Earth's 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 organism's 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.

1Earth's temperature is increasing due to anthropogenic CO 2 emissions; and organ-2 isms need either to adapt to higher temperatures, migrate into colder areas, or face 3 extinction. Temperature affects nearly all aspects of organism's physiology via its in-4 fluence on metabolic rate and protein structure. Compared to other abiotic stresses, 5 genetic adaptation to increased temperature may be much harder to achieve due to sys-6 temic effects of temperature. As the evolutionary potential for adaptation to higher 7 temperatures is relatively unknown, we studied the quantitative genetics of thermal 8 performance curves of the fungal model system Neurospora crassa. We asked whether 9 there is genetic variation for thermal performance curves and examined possible ge-10 netic of evolution constraints by estimating the G-matrix. We observed substantial 11 amount of genetic variation for growth in different temperatures, and most genetic 12 variation was for performance curve elevation. Contrary to common theoretical as-13 sumptions we did not find strong evidence for genetic trade-offs for growth between 14 hotter and colder temperatures. We also simulated short term evolution of thermal per-15 formance curves of N. crassa, and suggest that they can have versatile responses to 16 selection. 17 Earth's temperature is rising due to anthropogenic activities (IPCC, 2013). The challenge most 19 organisms will face in a warming world is that they have to either adapt to warmer conditions or 20 migrate into colder areas to avoid extinction (Deutsch et al., 2008; Dillon et al., 2010; Araújo et al., 21 2013; Merilä and Hendry, 2014). Temperature is a unique abiotic stress, because the kinetics of 22 all biochemical reactions and protein stability are affected by temperature. As such, temperature 23 influences nearly all aspects of an ectothermic organism's physiology (Schulte, 2015; Arcus et al., 24 2016). Therefore, adapting to a higher temperature may be much more difficult than adapting to 25 a more specific environmental stress. For some anthropogenic stresses, such as antibiotics or her-26 bicides, decades of research have revealed strong evolutionary adaptation to these stresses (Davies 27 and Davies, 2010; Powles and Yu, 2010). However, genetic basis of adaptation to temperature is 28 likely to much more complex (Hochachka and Somero, 2002). 29According to quantitative genetic theory, evolution is possible if variation in a trait is heritable 30 and selection acts on this variation. However, the evolution of multivariate traits can be complicated 31 by genetic correlations, allowing evolution to proceed only in few directions or possibly preventing 32 it altogether (Walsh and Blows, 2009). The more entangled traits are with each other, the more 33 difficult the evolution of the underlying genetic network and the phenotype can be. 34The ability of an organism to tolerate different temperatures is often described by thermal per-35 formance curve (Huey and Kingsolver, 1989, 1993), which describes the fitn...

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