Aposematism increases acoustic diversification and speciation in poison frogs

Multimodal signals facilitate communication with conspecifics during courtship, but they can also alert eavesdropper predators. Hence, signallers face two pressures: enticing partners to mate and avoiding detection by enemies. Undefended organisms with limited escape abilities are expected to minimize predator recognition over mate attraction by limiting or modifying their signalling. Alternatively, organisms with anti-predator mechanisms such as aposematism (i.e. unprofitability signalled by warning cues) might elaborate mating signals as a consequence of reduced predation. We hypothesize that calls diversified in association with aposematism. To test this, we assembled a large acoustic signal database for a diurnal lineage of aposematic and cryptic/non-defended taxa, the poison frogs. First, we showed that aposematic and non-aposematic species share similar extinction rates, and aposematic lineages diversify more and rarely revert to the non-aposematic phenotype. We then characterized mating calls based on morphological (spectral), behavioural/physiological (temporal) and environmental traits. Of these, only spectral and temporal features were associated with aposematism. We propose that with the evolution of anti-predator defences, reduced predation facilitated the diversification of vocal signals, which then became elaborated or showy via sexual selection.     

Owl monkey MHC-DRB exon 2 reveals high similarity with several HLA-DRB lineages

One hundred and ten novel MHC-DRB gene exon 2 nucleotide sequences were sequenced in 96 monkeys from three owl monkey species (67 from Aotus nancymaae, 30 from Aotus nigriceps and 13 from Aotus vociferans). Owl monkeys, like humans, have high MHC-DRB allele polymorphism, revealing a striking similarity with several human allele lineages in the peptide binding region and presenting major convergence with DRB lineages from several Catarrhini (humans, apes and Old World monkeys) rather than with others New World monkeys (Platyrrhini). The parallelism between human and Aotus MHC-DRB reveals additional similarities regarding variability pattern, selection pressure and physicochemical constraints in amino acid replacements. These observations concerning previous findings of similarity between the Aotus immune system molecules and their human counterparts affirm this specie’s usefulness as an excellent animal model in biomedical research.Experiments carried out in this work complied with current Colombian Ministry of Health law and regulations governing animal care and handling.An erratum to this article can be found at     

Comparative molecular and three-dimensional analysis of the peptide–MHC II binding region in both human and Aotus MHC-DRB molecules confirms their usefulness in antimalarial vaccine development

A vaccine against malaria is desperately needed, and Aotus monkeys are highly susceptible to experimental infection with malarial parasites. A thorough analysis of this monkey’s immune system molecules was thus undertaken in our institute. Cloning and sequencing, followed by three-dimensional analysis, has revealed high homology with some HLA-DRB1 molecules in terms of their peptide binding region pockets. Molecules such as HLA-DRB1*03, 11, 08, and HLA-DRB1*04 are so similar to Aotus MHC-DRB molecules that peptides identified as binding to these molecules and inducing protective immunity in these monkeys could be used in humans without further refinement, while small modifications seem to be needed for those binding to HLA-DRB1*07, HLA-DRB1*15, 16, and HLA-DRB1*10-like molecules, making this New World monkey an excellent model for tailor-made vaccine development, especially against malaria.     

Evolutionary Trajectories of Beta-Lactamase CTX-M-1 Cluster Enzymes: Predicting Antibiotic Resistance

