Social dominance does not increase oxidative stress in a female dominance hierarchy of an African cichlid fish

In many group living animal species, individuals use aggression to gain and maintain social dominance to secure access to ecological resources and potential mates. While social dominance has many fitness benefits, there are also potential costs associated with frequent agonistic interactions and status display. One potential cost of social dominance is oxidative stress, the imbalance of reactive oxygen species and antioxidant capacity. In the cichlid species Astatotilapia burtoni, dominant males are aggressive, hold a breeding territory, and have an activated reproductive system resulting in larger gonads. Subordinate males are submissive, school with females, and are nonreproductive. Females are submissive under natural conditions, but in a female-only group, a dominance hierarchy will form with dominant females taking on male-typical behaviours including aggression, territory defence, and increased androgen levels. However, in contrast to males, social dominance is not linked to increased activation of the reproductive system in females, allowing us to test whether social dominance alone exposes individuals to increased oxidative stress. We compared dominant and subordinate females in female-only groups in five markers of oxidative stress. Dominant females did not have higher levels of oxidative damage compared to same-sex subordinates. This result contrasted to the trend in males in which dominant males had higher oxidative damage than their subordinate counterparts. Our findings suggest that the oxidative cost of social dominance is limited and support the notion that previously reported associations between high rank and increased oxidative stress is most likely driven by increased investment in reproduction.     

Crystal structure of quinone‐dependent alcohol dehydrogenase from Pseudogluconobacter saccharoketogenes. A versatile dehydrogenase oxidizing alcohols and carbohydrates

The quinone‐dependent alcohol dehydrogenase (PQQ‐ADH, E.C. 1.1.5.2) from the Gram‐negative bacterium Pseudogluconobacter saccharoketogenes IFO 14464 oxidizes primary alcohols (e.g. ethanol, butanol), secondary alcohols (monosaccharides), as well as aldehydes, polysaccharides, and cyclodextrins. The recombinant protein, expressed in Pichia pastoris, was crystallized, and three‐dimensional (3D) structures of the native form, with PQQ and a Ca²⁺ ion, and of the enzyme in complex with a Zn²⁺ ion and a bound substrate mimic were determined at 1.72 Å and 1.84 Å resolution, respectively. PQQ‐ADH displays an eight‐bladed β‐propeller fold, characteristic of Type I quinone‐dependent methanol dehydrogenases. However, three of the four ligands of the Ca²⁺ ion differ from those of related dehydrogenases and they come from different parts of the polypeptide chain. These differences result in a more open, easily accessible active site, which explains why PQQ‐ADH can oxidize a broad range of substrates. The bound substrate mimic suggests Asp333 as the catalytic base. Remarkably, no vicinal disulfide bridge is present near the PQQ, which in other PQQ‐dependent alcohol dehydrogenases has been proposed to be necessary for electron transfer. Instead an associated cytochrome c can approach the PQQ for direct electron transfer.     

Responses of Ecosystem Carbon Cycling to Climate Change Treatments Along an Elevation Gradient

Global temperature increases and precipitation changes are both expected to alter ecosystem carbon (C) cycling. We tested responses of ecosystem C cycling to simulated climate change using field manipulations of temperature and precipitation across a range of grass-dominated ecosystems along an elevation gradient in northern Arizona. In 2002, we transplanted intact plant?Csoil mesocosms to simulate warming and used passive interceptors and collectors to manipulate precipitation. We measured daytime ecosystem respiration (ER) and net ecosystem C exchange throughout the growing season in 2008 and 2009. Warming generally stimulated ER and photosynthesis, but had variable effects on daytime net C exchange. Increased precipitation stimulated ecosystem C cycling only in the driest ecosystem at the lowest elevation, whereas decreased precipitation showed no effects on ecosystem C cycling across all ecosystems. No significant interaction between temperature and precipitation treatments was observed. Structural equation modeling revealed that in the wetter-than-average year of 2008, changes in ecosystem C cycling were more strongly affected by warming-induced reduction in soil moisture than by altered precipitation. In contrast, during the drier year of 2009, warming induced increase in soil temperature rather than changes in soil moisture determined ecosystem C cycling. Our findings suggest that warming exerted the strongest influence on ecosystem C cycling in both years, by modulating soil moisture in the wet year and soil temperature in the dry year.     

