Fluctuating Life-History Parameters Indicating Temporal Variability in Metal Adaptation in Riverine Chironomids |
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Authors: | D Groenendijk B van Opzeeland L M Dionisio Pires J F Postma |
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Institution: | (1) Department of Aquatic Ecology and Ecotoxicology, ARISE, University of Amsterdam, Kruislaan 320, 1098 SM, Amsterdam, The Netherlands , NL |
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Abstract: | Adaptation to toxicants in animal populations is influenced primarily by two counteracting forces. First, the intensity
and duration of peak concentrations of toxicants is responsible for the actual level of selection pressure on the population.
Second, the process of adaptation can be disrupted by gene flow as a result of crossings with nontolerant individuals. These
counteracting forces were analyzed in riverine insects in which we expected that the level of metal adaptation is subject
of considerable fluctuations, due to variable dilution of metals and a variable transport of nontolerant individuals in river
water. To this purpose, the stability of metal adaptation in different Chironomus riparius populations was analyzed during a 5-month period in a heavily polluted lowland river. This was examined by measuring mortality,
larval dry weight, and accumulation of zinc under laboratory conditions. The results showed that in midge populations originating
from metal-contaminated field sites several life-history parameters (like control mortality and growth response under cadmium
exposure) of the laboratory reared F1 generations showed considerable temporal variation. In addition, the presence of metal-adapted
midge populations was indicated on several occasions on the metal-exposed field sites. Reference populations on the other
hand, showed stable life history patterns throughout the sampling period, and no signs of metal adaptation were found. These
observations showed that the actual level of metal adaptation varies considerably, both in time and space. Adaptation to metals
in riverine chironomids, therefore, should be looked on as a highly dynamic process.
Received: 9 November 1998/Accepted: 14 March 1999 |
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