Extended-spectrum beta-lactamases (ESBL) constitute a key antibiotic-resistance mechanism affecting Gram-negative bacteria, and also an excellent model for studying evolution in real time. A shift in the epidemiology of ESBLs is being observed, which is characterized by the explosive diversification and increase in frequency of the CTX-M-type β-lactamases in different settings. This provides a unique opportunity for studying a protein evolutionary radiation by the sequential acquisition of specific mutations enhancing protein efficiency and fitness concomitantly. The existence of driver antibiotic molecules favoring protein divergence has been investigated by combining evolutionary analyses and experimental site-specific mutagenesis. Phylogenetic reconstruction with all the CTX-M variants described so far provided a hypothetical evolutionary scenario showing at least three diversification events. CTX-M-3 was likely the enzyme at the origin of the diversification in the CTX-M-1 cluster, which was coincident with positive selection acting on several amino acid positions. Sixty-three CTX-M-3 derivatives containing all combinations of mutations under positively selected positions were constructed, and their phenotypic efficiency was evaluated. The CTX-M-3 diversification process can only be explained in a complex selective landscape with at least two antibiotics (cefotaxime and ceftazidime), indicating the need to invoke mixtures of selective drivers in order to understand the final evolutionary outcome. Under this hypothesis, we found congruent results between the in silico and in vitro analyses of evolutionary trajectories. Three pathways driving the diversification of CTX-M-3 towards the most complex and efficient variants were identified. Whereas the P167S pathway has limited possibilities of further diversification, the D240G route shows a robust diversification network. In the third route, drift may have played a role in the early stages of CTX-M-3 evolution. Antimicrobial agents should not be considered only as selectors for efficient mechanisms of resistance but also as diversifying agents of the evolutionary trajectories. Different trajectories were identified using a combination of phylogenetic reconstructions and directed mutagenesis analyses, indicating that such an approach might be useful to fulfill the desirable goal of predicting evolutionary trajectories in antimicrobial resistance.     

Myosporidium merluccius n. g., n. sp. infecting muscle of commercial hake (Merluccius sp.) from fisheries near Namibia

A new species of Microsporidia classified to a new genus was observed in the trunk muscle of commercial hake (Merluccius capensis/paradoxus complex) from Namibian fisheries. Macroscopic examination revealed thin and dark filaments inserted among muscle fibers. Inside the filaments were many sporophorous vesicles with about 30-50 spores per vesicle. The shape of the spore was pyriform and the extruded polar filament was of moderate length (up to 4.29 microm, n=12). This new species of Microsporidia is described using macrophotography, microphotography, staining, and transmission electron microscopy (TEM), as well as molecular methods. Its 16S rRNA was found to be similar to that of Microsporidium prosopium Kent et al., 1999, while both sequences were quite different from 16S rRNA sequences known for other Microsporidia. Nevertheless, this new species is separated morphologically from M. prosopium by the presence of 11-12 anisofilar coils and the formation of the xenoma at the site of infection. Type species.     

Characterization of canarypox-like viruses infecting endemic birds in the Galápagos Islands

The presence of avian pox in endemic birds in the Galápagos Islands has led to concern that the health of these birds may be threatened by avipoxvirus introduction by domestic birds. We describe here a simple polymerase chain reaction-based method for identification and discrimination of avipoxvirus strains similar to the fowlpox or canarypox viruses. This method, in conjunction with DNA sequencing of two polymerase chain reaction-amplified loci totaling about 800 bp, was used to identify two avipoxvirus strains, Gal1 and Gal2, in pox lesions from yellow warblers (Dendroica petechia), finches (Geospiza spp.), and Galápagos mockingbirds (Nesomimus parvulus) from the inhabited islands of Santa Cruz and Isabela. Both strains were found in all three passerine taxa, and sequences from both strains were less than 5% different from each other and from canarypox virus. In contrast, chickens in Galápagos were infected with a virus that appears to be identical in sequence to the characterized fowlpox virus and about 30% different from the canarypox/Galápagos group viruses in the regions sequenced. These results indicate the presence of canarypox-like viruses in endemic passerine birds that are distinct from the fowlpox virus infecting chickens on Galápagos. Alignment of the sequence of a 5.9-kb region of the genome revealed that sequence identities among Gal1, Gal2, and canarypox viruses were clustered in discrete regions. This indicates that recombination between poxvirus strains in combination with mutation led to the canarypox-like viruses that are now prevalent in the Galápagos.     

H-NS and RpoS regulate emergence of Lac Ara+ mutants of Escherichia coli MCS2.

Two master growth-phase regulatory proteins, H-NS and sigmaS, are involved in the formation of araB-lacZ fusion clones of Escherichia coli MCS2. The stationary-phase sigma factor RpoS is strictly required for the appearance of such mutants, whereas the histone-like protein H-NS represses their emergence. Our results support the idea that genetic changes leading to adaptive mutation in this model system are regulated by physiological signal transduction networks.