Change in reproductive and dispersal traits in the water strider, <i>Aquarius paludum</i> (Fabricius) and global warming

Abstract

This study aims to examine the following three hypotheses on the impact of global warming on the populations of the water strider, Aquarius paludum in the Kochi-Nankoku area (33 。 30 ' N) of Kochi prefecture, Japan through the recent data collected in 2009-2011. 1) Has the generation number increased ? 2) Has aestivation appeared in adults ? 3) Have overwintering adults stopped dispersing between the water surface and overwintering lands-sites far away from water and, instead, overwintered on/near the shore ? Sampling data showed that the number of generations may have increased from three (1989-2002 strains) and four (2004-2008) to five (2009-2011) per year in Kochi (33 。 N). The ratio of adults having well developed flight muscles decreased from 45% in 1995 to 24% - 28% in 2009-2011 inoverwintering adults collected from the field in fall likely as a result of histolysis. “Mo saic-typed” wing morph group with long fore-wings and short hind-wings newly appeared in 2009-2011 in the Kochi-Nankoku overwintering populations. The mosaic-typed wings group cannot fly and the black and long fore wings might function as absorbing apparatus of sun-lights in the daytime of winter. Some overwintering adults seem to stop migrating between water bodies and overwintering sites on land far from the water bodies and overwinter, instead, near the shore. The use of Aquarius paludum as a biological indicator would be possible in the future, because this species can respond and change their reproductive and dispersal characteristics to the global change.