Genetic Response to Rapid Climate Change

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1 Genetic Response to Rapid Climate Change William E. Bradshaw & Christina M. Holzapfel Center for Ecology & Evolutionary Biology University of Oregon, Eugene, OR 97403, USA Our Students & Post-Doctoral Fellows

2 Northern climates are becoming more like southern climates Warming winters Earlier springs Later onset of winters Longer growing seasons Selection on seasonal timing of development, reproduction, migration and dormancy Annual change in day length remains the same from year to year. Unlike temperature, annual change in day length is not affected by global warming. Many animals use this highly reliable length of day to anticipate and prepare for future seasonal change in the environment. Response to day length is genetically determined and often highly heritable.

3 Is rapid climate change driving evolution (genetic change) in animal populations? What are the relative roles of temperature and response to day length in this process?

4 Day length can be used to anticipate seasonal change Seasonality and the onset of winter select for the optimal response to day length. 17 Onset of Winter North South 15 Day Length Day Length Julian Date Julian Date Northern populations should use a longer day length to switch from continuous development to dormancy

5 How should climate warming affect response to day length? Onset of Winter Climate Warming In the climate warming literature, the overwhelming emphasis is on the direct effects of temperature. Day Leng th Winter comes later Given the predictions to the left, what is the relative importance of temperature and response to day lengths as targets of selection during rapid climate warming? Julian Date Later onset of winter will select for a shorter switching day length.

6 What is the relative importance of temperature vs. the correct interpretation of day length to fitness in natural populations? North = 50 N = 200 years of climate warming at present rate South = 40 N

7 When we controlled for differences in day length and temperature. No change in fitness when northern animals were exposed to 200 years of climate warming but there was an 88% loss of fitness due to experiencing the wrong day length. Hence, rapid climate change is driving evolution NOT through the direct effects of temperature, but rather through the genetically-determined response to day length. Consequently, one cannot assess the potential impact of climate change by transplanting from north to south in nature, because such transplants will always confound the effects of temperature with the effects of novel day lengths.

8 How widespread is the use of day length among animals to control the seasonal timing of development, reproduction, hibernation or migration?

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11 There are already five examples of evolutionary (genetic) response to recent, rapid climate change: all involve decadal studies all involve a genetic shift in seasonality. Except for Drosophila, all of these evolutionary responses involve the use of day length

12 Biological Implications for Policy Makers Recognize that the primary selection imposed by climate warming is on the mechanisms regulating seasonal events, especially response to day length. Recognize that transplants between northern and southern localities in nature are misleading because they always confound the effects of temperature and day length. Recognize that the emphasis on the direct effects of temperature as the major selective force driving evolutionary response to rapid climate warming is misdirected. Recognize that the earth is warming and is will continue to do so through at least the next century. Therefore, in addition to mitigation, we must plan in advance for temperate and polar climates to become more southern-like. Plans should include development of policies emphasizing response to day length, appropriate for longer growing seasons, earlier springs and later winters. This planning is especially important for long-lived organisms such as forest trees and organisms with complex life cycles such as salmon.