Sex pheromone and period gene characterization of Lutzomyia longipalpis sensu lato (Lutz & Neiva) (Diptera: Psychodidae) from Posadas, Argentina

Lutzomyia longipalpis s.l. is the primary vector of Leishmania (L.) infantum in the New World. In this study, male Lutzomyia longipalpis specimens from Posadas, Argentina were characterized for two polymorphic markers: the male sex pheromone and the period (per) gene. The male sex pheromone was identified as (S)-9-methylgermacrene-B, the same compound produced by Lu. longipalpis from Paraguay and many populations from Brazil. The analysis of per gene sequences revealed that the population from Argentina is significantly differentiated from previously studied Brazilian populations. Marker studies could contribute to the understanding of the distribution and spread of urban American visceral leishmaniasis, thus aiding in the design of regional surveillance and control strategies.     

Lipid packing determines protein-membrane interactions: Challenges for apolipoprotein A-I and high density lipoproteins

Protein and protein-lipid interactions, with and within specific areas in the cell membrane, are critical in order to modulate the cell signaling events required to maintain cell functions and viability. Biological bilayers are complex, dynamic platforms, and thus in vivo observations usually need to be preceded by studies on model systems that simplify and discriminate the different factors involved in lipid-protein interactions. Fluorescence microscopy studies using giant unilamellar vesicles (GUVs) as membrane model systems provide a unique methodology to quantify protein binding, interaction, and lipid solubilization in artificial bilayers. The large size of lipid domains obtainable on GUVs, together with fluorescence microscopy techniques, provides the possibility to localize and quantify molecular interactions. Fluorescence Correlation Spectroscopy (FCS) can be performed using the GUV model to extract information on mobility and concentration. Two-photon Laurdan Generalized Polarization (GP) reports on local changes in membrane water content (related to membrane fluidity) due to protein binding or lipid removal from a given lipid domain. In this review, we summarize the experimental microscopy methods used to study the interaction of human apolipoprotein A-I (apoA-I) in lipid-free and lipid-bound conformations with bilayers and natural membranes. Results described here help us to understand cholesterol homeostasis and offer a methodological design suited to different biological systems.     

Patterns of genetic diversity in colonizing plant species: Nassauvia lagascae var. lanata (Asteraceae: Mutisieae) on Volcan Lonquimay, Chile

The effect of colonization on the distribution of genetic diversity within and among populations in relation to species characteristics remains an open empirical question. The objective of this study was to contrast genetic diversity within and among established and colonizing populations of Nassauvia lagascae var. lanata on Volcán Lonquimay (Araucanía Region, Chile), which erupted on 25 December 1988, and relate genetic diversity to biological characteristics of the populations. We analyzed a total of 240 individuals from 15 populations distributed along the Andes Cordillera using AFLP and obtained a total of 307 AFLP bands, of which 97.7% are polymorphic. Values of population differentiation (F(ST)) did not differ significantly among established and colonizing populations, but colonizing populations did have reduced levels of genetic divergence (as indicated by private and rare bands) and genetic variation (e.g., Shannon index). We conclude that a founder effect through limited numbers of founding propagules derived from nearby source populations has not yet been compensated for by subsequent population growth and migration. Low rates of secondary dispersal via running water, kin-structure within populations, and slow population growth seem to contribute to the slow recovery of genetic diversity.     

Recovery of Populus tremuloides seedlings following severe drought causing total leaf mortality and extreme stem embolism

In contrast with other native Populus species in North America, Populus tremuloides (aspen) can successfully establish itself in drought‐prone areas, yet no comprehensive analysis has been performed on the ability of seedlings to withstand and recover from a severe drought resulting in complete leaf mortality. Here, we subjected 4‐month‐old aspen seedlings grown in two contrasting soil media to a progressive drought until total leaf mortality, followed by a rewatering cycle. Stomatal conductance (g_s), photosynthesis and transpiration followed a sigmoid decline with declining fraction of extractable soil water values. Cessation of leaf expansion occurred close to the end of the linear‐decrease phase, when g_s was reduced by 95%. Leaf mortality started after g_s reached the lowest values, which corresponded to a stem–xylem pressure potential (Ψ_xp) of ?2.0 MPa and a percent loss of stem hydraulic conductivity (PLC) of 50%. In plants with 50% leaf mortality, PLC values remained around 50%. Complete leaf mortality occurred at an average stem PLC of 90%, but all seedlings were able to resprout after 6–10 days of being rewatered. Plants decapitated at soil level before rewatering developed root suckers, while those left with a 4‐cm stump or with their stems intact resprouted exclusively from axillary buds. Resprouting was accompanied by recovery of stem hydraulic conductivity, with PLC values around 30%. The percentage of resprouted buds was negatively correlated with the stem %PLC. Thus, the recovery of stem hydraulic conductivity appears as an important factor in the resprouting capacity of aspen seedlings following a severe drought.     

