PARENT SESSION
TP6 - Evolutionary Responses to Environmental Change
Chair: Bagley, Mark1, 1 26 West Martin Luther King Drive, Cincinnati, Ohio, USA
Co-chair: Klerks, Paul2, 2 P.O. Box 42451, Lafayette, LA, USA
2:10 PM to 5:30 PM - Tuesday, 19 November 2002
Room Ballroom B
(458) A gradual shift in metal adaptation in soil collembola populations along a contamination gradient.
Posthuma, Leo*,1, Van der Pol, Joost2, 1 RIVM-Laboratory for Ecological Risk Assessment, Bilthoven, The Netherlands2 Alterra Green World Research, Wageningen, The Netherlands
ABSTRACT- Work in the 1990s has clearly shown the occurrence of genetic adaptation to heavy metals in various terrestrial invertebrates. Specifically, case studies on the collembolan Orchesella cincta have shown: (a) there is genetic variation for cadmium tolerance in non-exposed field populations, (b) there is inheritance of cadmium tolerance in laboratory-reared offspring from individuals collected at a range of contaminated sites, and (c) there are clues towards understanding the molecular and physiological basis of tolerance (cadmium sequestration, excretion, metallothioneins). The tolerance differed in degree between differently exposed field populations. A concern in the understanding of metal adaptation in this species is still that one of the population showed reduced values for tolerance in comparison to two reference populations, not explained by low local metal bioavailability. Research on that 'aberrant' population was carried out to address this concern. Seven sub-populations were sampled along the local gradient. Tolerance of sub-populations was quantified in laboratory-reared offspring by determination of mortality patterns over time under constant high cadmium exposure. A systematic and substantial increase of survival time was observed with increased field exposure levels. Hence, within this gradient, there is evidence for increased tolerance, while tolerance of all sub-populations is lower than that of reference populations. The apparently low tolerance can possibly be attributed to the relatively low calcium concentration in the gradient soils. It is hypothesized that this relates to the role of calcium-containing granules in cadmium sequestration and excretion. In general, this study highlights that each field population of a species has a unique array of inherited characteristics, shaped by the local uncontaminated conditions. It is the local array of characteristics that forms the raw material for micro-evolutionary change upon toxicant exposure.
Key words: Adaptation, Lethal time 50, Field gradient, Heavy metals