Submitted to: International Symposium on Earthworm Ecology
Publication Type: Abstract Only
Publication Acceptance Date: April 30, 2010
Publication Date: N/A
Lumbricus terrestris L. (the dew worm) forages, mates and migrates on the soil surface during the night. Its distribution covers a broad latitudinal gradient and variation in day length conditions. Since soil-surface activity is crucial for the survival and reproduction of dew worms, it is conceivable that northern populations that experience light nights in the summer have adapted to remain surface active in twilight and show less sensitivity to light compared with more southerly populations. We evaluated this hypothesis experimentally. Adult dew worms were collected from a wide latitudinal gradient in May 2009, from field sites in Jokioinen (Finland; 60º48’N, 23º28’E), Preston (UK, 53º46’N, 2º42’W) and Coshocton (USA, 40º16’N, 81º50’E). In Jokioinen there is a 3-week period without a dark-night interval (twilight prevails throughout the night) in the middle of summer, while in Preston even the shortest midsummer night has 5 hours of darkness and, respectively, 8 hours in Coshocton. Using the field-collected animals, an experiment was conducted in Jokioinen from 6th until 21st June - midsummer. Groups of three individuals from a particular geographic origin were housed in soil-filled PVC-tubes. Before the experiment they were kept in darkness and then under an artificial light-cycle to equally distort any inherent daily activity pattern. Three replicate tubes were exposed to either ambient natural light or artificially induced darkness during the night. Earthworm surface activities were recorded from above using low-light video cameras during 22.30-04.30 hrs, which covered the period between sunset and sunrise. As the main response variable we used surface activity (activity vs. no activity in 0.5 hr increments). Preliminary analysis of the data has shown that under artificial darkness, surface activity was high throughout the night for all three dew worm origins. Under ambient light, surface activity increased gradually after sunset, peaked after midnight and then declined towards sunrise. Giving tentative support for the initial hypothesis, under natural light Finnish earthworms began their surface activity earlier than the others and remained active for the longest period. In the conclusive statistical analyses currently underway, we are using air temperature and moisture together with an index of cloud cover as covariates. Our presentation will report the full results and discuss their importance and implications.