COS 132-2 - Sex-dependent phenological responses to climate vary across species’ ranges

Abstract: Anthropogenic climate change has significantly altered the timing of life history events (i.e., phenology) of plants worldwide, affecting their reproduction, survival, and interactions. Recent studies utilizing herbarium specimens have uncovered significant intra- and inter-specific variation in plant flowering phenology and its response to changes in climate. However, most of this research has been limited to animal pollinated species with large and/or showy flowers, and variation in phenological responses to climate remain largely unexplored among and within wind-pollinated dioecious species, and across sexes. Using both herbarium specimens and volunteer observations of cottonwood (Populus) species in North America, here we examined how phenological sensitivity to climate varies among species, across species ranges, between sexes, and between different phenophases to assess how climate change may affect the synchrony and reproduction of wind-pollinated dioecious species. The timing of flowering and fruiting varied significantly across and within species, as did their sensitivity to winter temperature. In particular, we found that male flowering generally happens earlier in the season and is more sensitive to warming (−2.2 d/°C) than female flowering (−1.6 d/°C). Further, the onset of flowering was more sensitive to changes in temperature than leaf out. Increased temporal gaps between male and female flowering time and between the first open flower date and first leaf out date were predicted in the near future. Our study demonstrates the presence of significant intra-specific variation in phenology and its responses to environmental cues, across species’ ranges, phenophases, and sex. These variations need to be taken into account to accurately predict the effects of climate change and assess their ecological and evolutionary consequences.