Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Campus sustainable food projects: critique and engagement

Campus sustainable food projects recently have expanded rapidly. A review of four components - purchasing goals, academic programs, direct marketing, and experiential learning - shows both intent and capacity to contribute to transformational change toward an alternative food system. The published rationales for campus projects and specific purchasing guidelines join curricular and cocurricular activities to evaluate, disseminate, and legitimize environmental, economic, social justice, and health concerns about conventional food. Emerging new metrics of food service practices mark a potential shift from rhetoric to market clout, and experiential learning builds new coalitions and can reshape relations with food and place. Campus projects are relatively new and their resilience is not assured, but leading projects have had regional, state, and national impact. The emergence of sustainability rankings in higher education and contract-based compliance around purchasing goals suggests that if support continues, higher education's leadership can extend to the broader agrifood system.     

Population dynamics of two invasive amphipods in the Southwestern Atlantic: Monocorophium acherusicum and Ericthonius punctatus (Crustacea)

Harbours are important sites for the containment and dispersal of invasive species throughout the world, so the study of life history traits of species is important to understand the success of their invasion and their potential effects on the habitat. In recent years several invasive species have been reported in Argentinian harbours; however, studies of the ecology and life history of these species are scarce. We studied the population dynamics and reproductive biology of Monocorophium acherusicum and Ericthonius punctatus, in order to update the published information on the introduced amphipods in Mar del Plata harbour. Both species showed a seasonal pattern characterized by high densities in warmer months, related to the highest reproductive activity and the increase of recruitment in summer and early autumn, and lower densities in the cold season. The sex ratio was always female-biased and the number of eggs carried by females was positively correlated to the size. The present study suggests that both species have colonized Mar del Plata harbour successfully, showing viable populations (cohorts of juveniles, males, females and ovigerous females). This work provides the basis for monitoring the impact generated by introduced amphipods over the existing fauna.     

Recombination between directly repeated origins of conjugative transfer cloned in M13 bacteriophage DNA models ligation of the transferred plasmid strand.

When two, directly-repeated copies of the origin of transfer (oriT) of the conjugatively mobilizable, broad host-range plasmid R1162 are cloned into bacteriophage M13mp9 DNA, they undergo recombination in the presence of one of the R1162-encoded proteins required for mobilization [Meyer, R. (1989) J. Bacteriol., 171, 799-806]. Mutations in the outer arm of the inverted repeat within oriT inhibit this recombination. These mutations also affect a late step in transfer. We propose that recombination on the phage DNA models the processing of single-stranded DNA after entry into a recipient cell. The two, directly-repeated oriTs are not equivalent during the recombination reaction, because they are differently affected by the outer-arm mutations. A mutation was also isolated that reduces the specificity of the cleavage site in one of the two oriTs. Together, the results with the mutations suggest that phage recombinants can form only when the first cleavage occurs at one of the two oriTs. This is followed by the resulting free 3' end joining to the 5' end at the cleavage site of the other oriT.     

The cost of incubation in relation to clutch-size in the Collared Flycatcher Ficedula albicollis

This study examines the importance of avian incubation costs as determinants of clutch-size variation by performing clutch-size and brood-size manipulations in the same population of Collared Flycatchers Ficedula albicollis during the same breeding season. In 2 5 cases when three or more clutches of the same size were completed on the same day, we moved two eggs on the day after the last egg had been laid from one randomly selected clutch (C) to another (C) and moved two other eggs from this to a third clutch (C⁺). In 20 other cases of simultaneously completed clutches of the same size, we moved two randomly selected young from one brood to a second and from that moved two other young to a third (B, B and B⁺groups). Most females were weighed the day after completion of the clutch and 1–4 days before hatching of the young, and some of them also 10–14 days after hatching of the young. We measured the daily energy expenditure of females incubating manipulated clutches of 4, 6 and 8 eggs by means of the doubly-labelled water (D₂¹⁸O) technique and also recorded their nest attendance. Hatching success of fertilized eggs was reduced in the enlarged clutches compared with control and reduced clutches. Females expired on average 3142.6 ml CO₂ and expended 78.6 kJ per day while incubating, which corresponds to a metabolic intensity of 3.3 times BMR. Daily energy expenditure increased with clutch-size due to higher costs while incubating, and not because of changed activity patterns. There were no significant differences in length of incubation, female mass or mass changes between phases for the C, C and C⁺groups. In both the C and B groups, enlarged broods produced significantly more fledged young than control broods, and those significantly more than reduced broods. Fledgling tarsus-length and mass did not differ significantly between treatments in either the C or B groups. There was no significant difference in breeding success between clutch and brood manipulations. In this season, incubation costs did not entail significant fitness losses, expressed either as fledgling production or female condition. Also, control females could have raised more young to fledging age than they did with no apparent costs.     

Uranium reduction and microbial community development in response to stimulation with different electron donors

Stimulating microbial reduction of soluble U(VI) to less soluble U(IV) shows promise as an in situ bioremediation strategy for uranium contaminated groundwater, but the optimal electron donors for promoting this process have yet to be identified. The purpose of this study was to better understand how the addition of various electron donors to uranium-contaminated subsurface sediments affected U(VI) reduction and the composition of the microbial community. The simple electron donors, acetate or lactate, or the more complex donors, hydrogen-release compound (HRC) or vegetable oil, were added to the sediments incubated in flow-through columns. The composition of the microbial communities was evaluated with quantitative PCR probing specific 16S rRNA genes and functional genes, phospholipid fatty acid analysis, and clone libraries. All the electron donors promoted U(VI) removal, even though the composition of the microbial communities was different with each donor. In general, the overall biomass, rather than the specific bacterial species, was the factor most related to U(VI) removal. Vegetable oil and HRC were more effective in stimulating U(VI) removal than acetate. These results suggest that the addition of more complex organic electron donors could be an excellent option for in situ bioremediation of uranium-contaminated groundwater.