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Phenotypic convergence in a natural Daphnia population acclimated to low temperature

ABSTRACT: Abstract Fluidity of a given membrane decreases at lower ambient temperatures, whereas it rises at increasing temperatures, which is achieved through changes in membrane lipid composition. In consistence with homeoviscous adaptation theory, lower temperatures result in increased tissue concentrations of polyunsaturated fatty acids (PUFAs) in Daphnia magna, suggesting a higher PUFA requirement at lower temperatures. However, so far homeoviscous adaptation has been suggested for single or geographically separated Daphnia genotypes only. Here, we investigated changes in relative fatty acid (FA) tissue concentrations in response to a lower temperature (15°C) within a D. magna population. We determined juvenile growth rates (JGR) and FA patterns of 14 genotypes that were grown on Chlamydomonas klinobasis at 15°C and 20°C. We report significant differences of JGR and the relative body content of various FAs between genotypes at either temperature and between temperatures. Based on slopes of reaction norms, we found genotype‐specific changes in FA profiles between temperatures suggesting that genotypes have different strategies to cope with changing temperatures. In a hierarchical clustering analysis, we grouped genotypes according to differences in direction and magnitude of changes in relative FA content, which resulted in three clusters of genotypes following different patterns of changes in FA composition. These patterns suggest a lower importance of the PUFA eicosapentaenoic acid (EPA, C20:5ω3) than previously assumed. We calculated an unsaturation index (UI) as a proxy for membrane fluidity at 15°C, and we neither found significant differences for this UI nor for fitness, measured as JGR, between the three genotype clusters. We conclude that these three genotype clusters represent different physiological solutions to temperature changes by altering the relative share of different FAs, but that their phenotypes converge with respect to membrane fluidity and JGR. These clusters will be subjected to different degrees of PUFA limitation when sharing the same diet. In consistence with the homeoviscous adaptation theory, the concept of maintaining a constant membrane fluidity at changing temperatures, it has been shown for single D. magna, genotypes that lower temperatures result in increased tissue concentrations of PUFAs, suggesting a higher PUFA requirement at lower temperatures. Here, we investigated homeoviscous adaptation to a lower temperature (15°C) within a D. magna population by calculating the change of the relative content of individual fatty acids between 15°C and 20°C for 14 genotypes of a natural D. magna population. We applied a hierarchical clustering analysis that grouped genotypes according to differences in their fatty acid alteration profiles, which resulted in three different clusters of genotypes, that differ in terms of changes in their fatty acid content but whose phenotypes converge in terms of an unsaturation index and juvenile somatic growth, which were determined for each genotype as well.

SUBMITTER: Werner C

PROVIDER: S-EPMC8571613 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:This study measured the differential expression of genes from a single clonal Daphnia pulex isolate obtained from an eutrophic flooded opencast mine near Gräfenhain (Saxony, Germany) and has been kept in the laboratory since 2002. The daphniids (50 adult animals per batch) were raised in 3-L glass beakers under a 16 h:8 h L:D photoperiod. Three-quarter of the culture medium (M4) was renewed once a week, and the animals were equally fed ad libitum with algae (Desmodesmus subspicatus; SAG 53.80, Göttingen, Germany). Long-term-acclimated animals were kept at three different temperatures (i.e., 10 ± 0.5°C, 20 ± 0.3°C, and 24 ± 0.3°C) under normoxia (Po2 ≥ 20 kPa) for at least twelve weeks. Time-resolved experiments (acute heat stress) were carried out with long-term 20°C acclimated animals, which were exposed for three different time intervals (2, 4, and 8 h) to either 30 ± 0.2°C (test conditions) or 20 ± 0.3°C (control conditions). For this, 50 animals each were rapidly transferred with a sieve (mesh size: 1.2 mm) from 20°C-medium to a set of beakers containing 30°C-medium. As control, 50 animals each were transferred from 20°C-medium to another set of beakers with 20°C-medium. Only adult female animals with a body length of 2−2.5 mm (between the base of the apical spine and the anterior part of the head) and carrying parthenogenetic eggs and embryos were used for experiments. Animals were not fed during short-term exposures. During experiments, all animals were in good physical condition. After thermal acclimation or heat exposure, animals were transferred into 1.5-ml microcentrifuge tubes and shock-frozen in liquid nitrogen after removing adhering water with a tissue paper. Samples were short-term stored at -80°C. For all experimental conditions, four independent replicates (50 animals each) were analyzed. This GEO record is for the acute heat stress temperature contrasts between animals conditioned to 20 degrees Celsius (condition 1) versus heat shock to 30 degrees Celsius (condition 2) exposed for 2 hours (treatment 1), 4 hours (treatment 2), and 8 hours (treatment 3).

