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Abstract Stomata play a critical role in regulating plant responses to climate. Where sister species differ in stomatal traits, interspecific gene flow can influence the evolutionary trajectory of trait variation, with consequences to adaptation.Leveraging six latitudinally-distributed transects spanning the natural hybrid zone betweenPopulus trichocarpa–P. balsamifera, we used whole genome resequencing and replicate common garden experiments to test the role that interspecific gene flow and selection play to stomatal trait evolution.While species-specific differences in the distribution of stomata persist betweenP. balsamiferaandP. trichocarpa, hybrids on average resembledP. trichocarpa. Admixture mapping identified several candidate genes associated with stomatal trait variation in hybrids includingTWIST, a homolog ofSPEECHLESSinArabidopsis, that initiates stomatal development via asymmetric cell divisions. Geographic clines revealed candidate genes deviating from genome-wide average patterns of introgression, suggesting restricted gene flow and the maintenance of adaptive differences. Climate associations, particularly with precipitation, indicated selection shapes local ancestry at candidate genes across transects.These results highlight the role of climate in shaping stomatal trait evolution inPopulusand demonstrate how interspecific gene flow creates novel genetic combinations that may enhance adaptive potential in changing environments.
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This content will become publicly available on December 1, 2026
Bounds on stomatal size can explain scaling with stomatal density in forest plants
Summary A prevailing hypothesis posits that achieving higher maximum rates of leaf carbon gain and water loss is constrained by geometry and/or selection to limit the allocation of epidermal area to stomata (fS). Under this ‘stomatal‐area minimization hypothesis’, highergs,maxis associated with greater numbers of smaller stomata because this trait combination increasesgs,maxwith minimal increase infS, leading to relative conservation offSsemi‐independent ofgs,maxdue to coordination in stomatal size, density, and pore depth. An alternative hypothesis is that the evolution of highergs,maxcan be enabled by a greater epidermal area allocated to stomata, leading to positive covariation betweenfSandgs,max; we call this the ‘stomatal‐area adaptation hypothesis’. Under this hypothesis, the interspecific scaling betweengs,max, stomatal density, and stomatal size is a by‐product of selection on a moving optimalgs,max.We integrated biophysical and evolutionary quantitative genetic modeling with phylogenetic comparative analyses of a global data set of stomatal density and size from 2408 vascular forest species. The models present specific assumptions of both hypotheses and deduce predictions that can be evaluated with our empirical analyses of forest plants.There are three main results. First, neither the stomatal‐area minimization nor adaptation hypothesis is sufficient to be supported. Second, estimates of interspecific scaling from common regression methods cannot reliably distinguish between hypotheses when stomatal size is bounded. Third, we reconcile both hypotheses with the data by including an additional assumption that stomatal size is bounded by a wide range and under selection; we refer to this synthetic hypothesis as the ‘stomatal adaptation + bounded size’ hypothesis.This study advances our understanding of scaling between stomatal size and density by mathematically describing specific assumptions of competing hypotheses, demonstrating that existing hypotheses are inconsistent with observations, and reconciling these hypotheses with phylogenetic comparative analyses by postulating a synthetic model of selection ongs,max,fS, and stomatal size.
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- Award ID(s):
- 2017949
- PAR ID:
- 10653937
- Publisher / Repository:
- New Phytologist
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 248
- Issue:
- 6
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- 2910 to 2926
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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