Explore the vast range of titles available.

Antimicrobial peptides (AMPs) play a key role in the defence mechanism of living organisms against microbial pathogens, displaying both bactericidal and immunomodulatory properties. They are considered as a promising alternative to the conventional antibiotics towards which bacteria are becoming highly resistant. Recently, a derivative of the frog skin AMP esculentin-1a, esculentin-1a(1-21)NH sub(2) [Esc(1-21)], showed a strong and fast membranolytic activity against Gram-negative bacteria but with a lower efficacy against Gram-positive ones. Here, with the aim to increase the alpha -helicity of Esc(1-21) and the expected potency against Gram-positive bacteria, we designed an analog bearing three alpha -aminoisobutyric acid (Aib) residues at positions 1, 10, and 18 of its primary structure. We demonstrated that the incorporation of Aib residues: (1) promoted the alpha -helix conformation of Esc(1-21), as confirmed by circular dichroism and two-dimensional nuclear magnetic resonance spectroscopies; (2) was sufficient to make this analog more active than the parent peptide against several Gram-positive bacterial strains without affecting its activity against Gram-negative bacteria; and (3) resulted to be devoid of toxic effect toward epithelial cells at the active antimicrobial concentrations. These results suggest that replacement of L-amino acids with Aib residues has beneficial effects on the structure and properties of the membrane-active peptide Esc(1-21), making it a better candidate for the design and development of selective drugs against Gram-positive bacteria.

Muscle fibres, isolated from frog tibialis anterior and mouse flexor digitorum brevis (FDB) were loaded with the fast dye MagFluo-4 to study the effects of potentiators caffeine, nitrate, Zn super(2+) and perchlorate on Ca super(2+) transients elicited by single action potentials. Overall, the potentiators doubled the transients amplitude and prolonged by about 1.5-fold their decay time. In contrast, as shown here for the first time, nitrate and Zn super(2+), but not caffeine, activated a late, secondary component of the transient rising phase of frog but not mouse, fibres. The rise time was increased from 1.9 ms in normal solution (NR) to 3.3 ms (nitrate) and 4.4 ms (Zn super(2+)). In NR, a single exponential, fitted the rising phase of calcium transients of frog ( tau sub(1) = 0.47 ms) and mouse ( tau sub(1) = 0.28 ms). In nitrate and Zn super(2+) only frog transients showed a secondary exponential component, tau sub(2) = 0.72 ms (nitrate) and 0.94 ms, (Zn super(2+)). We suggest that nitrate and Zn super(2+) activate a late slower component of the Delta F/F signals of frog but not of mouse fibres, possibly promoting Ca super(2+) induced Ca super(2+) release at level of the RyR3, that in frog muscle fibres are localized in the para-junctional region of the triads and are absent in mouse FDB muscle fibres.

Rapid spread of disease is a hazard in our interconnected world. The chytrid fungus Batrachochytrium dendrobatidis was identified in amphibian populations about 20 years ago and has caused death and species extinction at a global scale. Scheele et al. found that the fungus has caused declines in amphibian populations everywhere except at its origin in Asia (see the Perspective by Greenberg and Palen). A majority of species and populations are still experiencing decline, but there is evidence of limited recovery in some species. The analysis also suggests some conditions that predict resilience

Frogs (Anura) are one of the most diverse groups of vertebrates and comprise nearly 90% of living amphibian species. Their worldwide distribution and diverse biology make them well-suited for assessing fundamental questions in evolution, ecology, and conservation. However, despite their scientific importance, the evolutionary history and tempo of frog diversification remain poorly understood. By using a molecular dataset of unprecedented size, including 88-kb characters from 95 nuclear genes of 156 frog species, in conjunction with 20 fossil-based calibrations, our analyses result in the most strongly supported phylogeny of all major frog lineages and provide a timescale of frog evolution that suggests much younger divergence times than suggested by earlier studies. Unexpectedly, our divergence-time analyses show that three species-rich clades (Hyloidea, Microhylidae, and Natatanura), which together comprise ∼88% of extant anuran species, simultaneously underwent rapid diversification at the Cretaceous–Paleogene (K–Pg) boundary (KPB). Moreover, anuran families and subfamilies containing arboreal species originated near or after the KPB. These results suggest that the K–Pg mass extinction may have triggered explosive radiations of frogs by creating new ecological opportunities. This phylogeny also reveals relationships such as Microhylidae being sister to all other ranoid frogs and African continental lineages of Natatanura forming a clade that is sister to a clade of Eurasian, Indian, Melanesian, and Malagasy lineages. Biogeographical analyses suggest that the ancestral area of modern frogs was Africa, and their current distribution is largely associated with the breakup of Pangaea and subsequent Gondwanan fragmentation.

