Chronic Disturbance in a Tropical Dry Forest: Disentangling Direct and Indirect Pathways Behind the Loss of Plant Richness

Chronic disturbance is widely recognized as one of main triggers of diversity loss in seasonally dry tropical forests (SDTFs). However, the pathways through which diffuse disturbance is acting on the forest are little understood. This information is especially demanded in the case of vanishing Neotropical seasonally dry forests such as the Tumbesian ones. We proposed a conceptual model to analyze the factors behind the loss of woody species richness along a forest disturbance gradient, explicitly considering the existence of direct and indirect causal pathways of biodiversity loss. We hypothesized that the chronic disturbance can act on the woody species richness directly, either by selective extraction of resources or by browsing of palatable species for livestock, or indirectly, by modifying characteristics of the forest structure and productivity. To test our model, we sampled forest remnants in a very extensive area submitted to long standing chronic pressure. Our forests cells (200 × 200 m) were characterized both in terms of woody species composition, structure, and human pressure. Our structural equation models (SEMs) showed that chronic disturbance is driving a loss of species richness. This was done mainly by indirect effects through the reduction of large trees density. We assume that changes in tree density modify the environmental conditions, thus increasing the stress and finally filtering some specific species. The analysis of both, direct and indirect, allows us to gain a better understanding of the processes behind plant species loss in this SDTF.

Unfolded Protein Response as a Therapeutic Target in Cardiovascular Disease

Cardiovascular disease is the leading cause of death worldwide. Despite overwhelming socioeconomic impact and mounting clinical needs, our understanding of the underlying pathophysiology remains incomplete. Multiple forms of cardiovascular disease involve an acute or chronic disturbance in cardiac myocytes, which may lead to potent activation of the Unfolded Protein Response (UPR), a cellular adaptive reaction to accommodate protein-folding stress. Accumulation of unfolded or misfolded proteins in the Endoplasmic Reticulum (ER) elicits three signaling branches of the UPR, which otherwise remain quiescent. This ER stress response then transiently suppresses global protein translation, augments production of protein-folding chaperones, and enhances ER-associated protein degradation, with an aim to restore cellular homeostasis. Ample evidence has established that the UPR is strongly induced in heart disease. Recently, the mechanisms of action and multiple pharmacological means to favorably modulate the UPR are emerging to curb the initiation and progression of cardiovascular disease. Here, we review the current understanding of the UPR in cardiovascular disease and discuss existing therapeutic explorations and future directions.

Vegetation of a tropical dry forest in a landscape with chronic disturbance: the case of the indigenous community of San Nicolás Zoyatlan (Guerrero, Mexico)

<p><strong><span lang="EN-US">Background. </span></strong><span lang="EN-US">Tropical dry forests (TDF) provide numerous environmental services to its residents; this has led them to be humanized landscapes subjected to chronic disturbance with a high risk of disappearing.</span></p><p><strong><span lang="EN-US">Research question. </span></strong><span lang="EN-US"><span> </span>To establish </span><span lang="EN-US">the relationship of vegetation structure and composition of a chronically disturbed TDF, with some environmental factors and the intensity of agricultural land use.</span></p><p><strong><span lang="EN-US">Study site and period of research. </span></strong><span lang="EN-US">Our study was conducted during six months (July through November) in the TDF of the community of San Nicolas Zoyatlan (Guerrero, Mexico); a territory with a history of over 500 years of agricultural use. This use has led to a complex mosaic of vegetation fragments.</span></p><p><strong><span lang="EN-US">Methods. </span></strong><span lang="EN-US">A selection of 36 fragments was studied to determine vegetation <span>structure and composition as well as environmental factors</span>. </span><span lang="EN-US">Representative plants from sampled areas were collected<span>. </span><span>Data gathered was explored with regression and multivariate statistical analysis techniques.</span></span></p><p><strong><span lang="EN-US">Results. </span></strong><span lang="EN-US">59 families, 178 genera and 279 species were recorded. Species richness varied widely among fragments, in general with a low dominance and high turnover of species. Slope was the only factor that showed a solid relationship with vegetation variables. Three groups of fragments were established and the statistical differences between them were explained by the duration of fallow. The fragments with longer fallow period showed the best conditions in vegetation variables and 66.9% of the species were found in them.</span></p><p><strong><span lang="EN-US">Conclusions.</span></strong><span lang="EN-US"> Composition and structure of vegetation were related to intensity of agricultural land use. Although<strong> </strong>there is a process of impoverishment, vegetation dynamics involving species of the Fabaceae, Asteraceae and Burseraceae families show a potential for their use in the environmental restoration of Zoyatlan.</span></p>

The effect of chronic and acute stressors, and their interaction, on gonadal function: an experimental test during gonadal recrudescence

Organisms are expected to invest less in reproduction in response to a stressor, but theory predicts that this effect should depend on the frequency of stressors in the environment. Here we investigated how an acute stressor affected gonadal function in a songbird, and how long-term differences in the stress environment influenced these acute stress responses. We exposed male Dark-eyed Juncos (Junco hyemalis) either to chronic or minimal (control) disturbance during gonadal recrudescence, after which we measured baseline testosterone, testosterone after an acute handling stressor, and the ability to elevate testosterone in response to hormonal stimulation. In a 2x2 design, we then euthanized males from the two chronic treatment groups either immediately or after an acute stressor to investigate the effect of these treatments on the gonadal transcriptome. We found that chronically disturbed birds had marginally lower testosterone. The acute stressor suppressed testosterone in control birds, but not in the chronic disturbance group. The ability to elevate testosterone did not differ between the chronic treatments. Surprisingly, chronic disturbance had a weak effect on the testicular transcriptome, and did not affect transcriptomic response to the acute stressor. The acute stressor, on the other hand, upregulated cellular stress response, and affected expression of genes associated with hormonal stress-response. Overall, we show that both chronic and acute stressors affect reproductive function, and that chronic stress changes how acute stressors affect testosterone physiology. Our findings also suggest that acute and chronic stressors affect testes differently, and that gonadal function is relatively robust to long-term stressors.Summary statementAn acute stressor downregulated testosterone production, but this effect was absent in chronically disturbed birds. The acute stressor had a strong effect on the gonadal transcriptome, whereas chronic disturbance had a negligible effect.

Chronic anthropogenic disturbance as a secondary driver of ant community structure: interactions with soil type in Brazilian Caatinga

SUMMARYHabitat loss is widely recognized as the major cause of global biodiversity decline, but remaining habitat is increasingly threatened by chronic human disturbances. Using a multi-model averaging approach we examined the association between five chronic disturbance surrogates and the richness and taxonomic and functional composition of ants in Brazilian Caatinga. Using pitfall traps in 47 plots near Parnamirim city (Pernambuco) across two soil types (sand and clay), we recorded 53 species from 27 genera. Ant species richness on sand was slightly higher than on clay, and was negatively related to most surrogates of anthropogenic disturbance. Soil type and human population size were the main predictors of ant species richness. Soil type was the most important predictor of functional group abundance. Taxonomic and functional composition were influenced by soil type and disturbance, but this relationship varied between clay and sandy soils. Ant functional composition showed a weak relationship with disturbance on sandy soils, but on clay soils it showed predictable winner–loser replacement. We attribute the greater effect of disturbance on clay soils to higher intensity of land use, and our study highlights the importance of considering context dependence when evaluating biodiversity responses to disturbance.