Researcher Institute of Environmental Sciences, Jagiellonian Univeristy Krakow, Poland
Background/Question/Methods
Body size decrease with increasing temperature was invoked one of the most important factors affecting communities exposed to global warming. What is the role of oxygen in size-to-temperature response? Theoretical predictions and some empirical evidence show that this variable may drive the pattern of size decrease with increasing temperature. However, the number of studies addressing this issue is not sufficient to draw the reliable conclusions. We used an experimental evolution tool to test for the body size evolution in rotifers exposed to normoxic vs. hypoxic conditions. The three experimental treatments had the same thermal conditions (three temperatures fluctuating in regular cycles) and were differentiated by oxygenic conditions, into normoxia, hypoxia at all temperatures and hypoxia at highest temperature only. After the six-month experiment, post-evolution rotifers were tested for plastic body size response to temperature at five temperatures, three of which mimicked the temperatures from experimental evolution and two additional temperatures were lower than experimental temperatures. Additionally, we estimated population growth rate as a proxy of fitness, to be able to interpret the evolutionary meaning of the plastic body size response.
Results/Conclusions
Normoxic rotifers evolved significantly larger size than two hypoxic rotifer groups, with no difference in size between the two. All three groups displayed similar ability to plastic size-to-temperature response, but only at temperatures which they were previously exposed to, while responses at two lower temperatures were complex and differed among rotifer groups. Regardless the response pattern, rotifer post-evolutionary groups did not differ in fitness. We conclude that rotifers show genetic basis for size decrease under hypoxia, and that this response is specifically important at highest temperatures, when the shortage of oxygen availability is more pronounced. Plastic size-to-temperature response is sensitive to environmental cues which means that it is subjected to evolution. Finally, in the short-term response, any response to acute thermal conditions, whether plastic or (possibly) physiological, does not lower fitness. It is not known whether different responses would become costly in the longer time-scale. Our results show how important is to incorporate oxygen conditions, along with thermal conditions, into the models and field studies which aim to predict and/or unravel the issue of possible consequences of global climatic changes on the whole communities.