Project description:This study measured the differential expression of genes from a single clonal Daphnia pulex isolate obtained from an eutrophic flooded opencast mine near Gräfenhain (Saxony, Germany) and has been kept in the laboratory since 2002. The daphniids (50 adult animals per batch) were raised in 3-L glass beakers under a 16 h:8 h L:D photoperiod. Three-quarter of the culture medium (M4) was renewed once a week, and the animals were equally fed ad libitum with algae (Desmodesmus subspicatus; SAG 53.80, Göttingen, Germany). Long-term-acclimated animals were kept at three different temperatures (i.e., 10 ± 0.5°C, 20 ± 0.3°C, and 24 ± 0.3°C) under normoxia (Po2 ≥ 20 kPa) for at least twelve weeks. Time-resolved experiments (acute heat stress) were carried out with long-term 20°C acclimated animals, which were exposed for three different time intervals (2, 4, and 8 h) to either 30 ± 0.2°C (test conditions) or 20 ± 0.3°C (control conditions). For this, 50 animals each were rapidly transferred with a sieve (mesh size: 1.2 mm) from 20°C-medium to a set of beakers containing 30°C-medium. As control, 50 animals each were transferred from 20°C-medium to another set of beakers with 20°C-medium. Only adult female animals with a body length of 2−2.5 mm (between the base of the apical spine and the anterior part of the head) and carrying parthenogenetic eggs and embryos were used for experiments. Animals were not fed during short-term exposures. During experiments, all animals were in good physical condition. After thermal acclimation or heat exposure, animals were transferred into 1.5-ml microcentrifuge tubes and shock-frozen in liquid nitrogen after removing adhering water with a tissue paper. Samples were short-term stored at -80°C. For all experimental conditions, four independent replicates (50 animals each) were analyzed. This GEO record is for the contrasts between animals conditioned to 10 degrees Celsius (condition 1) versus 20 degrees Celsius (condition 2), 10 degrees Celsius (condition 1) versus 24 degrees Celsius (condition 3), and 20 degrees Celsius (condition 2) versus 24 degrees Celsius (condition 3)

Project description:BackgroundPhenotypic convergence between distinct species provides an opportunity to examine the predictability of genetic evolution. Unrelated species sharing genetic underpinnings for phenotypic convergence suggests strong genetic constraints, and thus high predictability of evolution. However, there is no clear big picture of the genomic constraints on convergent evolution. Genome-based phylogenies have confirmed many cases of phenotypic convergence in birds, making them a good system for examining genetic constraints in phenotypic convergence. In this study, we used hierarchical genomic approaches to estimate genetic constraints in three convergent avian traits: nocturnality, raptorial behavior and foot-propelled diving.ResultsPhylogeny-based hypothesis tests and positive selection tests were applied to compare 16 avian genomes, representing 14 orders, and identify genes with strong convergence signals. We found 43 adaptively convergent genes (ACGs) associated with the three phenotypic convergence cases and assessed genetic constraints in all three cases, from (amino acid) site mutations to genetic pathways. We found that the avian orders shared few site mutations in the ACGs that contributed to the convergent phenotypes, and that these ACGs were not enriched in any genetic pathways. In addition, different pairs of orders with convergent foot-propelled diving or raptorial behaviors shared few ACGs. We also found that closely related orders that shared foot-propelled diving behavior did not share more ACGs than did distinct orders, suggesting that convergence among these orders could not be explained by their initial genomic backgrounds.ConclusionsOur analyses of three avian convergence events suggest low constraints for phenotypic convergence across multiple genetic levels, implying that genetic evolution is unpredictable at the phylogenetic level of avian order. Ours is one of first studies to apply hierarchical genomic examination to multiple avian convergent cases to assess the genetic constraints in life history trait evolution.

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Phenotypic convergence in a natural Daphnia population acclimated to low temperature

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