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IMPACTS OF PROJECTED CLIMATE CHANGE ON THE EVOLUTION OF BEHAVIOR AND LIFE HISTORY IN SEED BEETLES

The most recent (sixth) assessment report from the Intergovernmental Panel on Climate Change (IPCC, 2021) states:听鈥淗uman-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5).鈥�

Although it is now widely accepted that anthropogenic greenhouse gas emissions are driving many of these observed climate changes, the impacts of projected climate change on biological systems is notoriously difficult to measure. Ecosystem dynamics are highly nonlinear and multidimensional, and communities that may appear stable in the face of temperature change or shifts in precipitation may suddenly crash. To make matters worse, regional climate change may come in the form of slight changes in the temperature or precipitation means, or as increased occurrences of their extreme high or low values, or as changes in the timing of seasonal phenomena, or as unanticipated statistically subtle changes which, nevertheless, may have significant impacts on individual communities within a larger ecosystem. This highlights the need for carefully controlled climate change impact experiments, conducted in closely monitored laboratory settings.

To address this need, Professors Berg and Piani are investigating the impact of daily and seasonal temperature shifts on the behavior, life history and evolution of seed beetles (Callosobruchus maculatus) in AUP鈥檚 laboratory. Their goal is to assess not only which traits various temperature shifts affect, but how quickly and effectively beetles are able to adapt to projected future climate changes. The seed beetle is an excellent model system in which to test the potential effects of climate change on wildlife. C.听maculatus听is a common pest of stored legumes, and the laboratory environment represents a close approximation of this beetle鈥檚 natural habitat (Fox et al. 2003). We already know a huge amount about C.听maculatus鈥檚听behavior and life history (for example, see the many publications of Professor Charles Fox, University of Kentucky). Males and females are easy to tell apart, hatch success is high, and generation time is short 鈥� a mere three weeks (Beck & Blumer 2014). All the beetles need to thrive is a jar with some host beans (for example, mung beans) and a controlled environment. The lab is equipped with two state-of-the-art climate chambers that we can program to different temperatures, humidities and light cycles.

Our research is divided into two major phases. During the first phase of experiments, we maintained two distinct populations of seed beetles in two different chambers over the course of 19 generations (about 15 months). The 鈥渃ontrol鈥� chamber was set to a constant and universally accepted baseline for lab populations of this species (29掳C, 50% relative humidity, and a 12-hour light:dark cycle). In the second 鈥渆xperimental鈥� chamber, daily temperatures fluctuated around a higher mean of 33掳C, more stressful conditions that are representative of the current base climate of this species鈥� native environment of southern India. In a series of 16 simultaneous experiments, completed in the Spring of 2017 with the help of undergraduate Wei-Tse Hung, we exposed beetles to different conditions and measured subsequent reproductive success, body size and development time (time from when an egg was laid until an adult emerged). We found that beetles that had evolved in the more stressful fluctuating conditions were smaller in body size when switched to a constant 29掳C and had far greater reproductive fitness in comparison to beetles from both the constant control and continuously stressful 33掳C environments. This suggests that beetles raised in environments under thermal stress were more 鈥減lastic鈥� in their response and had greater genetic variability than control treatment beetles and indicates that populations that experience fluctuations in temperature may be better able to respond to short-term changes in environmental conditions. We are in the process of submitting a manuscript for publication in an evolutionary journal.

Click here to see the full听Fluctuating Temperature Experimental Design.

In phase two of this project, we will run a similar set of experiments on beetles that have been exposed to periodic heat waves for 19鈥�20 generations (15鈥�16 months). Heat waves are projected to increase in frequency, duration and intensity in southern India in the coming decades, and our aim is to understand how organisms might respond. We began exposing populations to heat waves in Fall 2021 with the hopes of conducting our experiments in Spring 2023.

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REFERENCES:

• Beck, C.W. & Blumer, L.S. 2014. A handbook on bean beetles,听Callosobruchus maculatus.听Downloaded from
• Fox, C.W., Bush, M.L. & Wallin, W.G. 2003 Maternal age affects offspring lifespan of the seed beetle,听Callosobruchus maculatus.听Functional Ecology听17: 811-820.
• IPCC. 2013.听Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change听[Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
• IPCC. 2021. Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [MassonDelmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. P茅an, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelek莽i, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press