ELENA ALVAREZ BUYLLA | UNAM (original) (raw)

Papers by ELENA ALVAREZ BUYLLA

Note: Ten chapters were prepared as background for the work of the Maize Advisory Group and for i... more Note: Ten chapters were prepared as background for the work of the Maize Advisory Group and for input to the public symposium, held 11 March 2004, in Oaxaca as part of the CEC Article 13 study on maize and biodiversity. These chapters were later reviewed and revised prior to this release, based on comments received at the symposium and during the subsequent comment period. Responses to reviewers are provided at <www.cec.org/maize/>.

Trends in Plant Science, 1998

Trends in Ecology and Evolution, 2000

Flowers, as reproductive structures of the most successful group of land plants, have been a cent... more Flowers, as reproductive structures of the most successful group of land plants, have been a central focus of study for both evolutionists and ecologists. Recent advances in unravelling the genetics of flower development have provided insight into the evolution of floral structures among angiosperms. The study of the evolution of genes that control floral morphogenesis permits us to draw inferences on the diversification of developmental systems, the origin of floral organs and the selective forces that drive evolutionary change among these plant reproductive structures.

Agroforestry Systems, 1989

The major components of the process of production in the homegardens of a tropical Mexican commun... more The major components of the process of production in the homegardens of a tropical Mexican community are described and analyzed. Specifically, management tasks, means of production, and the amount, quality and temporal distribution of the products are discussed. The ecological, technological and productive advantages generally attributed to this kind of agroforestry cropping system in comparison to monocultures were also found in the homegardens of Balzapote. However, the area presently managed under this system is restricted, and its local and regional impact is thus very limited. Based on the detailed analysis of the functional differences in 8 homegardens and the socioeconomic roles they play in the economic organization of peasant families, the possible expansion of homegardens in the Mexican tropics is discussed. Se describen y analizan los principales componentes del proceso de producción en los solares de una comunidad tropical mexicana. A saber: las prácticas de manejo, los medios de trabajo y la cantidad, calidad y distribución temporal de la producción. Para el caso de Balzapote se cumplen en general las ventajas ecológicas, tecnológicas y productivas que se les ha atribuído a este tipo de sistemas agroforestales en comparación con los monocultivos. Sin embargo, actualmente el impacto de este tipo de manejo a nivel local y regional es muy restringido, debido a la pequeña área cultivada bajo este sistema. Se presenta una discusión sobre las posibilidades de expansión de este tipo de cultivo agroforestal para el trópico mexicano con base en las causas de las diferencias encontradas en 8 solares analizados detalladamente y en el papel que actualmente juega el solar en la organización económica de la familia campesina.

Chaos, 2006

Dynamic models of molecular networks and pathways enable in silico evaluations of the consistency... more Dynamic models of molecular networks and pathways enable in silico evaluations of the consistency of proposed interactions and the outcomes of perturbations as well as of hypotheses on system-level structure and function. We postulate a continuous model of the activation dynamics of the ethylene response factor 1 (ERF1) gene in response to ethylene signaling. This activation elicits the response of the plant defensin 1 (PDF1) gene, which also responds to jasmonic acid, and the inhibition of the putative auxin responsive factor 2 (ARF2) gene, that also responds to auxin. Our model allows the effect of different ethylene concentrations in eliciting contrasting genetic and phenotypic responses to be evaluated allows the effect of different ethylene concentrations in eliciting contrasting genetic and phenotypic responses to be evaluated and seems to consider key components of the ethylene pathway because the ERF1 dose-response curve that we predict has the same qualitative form as the phenotypic dose-response curves obtained experimentally. Therefore, our model suggests that the phenotypic dose-response curves obtained experimentally could be due, at least in part, to ERF1 changes to different ethylene concentrations. Stability analyses show that the model's results are robust to parameter estimates. Of interest is that our model predicts that the ethylene pathway may filter stochastic and rapid chaotic fluctuations in ethylene availability. This novel approach may be applied to any cellular signaling and response pathway in plants and animals.

