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.