Copper-contaminated soil compromises thermal performance in the springtail Folsomia candida (Collembola).

The widespread agricultural and industrial emissions of copper-based chemicals have increased copper levels in soils worldwide. Copper contamination can cause a range of toxic effects on soil animals and influence thermal tolerance. However, toxic effects are commonly investigated using simple endpoints (e.g., mortality) and acute tests. Thus, how organisms respond to ecological realistic sub-lethal and chronic exposures across the entire thermal scope of an organism is not known. In this study, we investigated the effects of copper exposure on the thermal performance of a springtail (Folsomia candida), regarding its survival, individual growth, population growth, and the composition of membrane phospholipid fatty acids. Folsomia candida (Collembola) is a typical representative of soil arthropods and a model organism that has been widely used for ecotoxicological studies. In a full-factorial soil microcosm experiment, springtails were exposed to three levels of copper (ca. 17 (control), 436, and 1629 mg/kg dry soil) and ten temperatures from 0 to 30 °C. Results showed that three-week copper exposure at temperatures below 15 °C and above 26 °C negatively influenced the springtail survival. The body growth was significantly lower for the springtails in high-dose copper soils at temperatures above 24 °C. A high copper level reduced the number of juveniles by 50 %, thereby impairing population growth. Both temperature and copper exposure significantly impacted membrane properties. Our results indicated that high-dose copper exposure compromised the tolerance to suboptimal temperatures and decreased maximal performance, whereas medium copper exposure partially reduced the performance at suboptimal temperatures. Overall, copper contamination reduced the thermal tolerance of springtails at suboptimal temperatures, probably by interfering with membrane homeoviscous adaptation. Our results show that soil organisms living in copper-contaminated areas might be more sensitive to thermally stressful periods.

Antifreeze protein complements cryoprotective dehydration in the freeze-avoiding springtail Megaphorura arctica.

The springtail, Megaphorura arctica, is freeze-avoiding and survives sub-zero temperatures by cryoprotective dehydration. At the onset of dehydration there is some supercooling of body fluids, and the danger of inoculative freezing, which would be lethal. To see if the springtails are protected by antifreeze proteins in this pre-equilibrium phase, we examined extracts from cold-acclimated M. arctica and recorded over 3 °C of freezing point depression. Proteins responsible for this antifreeze activity were isolated by ice affinity. They comprise isoforms ranging from 6.5 to 16.9 kDa, with an amino acid composition dominated by glycine (>35 mol%). Tryptic peptide sequences were used to identify the mRNA sequence coding for the smallest isoform. This antifreeze protein sequence has high similarity to one characterized in Hypogastrura harveyi, from a different springtail order. If these two antifreeze proteins are true homologs, we suggest their origin dates back to the Permian glaciations some 300 million years ago.