Abstract Detail


Smith, Chelsea R. [1], Teisher, Jordan [2], Straub, Shannon [3], Livshultz, Tatyana [4].

Does herbivore co-option of a plant defense drive its loss?: Testing the defense de-escalation of pyrrolizidine alkaloid evolution in Apocynaceae (the dogbane and milkweed family).

Plant secondary metabolites can function as anti-herbivore defenses and thereby increase plant fitness. Adapted herbivores can, in turn, de-activate or co-opt plant secondary metabolites for host plant location or their own defense, potentially rendering these compounds selectively neutral or deleterious. Thus, plants exploited primarily by adapted herbivores may be under selection to lose (de-escalate) the co-opted compounds. Pyrrolizidine alkaloids (PAs) are secondary metabolites that have evolved independently in 12 flowering plant families, including Apocynaceae (the dogbane and milkweed family). Multiple insect lineages have co-opted PAs, including Lepidoptera subfamily Danainae (the milkweed and clearwing butterflies), whose ancestral larval host plants are widely hypothesized to belong to the Apocynaceae. We have shown that that the first gene of the PA biosynthetic pathway, homospermidine synthase (hss), evolved early in the diversification of one lineage of Apocynaceae (the APSA clade) and that 92% of larval host plant species documented for Danainae belong to this clade. Hss function, and by inference PAs, has been lost at least four times within the APSA clade, evidenced by loss of an hss-specific amino acid motif. However, it is unknown whether loss of hss function in a lineage is correlated with level of exploitation by Danainae. We obtained the entire hss locus from 141 APSA clade species, representing 13 of 15 major lineages classified as tribes or subfamilies, as well as 840 putatively single copy genes for phylogenetic reconstruction, using targeted enrichment and sequencing by synthesis. Loss of the hss-specific amino acid motif and/or pseudogenization were interpreted as evidence of PA loss. PA-losses were mapped on the species phylogeny and their correlation with the distribution of Danainae larval host plants tested to investigate whether exploitation by Danainae could have driven PA loss.

Related Links:
Previous work: "Evolution of pyrrolizidine alkaloid biosynthesis in Apocynaceae: revisiting the defence de-escalation hypothesis"

1 - Drexel University, Department of Biodiversity, Earth, and Environmental Sciences, 3141 Chestnut Stree, Philadelphia, PA, 19104, USA
2 - The Academy Of Natural Sciences Of Drexel University, Botany, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103, United States
3 - Hobart and William Smith Colleges, Department of Biology, 300 Pulteney St., Geneva, NY, 14456, USA
4 - Drexel University, Biodiversity Earth and Environmental Sciences, Academy Of Natural Sciences Of Drexel University, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103, United States

secondary chemistry
biochemical evolution
plant-insect interactions
target enrichment.

Presentation Type: Poster
Number: PME002
Abstract ID:661
Candidate for Awards:None

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