Temperature increases but day length does not: an additional problem caused by climate change
Keskiviikko 18.9.2019 klo 15:59 - Mikko Nikinmaa
In temperate and arctic environments most organisms use the predictable day length changes as cues to respond appropriately to oncoming temperature changes (coming of winter or spring; availability of food; time to reproduce; change of fur colour). The day length-temperature interrelationship has remained constant so long that many evolutionary adaptations have taken place. Hares and squirrels change fur colour, hedgehogs start to hibernate, virtually all temperate and arctic mammals and birds reproduce, when food is plentiful, and coastal Arctic fish produce mRNA from gene encoding antifreeze protein in expectation that the protein is needed.
The day length-temperature relationship is unique for geographically distinct populations. For this reason, even if the temperature tolerance of a southern population of a species would be right for migration to north, the day length temperature mismatch would, for example, make the animal to reproduce, when the food availability is not optimal. Similarly, animals from different latitude change their fur colour at different times. Because of this, even if climate change resulted in temperatures that would be suitable for a southern population of a species, its day length requirements would be inappropriate.
With climate change, the day length-temperature mismatch becomes a serious problem. It is aggravated by the fact that plants and insects with short generation time will be able to respond to temperature increase much more rapidly than vertebrates, which have evolved seasonality. Consequently, food availability during breeding may not be optimal, leading to reduced reproductive success. This kind of indirect effect of climate change on animals is seldom mentioned, but can be even greater that temperature effects themselves alone. We pointed out the problem in Prokkola and Nikinmaa (2018) Circadian rhythms and environmental disturbances – underexplored interactions. J. Exp. Biol. 221, jeb179267; it has recently been reviewed by Walker et al. (2019) Global climate change and invariable photoperiods: A mismatch that jeopardizes animal fitness. Ecology and Evolution 9:10044–10054. Owing to their long generation time, vertebrates can hardly adapt (i.e. accumulate required genetic changes) to the changing day length-temperature relationship. However, tolerance is possible if the plasticity is large: this requires either large genetic variability within population or large phenotypic plasticity (=individual variation) of a genotype.