The role of genetic diversity and past-history selection pressures in the susceptibility of Chironomus riparius populations to environmental stress.
Natural populations experiencing intense selection and genetic drift may exhibit limited potential to adapt to environmental change. The present study addresses the following aspects of the "genetic erosion" hypothesis in the midge Chironomus riparius: does long-term mercury (Hg) contamination affect the Hg tolerance of midge populations inhabiting such impacted areas? If so, is there any fitness cost under changing environmental conditions? And does genetic impoverishment influence the susceptibility of C. riparius to cope with environmental stressful conditions? For this end, we tested the acute and chronic tolerance to Hg and salinity in four C. riparius populations differing in their levels of genetic diversity (assessed through microsatellite markers) and past-histories of Hg exposure. Results showed that the midge population collected from a heavily Hg-contaminated site had higher Hg tolerance compared to the population collected from a closely-located reference site suggesting directional selection for Hg-tolerant traits in its native environment despite no genetic erosion in the field. No increased susceptibility under changing environmental conditions of salinity stress was observed. Moreover, results also showed that populations with higher genetic diversity performed better in the partial life-cycle assays providing evidence on the key role that genetic diversity plays as mediator of populations' susceptibility to environmental stress. Our findings are discussed in terms of the suitability of C. riparius as a model organism in evolutionary toxicology studies as well as the validity of ecotoxicological assessments using genetically eroded laboratory populations.
Departamento de Biologia & CESAM, Universidade de Aveiro, 3810-193 Aveiro, Portugal; Conservation Genetics Group, Senckenberg Research Institute, Clamecystrasse 12, 63571 Gelnhausen, Germany.
João A M
JAM
Pedrosa
Conservation Genetics Group, Senckenberg Research Institute, Clamecystrasse 12, 63571 Gelnhausen, Germany.
Berardino
B
Cocchiararo
Departamento de Biologia & CESAM, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
Maria D
MD
Bordalo
Departamento de Biologia & CESAM, Universidade de Aveiro, 3810-193 Aveiro, Portugal; Department of Environmental Chemistry (IDAEA-CSIC), Jordi Girona, 18-26, 08034 Barcelona, Spain.
Andreia C M
ACM
Rodrigues
Departamento de Biologia & CESAM, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
Amadeu M V M
AMVM
Soares
Department of Environmental Chemistry (IDAEA-CSIC), Jordi Girona, 18-26, 08034 Barcelona, Spain.
Carlos
C
Barata
Conservation Genetics Group, Senckenberg Research Institute, Clamecystrasse 12, 63571 Gelnhausen, Germany.
Carsten
C
Nowak
Departamento de Biologia & CESAM, Universidade de Aveiro, 3810-193 Aveiro, Portugal. Electronic address: jpestana@ua.pt.
João L T
JLT
Pestana
D000818:Animals; D002683:Chironomidae / Q000187:drug effects* / Q000235:genetics*; D054750:Ecotoxicology; D014644:Genetic Variation; D008018:Life Cycle Stages; D008628:Mercury / Q000633:toxicity*; D018895:Microsatellite Repeats; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D014874:Water Pollutants, Chemical; D008628:Mercury
Freshwater; Genetic adaptation; Genetic erosion; Mercury; Microsatellites; Salinity