Life histories and post-glacial origins of tundra caddisflies (Trichoptera) from the Tuktoyaktuk Peninsula, Northwest Territories
Date
1984
Authors
Winchester, Neville Norman
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Abstract
Life histories, species composition and post-glacial origins of Trichoptera from the Tuktoyaktuk Peninsula, Northwest Territories were examined. Nineteen species were identified while eight others could not be identified to species. Eighty-two percent of this fauna represented new Canadian arctic reports and all species represented Nearctic range extensions. Sphagnophylax meiops, gen. et sp. nov. was discovered.
Time available for insect growth in arctic regions is short and in this study was confined to early June - late September. Life cycles were completed in temperatures that consistently remained above 0c. For the remainder of the year complete freezing of the stream and shallow areas of the surrounding drainage basin occurred. Trichoptera overwintered in several larval instars and survived ice encasement. These larvae were probably freezing tolerant, although more than one mechanism may exist to allow survival at sub-zero temperatures.
Thawing, which began in mid-May, was completed by mid-June and created a mosaic of flooded lowland marsh. This continuous littoral zone dominated by rooted macrophytes provided large areas for caddisfly aggregations. A small portion of the total fauna resided in the stream channel. This limited stream habitat contributed to the exclusion of strict lotic Trichoptera.
Life history information for 10 of 19 species suggested that all species have a one year life cycle. Adult emergence coincided with the onset of drought. Developmental rates and number of instars were constant among all species. Rates of increase varied between 1.13 and 1.44. All rates agreed with Dyar's Rule except that of Sphagnophylax meiops.
Three patterns of flight period were recognized, defined on the basis of flight duration. Flight periods did not show a progression towards short and highly synchronized emergence with increased latitude.
The systematic and biogeographic relationships within the Trichoptera of northwestern North America were affected by past glacial events. The post-glacial origin of this fauna was composed of three groups that included Trichoptera that spent the glaciation: (1) in Beringia, (2) south of the ice sheets, or (3) in both areas. The Beringian element was subdivided into 3 groups based on species distributional patterns. Group A was found only in Beringia (in North America). Group B was Beringian and widespread in North America but absent in the Palearctic. Group C included Amphi-Beringian species with Nearctic and Palearctic distributions.
Populations may have been split and were present in both areas simultaneously. The probable post-glacial sources of this fauna were:
Beringia, 47%; south of the ice sheets, 23.5%; and both of these areas, 29.5%. The composition of the Beringian elements including those species thought to have re-colonized from both areas was: Group 1, 31%; Group 2, 31%; and Group 3, 38%.
This study notes that a diverse caddisfly assemblage exists in the low arctic. Species survive extended cold periods, periods of drought, and are able to complete their life cycles in one year. Beringia is considered an important source area contributing to the observed species diversity.