Secondary metabolites related to plant defense against natural enemies and enzymes involved in their biosynthesis vary during gall development. We assessed the differential gene expression related to defensive metabolites in cynipid wasp galls of Quercus castanea induced by Amphibolips michoacaensis throughout gall development. We assembled de novo transcriptomes from galls in three phases of growth and compared the differential expression of phenolic-related genes. We found that (1) Phenylalanine ammonia lyase (PAL) enzyme genes were upregulated at the intermediate and late growth stages. (2) Phenylpropanoid genes were upregulated at the intermediate stage and downregulated at the late stage. (3) Lignin genes were upregulated at the late stage. The transcriptomic profile of wasp galls exposes the switches in secondary metabolism during development. Patterns of differential expression shown in wasp galls suggest phenotype manipulation by the wasp larvae and physiological constraints of the host plant for enzyme channeling in different biosynthetic branches of phenolic compounds.

Abstract:A gall is the result of complex interactions between a gall inducing-insect and its host plant. Certain groups of insects have the ability to induce a new structure, a gall, on plant organs by altering the normal growth of the host involved plant organ. The gall usually provides shelter and nutrients, in addition to protection against adverse environmental conditions and natural enemies to the inducing insect and its offspring. The ecological uniqueness of a gall is that it allows the inducing-insect to complete their life cycles. In this study, we have described the structures of different stages of growth of a gall induced by Amphibolips michoacaensis on the buds of leaves on Quercus castanea (Fagaceae) to know the subcellular changes during development. The gall consist of various layers such as a nutritive tissue, a lignifi ed sheath, a spongy layer and an outermost epidermis around a centrally located larval chamber. The nutritive cell of the larval chamber show nuclear and nucleolar hypertrophy in the early phases of growth. The granular profi le of the nucleolus suggests an active synthesis of ribosomes indicating an accelerated protein synthesis in these cells. During early stages of growth, the cells of the spongy layers within galls are nucleate and nucleolate and include amyloplasts, and the cytoplasm is less abundant. During later growth stages, the spongy cells are enucleate and enucleolate. Chloroplasts occur in the epidermal cells during early stages of growth, indicating that galls are photosynthetically active in early stages of growth. During intermediate stages of growth, a gradual loss of cellular components occurs commencing in the epidermal cells and progressing towards the nutritive cells. Key words: Amphibolips michoacaensis, Cynipidae, gall morphology, Hymenoptera, Quercus castanea Resumen: La formación de una agalla es el resultado de una compleja interacción entre el insecto inductor de agallas y su planta hospedera. Ciertos grupos de insectos tienen la habilidad de inducir una nueva estructura, la agalla, sobre los órganos de las plantas alterando el crecimiento normal del órgano de la planta involucrado. Las agallas usualmente proveen refugio y nutrientes, además de protección contra condiciones ambientales adversas y enemigos naturales al insecto inductor y a su descendencia. La particularidad ecológica de la agalla es que permite al insecto inductor completar su ciclo de vida. En este estudio, nosotros hemos descrito la estructura de los diferentes estadios de crecimiento de la agalla inducida por Amphibolips michoacaensis sobre brotes de hojas de Quercus castanea Née (Fagaceae) para conocer los cambios subcelulares durante su desarrollo. La agalla consiste de varias capas tales como tejido nutritivo, una capa de células lignifi cadas, tejido esponjoso y una capa epidérmica externa que rodean a una cámara larval central. Las células del tejido nutritivo de la cámara larval presentan hipertrofi a de núcleo y nucléolo en las fases tempranas de crecimiento. El perfi l granula...

Habitat disturbance in tropical forests has affected the viability of several tree species. In Mexico, populations of Guaiacum sanctum have disappeared in some regions due to a strong habitat reduction which could endanger the genetic diversity and connectivity of remnant populations. In this study, 17 populations from the Yucatán Peninsula were analyzed with seven nuclear microsatellites. Several parameters describing the genetic diversity were estimated. The genetic structure was evaluated using Bayesian cluster analysis. Population bottlenecks, effective population size, and genetic connectivity were estimated. Populations of G. sanctum showed high values of genetic diversity. Two genetic groups with contrasting distributions were detected, the first one located in northern Yucatán and Quintana Roo and the second, in southern Campeche. Evidence of population bottleneck was detected only for Campeche populations. Also, we found indications of significant levels of inbreeding and a low effective population size. The connectivity analysis revealed exchange among populations of G. sanctum but the habitat fragmentation may act to impede gene flow, contributing to the division observed between clusters. This genetic differentiation was possibly caused by environmental pressures, although effects of historical extensive logging practices occurred in southern Mexico during the last few decades cannot be discarded. Fragmentation has a negative effect on ecosystem services and on the availability of favorable sites for seedling establishment, which could disturb pollination and dispersion processes, modifying in the long term the effective population size.