Biochemical and Biophysical Research Communications, 2001

We are interested in identifying potential protein interactors of MADS domain transcription facto... more We are interested in identifying potential protein interactors of MADS domain transcription factors during Arabidopsis thaliana flower development. We based our biochemical search on a conserved motif in the MADS domain that includes putative phosphatase and phosphorylation sites that may mediate protein interactions. An affinity column with this motif and a few surrounding hypervariable amino acids derived from the AGAMOUS sequence was prepared and used to isolate potential interactors from floral crude extracts. Only two proteins were specifically bound to the affinity column. The first corresponds to a carpel specific storage protein, VSP1, that presents acid phosphatase activity, and the second is a novel leucine-rich repeat protein that we have named FLOR1. Coimmunoprecipitation, two-hybrid yeast, and affinity column assays show that the FLOR1-VSP1 complex interacts with AGAMOUS and that this transcription factor directly interacts with FLOR1. This is the first assay to show an interaction between plant MADS domain factors and non-MADS proteins.

Oecologia, 1990

We used the tropical pioneer tree, Cecropia obtusifolia to evaluate the relative importance of di... more We used the tropical pioneer tree, Cecropia obtusifolia to evaluate the relative importance of different sources of seeds in the regeneration of species that depend on ephemeral sites. We studied seed production in a population established in a 5 ha plot, and dispersal, dormancy and seed predation in two recent treefall gaps (<1 year-old), two building or successional forest patches (10–15 since disturbed), and two mature forest patches (>35 years since disturbed) for a one year period at Los Tuxtlas (Mexico). Flowers and fruits were counted at monthly intervals. Annual fecundity per tree ranged from 1.4×104 to 1.4×107 seeds. Seeds were continuously available on the trees and on the ground. Average annual seed rain per m2 (as measured by 0.5×0.5 m seed traps) varied from 184 to 1925 among the six sites. Distance to nearest seed source and patch type explained more than 60% of the seed rain variation among sites. Soil seed density, estimated by counting seeds from ten samples (78.5 cm2×10 cm deep) collected from each site in October and January, ranged among the six sites from 269 to 4485 seeds per m2 in January and from 204 to 5073 in October. Soil seed viabilities were much lower (17.1% in October and 5.1% in January) than those of rain seeds (48.26%). Annual survivorships of 2.2% were estimated for seeds artificially sown on the soil surface of a gap and a mature patch, and 3.75% in a building patch. In two other experiments seed removal rates ranged from 27% to 98% in 4 days. Removal rates were significantly higher in gap and mature patches than in building patches. Ants (Paratrechina vividula) and grasshopper nymphs (Hygronemobius. sp.) were the main predators. We draw three main conclusions from our data: (1) Pathogens and predators determine low survivorship of C. obtusifolia's seeds in the soil and a rapid turnover rate (1.07 to 1.02 years) of its seed bank; (2) a continuous and copious seed production and an abundant and extensive seed rain replenish the soil seed pool in patches with different disturbance ages at least up to 86 m from nearest source; (3) more than 90% of the seeds contributing to C. obtusifolia seedling recruitment in gaps are less than one year-old. We discuss our results in the context of previous similar studies for tropical forests.

Developmental Biology, 2007

PLOS One, 2010

In this paper we propose a model to describe the mechanisms by which undifferentiated cells attai... more In this paper we propose a model to describe the mechanisms by which undifferentiated cells attain gene configurations underlying cell fate determination during morphogenesis. Despite the complicated mechanisms that surely intervene in this process, it is clear that the fundamental fact is that cells obtain spatial and temporal information that bias their destiny. Our main hypothesis assumes that there is at least one macroscopic field that breaks the symmetry of space at a given time. This field provides the information required for the process of cell differentiation to occur by being dynamically coupled to a signal transduction mechanism that, in turn, acts directly upon the gene regulatory network (GRN) underlying cell-fate decisions within cells. We illustrate and test our proposal with a GRN model grounded on experimental data for cell fate specification during organ formation in early Arabidopsis thaliana flower development. We show that our model is able to recover the multigene configurations characteristic of sepal, petal, stamen and carpel primordial cells arranged in concentric rings, in a similar pattern to that observed during actual floral organ determination. Such pattern is robust to alterations of the model parameters and simulated failures predict altered spatio-temporal patterns that mimic those described for several mutants. Furthermore, simulated alterations in the physical fields predict a pattern equivalent to that found in Lacandonia schismatica, the only flowering species with central stamens surrounded by carpels.