Paraquat-induced oxidative stress response during amphibian early embryonic development

In addition to the endogenous production of reactive oxygen species (ROS) as a result of normal development, amphibian external development often forces embryos to deal with oxidative stress-producing agents present in the environment. Embryos should therefore develop protective systems to reduce ROS toxicity and achieve successful development. The present work was aimed to characterize the effects produced by the widespread-used ROS-generator pesticide Paraquat during early embryonic development in the toad Chaunus arenarum, as well as to get insights into the defense response elicited by amphibian embryos. The approach consisted in generating a sharp and brief oxidative stress condition early during embryonic development to stimulate the cellular mechanisms involved in ROS-antioxidant response. Results revealed that Paraquat-treatment reduced the ability of embryos to develop normally, leading to arrests of development and severe malformations such as tail abnormalities, abdominal edema, reduced head development and curved dorsal structures. Although Paraquat effects were morphologically evident from gastrula stage on, alterations such as chromatin condensation were observed even at blastula stage by histological examinations. Regarding detoxifying enzymes, a significant induction of Mn-superoxide dismutase activity was detected at stages beyond gastrula in embryos surviving Paraquat treatment, suggesting a major role of this enzyme in the antioxidant response during early embryonic development.     

Conserved changes in envelope function during human immunodeficiency virus type 1 coreceptor switching

We studied the evolution of human immunodeficiency virus type 1 (HIV-1) envelope function during the process of coreceptor switching from CCR5 to CXCR4. Site-directed mutagenesis was used to introduce most of the possible intermediate mutations in the envelope for four distinct coreceptor switch mutants, each with a unique pattern of CCR5 and CXCR4 utilization that extended from highly efficient use of both coreceptors to sole use of CXCR4. Mutated envelopes with some preservation of entry function on either CCR5- or CXCR4-expressing target cells were further characterized for their sensitivity to CCR5 or CXCR4 inhibitors, soluble CD4, and the neutralizing antibodies b12-IgG and 4E10. A subset of mutated envelopes was also studied in direct CD4 or CCR5 binding assays and in envelope-mediated fusion reactions. Coreceptor switch intermediates displayed increased sensitivity to CCR5 inhibitors (except for a few envelopes with mutations in V2 or C2) that correlated with a loss in CCR5 binding. As use of CXCR4 improved, infection mediated by the mutated envelopes became more resistant to soluble CD4 inhibition and direct binding to CD4 increased. These changes were accompanied by increasing resistance to the CXCR4 inhibitor AMD3100. Sensitivity to neutralizing antibody was more variable, although infection of CXCR4-expressing targets was generally more sensitive to neutralization by both b12-IgG and 4E10 than infection of CCR5-expressing target cells. These changes in envelope function were uniform in all four series of envelope mutations and thus were independent of the final use of CCR5 and CXCR4. Decreased CCR5 and increased CD4 binding appear to be common features of coreceptor switch intermediates.     

Edge effects on palm diversity in rain forest fragments in western Ecuador

At the edges of tropical rain forest fragments, altered abiotic and biotic conditions influence the structure and dynamics of plant communities. In Neotropical rain forests, palms (Arecaceae) are important floristic and ecological elements. Palms’ responses to edge effects appear to be idiosyncratic and to depend on the level of disturbance at edges. This paper explores how variation in forest structure at the edges of two old-growth forest fragments in a tropical rain forest in western Ecuador affects palms of different species, life-forms, and size classes. We investigate (1) how edge effects influence the relative proportion of palm adults and juveniles, (2) how distance from the forest edge affects palm density and species richness, (3) how altered forest structure along edges affects palm density. We found that at edges (1) palm communities had a lower proportion of adults relative to juvenile individuals compared to continuous forests, (2) the density of two species of palms and the overall species richness of the palm community tended to decrease toward the edges within forest fragments, and, (3) altered forest structure decreased the density of adult palms. Hence, edge effects on palms were controlled by the degree of modification of the forest structure, and by species responses to edge-related disturbance.     

The role of vitellogenin during gestation of Girardinichthys viviparus and Ameca splendens; two goodeid fish with matrotrophic viviparity

Goodeid fish have matrotrophic viviparity, and unlike lecitotrophic fish, yolk loss forces the female to provide the nutritional requirements for embryonic development. Vitellogenin (VTG) is the yolk precursor protein synthesized in the maternal liver, but there is only circumstantial evidence regarding VTG supply during the ontogenesis of bony fish with matrotrophic viviparity. Therefore, the goal of the present study was to identify and quantify VTG during gestation of the black fin goodeid Girardinichthys viviparus and the butterfly split-fin goodeid Ameca splendens. Females at different gonadic developmental stages were selected in order to evaluate VTG mRNA expression in the maternal liver using RT-PCR; VTG quantification in maternal muscle and liver, as well as in the embryos, was done using ELISA, and immunohistochemical detection of VTG was done in the black fin goodeid. The results suggest that VTG supplies nutrients during embryonic development of both species, which have different life histories. It is possible that the transition from lecitotrophy to matrotrophic viviparity in bony fish with intraluminal gestation involved adaptive transition strategies that included changes in the relationship between oocytes and follicular cells, as well as a gradual loss of VTG synthesis during embryonic development.