Interchromosomal duplication of major histocompatibility complex class I regions in rainbow trout (Oncorhynchus mykiss), a species with a presumably recent tetraploid ancestry

Salmonid fishes are among the few animal taxa with a probable recent tetraploid ancestor. The present study is the first to compare large (>100 kb) duplicated genomic sequence fragments in such species. Two contiguous stretches with major histocompatibility complex (MHC) class I genes were detected in a rainbow trout BAC library, mapped and sequenced. The MHC class I duplicated regions, mapped by fluorescence in situ hybridization (FISH), were shown to be located on different metaphase chromosomes, Chr 14 and 18. Gene organization in both duplications is similar to that in other fishes, in that the class I loci are tightly linked with the PSMB8, PSMB9, PSMB10 and ABCB3 genes. Whereas one region, Onmy-IA, has a classical MHC class I locus (UBA), Onmy-IB encodes only non-classical class Ib proteins. The nucleotide diversity between the Onmy-IA and Onmy-IB noncoding regions is about 14%. This suggests that the MHC class I duplication event has occurred about 60 mya close to the time of an hypothesized ancestral tetraploid event. The present article is the first convincing report on the co-existence of two closely related MHC class I core regions on two different chromosomes. The interchromosomal duplication and the homology levels are supportive of the tetraploid model.Nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank database under the accession numbers AB162342, AB162343 and from AY525774 to AY525776.     

FREQUENCY‐DEPENDENT SOCIAL DOMINANCE IN A COLOR POLYMORPHIC CICHLID FISH

A mechanism commonly suggested to explain the persistence of color polymorphisms in animals is negative frequency‐dependent selection. It could result from a social dominance advantage to rare morphs. We tested for this in males of red and blue color morphs of the Lake Victoria cichlid, Pundamilia. Earlier work has shown that males preferentially attack the males of their own morph, while red males are more likely to win dyadic contests with blue males. In order to study the potential contribution of both factors to the morph co‐existence, we manipulated the proportion of red and blue males in experimental assemblages and studied its effect on social dominance. We then tried to disentangle the effects of the own‐morph attack bias and social dominance of red using simulations. In the experiment, we found that red males were indeed socially dominant to the blue ones, but only when rare. However, blue males were not socially dominant when rare. The simulation results suggest that an own‐morph attack bias reduces the social dominance of red males when they are more abundant. Thus, there is no evidence of symmetric negative frequency‐dependent selection acting on social dominance, suggesting that additional fitness costs to the red morph must explain their co‐existence.     

The X-ray structure of the haloalcohol dehalogenase HheA from Arthrobacter sp. strain AD2: insight into enantioselectivity and halide binding in the haloalcohol dehalogenase family

Haloalcohol dehalogenases are bacterial enzymes that cleave the carbon-halogen bond in short aliphatic vicinal haloalcohols, like 1-chloro-2,3-propanediol, some of which are recalcitrant environmental pollutants. They use a conserved Ser-Tyr-Arg catalytic triad to deprotonate the haloalcohol oxygen, which attacks the halogen-bearing carbon atom, producing an epoxide and a halide ion. Here, we present the X-ray structure of the haloalcohol dehalogenase HheA(AD2) from Arthrobacter sp. strain AD2 at 2.0-A resolution. Comparison with the previously reported structure of the 34% identical enantioselective haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1 shows that HheA(AD2) has a similar quaternary and tertiary structure but a much more open substrate-binding pocket. Docking experiments reveal that HheA(AD2) can bind both enantiomers of the haloalcohol substrate 1-p-nitrophenyl-2-chloroethanol in a productive way, which explains the low enantiopreference of HheA(AD2). Other differences are found in the halide-binding site, where the side chain amino group of Asn182 is in a position to stabilize the halogen atom or halide ion in HheA(AD2), in contrast to HheC, where a water molecule has taken over this role. These results broaden the insight into the structural determinants that govern reactivity and selectivity in the haloalcohol dehalogenase family.     