Canadian Journal of Botany-revue Canadienne De Botanique, 2001

Mexico is a major center of diversity for the genus Pinus as it has the greatest number of specie... more Mexico is a major center of diversity for the genus Pinus as it has the greatest number of species in the world. Many species are now restricted to Mexico, and some are represented by very small populations and are in danger of extinction. In this study we examined allozyme variation in three rare species of Mexican pines: Pinus pinceana Gord., Pinus lagunae M.F. Passini, and Pinus muricata D. Don, with the objective of providing conservation guidelines. The three species had relatively high levels of genetic variation with mean expected heterozygosities of 0.373, 0.386, and 0.346 for P. pinceana, P. lagunae, and P. muricata, respectively. We found marked differentiation among populations and significant inbreeding within populations of the three species. These values are larger than the range reported for most conifers and suggest that conservation strategies of these rare pines require focusing on the viability of several populations. Given that our knowledge about the demographic status of the three species is scarce, we propose a mixed strategy of conservation. For P. lagunae, we propose an in situ strategy, whereas for P. pinceana and P. muricata we propose an ex situ strategy of conservation until permanent protection can be provided for several of their populations.

American Naturalist, 1991

American Journal of Botany, 1999

Pinus rzedowskii is an endangered pine species from Michoacán (central México), which has been pr... more Pinus rzedowskii is an endangered pine species from Michoacán (central México), which has been previously reported from only three localities. Classified within the subgenus Strobus, it exhibits intermediate morphological characters between subgenera Strobus and Pinus. We analyzed genetic aspects that could shed light on the evolution and conservation of this species. The genetic structure of nine populations was examined using 14 isozyme loci. Pinus rzedowskii has a relatively high level of genetic variation with 46.8% of the loci assayed being polymorphic, a total of 35 alleles, and a mean heterozygosity per population of 0.219. We calculated Wright's F ST statistic to estimate gene flow indirectly and to evaluate whether or not there was genetic structuring among populations. We found a marked differentiation among populations (F ST ϭ 0.175) and significant inbreeding (F IS ϭ 0.247). No pattern of isolation by distance was found. We also constructed a dendrogram based on a genetic distance matrix to obtain an overview of the possible historical relationships among populations. Finally, we found a convex relationship between the genetic distance among populations and the number of ancestral lineages, suggesting that demographically this species has not been at risk recently. Although endangered, with small and fragmented populations, P. rzedowskii shows higher levels of genetic variation than other conifer species with larger populations or similar conservation status.

Molecular Phylogenetics and Evolution, 1999

A 650-bp portion of the nuclear ribosomal DNA internal transcribed spacer region was sequenced in... more A 650-bp portion of the nuclear ribosomal DNA internal transcribed spacer region was sequenced in 47 species of Pinus, representing all recognized subsections of the genus, and 2 species of Picea and Cathaya as outgroups. Parsimony analyses of these length variable sequences were conducted using a manual alignment, 13 different automated alignments, elision of the automated alignments, and exclusion of all alignment ambiguous sites. High and moderately supported clades were consistently resolved across the different analyses, while poorly supported clades were inconsistently recovered. Comparison of the topologies highlights taxa of particularly problematic placement including Pinus nelsonii and P. aristata. Within subgenus Pinus, there is moderate support for the monophyly of a narrowly circumscribed subsect. Pinus (=subsect. Sylvestres) and strong support for a clade of North and Central American hard pines. The Himalayan P. roxburghii may be sister species to these "New World hard pines," which have two well-supported subgroups, subsect. Ponderosae and a clade of the remaining five subsections. The position of subsect. Contortae conflicts with its placement in a chloroplast DNA restriction site study. Within subgenus Strobus there is consistent support for the monophyly of a broadly circumscribed subsect. Strobi (including P. krempfii and a polyphyletic subsect. Cembrae) derived from a paraphyletic grade of the remaining soft pines. Relationships among subsects. Gerardianae, Cembroides, and Balfourianae are poorly resolved. Support for the monophyly of subgenus Pinus and subgenus Strobus is not consistently obtained.

Journal of Theoretical Biology, 1998

We present a network model and its dynamic analysis for the regulatory relationships among 11 gen... more We present a network model and its dynamic analysis for the regulatory relationships among 11 genes that participate in Arabidopsis thaliana flower morphogenesis. The topology of the network and the relative strengths of interactions among these genes were based from published genetic and molecular data, mainly relying on mRNA expression patterns under wild type and mutant backgrounds. The network model is made of binary elements and we used a particular dynamic implementation for the network that we call semi-synchronic. Using this method the network reaches six attractors; four of them correspond to observed patterns of gene expression found in the floral organs of Arabidopsis (sepals, petals, stamens and carpels) as predicted by the ABC model of flower morphogenesis. The fifth state corresponds to cells that are not competent to flowering, and the sixth attractor predicted by the model is never found in wild-type plants, but it could be induced experimentally. We discuss the biological implications and the potential use of this network modeling approach to integrate functional data of regulatory genes of plant development.

