Table 1.
A review of the potential traits associated with hybridization in plants, as identified by a literature search, with further information on data types and sources in our analysis
| Category | Trait | Prediction | Prediction type | Data description | Data source |
|---|---|---|---|---|---|
| Life history | Perenniality | + | Empirical1–5 Theoretical2 | Mean score (0 = annual, 0.5 = annual/biennial/perennial, 1 = perennial) | Floras |
| Woodiness | + | Empirical5 , 6 | Mean score (0 = herbaceous, 0.5 = either, 1 = woody) | Floras | |
| Reproductive | Pollination syndrome | ± | Empirical4 , 7 | Mean score (0 = abiotic, 0.5 = both, 1 = biotic) | TRY (Kattge et al. 2011) |
| Floral symmetry | + | Theoretical6 , 8 | Mean score (0 = actinomorphic, 0.5 = both, 1 = zygomorphic) | TRY (Kattge et al. 2011) | |
| Outcrossing | + | Empirical2 , 4 Theoretical1–3 | Mean outcrossing rate (t) | Goodwillie et al. 2005; Moeller et al. 2017 | |
| Breeding system | + | Theoretical2 | Mean score (0 = asexual, 0.5 = both, 1 = sexual) | TRY (Kattge et al. 2011) | |
| Reproductive system | – | Empirical4 Theoretical1 | Mean score (0 = vegetative, 0.5 = both, 1 = generative) | TRY (Kattge et al. 2011) | |
| Genetic predisposition | C‐value | – | Empirical9 | Mean C‐value (genome size in picogram) | Bennett and Leitch (2005) |
| C.V. C‐value | ± | Theoretical | Mean coefficient of variation of C‐value | Bennett and Leitch (2005) | |
| Chromosomal translocations | – | Theoretical2 | Not analyzed | ||
| Genetic divergence | ± | Empirical10 , 11 Reviewed12 , 13 | Not analyzed | ||
| Opportunity/environment | Agricultural status | + | Theoretical14 | Mean score (0 = noncrop species, 1 = crop species) | SINGER |
| Red List | – | Theoretical15 | Mean score (0 = LC, 0.5 = NT, LR/nt, 1 = LR/cd, 2 = VU, 3 = EN, 4 = CR, 5 = EX, EW) | Baillie et al. (2004) |
The “Prediction” column gives the predicted sign of the association between the trait and hybridization propensity, relative to the orientation in the “Data Description” column. “Prediction Type” distinguishes whether predictions from the literature are based on a theoretical argument or simply on an observed (but not phylogenetically corrected) empirical association. We expand on proposed mechanisms in Table S1. Data used in analyses were mean scores across all species within the group of interest (family or genus). When we did not have data to test the potential relationship, the “Data Source” column is blank. Descriptions of traits, how they were scored for this study, predictions (empirical or theoretical) from the literature (see superscripts for sources), and sources for the data used in this study.
1Grant (1958); 2Grant (1981); 3Stace (1975); 4Ellstrand et al. (1996); 5Beddows and Rose (2018); 6Stebbins (1959); 7Rieseberg and Wendel (1993); 8Sargent (2004); 9Bureš et al. (2004); 10Paun et al. (2009); 11Stelkens and Seehausen (2009); 12Mallet (2005); 13Mavarez and Linares (2008); 14Allard (1999); 15Allendorf et al. (2001).
LC, least concern; NT, near threatened; LR/nt, lower risk/near threatened; LR/cd, lower risk/conservation dependent; VU, vulnerable; EN, endangered; CR, critically endangered; EX, extinct; EW, extinct in the wild.