Defence variation within a guild of aphid-tending ants explains aphid population growth

• Mutualism studies often focus on the service provided by single species, while variation in benefits provided by multiple partners is less understood. Ant-aphid food-for-protection mutualisms are suitable to study the implications of intra-guild service variation because they often involve several ant species with varying levels of aggressiveness.
• We studied an aphid species and its associated ant guild to address whether intra-guild defence variation against aphid natural enemies explains aphid performance on plants (thistles). We surveyed plants with natural abundances of aphids associated with different ant species and estimated aphid population growth. We conducted confrontation experiments between ant species and aphid natural enemies (ladybugs and hoverfly larvae). In plants patrolled by the most aggressive ant species, we determined the ant's probability of expelling aphid natural enemies and tested whether ant exclusion affects the abundance of aphids and their natural enemies.
• The ant Dorymyrmex tener was the most abundant and frequent species on plants and the most aggressive against aphid natural enemies. Aphid populations grew faster on plants patrolled by D. tener compared to plants patrolled by Camponotus distinguendus or D. richteri. Field experiments confirmed that D. tener effectively expels aphid natural enemies from plants. When D. tener was excluded, the density of aphids decreased, while the abundance of aphid natural enemies increased.
• The disruption of aphid predation by aggressive and numerically dominant ant species is a determinant of aphid population dynamics. This study illustrates the importance of considering intra-guild service variation to better understand multi-partner mutualisms.

     

Guanosine,a guanine-based nucleoside relaxed isolated corpus cavernosum from mice through cGMP accumulation

In corpus cavernosum (CC), guanosine triphosphate (GTP) is converted into cyclic guanosine monophosphate (cGMP) to induce erection. The action of cGMP is terminated by phosphodiesterases and efflux transporters, which pump cGMP out of the cell. The nucleotides, GTP, and cGMP were detected in the extracellular space, and their hydrolysis lead to the formation of intermediate products, among them guanosine. Therefore, our study aims to pharmacologically characterize the effect of guanosine in isolated CC from mice. The penis was isolated and functional and biochemical analyses were carried out. The guanine-based nucleotides GTP, guanosine diphosphate, guanosine monophosphate, and cGMP relaxed mice corpus cavernosum, but the relaxation (90.7?±?12.5%) induced by guanosine (0.000001–1 mM) was greater than that of the nucleotides (~?45%, P?<?0.05). Guanosine-induced relaxation was not altered in the presence of adenosine type 2A and 2B receptor antagonists. No augment was observed in the intracellular levels of cyclic adenosine monophosphate in tissues stimulated with guanosine. Inhibitors of nitric oxide synthase (L-NAME, 100 μM) and soluble guanylate cyclase (ODQ, 10 μM) produced a significant reduction in guanosine-induced relaxation in all concentrations studied, while in the presence of tadalafil (300 nM), a significant increase was observed. Pre-incubation of guanosine (100 μM) produced a 6.6-leftward shift in tadalafil-induced relaxation. The intracellular levels of cGMP were greater when CC was stimulated with guanosine. Inhibitors of ecto-nucleotidases and xanthine oxidase did not interfere in the response induced by guanosine. In conclusion, our study shows that guanosine relaxes mice CC and opens the possibility to test its role in models of erectile dysfunction.

     

The protein scaffold calibrates metal specificity and activation in MerR sensors

MerR metalloregulators are the central components of many biosensor platforms designed to report metal contamination. However, most MerR proteins are non-specific. This makes it difficult to apply these biosensors in the analysis of real environmental samples. On-demand implementation of molecular engineering to modify the MerR metal preferences is innovative, although it does not always yield the expected results. As the metal binding loop region (MBL) of these sensors has been proposed to be the major modulator of their specificity, we surgically switched this region for that of well-characterized specific and non-specific homologues. We found that identical modifications in different MerR proteins result in synthetic sensors displaying particular metal-detection patterns that cannot be predicted from the nature of the assembled modules. For instance, the MBL from a native Hg(II) sensor provided non-specificity or specificity toward Hg(II) or Cd(II) depending on the MerR scaffold into which it was integrated. These and other evidences reveal that residues outside the MBL are required to modulate ion recognition and transduce the input signal to the target promoter. Revealing their identity and their interactions with other residues is a critical step toward the design of more efficient biosensor devices for environmental metal monitoring.     

Length–weight relationships for freshwater fish species from the Pantanal of the Negro River,Brazil

The present study describes the length‐weight relationships (LWRs) of 28 species captured in Santa Virgínia Bay, in the Pantanal of the Negro River, Mato Grosso do Sul State, Brazil, over 3 years (1999 to 2001). The study provides the first references on LWRs for thirteen of these species.     

Comparative genomic analysis of Leishmania (Viannia) peruviana and Leishmania (Viannia) braziliensis

Background

The Leishmania (Viannia) braziliensis complex is responsible for most cases of New World tegumentary leishmaniasis. This complex includes two closely related species but with different geographic distribution and disease phenotypes, L. (V.) peruviana and L. (V.) braziliensis. However, the genetic basis of these differences is not well understood and the status of L. (V.) peruviana as distinct species has been questioned by some.Here we sequenced the genomes of two L. (V.) peruviana isolates (LEM1537 and PAB-4377) using Illumina high throughput sequencing and performed comparative analyses against the L. (V.) braziliensis M2904 reference genome. Comparisons were focused on the detection of Single Nucleotide Polymorphisms (SNPs), insertions and deletions (INDELs), aneuploidy and gene copy number variations.

