Abstract
Hybridization is a biological phenomenon increasingly recognized as an important evolutionary process in both plants and animals, as it is linked to speciation, radiation, extinction, range expansion and invasion, and allows for increased trait diversity in agricultural and horticultural systems. Estimates of hybridization frequency vary across taxonomic groups, but causes of this variation are unknown. Here, we ask on a global scale whether hybridization is linked to any of 11 traits related to plant life history, reproduction, genetic predisposition, and environment or opportunity. Given that hybridization is not evenly distributed across the plant tree of life, we use phylogenetic generalized least squares regression models and phylogenetic path analysis to detect statistical associations between hybridization and plant traits at both the family and genus levels. We find that perenniality and woodiness are each weakly associated with an increased frequency of hybridization in univariate analyses, but path analysis suggests that the direct linkage is between perenniality and increased hybridization (with woodiness having only an indirect relationship with hybridization via perenniality). Weak associations between higher rates of hybridization and higher outcrossing rates, abiotic pollination syndromes, vegetative reproductive modes, larger genomes, and less variable genome sizes are detectable in some cases but not others. We argue that correlational evidence at the global scale, such as that presented here, provides a robust framework for forming hypotheses to examine and test drivers of hybridization at a more mechanistic level.
Highlights
Hybridization is increasingly recognized as an important evolutionary phenomenon in plants (Mallet 2005; Arnold and Arnold 2006; Whitney et al 2010), animals (Mallet 2005; Schwenk et al 2008), and fungi (reviewed in (Albertin and Marullo 2012)
Ellstrand et al 1996, Rieseberg and Wendel 1993 for raw correlations, in both directions), and our results suggest that perhaps the less-discriminant abiotic pollination mode may lead to more hybridization
We found several strong phylogenetically informed associations between hybridization rates and plant attributes
Summary
Hybridization is increasingly recognized as an important evolutionary phenomenon in plants (Mallet 2005; Arnold and Arnold 2006; Whitney et al 2010), animals (Mallet 2005; Schwenk et al 2008), and fungi (reviewed in (Albertin and Marullo 2012). More modern analyses based on floras or surveys of the literature have found different rates of hybridization in different taxonomic groups, with evidence for phylogenetic signal (Ellstrand et al 1996; Whitney et al.2010; Abbott 2017; Beddows and Rose 2018). Ferns and their allies and specific flowering plant families (such as Orchidaceae, Lamiaceae, Asparagaceae, and Asteraceae) contain high numbers of hybridizing species, while other families appear to contain few hybrids (such as Caryophyllaceae, Cyperaceae, and Apiaceae) (Whitney et al 2010)
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