The Butterfly Effect

This might just take the prize for the ‘spiciest’ story in molecular co-evolution for 2015, yet. While a lot of the press coverage sounds like caterpillar thanksgiving, the science behind this study stands for the almost incredible power of molecular phylogenetics in unveiling the adaptive evolution of traits.

Edger et al. (2015) in a recent study report the coincident evolutionary arms-race of Brassicales (angiosperms that include mustard, horseradish, cabbage, broccoli, etc.), and their predatory butterflies in the family Pieridae. Using whole transcriptome sequences of Brassicales, and nuclear gene phylogneis for Pieridae, Edger et al. (2015) perform phylogenetic analyses across 1155 genes, calibrated using fossil estimates to date/delineate genome duplication, and diversification events in glucosinolate(purportedly evolved toxic plant defenses against predatory Pierid caterpillars, but rendering the characteristic sharp tastes to edible Brassicales) pathways.

Fossil calibrated phylogenetic reconstructions of Brassicales, and Pieridae showing co-evolutionary diversification (of glucosinolates) in Brassicales, and detoxification in Pieridae. Image courtesy: Fig. 1 of Edger et al. (2015).

Key findings of this study include:

  1. the appearance of glucosinolates after a whole genome duplication event in Brassicales (~78 Mya),
  2. the ability of Brassicales to synthesize glucosinolates from substrates was ancestral,
  3. the escalation of glucosinolate diversity in Brassicales was a result of an arms-race against butterflies due to retention and neofunctionalization of genes after single gene, and whole genome duplications, and
  4. subsequent evolution of adaptation to toxicity of glucosinolates in different Pieridae coincides with diversification events in Brassicales and vice versa.

Consistent with the hypothesis that retention of duplicates after WGD is driven by selective benefits, previous analyses indicates a high metabolic cost of glucosinolate production, a result incompatible with the retention of glucosinolate duplicate being neutral.

Edger, Patrick P., et al. “The butterfly plant arms-race escalated by gene and genome duplications.” Proceedings of the National Academy of Sciences(2015): 201503926.

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