Biology subjects

Summanen, P. A. M.

Publications and source records attributed to Summanen, P. A. M..

6 recordsLinked to original sources

bioRxiv2024

The effect of population size on adaptation to fluctuating temperatures

Climate change exposes populations to more frequent periods of extreme temperatures and faster temperature fluctuations. Theoretical models suggest that different types of adaptations should occur in constant versus fluctuating environments of varying frequency. Furthermore, evolutionary adaptation to one environment may weaken the adaptations to alternative environments due to antagonistically pleiotropic alleles. However, fitness trade-offs are rarely observed in experiments and it has been hypothesized that the number and severity of trade-offs evolving in fluctuating environments might depend on population size. To evaluate whether specific types of adaptations evolve at fluctuating temperatures and how population size affects the evolution of trade-offs, we performed an evolution experiment with fission yeast (Schizosaccharomyces pombe). The small and large populations evolved for 500 generations at constant and fluctuating temperatures, after which the evolved strains competed against ancestral strains in respective selection environments and in alternative environments to detect trade-offs. We observed significant adaptation and maladaptation only to constant heat, but not to fluctuating temperatures. Overall, the population size did not have significant effects on adaptation capacity or trade-offs in alternative environments. Our results suggest that constant extreme temperatures may act as stronger selective pressures than temperature variation and that trade-offs are unlikely to constrain adaptation to fluctuating temperatures.

evolutionary biology↗

bioRxiv2024

Genome-wide association mapping for growth rate at fluctuating and extreme temperatures

Constant temperatures and fluctuations of varying frequency affect fitness differently, which has led to suggestions of distinct genetic architectures and adaptation strategies between constant and fluctuating thermal environments. However, very little is known about the possible fitness trade-offs and genetic constraints underlying thermal adaptation and how they affect species ability to confront climatic changes. We addressed this gap in knowledge by integrating quantitative genetics and genome-wide association mapping in the filamentous fungus Neurospora crassa. Growth rates were measured for 434 strains under fast and slow frequency fluctuations, at high and low temperature range with respect to the species tolerance, and at constant mean and extreme temperatures of these ranges. We found strong genetic correlations between fast and slow frequency fluctuations, and between fluctuations and their mean temperatures, but not with the highest extreme temperature. Positive correlations were supported by high heritability values, pointing that in N. crassa there are no significant trade-offs or genetic constraints in adaptation when variance in temperature increases. Altogether, our results indicated clearly polygenic basis of thermal tolerance, with most of the variation in overall performance (83 %), and clearly less in hot-cold trade-off (8 %), or heat stress tolerance (4 %). Interestingly, GWAS discovered many SNPs associated with growth rate only at constant temperatures or at fast and slow fluctuations at high and low thermal range. However, the cellular functions of the associated genes were overlapping, and no opposite allelic effects were found between treatments. Hence, large-effect loci indicated no trade-offs, but a shared physiology across temperatures, probably owing to the general stress response or individuals overall fitness.

evolutionary biology↗

bioRxiv2024

Genome-wide association for loci influencing thermal performance curves in Neurospora crassa

Temperature poses a unique challenge to ectothermic species, as it affects all biochemical reactions in the cell and causes physiological stress. The effect of temperature on an organism can be described by a thermal performance curve (TPC), which displays organismal performance, such as growth rate, as a function of temperature. Previous studies on thermal performance have revealed different amounts of genetic variation and trade-offs in TPC shape and position within species and populations. However, very little is known about the genetic architecture of TPCs on the level of individual loci and alleles. We asked what is the identity of loci contributing to genetic variation in TPCs, and do the alleles exhibit trade-offs or thermodynamic scaling across the temperature range? We used genome-wide association mapping to find loci influencing growth rate at different temperatures and TPC traits in the filamentous fungus Neurospora crassa. We also evaluated the directions and magnitudes of allelic effects to investigate possible trade-offs. We observed both unique associations at specific temperatures, as some loci affected growth rate only at low, intermediate, or high temperatures, and associations that were shared across multiple temperatures. However, only weak evidence of trade-offs was detected, indicating that the evolution of TPCs in N. crassa is not constrained by allelic effects in opposite directions at hot and cold temperatures. Our findings indicate that trade-offs contribute little to variation in TPCs.

