Across systems, pollinators are visually attracted to larger flowers due to the association with greater pollen reward and nectar quantities (Lavi and Sapir 2015; Parachnowitsch et al. 2019). Pollinators are then potent agents of directional selection that favors larger flower size (Caruso et al. 2019). While animals pollinate about 85% of all species of flowering plants (Ollerton et al. 2011), climate change has resulted in a global decline in pollinator abundance and is expected to disrupt these pollinator-mediated selection regimes (Potts et al. 2010). I. missouriensis with a pollinator, Lycaeides melissa. Photo taken by Samantha Day. Abiotic factors such as drought and thermal stress can increase water loss through transpiration from larger flowers resulting in selection for smaller floral displays (Gallagher and Campbell 2017). Climate change is expected to disrupt rainfall patterns and increase global aridity (IPCC 2014), while also reducing the overlap between flowering times and pollinator activity periods (Memmott et al. 2007). These shifts risk the extinction of pollinators that require floral food sources and obligate outcrossing plants that require pollinators for reproduction (Fox and Jönsson 2019). Pollinator selection for larger flower size directly contrasts drought-mediated selection for smaller flowers due to increased water loss from larger floral displays (Sapir et al. 2002). We are using the Colorado native species Iris missouriensis to investigate this balance of abiotic and biotic factors acting as conflicting selective agents on flower size. Our work is based out of the Rocky Mountain Biological Laboratory in Gothic, Colorado. In this mountain range, elevation is tightly associated with aridity, such that low elevation locales are hot and dry while elevation gain leads to cooler and moist climates (Wadgymar et al. 2017; Wadgymar et al. 2018). We predict that selection on flower size will change in response to the climatic gradient: flowers will be larger at higher elevations where pollinator selection will dominate, while in the arid lower elevation locales water loss and drought stress will tip the balance and induce selection for smaller flowers. Beginning in the summer of 2020, we have collected floral measurements from natural populations of I. missouriensis across an elevational gradient. In future field seasons, we will continue floral measurements of natural populations to document clines in flower size across years where climates may vary. We plan to evaluate pollinator communities and preferences for flower size in these natural populations. We will also conduct common garden experiments that will allow us to identify patterns of selection and disentangle the balance of conflicting selection on flower size. We anticipate that this work will contribute to conservation practices for flowering species under climate change conditions Samantha Day with I. missouriensis. Photo taken by Inam Jameel. References: Caruso, C. M., K. E. Eisen, R. A. Martin, and N. Sletvold. 2019. A meta-analysis of the agents of selection on floral traits. Evolution 73:4-14. Fox, N. and A. M. Jönsson. 2019. Climate effects on the onset of flowering in the United Kingdom. Environmental Sciences Europe 31. Gallagher, M. K. and D. R. Campbell. 2017. Shifts in water availability mediate plant-pollinator interactions. New Phytol 215:792-802. IPCC. 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change in R. K. P. a. L. A. M. e. [Core Writing Team, ed, Geneva, Switzerland. Lavi, R. and Y. Sapir. 2015. Are pollinators the agents of selection for the extreme large size and dark color in Oncocyclus irises? New Phytol 205:369-377. Memmott, J., P. G. Craze, N. M. Waser, and M. V. Price. 2007. Global warming and the disruption of plant-pollinator interactions. Ecol Lett 10:710-717. Ollerton, J., R. Winfree, and S. Tarrant. 2011. How many flowering plants are pollinated by animals? Oikos 120:321-326. Parachnowitsch, A. L., J. S. Manson, and N. Sletvold. 2019. Evolutionary ecology of nectar. Ann Bot 123:247-261. Potts, S. G., J. C. Biesmeijer, C. Kremen, P. Neumann, O. Schweiger, and W. E. Kunin. 2010. Global pollinator declines: trends, impacts and drivers. Trends Ecol Evol 25:345-353. Sapir, Y., A. Shmida, O. Fragman, and H. P. Comes. 2002. Morphological variation of the Oncocyclus irises (Iris: Iridaceae) in the southern Levant. Botanical Journal of the Linnean Society 139:369-382. Wadgymar, S. M., S. C. Daws, and J. T. Anderson. 2017. Integrating viability and fecundity selection to illuminate the adaptive nature of genetic clines. Evol Lett 1:26-39. Wadgymar, S. M., R. M. Mactavish, and J. T. Anderson. 2018. Transgenerational and Within-Generation Plasticity in Response to Climate Change: Insights from a Manipulative Field Experiment across an Elevational Gradient. Am Nat 192:698-714
