Interactions Between Chemical and Mechanical Defenses in the Plant Genus Bursera and Their Implications for Herbivores1

Wound Healing Activity of α-Pinene and α-Phellandrene

Bursera morelensis is used in Mexican folk medicine to treat wounds on the skin. Recently, it was shown that the essential oil (EO) of B. morelensis has wound healing activity, accelerating cutaneous wound closure and generating scars with good tensile strength. α-pinene (PIN) and α-phellandrene (FEL) are terpenes that have been found in this EO, and it has been shown in different studies that both have anti-inflammatory activity. The aim of this study was to determine the wound healing activity of these two terpenes. The results of in vitro tests demonstrate that PIN and FEL are not cytotoxic at low concentrations and that they do not stimulate fibroblast cell proliferation. In vivo tests showed that the terpenes produce stress-resistant scars and accelerate wound contraction, due to collagen deposition from the early stages, in wounds treated with both terpenes. Therefore, we conclude that both α-pinene and α-phellandrene promote the healing process; this confirms the healing activity of the EO of B. morelensis, since having these terpenes as part of its chemical composition explains part of its demonstrated activity.

Phylogenetic correlations among chemical and physical plant defenses change with ontogeny

Theory predicts patterns of defense across taxa based on notions of tradeoffs and synergism among defensive traits when plants and herbivores coevolve. Because the expression of characters changes ontogenetically, the evolution of plant strategies may be best understood by considering multiple traits along a trajectory of plant development. Here we addressed the ontogenetic expression of chemical and physical defenses in 12 Datura species, and tested for macroevolutionary correlations between defensive traits using phylogenetic analyses. We used liquid chromatography coupled to mass spectrometry to identify the toxic tropane alkaloids of Datura, and also estimated leaf trichome density. We report three major patterns. First, we found different ontogenetic trajectories of alkaloids and leaf trichomes, with alkaloids increasing in concentration at the reproductive stage, whereas trichomes were much more variable across species. Second, the dominant alkaloids and leaf trichomes showed correlated evolution, with positive and negative associations. Third, the correlations between defensive traits changed across ontogeny, with significant relationships only occurring during the juvenile phase. The patterns in expression of defensive traits in the genus Datura are suggestive of adaptation to complex selective environments varying in space and time.

Three new diarylbutane lignans from the resin of Bursera fagaroides

Three new diarylbutane lignans, named 9-acetyl-9'-pentadecanoil-dihydroclusin (1), 2,3-demethoxy-secoisolintetralin monoacetate (4) and dihydroclusin monoacetate (5), have been isolated from the resin of Bursera fagaroides, together with two known ones, 2,3-demethoxy-secoisolintetralin diacetate (2) and dihydroclusin diacetate (3). The complete structure assignments were obtained by means of (1)H and (13)C NMR spectra.

Biology of Blepharida-group flea beetles with first notes on natural history of Podontia congregata Baly, 1865 an endemic flea beetle from southern India (Coleoptera, Chrysomelidae, Galerucinae, Alticini)

The biology, host plants, and pest status of Podontia Dalman, 1824 species are reviewed. Natural history of Podontia congregata Baly, 1865 a flea beetle endemic to southern India, is reported for the first time. It is distributed from the Western Ghats Mountains westward to the plains. Clusiaceae is reported as a new host plant family for Blepharida-group species, with Garcinia gummi-gutta (L.) N. Robson (Clusiaceae) as the host plant for Podontia congregata. Pentatomid bugs attack the larvae but not eggs, pupae, or adults. A new egg parasitoid species, Ooencyrtus keralensis Hayat and Prathapan, 2010 (Hymenoptera: Encyrtidae), was discovered. Aspects of Podontia congregata host selection, life cycle, and larval fecal defenses are consistent with its inclusion in the Blepharida-genus group.

Germacrene D, a common sesquiterpene in the genus Bursera (Burseraceae)

The volatile components of the leaves of five Bursera species, B. copallifera, B. exselsa, B. mirandae, B. ruticola and B. fagaroides var. purpusii were determined by gas chromatography–mass spectrometry (GC–MS). Germacrene D was one of the predominant components (15.1–56.2%) of all of these species. Germacrene D has also been found in other Bursera species and some species of Commiphora, the sister group of Bursera, suggesting that the production of germacrene D might be an ancient trait in the genus Bursera.