Effects of multiple global change treatments on soil N2O fluxes

Global environmental changes are expected to alter ecosystem carbon and nitrogen cycling, but the interactive effects of multiple simultaneous environmental changes are poorly understood. Effects of these changes on the production of nitrous oxide (N₂O), an important greenhouse gas, could accelerate climate change. We assessed the responses of soil N₂O fluxes to elevated CO₂, heat, altered precipitation, and enhanced nitrogen deposition, as well as their interactions, in an annual grassland at the Jasper Ridge Global Change Experiment (CA, USA). Measurements were conducted after 6, 7 and 8?years of treatments. Elevated precipitation increased N₂O efflux, especially in combination with added nitrogen and heat. Path analysis supported the idea that increased denitrification due to increased soil water content and higher labile carbon availability best explained increased N₂O efflux, with a smaller, indirect contribution from nitrification. In our data and across the literature, single-factor responses tended to overestimate interactive responses, except when global change was combined with disturbance by fire, in which case interactive effects were large. Thus, for chronic global environmental changes, higher order interactions dampened responses of N₂O efflux to multiple global environmental changes, but interactions were strongly positive when global change was combined with disturbance. Testing whether these responses are general should be a high priority for future research.     

Functional and structural characterization of α-(1->2) branching sucrase derived from DSR-E glucansucrase

ΔN₁₂₃-glucan-binding domain-catalytic domain 2 (ΔN₁₂₃-GBD-CD2) is a truncated form of the bifunctional glucansucrase DSR-E from Leuconostoc mesenteroides NRRL B-1299. It was constructed by rational truncation of GBD-CD2, which harbors the second catalytic domain of DSR-E. Like GBD-CD2, this variant displays α-(1→2) branching activity when incubated with sucrose as glucosyl donor and (oligo-)dextran as acceptor, transferring glucosyl residues to the acceptor via a ping-pong bi-bi mechanism. This allows the formation of prebiotic molecules containing controlled amounts of α-(1→2) linkages. The crystal structure of the apo α-(1→2) branching sucrase ΔN₁₂₃-GBD-CD2 was solved at 1.90 Å resolution. The protein adopts the unusual U-shape fold organized in five distinct domains, also found in GTF180-ΔN and GTF-SI glucansucrases of glycoside hydrolase family 70. Residues forming subsite −1, involved in binding the glucosyl residue of sucrose and catalysis, are strictly conserved in both GTF180-ΔN and ΔN₁₂₃-GBD-CD2. Subsite +1 analysis revealed three residues (Ala-2249, Gly-2250, and Phe-2214) that are specific to ΔN₁₂₃-GBD-CD2. Mutation of these residues to the corresponding residues found in GTF180-ΔN showed that Ala-2249 and Gly-2250 are not directly involved in substrate binding and regiospecificity. In contrast, mutant F2214N had lost its ability to branch dextran, although it was still active on sucrose alone. Furthermore, three loops belonging to domains A and B at the upper part of the catalytic gorge are also specific to ΔN₁₂₃-GBD-CD2. These distinguishing features are also proposed to be involved in the correct positioning of dextran acceptor molecules allowing the formation of α-(1→2) branches.     

Backbone and side chain NMR assignments for the intrinsically disordered cytoplasmic domain of human neuroligin-3

Neuroligins act as heterophilic adhesion molecules at neuronal synapses. Their cytoplasmic domains interact with synaptic scaffolding proteins, and have been shown to be intrinsically disordered. Here we report the backbone and side chain ¹H, ¹³C and ¹⁵N resonance assignments for the cytoplasmic domain of human neuroligin 3.