Evolution at the tips: Asclepias phylogenomics and new perspectives on leaf surfaces

Abstract

PREMISE OF THE STUDY:Leaf surface traits, such as trichome density and wax production, mediate important ecological processes such as anti-herbivory defense and water-use efficiency. We present a phylogenetic analysis of Asclepias plastomes as a framework for analyzing the evolution of trichome density and presence of epicuticular waxes. METHODS:We produced a maximum-likelihood phylogeny using plastomes of 103 species of Asclepias. We reconstructed ancestral states and used model comparisons in a likelihood framework to analyze character evolution across Asclepias. KEY RESULTS:We resolved the backbone of Asclepias, placing the Sonoran Desert clade and Incarnatae clade as successive sisters to the remaining species. We present novel findings about leaf surface evolution of Asclepias-the ancestor is reconstructed as waxless and sparsely hairy, a macroevolutionary optimal trichome density is supported, and the rate of evolution of trichome density has accelerated. CONCLUSIONS:Increased sampling and selection of best-fitting models of evolution provide more resolved and robust estimates of phylogeny and character evolution than obtained in previous studies. Evolutionary inferences are more sensitive to character coding than model selection.

Integrated metabolic strategy: A framework for predicting the evolution of carbon‐water tradeoffs within plant clades

“…Mechanistic studies can be limited in the number of taxa to compare, and 20 species is quite high for these types of detailed physiological measurements. However, it is well established that phylogenetically controlled analyses are suspect to sampling bias, including Asclepias (Fishbein et al, ). Increased sampling may improve our understanding about the shifts in IMS among milkweed species.…”

“…We estimated the phylogeny of the 20 sampled species of Asclepias (Figure ) by adding new plastid genome (plastome) sequences for A. pumila and A. verticillata to a recently published dataset of 108 samples of Asclepias plus four outgroup sequences (Fishbein et al, ). The A. pumila sample was prepared using the NEBNext Ultra II DNA Library Prep Kit for Illumina (New England BioLabs, Ipswich, MA) with a NEXTflex‐HT™ Barcode (Bioo Scientific, Austin, TX) and sequenced on an Illumina NextSeq 500 at the Oklahoma State University Genomics and Proteomics Center.…”

“…Others occupy more mesic environments, such as grasslands and forests, while still others are restricted to wetlands, such as marshes and swamps (Woodson, 1954). To test for intrinsic, species-specific variation in metabolic strategies, we selected 20 taxa (19 species plus one subspecies), representing each major clade in Asclepias (Fishbein, Chuba, Ellison, & Mason-Gamer, 2011;Fishbein et al, 2018) that vary in leaf morphology (e.g., leaf size and thickness), and that naturally occur in habitats that differ substantially in water availability. Specifically, we asked the fol- We further hypothesized an association of higher IMS with smaller leaves, lower rates of stomatal conductance and larger rates of carboxylation.…”

“…The two copies of the inverted repeat were not distinguished in these assemblies. The phylogeny of the 114 samples was obtained following Fishbein et al (2018). Briefly, plastome sequences were aligned using MAFFT v. 7 (Katoh, Rozewicki, & Yamada, 2017) and ambiguously aligned regions were masked with the implementation of Gblocks (Castresana, 2000) in Mesquite 3.5 (Maddison & Maddison, 2018).…”

Agrobacterium tumefaciens–Mediated Transformation of Three Milkweed Species (Asclepias hallii, A. syriaca, and A. tuberosa: Apocynaceae)

“…The plant genus Asclepias contains more than 140 species that are commonly referred to as milkweeds because they produce white, sticky latex (Fishbein et al., 2018; Woodson, 1954). The latex and most other plant tissues contain cardenolides (steroidal toxins), which are inhibitors of animal sodium‐potassium ATPases that provide defense against insects (Agrawal, Petschenka, Bingham, Weber, & Rasmann, 2012).…”