Meeting Abstract
Climate change will increase both the average temperature of environment but also the frequency and duration of extreme thermal events as has been seen during summer 2018 in the whole northern hemisphere. These heat waves have led to mass fish death events around the world. The ability of ectotherms to respond to these sudden temperature changes can be exerted throughout a mechanism of phenotypic plasticity. There are, however, no studies how fish that have experienced long term (decades) increase of temperature in their habitat are able to respond to heat waves. The capacity of individuals to change their tolerance will, nevertheless, define survival capability of entire populations. We evaluate the thermal plasticity of critical thermal maximum (CTmax) in six populations of three-spined sticklebacks to a heat wave (increase of environmental temperature by 11°C for 8 days). Populations were from coastline and from areas that have been warmed by ~10°C by nuclear power plants for four decades in Finland. Surprisingly, the decades of warming has not increased the thermal tolerance of sticklebacks. Yet, all the individuals from each population were able to increase their tolerance after the heat shock by 2.5-4°C ( p < 0,001 ), but again there were no significant differences between the populations. We propose that adaptive capacity to increase the upper thermal tolerance may be limited in three-spined sticklebacks. Yet, studied sticklebacks possess some phenotypic plasticity to respond to heat waves as long as waves stay below their upper thermal limits.
