Abstracts (first author)
Constrating signatures of thermal stability evolution in ray-finned fish mitochondrial DNA-encoded proteinsPDF
Ray-finned fishes (actinopterygii) have successfully colonized almost all aquatic habitats, exploiting a wide range of temperature, salinity, oxygen level and hydrostatic pressure conditions. Temperature in particular is a strong environmental constraint driving adaptation, and several recent studies have detected signals of selection on mitochondrial genome along latitudinal or altitudinal gradients as well as an interaction between mitochondrial and nuclear genotypes in determining metabolic performance. Numerous actinopterygii complete mitochondrial genomes are now available and crystallographic structures have been determined for most of the 13 mitochondrial DNA-encoded proteins. Concomitantly, studies of the structural differences between mesophilic and thermophilic (optimal growth temperature > 50°C) microorganisms have provided useful insights into the general evolutionary patterns leading to increased protein thermal stability. In this context, we used all currently available actinopterygii mitochondrial genomes in relation with an environmental database (FishBase) to test whether there was an association between the thermal stability of mtDNA-encoded proteins and the environmental temperature commonly inhabited by the species. Several predictors of thermal stability (local structural entropy, amino acid compositional bias, hydrophobicity) were used with and without prior partitioning of the protein sequences into transmembrane and exposed regions. Phylogenetically independent contrasts were calculated to test the relationship between stability and environmental temperature. Signatures of increased predicted thermal stability with increasing environmental temperature were detected for some but not all of the proteins, thus suggesting that environmental temperature constrains the evolution of mtDNA-encoded protein stability in ray-finned fishes but that this constraint is not homogeneous among proteins.
Metabolism and energy storage strategies differ in nine-spined stickleback (Pungitius pungitius) populations from contrasting thermal environmentsPDF
Metabolic thermal adaptation is crucial for maintaining the necessary energy balance for survival in the face of seasonal temperature fluctuations. The plasticity of the thermal response and its potential for evolutionary adaptation are expected to differ between populations exposed to different thermal regimes. To understand how metabolic thermal responses differ in recently (< 11,000 years) isolated populations, we studied 4 populations of the nine-spined stickleback (Pungitius pungitius) from marine locations and spring-fed ponds from the Baltic region. We hypothesized that populations from cold, thermally stable ponds and from marine, thermally more variable locations would differ in their metabolic compensation thermal response. We acclimated wild-caught fish to 6, 11 and 19°C in the lab under constant photoperiod and measured their resting and active metabolic rates in order to determine their aerobic scope. Liver weight was used as a proxy for energy reserves. The fish from the coldest and most stable pond population exhibited complete temperature compensation for their aerobic scope while the marine populations underwent metabolic depression in the cold. Aerobic scopes were identical between all populations at 19°C. Marine populations had larger hepatosomatic index at all temperatures, with cold acclimation accentuating this effect. Our results suggest that differential energy storage and metabolism adaptations occurred in those populations, with the marine populations developing a winter-tolerance strategy while the cold pond population could potentially have a winter-exploitation strategy. This work demonstrates the metabolic versatility of the nine-spined stickleback and provide a potential energetic framework for the previously observed adaptations in energy-dependent traits in other nine-spined stickleback populations.