Fernanda S. Valdovinos

Epigenetic and phenotypic changes result from a continuous pre and post natal dietary exposure to phytoestrogens in an experimental population of mice

BackgroundDevelopmental effects of exposure to endocrine disruptors can influence adult characters in mammals, but could also have evolutionary consequences. The aim of this study was to simulate an environmental exposure of an experimental population of mice to high amounts of nutritional phytoestrogens and to evaluate parameters of relevance for evolutionary change in the offspring. The effect of a continuous pre- and post-natal exposure to high levels of dietary isoflavones was evaluated on sexual maturity, morphometric parameters and DNA methylation status in mice. Adult mice male/female couples were fed ad libitum either with control diet (standard laboratory chow) or ISF diet (control diet plus a soy isoflavone extract at 2% (w/w) that contained the phytoestrogens genistein and daidzein). In the offspring we measured: i) the onset of vaginal opening (sexual maturation) in females, ii) weight and size in all pups at 7, 14, 21 and 42 days post-natal (dpn) and iii) DNA methylation patterns in skeletal α-actin (Acta1), estrogen receptor-α and c-fos in adults (42 dpn).ResultsVaginal opening was advanced in female pups in the ISF group, from 31.6 ± 0.75 dpn to 25.7 ± 0.48. No differences in size or weight at ages 7, 14 or 21 dpn were detected between experimental groups. Nevertheless, at age 42 dpn reduced size and weight were observed in ISF pups, in addition to suppression of normal gender differences in weight seen in the control group (males heavier that females). Also, natural differences seen in DNA methylation at Acta1 promoter in the offspring originated in the control group were suppressed in the ISF group. Acta1 is known to be developmentally regulated and related to morphomotric features.ConclusionThis study demonstrates in mammals that individuals from a population subjected to a high consumption of isoflavones can show alterations in characters that may be of importance from an evolutionary perspective, such as epigenetic and morphometric characters or sexual maturation, a life history character.

Topological plasticity increases robustness of mutualistic networks

1. Earlier studies used static models to evaluate the responses of mutualistic networks to external perturbations. Two classes of dynamics can be distinguished in ecological networks; population dynamics, represented mainly by changes in species abundances, and topological dynamics, represented by changes in the architecture of the web. 2. In this study, we model the temporal evolution of three empirical plant-pollination networks incorporating both population and topological dynamics. We test the hypothesis that topological plasticity, realized through the ability of animals to rewire their connections after depletion of host abundances, enhances tolerance of mutualistic networks to species loss. We also compared the performance of various rewiring rules in affecting robustness. 3. The results show that topological plasticity markedly increased the robustness of mutualistic networks. Our analyses also revealed that network robustness reached maximum levels when animals with less host plant availability were more likely to rewire. Also, preferential attachment to richer host plants, that is, to plants exhibiting higher abundance and few exploiters, enhances robustness more than other rewiring alternatives. 4. Our results highlight the potential role of topological plasticity in the robustness of mutualistic networks to species extinctions and suggest some plausible mechanisms by which the decisions of foragers may shape the collective dynamics of plant-pollinator systems.

A network analysis of plant–pollinator interactions in temperate rain forests of Chiloé Island, Chile

This study characterizes the structure of a plant–pollinator network in a temperate rain forest of Chiloé Island, southern Chile, where woody species are strongly dependent on biotic pollinators, and analyzes its robustness to the loss of participating species. Degree distribution, nestedness, and expected species persistence were evaluated. In addition, we assessed the roles of predefined subsets of plants (classified by life forms) and pollinators (grouped by taxonomic orders) in the network’s structure and dynamics. For this, we simulated the complete removal of each plant and pollinator subset and analyzed the resultant connectivity patterns, as well as the expected long-term species losses by running a stochastic model. Finally, we evaluated the sensitivity of the network structure to the loss of single species in order to identify potential targets for conservation. Our results show that the plant–pollinator network of this Chilean temperate rain forest exhibits a nested structure of interactions, with a degree distribution best described by a power law model. Model simulations revealed the importance of trees and hymenopterans as pivotal groups that maintain the core structure of the pollination network and guarantee overall species persistence. The hymenopterans Bombus dahlbomii and Diphaglossa gayi, the shrubs Tepualia stipularis and Ugni molinae, the vines Mitraria coccinea and Asteranthera ovata, and the entire set of tree species exerted a disproportionately large influence on the preservation of network structure and should be considered as focal species for conservation programs given current threats from selective logging and habitat loss.

Nestedness of bee assemblages in an endemic South American forest: the role of pine matrix and small fragments

We assessed species richness and distribution of the apoidean fauna of the coastal Maulino forest, an endemic and threatened forest in central Chile. Remnant forest fragments are immersed in commercial pine plantations, who act as the habitat matrix. The bee assemblages depict a non-nested structure at the landscape level at times when pine plantations are standing. However, assemblages are nested in the fauna of forest fragments at times when plantations are harvested, suggesting that plantations might be acting as habitat providing connectivity between remnants of Maulino forest. Therefore, the conservation of apoideans might require a landscape level approach to be successful, including partial reliance on plantations.

Análisis de las consecuencias del comportamiento adaptativo individual sobre la estabilidad poblacional: El caso del forrajeo óptimo

Trabajos tempranos basados en la teoria de Sistemas Dinamicos, demostraron que mientras mayor sea el numero de poblaciones en interaccion ecologica, el sistema tiende a ser mas inestable. Sin embargo, la evidencia empirica indica que las poblaciones naturales presentan mas frecuentemente dinamicas estables, aun estando inmersas en comunidades complejas. Entre los mecanismos que promueven la estabilizacion poblacional, se encuentra el comportamiento adaptativo de los individuos componentes de las poblaciones. En este trabajo se analizan los avances teoricos respecto del rol del forrajeo optimo (FO) como fuerza estabilizadora de las dinamicas poblacionales, en comunidades modelo de diferente nivel de complejidad estructural. El analisis se organiza en torno a tres preguntas centrales: i) ?cual es el sistema control contra el cual se compara la estabilidad de una poblacion cuyos individuos presentan FO?, ii) ?cual es el concepto de estabilidad utilizado? y iii) ?como se incorporan los supuestos del FO en las reglas que gobiernan la dinamica poblacional? En base a este analisis, especificamos los puntos que deben atenderse para evaluar correctamente el rol estabilizador del FO y otros comportamientos adaptativos que satisfagan los supuestos de la Teoria Ecologica de la Optimizacion. Finalmente, conjeturamos que el efecto estabilizador del FO dependera cualitativamente tanto del nivel de recursos en el sistema, como de la relacion entre tasa de perturbacion ambiental y tasa de adaptacion del depredador.