genetics↗

bioRxiv2022

Parental effects in a filamentous fungus: phenotype, fitness, and mechanism

Adaptation to changing environments often requires meaningful phenotypic modifications to match the current conditions. However, obtaining information about the surroundings during an organisms own lifetime may only permit accommodating relatively late developmental modifications. Therefore, it may be advantageous to rely on inter-generational or trans-generational cues that provide information about the environment as early as possible to allow development along an optimal trajectory. Transfer of information or resources across generations, known as parental effects, is well documented in animals and plants but not in other eukaryotes, such as fungi. Understanding parental effects and their evolutionary consequences in fungi is of vital importance as they perform crucial ecosystem functions. In this study, we investigated whether parental effects are present in the filamentous fungus Neurospora crassa, how long do they last, are the effects adaptive, and what is their mechanism. We performed a fully factorial match / mismatch experiment for a good and poor quality environment, in which we measured mycelium size of strains that experienced either a matched or mismatched environment in their previous generation. We found a strong silver spoon effect in initial mycelium growth, which lasted for one generation, and increased fitness during competition experiments. By using deletion mutants that lacked key genes in epigenetic processes, we show that epigenetic mechanisms are not involved in this effect. Instead, we show that spore glycogen content, glucose availability and a radical transcription shift in spores are the main mechanisms behind this parental effect.

microbiology↗

bioRxiv2022

Variation in spontaneous mutation rate and spectrum across the genome of Neurospora crassa

While mutation rates have been extensively studied, variation in mutation rates throughout the genome is poorly understood. To understand patterns of genetic variation, it is important to understand how mutation rates vary. Chromatin modifications may be an important factor in determining variation in mutation rates in eukaryotic genomes. To study variation in mutation rates, we performed a mutation accumulation experiment in the filamentous fungus Neurospora crassa, and sequenced the genomes of the 40 MA lines that had been propagated asexually for approximately 1015 [1003, 1026] mitoses. We detected 1322 mutations in total, and observed that the mutation rate was higher in regions of low GC, in domains of H3K9 trimethylation, in centromeric regions, and in domains of H3K27 trimethylation. The rate of single nucleotide mutations in euchromatin was 2.46 [2.19, 2.77] x 10-10. In contrast, the mutation rate in H3K9me3 domains was tenfold higher: 2.43 [2.25, 2.62] x 10-9. We also observed that the spectrum of single nucleotide mutations was different between H3K9me3 and euchromatic domains. Our statistical model of mutation rate variation predicted a moderate amount of extant genetic variation, suggesting that the mutation rate is an important factor in determining levels of natural genetic variation. Furthermore, we characterized mutation rates of structural variants, complex mutations, and the effect of local sequence context on the mutation rate. Our study highlights that chromatin modifications are associated with mutation rates, and accurate evolutionary inferences should take variation in mutation rates across the genome into account.

genetics↗

bioRxiv2020

Quantitative genetics of temperature performance curves of Neurospora crassa

Earths temperature is increasing due to anthropogenic CO2 emissions; and organisms need either to adapt to higher temperatures, migrate into colder areas, or face extinction. Temperature affects nearly all aspects of an organisms physiology via its influence on metabolic rate and protein structure, therefore genetic adaptation to increased temperature may be much harder to achieve compared to other abiotic stresses. There is still much to be learned about the evolutionary potential for adaptation to higher temperatures, therefore we studied the quantitative genetics of growth rates in different temperatures that make up the thermal performance curve of the fungal model system Neurospora crassa. We studied the amount of genetic variation for thermal performance curves and examined possible genetic constraints by estimating the G-matrix. We observed a substantial amount of genetic variation for growth in different temperatures, and most genetic variation was for performance curve elevation. Contrary to common theoretical assumptions, we did not find strong evidence for genetic trade-offs for growth between hotter and colder temperatures. We also simulated short term evolution of thermal performance curves of N. crassa, and suggest that they can have versatile responses to selection.

evolutionary biology↗