Sexual size dimorphism (SSD) is common across animal taxa and is thought to stem from sexual selection and fecundity selection, favouring large male or female body size, respectively. Environmental drivers are likely to affect variation in SSD between populations. However, if and how global warming affects SDD is largely unknown and the extent to which such effects may be caused by size- and sex-specific growth responses is not known at all. Here we studied if temperature and warming can affect SSD. Specifically we ask if body growth responses to warming vary between sexes, and if sex-specific responses vary with size and age. To this end, we analysed sex-specific responses of the fish species European perch (Perca fluviatilis), using data from (i) a 40-year whole ecosystem warming experiment and (ii) monitoring data from 100 temperate and subarctic lakes in Sweden and Finland across a large temperature gradient.
Results/Conclusions
We show for the first time that warming can increase the degree of SSD in fish, as evident from an observed increase in SSD with temperature over both time and space. The positive relationship between temperature (warming) and SSD increased with age and length. We show that this is caused by sex- and size-specific growth responses, as high temperature has stronger negative effects on body growth at old age/large size in males than in females. Given the importance of large females for population productivity, and therefore population dynamics and stability, not accounting for sustained high body growth of females in warm waters may give erroneous predictions on population productivity. Our results imply that global climate change may have very different effects on males and females. Accurate predictions on fish body growth and production in a warming climate require acknowledging that growth responses can be sex-specific.