Fig. 1.

Phylogenetic constraints on individual toxins and their combinations. (a) A lack of significant values (only significant values labeled) in the PCOV matrix denotes a lack of phylogenetic constraint between toxin families. (b) Components show a significant presence of a phylogenetic signal, indicating that closely related species are likely to evolve the same way. Lambda, represents phylogenetic signal, which is a measure of dependency of trait evolution with phylogeny. Lambda values, are estimated as toxin variance on the diagonal, divided by the sum of diagonal variance and residuals. TFTx, SVMP, KSPI, LAAO, and CRISP showed the highest signal, with greatest significance, whereas the rest showed comparatively weaker signals. Phylogenetic constraints determine convergence and parallel evolution, where high constraint reduces the likelihood of genes contributing to different convergent regimes (Rosenblum et al. 2014). Yet, for snake venom genes, we see no such constraints in gene expression despite the high phylogenetic signal, suggesting that all toxin combinations, in principle, are possible.