The T-Cell Antigen Receptor: A Logical Response to an Unknown Ligand

The immune system can be roughly divided into innate and adaptive compartments. The adaptive compartment includes the B and T lymphocytes, whose antigen receptors are generated by recombination of gene segments. The consequence is that the creation of self-reactive lymphocytes is unavoidable. For the host to remain viable, the immune system has evolved a strategy for removing autoimmune lymphocytes during development. This review discusses how T lymphocytes are generated, how they recognize antigens, and how their antigen receptor directs the removal of self-reactive T cells.     

Assessing Compensatory Versus Additive Harvest Mortality: An Example Using Greater Sage-Grouse

ABSTRACT We used band-recovery data from 2 populations of greater sage-grouse (Centrocercus urophasianus), one in Colorado, USA, and another in Nevada, USA, to examine the relationship between harvest rates and annual survival. We used a Seber parameterization to estimate parameters for both populations. We estimated the process correlation between reporting rate and annual survival using Markov chain Monte Carlo methods implemented in Program MARK. If hunting mortality is additive to other mortality factors, then the process correlation between reporting and survival rates will be negative. Annual survival estimates for adult and juvenile greater sage-grouse in Nevada were 0.42±0.07 (x̄±SE) for both age classes, whereas estimates of reporting rate were 0.15±0.02 and 0.16±0.03 for the 2 age classes, respectively. For Colorado, average reporting rates were 0.14±0.016, 0.14±0.010, 0.19±0.014, and 0.18±0.014 for adult females, adult males, juvenile females, and juvenile males, respectively. Corresponding mean annual survival estimates were 0.59±0.01, 0.37±0.03, 0.78±0.01, and 0.64±0.03. Estimated process correlation between logit-transformed reporting and survival rates for greater sage-grouse in Colorado was ρ = 0.68±0.26, whereas that for Nevada was ρ = 0.04±0.58. We found no support for an additive effect of harvest on survival in either population, although the Nevada study likely had low power. This finding will assist mangers in establishing harvest regulations and otherwise managing greater sage-grouse populations.     

Indirect sperm transfer and male mating strategies in soil invertebrates

Summary

Many soil invertebrates transfer their sperm indirectly by means of spermatophores. Among the different taxa there is great variation in spermatophore architecture, auxiliary structures and behaviour. The behaviour, ranging from elaborate courtship rituals to seemingly indifferent scattering of spermatophores, can roughly be classified as association and dissociation. Which of the two is adaptive depends on many factors which can be summarized in a simple functional response model showing that in some cases the best choice depends on density.     

Disentangling stocking introgression and natural migration in brown trout: survival success and recruitment failure in populations with semi‐supportive breeding

1. Introgression into natural salmonid populations from stocked conspecifics has been widely studied. Outcomes vary from no effect even after decades of stocking, to population replacement after only a couple of generations. Potential introgression caused by semi‐supportive breeding (i.e. using a mixture of local strains as brood stock) is, however, less well studied. 2. We investigated population structure of brown trout (Salmo trutta) in a regulated alpine lake with three natural, environmentally contrasting tributaries used as spawning and rearing habitat. Massive semi‐supportive breeding of admixed local strains has been implemented for decades. Stocked trout represented c. 17% of the total lake population, and a substantial post‐release survival reflects a considerable potential for introgression. However, the mark‐recapture studies indicate no spawning runs of stocked fish. 3. Using 13 polymorphic microsatellite loci, we found natural straying and non‐native reproduction, especially among wild populations inhabiting environmentally unstable habitat. Retained genetic structure across tributaries indicated low reproductive success of wild‐born non‐natives. Moreover, the genetic structure among tributaries has probably not been influenced by semi‐supportive breeding, because of recruitment failure of stocked trout.     

Construction and evaluation of multisite recombinatorial (Gateway) cloning vectors for Gram-positive bacteria

Background  

The Gateway recombinatorial cloning system allows easy and rapid joining of DNA fragments. Here we report the construction and evaluation of three different Gram-positive vectors that can be used with the Multisite Gateway cloning system to rapidly produce new gene arrangements in plasmid constructs for use in a variety of Gram-positive bacteria.     

Polymorphism of transferrin and esterase in Alaskan wolves: evidence of close molecular homology with the dog

By the use of isoelectric focusing in polyacrylamide gels serum samples from 146 Alaskan wolves were studied with regard to transferrin (Tf) and esterase (ArE) polymorphism, comparing the phenotypic band patterns with those of selected Norwegian dogs. The study revealed Tf and ArE polymorphisms in the wolf with phenotypic band patterns being indistinguishable from the corresponding ones in dogs. This suggests the occurrence of the same two common Tf alleles in the wolf as in the dog. In the ArE system the results are consistent with the occurrence of three alleles which also occur in dogs whereas a fourth allele, so far not seen in dogs, is seen in Alaskan wolves.     

Xylem Hydraulic Characteristics, Water Relations and Wood Anatomy of the Resurrection PlantMyrothamnus flabellifoliusWelw.

Myrothamnus flabellifoliusWelw. is a desiccation-tolerant (‘resurrection’)plant with a woody stem. Xylem vessels are narrow (14 µmmean diameter) and perforation plates are reticulate. This leadsto specific and leaf specific hydraulic conductivities thatare amongst the lowest recorded for angiosperms (k_s0.87 kg m^-1MPa^-1s^-1;k_l3.28x10^-5kg m^-1MPa^-1s^-1, stem diameter 3 mm). Hydraulic conductivitiesdecrease with increasing pressure gradient. Transpiration ratesin well watered plants were moderate to low, generating xylemwater potentials of -1 to -2 MPa. Acoustic emissions indicatedextensive cavitation events that were initiated at xylem waterpotentials of -2 to -3 MPa. The desiccation-tolerant natureof the tissue permits this species to survive this interruptionof the water supply. On rewatering the roots pressures thatwere developed were low (2.4 kPa). However capillary forceswere demonstrated to be adequate to account for the refillingof xylem vessels and re-establishment of hydraulic continuityeven when water was under a tension of -8 kPa. During dehydrationand rehydration cycles stems showed considerable shrinking andswelling. Unusual knob-like structures of unknown chemical compositionwere observed on the outer surface of xylem vessels. These maybe related to the ability of the stem to withstand the mechanicalstresses associated with this shrinkage and swelling.Copyright1998 Annals of Botany Company cavitation, desiccation, hydraulic conductivity, refilling, resurrection plant, root pressure, xylem anatomy,Myrothamnus flabellifolius