Abstract: Problems concerning the concept of biocoenosis in ecology (the antecedent of the pathocoenosis concept) are discussed first of all. Six main problems are identified: the problem of emergent properties of ecological communities; the problem of ambiguity; the problem of heterogeneity; the boundary problem; the problem of retrospective differential diagnosis; and the problem of explaining change over time. The rest of the paper gives illustrations of these problems in relation to human pathogens drawn mainly from the interactions of malaria with other diseases, particularly but not exclusively in the Mediterranean world, from antiquity through to modern times.
Abstract: We present DNA sequence data showing population variation in the intergenic spacer (IGS) regions of the ribosomal DNAs (rDNAs) on the A genomes of 27 diploid and polyploid wheats. PCRs (polymerase chain reactions) specific for the A(m) genome gave products with five populations of Triticum monococcum but did not give products with AABB or AABBDD wheats. PCRs specific to the A(u) genome of T. urartu gave products with all the AABB and AABBDD polyploids that were tested, but not with T. monococcum. AAGG tetraploids gave products only with the A(u)-specific primers, but the AAAAGG hexaploid T. zhukovskyi gave products with both the A(u) and A(m) primers. Phylogenetic analysis showed a substantial degree of IGS divergence for both the A(m) and A(u) genomes in diploids and polyploids compared with other genomes of Triticum and Aegilops. The rate of evolution of the IGS is much greater than previously reported for the internal transcribed region of the rDNAs but the view that the IGS only gives random noise is rejected, the IGS sequences presented here reflecting the general evolutionary trends affecting the wheat genome as a whole.
Abstract: We describe a PCR system that distinguishes the A, B and D genomes in wheat DNA extracts. PCRs were directed at the 'non-transcribed spacer' regions of the rDNA loci. The spacers within the D genome locus have a 71-bp insertion that is absent from the corresponding A and B loci. PCR product sizes therefore enable D- and D+ genomes to be distinguished. The A and B genomes can be differentiated by PCR with an internal primer which does not anneal to A genome sequences. This work is relevant to the ancient ecology of wheat, as it is often difficult to determine ploidy level from morphological examination of archaeobotanical remains.
Abstract: We have used hybridization analysis to detect ancient DNA in wheat seeds collected from three archaeological sites in Europe and the Middle East. One of these samples, carbonized T. spelta dated to the first millennium BC, has yielded PCR products after amplification with primers directed at the leader regions of the HMW (high molecular weight) glutenin alleles. Sequences obtained from these products suggest that the DNA present in the Danebury seeds is chemically damaged, as expected for ancient DNA, and also indicate that it should be possible to study the genetic variability of archaeological wheat by ancient DNA analysis. Finally, we describe a PCR-based system that enables tetraploid and hexaploid wheats to be distinguished.