Debates over the relationship between biodiversity and disease dynamics underscore the need for a more mechanistic understanding of how changes in host community composition influence parasite transmission. Focusing on interactions between larval amphibians and trematode parasites, we experimentally contrasted the effects of host richness and species composition to identify the individual and joint contributions of both parameters on the infection levels of three trematode species. By combining experimental approaches with field surveys from 147 ponds, we further evaluated how richness effects differed between randomized and realistic patterns of species loss (i.e. community disassembly). Our results indicated that community-level changes in infection levels were owing to host species composition, rather than richness. However, when composition patterns mirrored empirical observations along a natural assembly gradient, each added host species reduced infection success by 12–55%. No such effects occurred when assemblages were randomized. Mechanistically, these patterns were due to non-random host species assembly/disassembly: while highly competent species predominated in low diversity systems, less susceptible hosts became progressively more common as richness increased. These findings highlight the potential for combining information on host traits and assembly patterns to forecast diversity-mediated changes in multi-host disease systems.

The reproductive modes of anurans (frogs and toads) are the most diverse of terrestrial vertebrates, and a major challenge is identifying selective factors that promote the evolution or retention of reproductive modes across clades. Terrestrialized anuran breeding strategies have evolved repeatedly from the plesiomorphic fully aquatic reproductive mode, a process thought to occur through intermediate reproductive stages. Several selective forces have been proposed for the evolution of terrestrialized reproductive traits, but factors such as water systems and co-evolution with ecomorphologies have not been investigated. We examined these topics in a comparative phylogenetic framework using Afrobatrachian frogs, an ecologically and reproductively diverse clade representing more than half of the total frog diversity found in Africa (~400 species). We infer direct development has evolved twice independently from terrestrialized reproductive modes involving subterranean or terrestrial oviposition, supporting evolution through intermediate stages. We also detect associations between specific ecomorphologies and oviposition sites, and demonstrate arboreal species exhibit an overall shift toward using lentic water systems for breeding. These results indicate that changes in microhabitat use associated with ecomorphology, which allow access to novel sites for reproductive behavior, oviposition, or larval development, may also promote reproductive mode diversity in anurans.

Jeffries, D.L., Lavanchy, G., Sermier, R., Sredl, M.J., Miura, I., Borzée, A., Barrow, L.N., Canestrelli, D., Crochet, P.-A., Dufresnes, C., Fu, J., Ma, W.-J., Garcia, C.M., Ghali, K., Nicieza, A.G., O’Donnell, R.P., Rodrigues, N., Romano, A., Martínez-Solano, Í., Stepanyan, I., Zumbach, S., Brelsford, A., Perrin, N.

Assemblages that are exposed to recurring temporal environmental changes can show changes in their ecological properties. These can be expressed by differences in diversity and assembly rules. Both can be identified using two measures of diversity: functional (FD) and phylogenetic diversity (PD). Frog communities are understudied in this regard, especially during the tadpole life stage. We utilised tadpole assemblages from Madagascan rainforest streams to test predictions of seasonal changes on diversity and assemblage composition and on diversity measures. From the warm-wet to the cool-dry season, species richness (SR) of tadpole assemblages decreased. Also FD and PD decreased, but FD less and PD more than expected by chance. During the dry season, tadpole assemblages were characterised by functional redundancy (among assemblages-with increasing SR), high FD (compared to a null model), and low PD (phylogenetic clustering; compared to a null model). Although mutually contradictory at first glance, these results indicate competition as tadpole community assembly driving force. This is true during the limiting cool-dry season but not during the more suitable warm-wet season. We thereby show that assembly rules can strongly depend on season, that comparing FD and PD can reveal such forces, that FD and PD are not interchangeable, and that conclusions on assembly rules based on FD alone are critical.

Type II phosphatidylinositol 5-phosphate 4-kinase (PIPKIII-) catalyzes the synthesis of phosphatidylinositol-4,5-bisphosphate (PI-4,5-P sub(2)), an essential lipid second messenger that may be involved in the regulation of phototransduction, neuroprotection, and morphogenesis in the vertebrate retina. Here we report that in rodent and transgenic frogs, the light-mediated activity and membrane binding of PIPKIII- in rod outer segments (ROS) is dependent on tyrosine phosphorylation of ROS proteins. The greater type II I- PIP kinase activity in the light-adapted ROS membrane results from light-driven translocation of PIPKIII- from the rod inner segment to ROS, and subsequent binding to the ROS membrane, thus improving access of the kinase to its lipid substrates. These results indicate a novel mechanism of light regulation of the PIPKIII- activity in photoreceptors, and suggest that the greater PIPKIII- activity in light-adapted animals and the resultant accumulation of PI-4,5-P sub(2) within the ROS membrane may be important for the function of photoreceptor cells.