Biometry and biology of Constempellina brevicosta (Chironomidae) in a subarctic lake

Abstract

Grimås, U. and Wiederholm, T. 1979. Biometry and biology of Constempellina brevicosta (Chironomidae) in a subarctic lake. – Holarct. Ecol. 2: 119‐124. Constempellina brevicosta Edw. made up about 50% of the chironomids emerging from the littoral of Lake Blåsjön. The lake is impounded for hydroelectrical purposes. Constempellina was less abundant at an earlier, smaller amplitude of water level fluctuations in the same lake and much less abundant in a nearby natural lake. The species is able to survive in a frozen substratum on ice‐covered bottoms. Records of early life stages and emergence data indicated a one‐year life cycle with peak emergence from the littoral zone occurring in mid July. Statistical comparisons were made of size characteristics with respect to time and site of emergence and swarming. Swarming individuals were found to be significantly larger than emerging ones as measured in length of body, wing, tibia, and tarsi. Individuals swarming from mid July to August were successively smaller in all characters except basal antennal segments. Individuals swarming in June were smaller than those occurring somewhat later. The changes in size seem to reflect differences in larval habitat, with early summer material emanating from areas exposed to winter freezing. Males swarming at different sites at the same date were similar in all respects except for body size. Individuals emerging from different depths within the littoral zone at a single date were different in most respects, those from more shallow areas being smaller. Linear regression of swarm material from different dates showed a positive correlation for most characters. The correlations were particularly strong, and applied to all characters, when the early summer material was excluded. Mean AR values were successively lower throughout the season and positively correlated with size. Mean LR values were slightly higher in early summer than later. The LR values varied independantly of size. AR and LR values in swarm material varied between extremes for single individuals which were usually within 20% of the arithmetic mean, or 0.92–1.36 for AR and 0.78–1.06 for LR. Confidence limits for population estimates were within 0.04 units of the means.