Population genetic structure and hybridization patterns in the cryptic sister species Chironomus riparius and Chironomus piger across differentially polluted freshwater systems

• Published in: Ecotoxicology and environmental safety Vol. 141; no. C; pp. 280 - 289
• Main Authors: Pedrosa, João A.M., Cocchiararo, Berardino, Verdelhos, Tiago, Soares, Amadeu M.V.M., Pestana, João L.T., Nowak, Carsten
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01-07-2017; Elsevier
• Subjects: Animals; Chironomidae - drug effects; Chironomidae - genetics; Cluster Analysis; Fresh Water - chemistry; Genetic diversity; Genetic erosion; Genetic Variation - drug effects; Genetics, Population; Genome-Wide Association Study; Hybridization, Genetic; Interspecific hybridization; Metal contamination; Metals - analysis; Metals - toxicity; Microsatellites; Portugal; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - toxicity; Genetic diversity; Genetic erosion; Microsatellites; Metal contamination; Interspecific hybridization
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2017.03.004

Chironomids are an integral and functionally important part of many freshwater ecosystems. Yet, to date, there is limited understanding of their microevolutionary processes under chemically polluted natural environments.
In this study, we investigated the genetic variation within populations of the ecotoxicological model species Chironomus riparius and its cryptic sister species Chironomus piger at 18 metal-contaminated and reference sites in northwestern Portugal. Microsatellite analysis was conducted on 909 samples to answer if metal contamination affects genetic variation in natural chironomid populations as previously suggested from controlled laboratory experiments.
Similarly high levels of genetic diversity and significant but weak genetic substructuring were found across all sites and temporal replicates, with no effects of metal contamination on the genetic variation or species’ abundance, although C. piger tended to be less frequent at highly contaminated sites. Our results indicate that high levels of gene flow and population dynamic processes may overlay potential pollutant effects. At least for our study species, we conclude that the “genetic erosion hypothesis”, which suggests that chemical pollution will reduce genome-wide genetic variability in affected populations, does not hold under natural conditions. Interestingly, our study provides evidence of successful hybridization between the two sister species under natural conditions.
•Evolutionary responses of C. riparius and C. piger to metal pollution were assessed.•No genetic erosion or genetic structure was found with metal pollution of sites.•There was a signature of isolation by distance in C. riparius.•There was evidence of interspecific hybridization under natural conditions.•High spatiotemporal population dynamics and gene flow prevent genetic erosion.