Tiistai 29.12.2020 klo 16:28 - Mikko Nikinmaa
A temperature increase will affect fish populations everywhere. Depending on the species, the depth of the aquatic body and its accessibility the effects can be drastic – the most extreme outcome being the total disappearance of the fish from the habitat. Because of this, the research on temperature biology of fish has become an important field of study in climate change research. The importance of fish studies is strengthened, as they can be an primary source of animal protein in food.
Fish can be either stenothermal or eurythermal. The definitions indicate the phenotypic plasticity of species with regard to temperature. Stenothermal species tolerate only small temperature changes, whereas eurythermal species can live in wide temperature range. It should be noted that most of the preferred fisheries species have narrow genotypic temperature tolerance. If they live in environments with different temperatures, their genotypes are different, each still having narrow temperature tolerance so that the cold-temperature genotype would not be able to tolerate the temperatures that the warm-temperature genotype lives in and vise versa. Although a temperature increase may actually increase the amount of fish flesh produced per unit time, the species accounting for the increased productivity are not preferred catch or food.
The roles of phenotypic plasticity and the speed of heritable genetic adaptation to temperature changes has been surprisingly little studied.
Further, it is almost completely unknown, if the temperature tolerance is affected by environmental contaminants. One important recent study with zebrafish (Morgan et al. PNAS 2020: https://www.pnas.org/cgi/doi/10.1073/pnas.2011419117) suggests that the genetic adaptation to increased temperature is not fast enough to keep pace with the temperature increase that is currently occurring. It also appears that the plasticity of tolerated temperatures decreases, when the population adapts to increased maximal temperature.
So, this is bad news throughout. The fish that we like to eat are stenothermal. The eurythermal species could substitute for them, but even they have problems in genetic adaptation. Furthermore, it seems that tolerance to reduced temperature evolves faster than that to increased temperature. All of these points make the case for markedly slowing down and stopping the current temperature increase stronger. If we want to eat fish, climate change must be stopped.
Tiistai 25.12.2018 klo 13:10 - Mikko Nikinmaa
When animal (or plant) populations must face environmental change such as increased themperature, eutrophication etc. the greater the variability between organisms, the more likely it is that at least some specimens are able to tolerate the disturbed conditions. Hitherto it has been virtually always been thoght that the only important thing in this regard is genetic variability. However, individual variation is possible also without genetic variation: a single genotype can have quite different phenotypes, which tolerate different conditions.
In the case that the environment is very labile such phenotypic plasticity - i.e. individual variations in physiological function of one genotype - is better way of tolerating unfavourable environment than having genetically heterogenous populatio with one genotype tolerating that environmental problem. This is because the plasticity of the individuals that tolerate the unfavourable environment is as large as that of the original population. If, however, the tolerance depends on the genotypic variation, it is likely that the overall plasticity of the tolerant genotype is smaller than that of the original, genetically variable population. Genetical variability can be of significant benefit only in cases where the change is to one direction. The possible importance of measures of individual variation in environmental response has recently been discussed in our article (Nikinmaa and Anttila, Aquatic Toxicology, 207, 29-33; open access). Our experimental results on oil-exposed water fleas also indicate that a change in individual variability can occur even when no change is seen in the mean of the measured parameter.