Heredity, 1998

We used a likelihood-based paternity analysis to examine pollen-mediated gene flow within and amo... more We used a likelihood-based paternity analysis to examine pollen-mediated gene flow within and among populations of Cecropia obtusifolia, a dioecious, wind-pollinated, tropical pioneer tree. We used allozyme data collected from leaf samples of adult trees and seeds from known mothers in an 8.64 ha study plot located in pristine forest in the Los Tuxtlas range in southern Mexico. Trees within the study plot have a patchy distribution. Four populations (including the reference population) were in natural forest areas, and these were paired with four 'acahual' populations (populations growing on human-disturbed sites). The paired sites were located from 1 to 43 km from the reference population, with a ninth (acahual) population 100 km away. We addressed the following questions: (1) Do males from the reference population contribute differentially to reproduction within the stand?; (2) How do intermate distance and patch affiliation affect pollination within the reference population?; (3) What are the relative male reproductive contributions from within and outside the study population? Male reproductive contributions were significantly uneven within the reference population (P0.001). We demonstrated modest isolation by distance and an effect of patch affiliation for mating pairs within the reference population (PO0.001), independent of the male-specific differences. The addition of the eight outpopulations to the model showed that 37% of the offspring in the reference population were probably fathered by males from the other populations. We observed a strong isolation by distance effect for these populations, but long-distance pollen flow is enough to have a strong homogenizing effect on the regional gene pool. None of the acahual populations appears to have contributed pollen. Paternity analysis yields a more detailed view of the effects of pollen-mediated gene flow than had emerged from previous F ST analyses.

Current Biology, 2001

ABC model of flower development was proposed to explain the activity of the floral organ identity... more ABC model of flower development was proposed to explain the activity of the floral organ identity genes .

International Journal of Developmental Biology, 2007

In Arabidopsis thaliana, leaf and root epidermis hairs exhibit contrasting spatial arrangements e... more In Arabidopsis thaliana, leaf and root epidermis hairs exhibit contrasting spatial arrangements even though the genetic networks regulating their respective cell-fate determination have very similar structures and components. We integrated available experimental data for leaf and root hair patterning in dynamic network models which may be reduced to activatorinhibitor models. This integration yielded expected results for these kinds of dynamic models, including striped and dotted cell patterns which are characteristic of root and leaf epidermis, respectively. However, these formal tools have led us to novel insights on current data and to put forward precise hypotheses which can be addressed experimentally. In particular, despite subtle differences in the root and leaf networks, these have equivalent dynamical behaviors. Our simulations also suggest that only when a biasing signal positively affects an activator in the network, the system recovers striped cellular patterns similar to those of root epidermis. We also postulate that cell shape may affect pattern stability in the root. Our results thus support the idea that in this and other cases, contrasting spatial cell patterns and other evolutionary morphogenetic novelties originate from conserved genetic network modules subject to divergent contextual traits.

Journal of Comparative and Physiological Psychology, 1975

It was found that a nervous mechanism is involved in eliciting a hypoglycemic response in rats. A... more It was found that a nervous mechanism is involved in eliciting a hypoglycemic response in rats. A conditioned reflex was established after a series of reinforcements in which an insulin injection (unconditioned stimulus) was associated with the sound of a bell (conditioning stimulus). The hypoglycemic conditioned response was statistically similar to that of insulin. The latency of the beginning of the hypoglycemic response to insulin was between 4 and 6 min. The latency of the conditioned hypoglycemic response to the conditioning stimulus was about 1 min. Blood extracted from a conditioned rat during the test of conditioning produced a hypoglycemic effect when injected into a nonconditioned receptor rat.

American Naturalist, 1994

Page 1. Vol. 143, No. 1 The American Naturalist January 1994 DENSITY DEPENDENCE AND PATCH DYNAMIC... more Page 1. Vol. 143, No. 1 The American Naturalist January 1994 DENSITY DEPENDENCE AND PATCH DYNAMICS IN TROPICAL RAIN FORESTS: MATRIX MODELS AND APPLICATIONS TO A TREE SPECIES Elena R. Alvarez ...

Annual Review of Ecology and Systematics, 1996

We review deterministic and stochastic demographic models as well as classical population genetic... more We review deterministic and stochastic demographic models as well as classical population genetic models that have been applied to tropical rain forest tree species. We discuss their implications for conservation. The main conclusions of deterministic demographic models ...