Limited evidence for a positive relationship between hybridization and diversification across seed plant families

Abstract

Hybridization has experimental and observational ties to evolutionary processes and outcomes such as adaptation, speciation, and radiation. Although it has been hypothesized that hybridization and diversification are positively correlated, this idea remains largely untested empirically, and hybridization can also potentially reduce diversity. Here, we use a hybridization database on 170 seed plant families, life history information, and a time‐calibrated phylogeny to test for phylogenetically‐corrected associations between hybridization and diversification rates, while also taking into account life‐history traits that may be correlated with both processes. We use three methods to estimate diversification rates and two metrics of hybridization. Although hybridization explains only a small amount of overall variation in diversification rates, we show that diversification and hybridization are sometimes positively correlated, although the effect sizes are very small. Moreover, the relationship remains detectable when incorporating the correlations between diversification and two other life history characteristics, perenniality and woodiness. We discuss potential mechanisms for this association under four different scenarios: hybridization may drive diversification, diversification may drive hybridization, both hybridization and diversification may jointly be driven by other factors, or, as an alternative, that there is in fact no relationship between the two. We suggest future studies to disentangle the causal structure.

The dynamics of introgression across an avian radiation

“… 2005 ), or by producing new hybrid species (Mallet 2007 ). This creative role for hybridization may explain observed correlations between hybridization frequency and net species diversification, as seen in salamanders and plants (Mitchell and Whitney 2021 ; Patton et al. 2020 ).…”

Deep reticulation: the long legacy of hybridization in vascular plant evolution

“…Is the propensity to hybridize itself an adaptive life history strategy? Our discussions here build on previous considerations of these questions (e.g., Grant 1971;Ellstrand et al 1996;Whitney et al 2010;Folk et al 2018a;Mitchell et al 2019;Mitchell and Whitney 2021). The prevalence of reticulation has also led some to question whether a bifurcating tree is the most appropriate way to model the diversification process and conceptualize evolutionary history more generally (e.g., Funk 1981;Linder and Rieseberg 2004;Bapteste et al 2013).…”

“…In fact, even in cases of tight pollinator specialization, such as figs, hybridization can still occur, perhaps in particular during pollinator-host switches (Wang et al 2021). A study by Mitchell et al (2021) examined the correlation of 11 different traits with hybridization and found weak positive associations between perenniality, woodiness, outcrossing, abiotic pollination, and larger genomes and increased frequencies of hybridization, but some of these results were scale dependent. Hybridization is a complex phenomenon that appears to require the confluence of several to multiple abiotic and biotic factors (and for populations to persist once formed), and so it is not surprising that particular traits generally show inconsistent relationships with hybridization frequency.…”

Hybrid evolution repeats itself across environmental contexts in Texas sunflowers ( Helianthus )

“…Hybridization is another key field in evolutionary biology, with a major question being the extent to which hybridization and/or introgression between taxa act as evolutionary fuel in promoting speciation, evolution, and diversification (Anderson and Stebbins 1954; Barrett and Schluter 2008;Stelkens et al 2014;Marques et al 2019;Taylor and Larson 2019) versus the circumstances under which these processes act as homogenizers, reducing diversity or leading to extinction (Rhymer and Simberloff 1996;Wolf et al 2001;Todesco et al 2016). At the macroevolutionary scale, hybridization has been linked to evolutionary radiation (Anderson and Stebbins 1954;Stebbins 1959;Barton 2001;Seehausen 2004;Yakimowski and Rieseberg 2014;Berner and Salzburger 2015;Stankowski and Streisfeld 2015;Grant and Grant 2019;Marques et al 2019;Meier et al 2019) and potentially diversification (Mitchell and Whitney 2021). Hybridization can also lead to adaptation (Lewontin and Birch 1966;Campbell and Snow 2007;Hovick et al 2012;Stankowski and Streisfeld 2015;Mitchell et al 2019) and speciation (Rieseberg 2003;Rieseberg et al 2007;Soltis and Soltis 2009;Abbott et al 2013).…”

“…2019; Meier et al. 2019) and potentially diversification (Mitchell and Whitney 2021). Hybridization can also lead to adaptation (Lewontin and Birch 1966; Campbell and Snow 2007; Hovick et al.…”