Hierarchical structure of mitochondrial DNA gene flow among humpback whales Megaptera novaeangliae, world-wide.

The genetic structure of humpback whale populations and subpopulation divisions is described by restriction fragment length analysis of the mitochondrial (mt) DNA from samples of 230 whales collected by biopsy darting in 11 seasonal habitats representing six subpopulations, or 'stocks', world-wide. The hierarchical structure of mtDNA haplotype diversity among population subdivisions is described using the analysis of molecular variance (AMOVA) procedure, the analysis of gene identity, and the genealogical relationship of haplotypes as constructed by parsimony analysis and distance clustering. These analyses revealed: (i) significant partitioning of world-wide genetic variation among oceanic populations, among subpopulations or 'stocks' within oceanic populations and among seasonal habitats within stocks; (ii) fixed categorical segregation of haplotypes on the south-eastern Alaska and central California feeding grounds of the North Pacific; (iii) support for the division of the North Pacific population into a central stock which feeds in Alaska and winters in Hawaii, and an eastern or 'American' stock which feeds along the coast of California and winters near Mexico; (iv) evidence of genetic heterogeneity within the Gulf of Maine feeding grounds and among the sampled feeding and breeding grounds of the western North Atlantic; and (v) support for the historical division between the Group IV (Western Australia) and Group V (eastern Australia, New Zealand and Tonga) stocks in the Southern Oceans. Overall, our results demonstrate a striking degree of genetic structure both within and between oceanic populations of humpback whales, despite the nearly unlimited migratory potential of this species. We suggest that the humpback whale is a suitable demographic and genetic model for the management of less tractable species of baleen whales and for the general study of gene flow among long-lived, mobile vertebrates in the marine ecosystem.

Abundant mitochondrial DNA variation and world-wide population structure in humpback whales.

Hunting during the last 200 years reduced many populations of mysticete whales to near extinction. To evaluate potential genetic bottlenecks in these exploited populations, we examined mitochondrial DNA control region sequences from 90 individual humpback whales (Megaptera novaeangliae) representing six subpopulations in three ocean basins. Comparisons of relative nucleotide and nucleotype diversity reveal an abundance of genetic variation in all but one of the oceanic subpopulations. Phylogenetic reconstruction of nucleotypes and analysis of maternal gene flow show that current genetic variation is not due to postexploitation migration between oceans but is a relic of past population variability. Calibration of the rate of control region evolution across three families of whales suggests that existing humpback whale lineages are of ancient origin. Preservation of preexploitation variation in humpback whales may be attributed to their long life-span and overlapping generations and to an effective, though perhaps not timely, international prohibition against hunting.

Continuing medical education for general practitioners in North Devon.

The establishment of a continuing medical education system for established Principals in a semi-rural area is described. The essential requirement is a 'link man' in each general practice in the area. Clinical tutors, course organisers and regional advisers are all actively involved to produce a regional educational policy.

Heat Shock Proteins and Their mRNAs in Dry and Early Imbibing Embryos of Wheat.

Two-dimensional gels of in vitro translation products of mRNAs isolated from quiescent wheat (Triticum aestivum) embryos demonstrate the presence of mRNAs encoding heat shock proteins (hsps). There were no detectable differences in the mRNAs found in mature embryos from field grown, from 25 degrees C growth chamber cultivated, or from plants given 38 degrees C heat stresses at different stages of seed development. The mRNAs encoding several developmentally dependent (dd) hsps were among those found in the dry embryos. Stained two-dimensional gels of proteins extracted from 25 degrees C growth chamber cultivated wheat embryos demonstrated the presence of hsps, including dd hsps. A study of the relationship of preexisting hsp mRNAs and the heat shock response during early imbibition was undertaken. Heat shocks (42 degrees C, 90 minutes) were administered following 1.5, 16, and 24 hours of 25 degrees C imbibition. While the mRNAs encoding the low molecular weight hsps decayed rapidly upon imbibition, the mRNAs for dd hsps persisted longer and were still detectable following 16 hours of imbibition. After 1.5 hours of imbibition, the mRNAs for the dd hsps did not accumulate in response to heat shock, even though the synthesis of the proteins was enhanced. Thus, an applied heat shock appeared to lead to the preferential translation of preexisting dd hsp mRNAs. The mRNAs for the other hsps, except hsp 70, were newly transcribed at all of the imbibition times examined. The behavior of the hsp 70 group of proteins during early imbibition was examined by RNA gel blot analysis. The mRNAs for the hsp 70 group were detectable at moderate levels in the quiescent embryo. The relative level of hsp 70 mRNA increased after the onset of imbibition at 25 degrees C and remained high through 25.5 hours of prior imbibition. The maximal levels of these mRNAs at 25 degrees C was reached at 17.5 hours of imbibition. Heat shock caused modest additional accumulation of hsp70 mRNA at later imbibition times.

