Does sexual dimorphism predispose dioecious riparian trees to sex ratio imbalances under climate change?
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Environmental changes have resulted in significant declines in native riparian forests that are comprised largely of dioecious tree taxa, including boxelder and iconic cottonwood/willow gallery forests. Dioecious species may be especially vulnerable to the effects of climate change given that they often exhibit skewed sex ratios that are reinforced by physiological and morphological specialization of each sex to specific microhabitats. A comprehensive data synthesis suggests that male individuals of boxelder and cottonwood taxa have a higher representation on dry microhabitats than females and are less physiologically sensitive to increased aridity than co-occurring females. Consequently, extreme male-biased sex ratios are possible under future climate conditions that could reduce population fitness below a sustainable threshold. Riparian willows, on the other hand, generally do not express obvious sexual dimorphism in habitat preference or physiological sensitivity to aridity. Thus, it is unclear whether climate change will impact population structure of willows in ways that parallel other dioecious riparian tree taxa. Future riparian tree restoration programs should aim to maintain future sex ratio balance that maximizes population fitness under projected hydro-climatological conditions. Recent advances in genomics will likely provide the critical tools for early sex determination in pre-reproductive trees across riparian tree species such that sex ratio balance could be targeted during initial stages of restoration, along with adaptations for drought tolerance and other key traits that are essential for survival under future conditions.
KeywordsRiparian cottonwoods Riparian willows Boxelder Leaf gas exchange Sex ratio bias
Financial support was provided by a grant from the National Science Foundation’s (Grant No. 1340856) MacroSystems Biology program awarded to KRH and grants awarded to JKW from the National Science Foundation’s Integrated Organismal Systems program. Additional financial support was provided to JKW by the University of Kansas.
Author contribution statement
KRH, JKW and TED originally formulated the idea for the manuscript. KRH conducted the literature review on dioecy patterns of gas exchange and growth, and wrote the text for the main body of the manuscript. KRH and SEB provided data for the manuscript and JKW provided comprehensive editorial input throughout the manuscript.
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