Assessment of mitochondrial functions inDaphnia pulexclones using high‐resolution respirometry

Abstract

The objectives of our study were to adapt a method to measure mitochondrial function in intact mitochondria from the small crustacean Daphnia pulex and to validate if this method was sensitive enough to characterize mitochondrial metabolism in clones of the pulex complex differing in ploidy levels, mitochondrial DNA haplotypes, and geographic origins. Daphnia clones belonging to the Daphnia pulex complex represent a powerful model to delineate the link between mitochondrial DNA evolution and mitochondrial phenotypes, as single genotypes with divergent mtDNA can be grown under various experimental conditions. Our study included two diploid clones from temperate environments and two triploid clones from subarctic environments. The whole animal permeabilization and measurement of respiration with high-resolution respirometry enabled the measurement of the functional capacity of specific mitochondrial complexes in four clones. When expressing the activity as ratios, our method detected significant interclonal variations. In the triploid subarctic clone from Kuujjurapik, a higher proportion of the maximal physiological oxidative phosphorylation (OXPHOS) capacity of mitochondria was supported by complex II, and a lower proportion by complex I. The triploid subarctic clone from Churchill (Manitoba) showed the lowest proportion of the maximal OXPHOS supported by complex II. Additional studies are required to determine if these differences in mitochondrial functions are related to differences in mitochondrial haplotypes or ploidy level and if they might be associated with fitness divergences and therefore selective value.

Draft genomes for one Microcystis-resistant and one Microcystis-sensitive strain of the water flea, Daphnia pulicaria

“…For each strain, we conducted reference-based assembly using the D. pulex PA42 genome assembly. D. pulex was determined to be a suitable, high-quality reference, as it is closely related to D. pulicaria and, interestingly, the two commonly hybridize in ecological communities ( Marková et al 2013 ; Kake‐Guena et al 2015 ). Furthermore, the PA42 genome was produced from starved Daphnia treated with antibiotics to reduce diet and endosymbiotic contaminants, and post-assembly, scaffolds were filtered for bacterial contamination ( Ye et al 2017 ).…”

Mitochondrial thermo-sensitivity in invasive and native freshwater mussels

“…Mitochondrial respiration was measured as volume-specific oxygen flux ( pmol O 2 s −1 ml −1 ) using DatLab Software V 5.2.1.51 (Oroboros Instruments, Innsbruck, Austria). Mitochondrial respiration was assessed using the substrate-inhibitor titration (SUIT) protocol proposed by Kake-Guena et al (2015, with the following modifications: glutamate was added to the protocol and a mitochondrial uncoupler (FCCP) was introduced following succinate addition (Fig. 1).…”