Results

We found 94,070 variants shared by both L. (V.) peruviana isolates (144,079 in PAB-4377 and 136,946 in LEM1537) against the L. (V.) braziliensis M2904 reference genome while only 26,853 variants separated both L. (V.) peruviana genomes.Analysis in coding sequences detected 26,750 SNPs and 1,513 indels shared by both L. (V.) peruviana isolates against L. (V.) braziliensis M2904 and revealed two L. (V.) braziliensis pseudogenes that are likely to have coding potential in L. (V.) peruviana. Chromosomal read density and allele frequency profiling showed a heterogeneous pattern of aneuploidy with an overall disomic tendency in both L. (V.) peruviana isolates, in contrast with a trisomic pattern in the L. (V.) braziliensis M2904 reference.Read depth analysis allowed us to detect more than 368 gene expansions and 14 expanded gene arrays in L. (V.) peruviana, and the likely absence of expanded amastin gene arrays.

Conclusions

The greater numbers of interspecific SNP/indel differences between L. (V.) peruviana and L. (V.) braziliensis and the presence of different gene and chromosome copy number variations support the classification of both organisms as closely related but distinct species.The extensive nucleotide polymorphisms and differences in gene and chromosome copy numbers in L. (V.) peruviana suggests the possibility that these may contribute to some of the unique features of its biology, including a lower pathology and lack of mucosal development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1928-z) contains supplementary material, which is available to authorized users.     

Involvement of an essential arginyl residue in the coupling activity of Rhodospirillum rubrum chromatophores.

The arginine reagents phenylglyoxal and 2,3-butanedione in borate buffer completely inhibited photophosphorylation and Mg-ATPase of Rhodospirillum rubrum chromatophores. The inactivation rates followed apparent first order kinetics. Oxidative phospho-rylation and the light-dependent ATP-P_i exchange reactions ofR. rubrum chromatophores and the Ca-ATPase activity of the soluble coupling factor were similarly inhibited by 2,3-butanedione in borate buffer. The apparent order of reaction with respect to inhibitor concentrations for all these reactions gave values of near 1 suggesting that inactivation was the consequence of modifying one arginine per active site. ATP synthesis and hydrolysis by R. rubrum chromatophores were strongly protected against inactivation by ADP and ATP, respectively, and by other nucleotides that are substrates of the reactions but not by the products. Similarly, the Ca-ATPase of the soluble coupling factor was protected by ATP but not by ADP. Inactivation of chromatophores reactions by butanedione in borate buffer was more rapid in the light than in the dark. The results suggest that the catalytic sites for ATP synthesis and hydrolysis on the chromatophore coupling factor are different and both contain an essential arginine.     

Inhibition of energy conservation reactions in chromatophores of Rhodospirillum rubrum by antibiotics

The antibiotics efrapeptin and leucinostatin inhibited photosynthetic and oxidative phosphorylation and related reactions such as the dark and light ATP-P_i exchange reactions and the Mg-ATPase in Rhodospirillum rubrum chromatophores. Higher concentrations of leucinostatin were required for inhibition of the phenazine methosulfate-catalyzed photophosphorylation and light ATP-P_i exchange reaction than for the endogenous or succinate-induced photophosphorylation and dark ATP-P_i exchange reaction. Efrapeptin and leucinostatin inhibited the ATP-driven transhydrogenase while only the latter inhibited the light-driven transhydrogenase, proton gradient formation, and NAD⁺ reduction by succinate in chromatophores. Efrapeptin, but not leucinostatin, inhibited the soluble Ca-ATPase activity of the coupling factor obtained from chromatophores. The inhibition was competitive with ATP. It is concluded that efrapeptin is an effective energy transfer inhibitor whose site of action may be localized in the soluble coupling factor, while the effects of leucinostatin are more complex and cannot be explained as a simple uncoupling.     

Bottom-up effects may not reach the top: the influence of ant-aphid interactions on the spread of soil disturbances through trophic chains

Soil disturbances that increase nutrient availability may trigger bottom-up cascading effects along trophic chains. However, the strength and sign of these effects may depend on attributes of the interacting species. Here, we studied the effects of nutrient-rich refuse dumps of the leaf-cutting ant, Acromyrmex lobicornis, on the food chain composed of thistles, aphids, tending ants and aphid natural enemies. Using stable isotopes tracers, we show that the nitrogen accumulated in refuse dumps propagates upward through the studied food chain. Thistles growing on refuse dumps had greater biomass and higher aphid density than those growing in adjacent soil. These modifications did not affect the structure of the tending ant assemblage, but were associated with increased ant activity. In contrast to the expectations under the typical bottom-up cascade effect, the increase in aphid abundance did not positively impact on aphid natural enemies. This pattern may be explained by both an increased activity of tending ants, which defend aphids against their natural enemies, and the low capacity of aphid natural enemies to show numerical or functional responses to increased aphid density. Our results illustrate how biotic interactions and the response capacity of top predators could disrupt bottom-up cascades triggered by disturbances that increase resource availability.