Response of the Nonbiting Midge <i>Chironomus riparius</i> to Multigeneration Toxicant Exposure

The ability of the nonbiting midge <i>Chironomus riparius</i> to withstand long-term toxicant exposure has been attributed to genetic adaptation. Recently, however, evidence has arisen that supports phenotypic plasticity. Therefore, the present study aimed to investigate if <i>Chironomus riparius</i> indeed copes with prolonged toxicant exposure through phenotypic plasticity. To this purpose, we performed a multigeneration experiment in which we exposed <i>C. riparius</i> laboratory cultures for nine consecutive generations to two exposure scenarios of, respectively, copper, cadmium, and tributyltin. Total emergence and mean emergence time were monitored each generation, while the sensitivity of the cultures was assessed at least every third generation using acute toxicity tests. We observed that the sublethally exposed cultures were hardly affected, while the cultures that were exposed to substantially higher toxicant concentrations after the sixth generation were severely affected in the eighth generation followed by signs of recovery. A marginal lowered sensitivity was only observed for the highly exposed cadmium culture, but this was lost again within one generation. We conclude that <i>C. riparius</i> can indeed withstand long-term sublethal toxicant exposure through phenotypic plasticity without genetic adaption

Response of the Nonbiting Midge <i>Chironomus riparius</i> to Multigeneration Toxicant Exposure

The ability of the nonbiting midge <i>Chironomus riparius</i> to withstand long-term toxicant exposure has been attributed to genetic adaptation. Recently, however, evidence has arisen that supports phenotypic plasticity. Therefore, the present study aimed to investigate if <i>Chironomus riparius</i> indeed copes with prolonged toxicant exposure through phenotypic plasticity. To this purpose, we performed a multigeneration experiment in which we exposed <i>C. riparius</i> laboratory cultures for nine consecutive generations to two exposure scenarios of, respectively, copper, cadmium, and tributyltin. Total emergence and mean emergence time were monitored each generation, while the sensitivity of the cultures was assessed at least every third generation using acute toxicity tests. We observed that the sublethally exposed cultures were hardly affected, while the cultures that were exposed to substantially higher toxicant concentrations after the sixth generation were severely affected in the eighth generation followed by signs of recovery. A marginal lowered sensitivity was only observed for the highly exposed cadmium culture, but this was lost again within one generation. We conclude that <i>C. riparius</i> can indeed withstand long-term sublethal toxicant exposure through phenotypic plasticity without genetic adaption

Response of the Nonbiting Midge <i>Chironomus riparius</i> to Multigeneration Toxicant Exposure

The ability of the nonbiting midge <i>Chironomus riparius</i> to withstand long-term toxicant exposure has been attributed to genetic adaptation. Recently, however, evidence has arisen that supports phenotypic plasticity. Therefore, the present study aimed to investigate if <i>Chironomus riparius</i> indeed copes with prolonged toxicant exposure through phenotypic plasticity. To this purpose, we performed a multigeneration experiment in which we exposed <i>C. riparius</i> laboratory cultures for nine consecutive generations to two exposure scenarios of, respectively, copper, cadmium, and tributyltin. Total emergence and mean emergence time were monitored each generation, while the sensitivity of the cultures was assessed at least every third generation using acute toxicity tests. We observed that the sublethally exposed cultures were hardly affected, while the cultures that were exposed to substantially higher toxicant concentrations after the sixth generation were severely affected in the eighth generation followed by signs of recovery. A marginal lowered sensitivity was only observed for the highly exposed cadmium culture, but this was lost again within one generation. We conclude that <i>C. riparius</i> can indeed withstand long-term sublethal toxicant exposure through phenotypic plasticity without genetic adaption

<i>C. riparius</i> transcriptome sequencing and assembly statistics.

<p><i>C. riparius</i> transcriptome sequencing and assembly statistics.</p

Array-based gene expression (aGE) experiment.

<p>(A) Schematic representation of the two mRNA linear amplification protocols. The coloured bar represents the mRNA with the 3′ polyA tail indicated by the stretch of A’s. The arrows represent the amplified cDNA products obtained for the regular procedure and the modified procedure, with the length of the arrows indicating the length of the synthesized cDNA’s. (B) MA-plot of the aGE data. The light grey dots represent all aCGH selected probes. The three coloured regions are expected to contain probes targeting transcripts at the 3′ side (blue), probes targeting the middle of the transcripts (red) and probes targeting the 5′side as well as probes with no target transcripts (green). (C) Density plot where the relative position of the three probe populations on the isotigs is demonstrated. The colours of the lines correspond to the colours used in panels A and B. The black line represents a random selection of probes that covers, as expected, the isotigs evenly over the entire length.</p

Taxonomic distribution of the best blastx hits matching <i>C. riparius</i> transcripts.

<p>Distribution of the best blastx hits that were matched to the isotigs (black) and the singletons (light grey) according to their taxonomic origin. (A) All transcripts (isotigs n = 16,824; singletons n = 24,129) that were matched to a BLASTX hit. (B) Transcripts (isotigs n = 16,537; singletons n = 4,7539) that were matched to a BLASTX hit and that are targeted by the final aGE microarray.</p

Strategy to obtain non-model organism transcriptomics resources.

<p>NGS: Next-generation sequencing; ESTs: Expressed Sequence Tags; aCGH: array-based Comparative Genomic Hybridization; GE: Gene Expression; GO: Gene Ontology; EC: Enzyme Commission numbers. * adapted from <a href="http://extension.missouri.edu/explorepdf/agguides/pests/g07402.pdf" target="_blank">http://extension.missouri.edu/explorepdf/agguides/pests/g07402.pdf</a>.</p

Array-based comparative genomic hybridization (aCGH) experiment.

<p>(A) Box- and-whisker plot summarizing the obtained log₂ signal intensity distributions for the four indicated probes collections, with the light grey boxes representing the <i>C. riparius</i> aCGH signal and the dark grey the aCGH <i>A. gambiae</i> signal. (B) MA-plot of the aCGH data. The dots with the different shades of grey represent the entire probe-library (with a GC-content below 50%). The three defined signal-intensity parameters are indicated by the dashed blue line and the captions I, II, III. The three categories containing the selected probes are indicated by different shades of grey and the letters A, B and C. The red dots are the negative control probes and the green dots the positive control (<i>A. gambiae</i> EST) probes.</p

<i>C. riparius</i> transcriptome annotation summery.

<p><i>C. riparius</i> transcriptome annotation summery.</p

Gene Ontology (GO) terms obtained for <i>C. riparius</i> transcripts.

<p>The data represents the distribution of the annotated isotigs (black) and the annotated singletons (light grey) over the various level-2 GO terms. Each bar represent the number of annotated transcripts associated with the specified level-2 GO term as a percentage of the total number of annotated transcripts belonging to the higher-ranked GO category, i.e. cellular component (isotigs n = 8,380; singletons n = 9,277), molecular function (isotigs n = 10,663; singletons n = 11,359) and biological process (isotigs n = 6,249; singletons n = 7,343).</p