Regrowth of tropical secondary forests following complete or nearly complete removal of forest vegetation actively stores carbon in aboveground biomass, partially counterbalancing carbon emissions ...from deforestation, forest degradation, burning of fossil fuels, and other anthropogenic sources. We estimate the age and spatial extent of lowland second-growth forests in the Latin American tropics and model their potential aboveground carbon accumulation over four decades. Our model shows that, in 2008, second-growth forests (1 to 60 years old) covered 2.4 million km(2) of land (28.1% of the total study area). Over 40 years, these lands can potentially accumulate a total aboveground carbon stock of 8.48 Pg C (petagrams of carbon) in aboveground biomass via low-cost natural regeneration or assisted regeneration, corresponding to a total CO2 sequestration of 31.09 Pg CO2. This total is equivalent to carbon emissions from fossil fuel use and industrial processes in all of Latin America and the Caribbean from 1993 to 2014. Ten countries account for 95% of this carbon storage potential, led by Brazil, Colombia, Mexico, and Venezuela. We model future land-use scenarios to guide national carbon mitigation policies. Permitting natural regeneration on 40% of lowland pastures potentially stores an additional 2.0 Pg C over 40 years. Our study provides information and maps to guide national-level forest-based carbon mitigation plans on the basis of estimated rates of natural regeneration and pasture abandonment. Coupled with avoided deforestation and sustainable forest management, natural regeneration of second-growth forests provides a low-cost mechanism that yields a high carbon sequestration potential with multiple benefits for biodiversity and ecosystem services.
The role of canopy gaps in tropical dry forest (TDF) dynamics remains unclear. Here, 75 canopy gaps, mostly formed by the fall of Bursera spp. and Pachycereus pecten-aboriginum individuals, are ...described, and their potential consequences for forest regeneration are analysed in a Mexican TDF. In 50 randomly selected gaps, understorey vegetation was sampled with a paired design (inside and outside gaps) and by distinguishing two plant height categories. In total, 1940 plants were recorded (63% in gaps and 37% in non-gap plots). Community attributes (density, community cover, taxonomic richness and Shannon diversity) were significantly higher for both height categories in gap plots. Conversely, neither an NMDS ordination nor a multinomial classification of 187 species by habitat affinities revealed floristic segregation between gaps and non-gaps; almost all species were classified as habitat generalists, with only a few opportunistic forbs (but no single tree species) being classified as gap specialists. The most important effects of gap formation are significant increases in plant abundance and species richness, but not a different species composition. Against earlier views that gap-phase dynamics is inconsequential for TDF dynamics, these results suggest a more active, albeit modest, role of treefall gaps in TDF, through promoting an abundant establishment.
The availability of geothermal resources in Baja California has been thoroughly documented in the past. This region currently experiences a deficit in electricity production and it is, to date, ...disconnected from the National Electric Grid. It is therefore essential to provide strategies for a sustainable production of geothermal electricity in this region that besides, contributes to the increasing need for decarbonization of electricity industry. Here we propose an updated conceptual model of the Las Tres Virgenes hydrothermal system, a currently exploited geothermal area that has been active for more than two decades. The objective of this model is to provide thermal and aquifer relationships that gave rise to this system in its natural state. To achieve this, an updated structural model is presented based on recent geological interpretations of the area. Geochemical and geophysical evidences are also integrated in a conceptual model. A detailed pre-processing step of geological data is incorporated to preserve as much as possible the critical field evidences in the discrete model. Numerical simulations are then conducted using TOUGH2 and the equation of state for water and air (EOS3). As a result, the geothermal field is conceived, and numerically validated, as a fault-hosted fossil aquifer. The upflow that feeds the reservoir interacts with a network of faults. Since the faults hosting the aquifer belong to the regional structural feature of Santa Rosalia Basin, it is imperative to deepen the study of these system with regard to their storativity and permeability since they may control the fate of the system in the long term.
•A revised conceptual model of a currently operating geothermal field in Mexico.•High resolution grids to represent geological structures.•TOUGH2 natural state simulations in a fault-controlled hydrothermal system.
