, with most animals found at 10m depth. Stony Lake mysids did show daily vertical migration, covering more than 20m depth ranges.

Previous authors (Vernberg and Vernberg, 1970) suggested that northern species may be restricted in southern distribution by abiotic factors, primarily increased metabolic rates associated with higher temperatures and a resulting inability to consume sufficient food. However, these authors point out that temperate lakes are usually much more productive than arctic lakes, so food supply is probably not limiting. Stony Lake mysids appear to be compensating for their warm environment by feeding in the productive surface waters but spending much of their time in cooler bottom waters.

The conclusions of this study are very interesting. Char Lake female mysids took two years and consumed about 200 calories to achieve maturity, and Stony Lake females took one year and consumed about 200 calories to achieve maturity. This possibility that a species uses the same total energy for maturity regardless of environmental conditions “should perhaps be further investigated”; I agree.