Early pleistocene habitat in member 1 Olorgesailie based on paleosol stable isotopes.

Stable carbon and oxygen isotope values from soil carbonates were used to determine the vegetation context of archaeological sites and local climatic conditions represented in a approximately 0.99 Ma paleosol that is exposed laterally in the Olorgesailie basin, southern Kenya rift valley. As part of this landscape-scale project, samples of an upper Member 1 paleosol were analyzed along nearly 4 km of outcrop in three adjacent parts of the basin. Modern East African soil and plant community analogs are used to interpret the isotope ratios. The carbon isotopic composition of the paleosol carbonates indicates that the area supported a local biomass of about 75-100% C(4)plants during the period of soil formation. After averaging the data for each trench, an open C(4)grassland is represented by half of the carbon values, with wooded grassland more abundant across the paleolandscape than it is in the area now. This vegetational reconstruction is supported by the mammalian faunal assemblage, which has a high percentage of grazers. Although the relatively small sample size outside the main excavation area precludes firm characterization of vegetational diversity across the basin in upper Member 1 times, eastern and western localities in the study area may have had more woody C(3)plants than the widely sampled zone in between. Oxygen isotopes indicate that the lowland basin was slightly cooler and moister than today's semi-arid climate, with greater annual rainfall. Archaeological traces have a virtually continuous distribution across the paleolandscape, but vary in density of occurrence. With the strong evidence for C(4)grassland as the primary vegetation context across most of the study area, no habitat preference by the Acheulean toolmakers at Olorgesailie is shown in our initial comparison between carbon isotope values and stone/bone densities.     

MHC-disassortative mating preferences reversed by cross-fostering.

House mice (Mus musculus domesticus) avoid mating with individuals that are genetically similar at the major histocompatibility complex (MHC). Mice are able recognize MHC-similar individuals through specific odour cues. However, to mate disassortatively for MHC genes, individuals must have a referent, either themselves (self-inspection) or close kin (familial imprinting), with which to compare the MHC identity of potential mates. Although studies on MHC-dependent mating preferences often assume that individuals use self-inspection, laboratory experiments with male mice indicate that they use familial imprinting, i.e. males learn the MHC identity of their family and then avoid mating with females carrying ''familial'' MHC alleles. To determine if female mice use familial imprinting, we cross-fostered wild-derived female mouse pups into MHC-dissimilar families, and then tested if this procedure reversed their mating preferences compared with in-fostered controls. Our observations of the female''s mating behaviour in seminatural social conditions and the genetic typing of their progeny both indicated that females avoided mating with males carrying MHC genes of their foster family, supporting the familial imprinting hypothesis. We show that MHC-dependent familial imprinting potentially provides a more effective mechanism for avoiding kin matings and reducing inbreeding than self-inspection.     

Comparison of two solid-phase peptide syntheses of a 32-amino acid carboxyl-terminal fragment of human parathyroid hormone,hPTH-(53–84)

Two approaches were employed in separate syntheses of the carboxyl-terminal third of human parathyroid hormone, hPTH-(53–84). The standard N,N′-dicychohexylcarbodiimide coupling method was compared to amino acid incorporation using in situ and preformed symmetrical anhydrides of tert-butoxycarbonyl-amino acids. Also, protection of the δ-carboxyl function of glutamic acid by the benzyl group was compared to protection by the chlorobenzyl group. The products of both synthetic strategies were chemically evaluated. The purified synthetic hormone fragment prepared by standard methods was found to be homogeneous and virtually identical to the native carboxyl-terminal region of the hormone by the analytical criteria employed. However, the synthetic product resulting from use of symmetrical anhydrides was heterogeneous. Also, several practical advantages were noted for amino acid incorporation by the standard method. Since the symmetrical anhydride method has been found to be extremely successful as an approach to the synthesis of other peptides, this report indicates that the choice of symmetrical anhydride versus standard coupling methods may in part be determined by the sequence selected for synthesis. In addition, both approaches produced a large number of side products. Hence, methods selected for purification of the desired product were essential to the successful preparation of this synthetic peptide.