BACKGROUND: Resistance to chemical insecticides plus high morbidity rates have lead to rising interest in fungi as candidates for biocontrol agents of mosquito vectors. In most studies fungal ...infections have been induced by exposure of mosquitoes to various surfaces treated with conidia. In the present study eight Mexican strains of Beauveria bassiana were assessed against Aedes aegypti by direct exposure of females to 6 × 10⁸ conidia ml⁻¹ on a filter paper, afterwards, the transmission of the least and most virulent isolates was evaluated by mating behavior from virgin, fungus-contaminated male to females, to examine this ethological pattern as a new approach to deliver conidia against the dengue vector. METHODS: In an exposure chamber with a filter paper impregnated with 6 × 10⁸ conidia ml⁻¹ of the least and most virulent strains of B. bassiana, 6-8 day old males of A. aegypti were exposed for 48 hours, and then transferred individually (each one was a replicate) to another chamber and confined with twenty healthy females of the same age. Clean males were used in controls. Survival, infection by true mating (insemination) or by mating attempts (no insemination) and fecundity were daily registered until the death of last female. Data analysis was conducted with proc glm for unbalanced experiments and means were separated with the Ryan test with SAS. RESULTS: All strains were highly virulent with LT₅₀ ranging from 2.70 (± 0.29) to 5.33 (± 0.53) days. However the most (Bb-CBG2) and least virulent (Bb-CBG4) isolates were also transmitted by mating behavior; both killed 78-90% of females in 15 days after being confined with males that had previously been exposed for 48 hours to fungi. Of these mortality rates, 23 and 38% respectively, were infections acquired by copulations where insemination occurred. The LT₅₀ for sexually-infected females were 7.92 (± 0.46) and 8.82 (± 0.45) days for both strains, while the one in control was 13.92 (± 0.58). Likewise, fecundity decreased by 95% and 60% for both Bb-CBG2 and Bb-CBG4 isolates in comparison with control. The role of mating attempts in this delivery procedure of B. bassiana is discussed. CONCLUSIONS: This is the first report about transmission of B. bassiana by mating behavior from virgin, fungus-contaminated males to females in A. aegypti. Fungal infections acquired by this route (autodissemination) infringed high mortality rates (90%) in mated or approached females. However, prior to releasing virgin, fungus-contaminated males to spread B. basasiana among females of A. aegypti, this novel alternative needs further investigations.
Studies of tropical secondary forest succession face strong limitations due to the slow pace of succession and the time-consuming task of monitoring processes. The occurrence of tree rings in ...secondary forest trees may help expand our knowledge on succession in these systems and may be useful for fallow dating in chronosequence studies. We examine here the potential of tree rings to study forest succession by sampling 70 species along chronosequences of dry and wet forests in southern Mexico. Based on wood anatomical features, we estimated that about 37 percent of the species presented distinct growth rings useful for ring studies. Overall, maximum number of rings matched well the interview-based fallow ages but, at some sites, trees had consistently higher numbers of rings, probably due to errors in fallow ages derived from interviews. Best fallow age estimations were obtained by examining rings in both pioneer and nonpioneer species. Reconstruction of species' establishment dates revealed that pioneer and nonpioneer species establish early during succession, and that species of both groups continue to recruit after many years. Our study clearly shows that tree ring analysis is a promising tool for studies on secondary forest succession in the tropics.
The existence of a wild population of Laelia dawsonii f. dawsonii is recorded for the first time in the Mexican State of Jalisco. Laelia dawsonii has a wide geographical distribution throughout the ...Sierra Madre del Sur (Oaxaca, Guerrero, and Jalisco); however, the populations are very isolated, and each one has very few individuals. Until now, no wild populations of this species had been registered outside of the State of Oaxaca. The population found in Jalisco is composed of about 100 plants. Due to its horticultural importance, L. dawsonii has been frequently extracted from the field, and its Oaxacan populations have been decimated since the end of the 19th century. Currently, this species is considered endangered in Mexico.
Keywords: biogeography, conservation, Laeliinae, Laelia anceps
Biopolymers are widely used for design sustained drug delivery systems (SDDS) and biomaterials for tissue engineering. Reducing wound infections still constitutes one of the major challenges facing ...the wound care. The aim of this study was to synthetize, characterize and evaluate a single (polymeric spheres) and a binary polymeric biomaterial (polymeric spheres imbedded in a poly(vinyl alcohol) (PVA) scaffold) as a SDDS. Polymeric spheres were prepared by complex coacervation and the binary system of the chitosan (CH) -PVA beads embedded in a PVA scaffold prepared by Ice Segregation Induced Self-Assembly (ISISA) process. Both systems were physicochemically characterized using Fourier Transform Infrared spectroscopy (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). In vitro ciprofloxacin (CFX) release kinetics were evaluated simulating physiological conditions under sink conditions. Physicochemical characterization showed interactions between all components forming beads; in contrast, beads-scaffold interactions were not detected making evident the presence of two different phases in the binary system. The CFX release kinetics revealed that both systems were SDDS, simple system release 97.0 ± 6.9% in 7 days, while the binary was 68.56 ± 6.6% during 14 days of evaluation. Binary system emerges as a potential tool for evaluate the long-lasting infection control in the treatment of skin wounds.