Heat shock response of germinating embryos of wheat : effects of imbibition time and seed vigor.

Seeds frequently face a hostile environment during early germination. In order to determine whether seeds have evolved unique mechanisms to deal with such environments, a survey of the heat shock response in isolated embryos of wheat (Triticum aestivum L.) was undertaken. Embryos simultaneously heat shocked and labeled following several different periods of prior imbibition up to 12 hours synthesized many groups of heat shock proteins (hsps) typical of other plant and animal systems. Also, five developmentally dependent hsps, present only in treatments imbibed less than 6 hours prior to heat shock, were detected. These proteins have relative molecular masses of 14, 40, 46, 58, and 60 kilodaltons. One of the developmentally dependent hsps is among the most highly labeled hsps found in early imbibed embryos. The possibility that this protein is the E(m) protein is discussed. The hypothesis that the capacity for hsp synthesis is affected by seed vigor was also tested. The heat shock responses of embryos from two high and two low vigor seed lots were compared using one- and two-dimensional electrophoresis of labelled protein extracts. The results indicate that both of the low vigor lots tested had weaker heat shock responses than their high vigor counterparts overall. Not all hsps were relatively less abundant in low vigor embryos. The developmentally dependent hsps showed little relationship to vigor. Some of the developmentally dependent hsps were actually made in greater amounts, relative to other proteins, in the low vigor seed lots. The results presented here demonstrate that imbibing embryos are capable of expressing an enhanced heat shock response, and that this response is related to seed vigor.

Thermotolerance is developmentally dependent in germinating wheat seed.

During the initial 9 to 12 hours of imbibition, the imbibing wheat (Triticum aestivum L.) seed was found to exhibit substantial tolerance to high temperature relative to later times of imbibition. Tolerance was assessed by seed viability and seedling growth. This initial high temperature tolerance gradually declines with increasing time of seed imbibition. A range of 2 hour heat pretreatments (38-42 degrees C) prior to imposition of a 2 hour heat shock (51-53 degrees C) during this same 9 to 12 hour interval was unable to increase survival or seedling growth over that of seed that did not receive a pretreatment. However, after 9 to 12 hours of imbibition the pretreatment provided both increased survival and increased seedling growth, measured 120 hours later, i.e., classical thermotolerance could be acquired. This response is called a ;thermotolerance transition.' Isolated embryos responded in a similar manner using a 2,3,5-triphenyltetrazolium chloride assay for viability determination following heat treatments. The high temperature tolerance during early imbibition indicates that the thermotolerance transition involves the loss of an existing thermotolerance coincident with acquiring the ability to become thermotolerant following heat pretreatment. Despite the inability to acquire thermotolerance, heat shock protein synthesis was induced by heat shock immediately upon imbibition of wheat seed or isolated embryos. Developmentally regulated heat shock proteins of 58 to 60, 46, 40, and 14 kilodaltons were detected at 1.5 hours of imbibition following heat shock, but were absent or greatly reduced by 12 hours. Constitutive synthesis of 70 and 90 kilodalton hsp groups appeared to be greater at 1.5 hours of imbibition than at 12 hours of imbibition.

An inventory of 13C abundances in coastal wetlands of Louisiana, USA: vegetation and sediments.

Organic carbon-rich sediments from the surface of fresh, intermediate, brackish and salt marshes of coastal Louisiana were sampled and analyzed for their 13C content. The average ∂13C from all sites within each wetland type was-27.8‰,-22.1‰,-16.9‰, and-16.2‰, for fresh, intermediate, brackish and salt marshes, respectively. Means from the fresh, intermediate and brackish marshes were significantly different at the 0.01 level. A mixing model using measurements of standing crop and ∂13C of plant carbon was applied to estimate the contribution of each species to the sedimentary carbon at four of the marsh sites. Sedimentary ∂13C values generally reflected that of the dominant species present at each site. Brackish and salt marsh samples, however, showed a negative shift of ∂13C with respect to whole plant carbon. We interpret these depeleted ∂13C values to be the result of more extensive organic matter decomposition and selective preservation of 13C-depleted refractory components in sediments from saline sites. The results of this study suggest that ∂13C composition of sedimentary carbon may offer a valuable tool for distinguishing subtle changes in paleohydrology of wetlands resulting from relative sea level changes.