Federica R. Schanz | MSc Student

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Project

 

M.Sc. in Environmental Sciences

 

Demographic responses of resurrected Lake Orta rotifers to changing copper pollution and food density 

An individual-based analysis

 

Adaptation allows populations to persist in changing environments. These adaptations manifest themselves as changes in life-history responses. Here, I investigated whether rotifers, Brachionus calyciflorus, adapted to changing copper concentrations in the polluted Lake Orta (Italy) and tested for a food density effect. I resurrected resting eggs from three sediment layers representing peakpollution (1950s – early 60s), early-recovery (late 1970s – 80s) and post-pollution (2000 – 2012) periods and recorded life-table data from 504 individually cultured rotifers. I kept experimental rotifers at three copper concentrations (0 µg Cu L-1, 40 µg Cu L-1, 80 µg Cu L-1) and two food densities (1 and 2 million Chlorella vulgaris mL-1). From these data, I estimated stage-specific vital rates and resulting population growth rates (λ). I then run retrospective perturbation analyses to assess vital rate contributions to λ differences among treatments and prospective perturbation analyses to investigate how current and future vital rate changes would affect λ under changing environmental conditions. The results showed that copper contamination negatively affected the rotifers’ demography, but I found no demographic signs of adaptive evolution to the historical copper pollution. In addition, food density had no positive effect on rotifers’ copper tolerance. The prospective analysis showed that adult survival, the probability of being an amictic adult (i.e., producing female offspring) and amictic adult’s fecundity contributed most to observed λ differences. The prospective analysis showed that λ were most elastic to amictic adult survival, followed by juvenile survival. Together, the perturbation analyses revealed that lowered adult survival is the key mechanism of rotifer responses to copper pollution. My approach of combining resurrection-ecology methods with laboratory experimentation and biodemographic analyses provides novel insights into the mechanisms underlying the life-history responses to environmental pollution of a common and widespread freshwater inhabitant.

 

During this Master project I was supervised by Stefan Sommer.

 

 

CV

  • 2016 – 2017, M.Sc. in Environmental Sciences, University of Zürich
  • 2012 – 2016, B.Sc. in Biology with special focus on Plant Ecology, University of Bern