Barkeria whartoniana is an epiphytic, microendemic orchid of southern Mexico. This species exclusively inhabits limestone outcrops within a tropical dry forest in Oaxaca State, and its current ...population size is very small. The goals of this study were to characterize its phorophyte preference, and to assess the success of the experimental reintroduction of young individuals into its habitat. In an area of 15 km2 we censused all individuals of this orchid and estimated its area of occupancy. The occurrence frequency on different phorophytes was compared with the estimated densities of potential phorophytes. In July 2014, 76 orchid plants obtained through in vitro cultivation were reintroduced by attaching them on the trunks of two phorophyte species, one with rugose bark (Comocladia engleriana) and the other with smooth bark (Plumeria rubra). In the estimated area of occupancy of this orchid (0.016 km2), we only recorded 254 individuals, 42.4% of which were located on C. engleriana, suggesting a strong preference for this phorophyte. In October 2016, 13 reintroduced plants (ca. 17%) were still alive, almost all of which had successfully established. Initial plant size (stem length) emerged as an important driver of future survival. The artificial reintroduction of orchids facing extinction risk into their habitats may represent an efficient way to skip two critical phases in their life cycles, namely seed dispersal and establishment.
Summary
Salmonella are successful pathogens that infect millions of people every year. During infection, Salmonella typhimurium changes the structure of its lipopolysaccharide (LPS) in response to ...the host environment, rendering bacteria resistant to cationic peptide lysis in vitro. However, the role of these structural changes in LPS as in vivo virulence factors and their effects on immune responses and the generation of immunity are largely unknown. We report that modified LPS are less efficient than wild‐type LPS at inducing pro‐inflammatory responses. The impact of this LPS‐mediated subversion of innate immune responses was demonstrated by increased mortality in mice infected with a non‐lethal dose of an attenuated S. typhimurium strain mixed with the modified LPS moieties. Up‐regulation of co‐stimulatory molecules on antigen‐presenting cells and CD4+ T‐cell activation were affected by these modified LPS. Strains of S. typhimurium carrying structurally modified LPS are markedly less efficient at inducing specific antibody responses. Immunization with modified LPS moiety preparations combined with experimental antigens, induced an impaired Toll‐like receptor 4‐mediated adjuvant effect. Strains of S. typhimurium carrying structurally modified LPS are markedly less efficient at inducing immunity against challenge with virulent S. typhimurium. Hence, changes in S. typhimurium LPS structure impact not only on innate immune responses but also on both humoral and cellular adaptive immune responses.
Summary
In Aspergillus nidulans, asexual differentiation requires the presence of the transcription factor FlbB at the cell tip and apical nuclei. Understanding the relationship between these two ...pools is crucial for elucidating the biochemical processes mediating conidia production. Tip‐to‐nucleus communication was demonstrated by photo‐convertible FlbB::Dendra2 visualization. Tip localization of FlbB depends on Cys382 in the C‐terminus and the bZIP DNA‐binding domain in the N‐terminus. FlbE, a critical FlbB interactor, binds the bZIP domain. Furthermore, the absence of FlbE results in loss of tip localization but not nuclear accumulation. flbE deletion also abrogates transcriptional activity indicating that FlbB gains transcriptional competence from interactions with FlbE at the tip. Finally, a bipartite nuclear localization signal is required for nuclear localization of FlbB. Those motifs of FlbB may play various roles in the sequence of events necessary for the distribution and activation of this transcriptionally active developmental factor. The tip accumulation, FlbE‐dependent activation, transport and nuclear import sketch out a process of relaying an environmentally triggered signal from the tip to the nuclei. As the first known instance of transcription factor‐mediated tip‐to‐nucleus communication in filamentous fungi, this provides a general framework for analyses focused on elucidating the set of molecular mechanisms coupling apical signals to transcriptional events.
Conidia production is the main mechanism used by fungal pathogens for their spread. In vegetative hyphae of the model filamentous fungus Aspergillus nidulans, the induction of conidiation requires a straight communication language between the growth region (the tip) and the nucleus, which is mediated by the transcription factor FlbB. This work describes the role of specific interactors and the functional domains within FlbB in its tip‐to‐nucleus dynamics.
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