Macroevolution of plant defense strategies

Theories of plant defense expression are typically based on the concepts of tradeoffs among traits and of phylogenetic conservatism within clades. Here, I review recent developments in phylogenetic approaches to understanding the evolution of plant defense strategies and plant-herbivore coevolutionary interactions. I focus particularly on multivariate defense against insect herbivores, which is the simultaneous deployment of multiple traits, often arranged as convergently evolved defense syndromes. Answering many of the outstanding questions in the biology of plant defense will require generating broad hypotheses that can be explicitly tested by using comparative approaches and interpreting phylogenetic patterns. The comparative approach has wide-spread potential to reinvigorate tests of classic hypotheses about the evolution of interspecific interactions.

PLANT DEFENSE SYNDROMES

Given that a plant's defensive strategy against herbivory is never likely to be a single trait, we develop the concept of plant defense syndromes, where association with specific ecological interactions can result in convergence on suites of covarying defensive traits. Defense syndromes can be studied within communities of diverse plant species as well as within clades of closely related species. In either case, theory predicts that plant defense traits can consistently covary across species, due to shared evolutionary ancestry or due to adaptive convergence. We examined potential defense syndromes in 24 species of milkweeds (Asclepias spp.) in a field experiment. Employing phylogenetically independent contrasts, we found few correlations between seven defensive traits, no bivariate trade-offs, and notable positive correlations between trichome density and latex production, and between C:N ratio and leaf toughness. We then used a hierarchical cluster analysis to produce a phenogram of defense trait similarity among the 24 species. This analysis revealed three distinct clusters of species. The defense syndromes of these species clusters are associated with either low nutritional quality or a balance of higher nutritional quality coupled with physical or chemical defenses. The phenogram based on defense traits was not congruent, however, with a molecular phylogeny of the group, suggesting convergence on defense syndromes. Finally, we examined the performance of monarch butterfly caterpillars on the 24 milkweed species in the field; monarch growth and survival did not differ on plants in the three syndromes, although multiple regression revealed that leaf trichomes and toughness significantly reduced caterpillar growth. The discovery of convergent plant defense syndromes can be used as a framework to ask questions about how abiotic environments, communities of herbivores, and biogeography are associated with particular defense strategies of plants.

Molecular systematics of Blepharida beetles (Chrysomelidae: Alticinae) and relatives

I investigated the phylogenetic relationships within the New World Blepharida and among related genera, using sequences of the Internal Transcriber Spacer 2 (ITS2) of nuclear ribosomal DNA and sequences of the COI and COII genes of the mitochondrial genome. Cladistic analyses were performed using parsimony, maximum likelihood, and Bayesian methods. These methods generated almost identical topologies using the combined data sets. The analyses suggest that Blepharida rhois, the type species, should be separated from the New World Blepharida and that the New World Blepharida might be congeneric with closely related Notozona. Also, according to this phylogeny, all of the New World Blepharida species that feed on Bursera (Burseraceae) form a single monophyletic clade, with the Afrotropical species forming its sister clade. The analyses also identified four main groups of species within the New World Blepharida.

Evolution of Mexican Bursera (Burseraceae) inferred from ITS, ETS, and 5S nuclear ribosomal DNA sequences

I reconstructed a phylogeny of 66 species and varieties of Bursera and 9 outgroup species using sequences of the internal transcribed spacer region (ITS), the 5S non-transcribed region (5S-NTS), and the external transcribed region (ETS) of nuclear ribosomal DNA. This study extends a previously proposed parsimony-based phylogenetic study that used the ITS sequences of 57 Bursera species and five outgroups. Parsimony and maximum likelihood methods were used to infer the phylogeny in this new study. Analyses of the combined data sets largely confirmed the phylogenetic relationships proposed by the previous molecular study but generated a considerably more robust topology. The new phylogenies corroborate the monophyly of the genus, and its division into the two monophyletic subgenera or sections, Bursera and Bullockia. The current analyses also identify four main groups of species in section Bursera, and two in section Bullockia, confirming some of the previously proposed groups based on fruit, flower, and leaf morphology. One previously problematic species B. sarcopoda, which has sometimes been placed in Commiphora, is shown to belong in Bursera. Another controversial species, Commiphora leptophloeos, which was thought to belong to Bursera, falls within Commiphora.