Abstract Detail

Macroevolution

Livshultz, Tatyana [1], Kaltenegger, Elisabeth [2], Ober, Dietrich [3].

Macroevolution of pyrrolizidine alkaloids in Apocynaceae: a case of defense de-escalation?

Macroevolutionary dynamics between plants and herbivorous insects have been a touchstone of co-evolution, informing our understanding of how species interactions can drive evolution of species and phenotypic diversity. Co-evolutionary theory predicts both evolutionary escalation of the diversity and potency of plant defense chemistry and de-escalation of initially defensive chemicals that are co-opted by specialist herbivores to increase their own fitness to the detriment of their host plants. Pyrrolizidine alkaloids (PAs) are plant secondary metabolites consisting of a necine base esterified to a necic acid that have evolved at least 10 times among flowering plants. The first step of PA biosynthesis is catalyzed by homospermidine synthase (HSS) which evolved repeatedly via duplication and neofunctionalization of deoxyhypusinesynthase (DHS), a ubiquitous eukaryotic gene. PAs are repellent to many generalist herbivores including mammals, insects, and nematodes but have been co-opted by species of at least 6 lineages of specialist insects for anti-predator defense and larval host plant location. Apocynaceae (the milkweed and dogbane family) are known for their secondary chemistry and for their specialized herbivore fauna, including Lepidoptera subfamily Danainae, the milkweed and clearwing butterflies. A physiological requirement for plant-derived PAs is a symplesiomorphy of Danainae. In Apocynaceae, PAs have been reported from species of only 6 of 366 genera. One of these species, Parsonsia alboflavescens, has functional HSS and DHS genes. Over 30 years ago, it was hypothesized that Danain co-option of PAs has driven their evolutionary loss in Apocynaceae. The HSS/DHS gene tree was reconstructed to investigate the evolution of PAs in Apocynaceae. HSS has evolved once via duplication of DHS early in the diversification of the APSA clade, a well-supported lineage that includes > ¾ of all Apocynaceae genera and most of the known Danain host plants. All 6 PA-positive genera have both HSS and DHS. At least 15 genera never reported to produce PAs have an HSS ortholog. Locus specific primers were designed to investigate whether PAs been lost via HSS deletion in any lineages. Evidence is presented that root-specific expression of PAs may be an alternative strategy for some Apocynaceae species to maintain PA-defense against root-feeding generalists while decreasing the fitness of foliage-feeding specialists.

1 - Drexel University, Biodiversity Earth and Environmental Sciences, Academy Of Natural Sciences, 1900 Benjamin Franklin Parkway, Philadelphia, Pennsylvania, 19103, United States
2 - Kiel University, Botanical Institute , Biochemical Ecology and Molecular Evolution, Am Botanischen Garten 1-9 , Kiel , D-24118, Germany
3 - Kiel University, Biochemical Ecology and Molecular Evolution, Botanical Institute, Am Botanischen Garten 1-9, Kiel, D-24118, Germany

Keywords:
Herbivory
gene duplication
secondary chemistry
defense
co-evolution
plant-insect interactions
genome evolution
Apocynaceae.

Presentation Type: Oral Paper
Session: 10, Macroevolution
Location: 202/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 2:00 PM
Number: 10003
Abstract ID:205
Candidate for Awards:None