Table 1.
Modeling the macroevolution of seven 7 milkweed traits using GEIGER
| Evolutionary model | Gradual mode |
Speciational mode |
Interpretation | ||||||
|---|---|---|---|---|---|---|---|---|---|
| P-value | Model parameter MLE | LL | AIC | P-value | Model parameter MLE | LL | AIC | ||
| Cardenolides | |||||||||
| Phylogenetic signal | P = 0.007 | P = 0.019 | Phylogenetic signal in both models. | ||||||
| Brownian motion | −120.8 | 245.6 | −124.2 | 252.4 | O-U (stable optimum) is favored under both branch- length models. | ||||
| Shifting tempo | δ = 3.810 | −117.6 | 241.1 | δ = 0.638 | −123.8 | 253.6 | |||
| O-U | α = 0.021 | −117.4 | 240.9 | α = 0.364 | −119.4 | 244.9 | |||
| Latex exudation | |||||||||
| Phylogenetic signal | P = 0.012 | P = 0.002 | Phylogenetic signal in both models. | ||||||
| Brownian motion | −58.1 | 120.1 | −68.1 | 140.2 | Constant rate Brownian motion favored under gradual evolution. | ||||
| Shifting tempo | δ = 0.504 | −57.6 | 121.2 | δ = 0.348 | −65.8 | 137.6 | |||
| O-U | α ≈ 0 | −58.1 | 122.1 | α = 0.129 | −66.6 | 139.1 | Shifting tempo evolution favored under speciational evolution (early burst, δ<1). | ||
| Trichome density | |||||||||
| Phylogenetic signal | P = 0.040 | P = 0.053 | Phylogenetic signal in both models. | ||||||
| Brownian motion | −219.2 | 442.5 | −224.5 | 453.0 | Constant rate Brownian motion favored under both branch-length models. | ||||
| Shifting tempo | δ = 0.564 | −218.8 | 443.7 | δ = 0.729 | −224.2 | 454.5 | |||
| O-U | α ≈ 0 | −219.2 | 444.5 | α ≈ 0.080 | −224.3 | 454.6 | |||
| Seed mass | |||||||||
| Phylogenetic signal | P = 0.003 | P = 0.384 | Phylogenetic signal only in gradual model. | ||||||
| Brownian motion | −193.4 | 390.7 | −219.9 | 443.8 | Shifting tempo evolution favored under gradual evolution (early burst, δ < 1). | ||||
| Shifting tempo | δ = 0.198 | −190.8 | 387.6 | δ = 0.096 | −211.9 | 429.8 | |||
| O-U | α ≈ 0 | −193.4 | 392.7 | α ≈ 0.422 | −208.7 | 423.5 | Stable optimum (O-U process) favored under speciational evolution. | ||
| Leaf water content | |||||||||
| Phylogenetic signal | P = 0.336 | P = 0.2756 | No phylogenetic signal in either model. | ||||||
| Brownian motion | −167.4 | 338.8 | −167.0 | 338.0 | O-U (stable optimum) is favored under both branch-length models. | ||||
| Shifting tempo | δ = 11.365 | −157.7 | 321.4 | δ = 1.964 | −162.5 | 331.0 | |||
| O-U | α ≈ 0.065 | −157.7 | 321.4 | α ≈ 0.735 | −157.5 | 321.1 | |||
| Specific leaf area | |||||||||
| Phylogenetic signal | P = 0.079 | P = 0.103 | No phylogenetic signal in either model. | ||||||
| Brownian motion | −173.3 | 350.6 | −174.5 | 353.0 | O-U (stable optimum) is favored under both branch-length models. | ||||
| Shifting tempo | δ = 8.329 | −167.5 | 340.9 | δ = 1.725 | −173.1 | 352.3 | |||
| O-U | α ≈ 0.047 | −167.4 | 340.9 | α ≈ 0.660 | −167.2 | 340.5 | |||
| Leaf size | |||||||||
| Phylogenetic signal | P = 0.268 | P = 0.4898 | No phylogenetic signal in either model. | ||||||
| Brownian motion | −200.5 | 405.1 | −204.7 | 413.4 | O-U (stable optimum) is favored under both branch-length models. | ||||
| Shifting tempo | δ = 8.243 | −192.2 | 390.3 | δ = 2.779 | −196.8 | 399.5 | |||
| O-U | α ≈ 0.048 | −192.2 | 390.4 | α ≈ 0.920 | −192.8 | 391.5 | |||
Models were fit under 2 modes of evolution: gradual, in which phylogenetic distance is scaled as time, and speciational, in which phylogenetic distance is scaled as number of nodes (speciation events). The presence of phylogenetic signal was assessed using PHYSIG.M; P values reflect the probability of the data under the null hypothesis of no signal. Log Likelihood (LL) and Akaike's Information Criterion (AIC) values signify model fit (higher LL and lower AIC values indicate a better fit). A difference of 2 units is the cutoff for significance for tests of superior fit of one model over another using a likelihood ratio test (with df = 1). Fitted models include Brownian motion, shifting tempo, and stable optimum (O-U, modeled by an Ornstein-Uhlenbeck process). The shifting-tempo model assumes underlying Brownian motion evolution with an additional parameter (δ) that scales the relationship between branch length and character evolution. The O-U model includes a parameter (α) specifying the character's optimum. These analyses do not model directional trait evolution.