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Resolving the mechanistic and genetic bases of reproductive barriers between species is essential to understanding the evolutionary forces that shape speciation. Intrinsic hybrid incompatibilities are often treated as fixed between species, yet there can be considerable variation in the strength of reproductive isolation between populations. The extent and causes of this variation remain poorly understood in most systems. We investigated the genetic basis of variable hybrid male sterility (HMS) between two recently diverged subspecies of house mice, and We found that polymorphic HMS has a surprisingly complex genetic basis, with contributions from at least five autosomal loci segregating between two closely related wild-derived strains of One of the HMS-linked regions on chromosome 4 also showed extensive introgression among inbred laboratory strains and transmission ratio distortion (TRD) in hybrid crosses. Using additional crosses and whole genome sequencing of sperm pools, we showed that TRD was limited to hybrid crosses and was not due to differences in sperm motility between strains. Based on these results, we argue that TRD likely reflects additional incompatibilities that reduce hybrid embryonic viability. In some common inbred strains of mice, selection against deleterious interactions appears to have unexpectedly driven introgression at loci involved in epistatic hybrid incompatibilities. The highly variable genetic basis to F1 hybrid incompatibilities between closely related mouse lineages argues that a thorough dissection of reproductive isolation will require much more extensive sampling of natural variation than has been commonly utilized in mice and other model systems.

Abstract. Assuming that there is no major chemical toxicity or deficiency, the major limitation in man‐made soil is the loss of its natural structure, which, in turn, controls the air‐water balance. Where such a soil has < 70% sand content this loss may adversely affect potential for use. Examples of man‐made soils ‐ sports turf and replaced opencast coal mining land ‐ are used to illustrate principles of management. Two strategies exist: to encourage earthworms, thereby promoting effective site drainage by infiltration or, to limit their activity and rely mainly on surface shed. The implications of each of these soil options for wider management and use are discussed.

Considerable variations in the apparent density of the fine earth fraction were recorded in stony soils in Cwmcadian, Merionethshire. A highly significant relationship between fine earth apparent density and stone content was observed which was not caused by disturbance during sampling. The relationship could be predicted by assuming that the bulk volume of a stony soil approximates to the sum of the self-packing volumes of the separated stone and fine earth components. It is suggested that in natural soils there is a similar relationship between soil apparent density and organic matter content, namely that the bulk volume of a soil containing organic matter approximates to the summed self-packing volumes of the mineral and organic components.

An investigation into the effects of physical and chemical enhancement on subsequent presumptive and confirmatory tests for human blood is presented. Human blood was deposited onto porous (white 80gsm paper and brown envelope) and non-porous (tile and linoleum) substrates in a depletion series (30 depletions on non-porous and 20 on porous) and subjected to three ageing periods; 1, 7 and 28 days. A number of enhancement techniques were tested [fluorescence, black magnetic powder (BMP), iron-oxide black powder suspension (PS), cyanoacrylate (CA) fuming, acid violet 17 (AV17), acid yellow 7 (AY7), ninhydrin, DFO and Bluestar Forensic Magnum (BFM) luminol] to evaluate their potential effects on subsequent presumptive and confirmatory tests. AV17 and Bluestar provided the best enhancement and fully enhanced all depletions in the series. The sensitivity of the Kastle-Meyer (KM) (presumptive), Takayama and RSID-Blood tests (confirmatory) was initially investigated to determine the range of detectable depletions. The KM test detected all depletions, whereas the Takayama test detected up to depletion 6 and RSID-Blood detected up to depletion 20 (paper), 10 (envelope), 15 (tile) and 9 (lino). The abilities of these tests to detect blood after enhancement were then observed.A number of techniques resulted in little to no effect on any of the blood tests, whereas adverse effects were observed for others. Ninhydrin and CA fuming caused weak but instantaneous positive KM results whereas methanol-based AV17 and AY7 delayed the reaction by as much as 1 minute. The Takayama test was not very sensitive, therefore, its performance was easily affected by enhancement and negative results were often observed. RSID-Blood tests were largely unaffected by chemical enhancement although a drop in positive results was observed for some of the techniques when compared to positive controls.Using a standard procedure for DNA extraction, all the tested blood samples (before and after enhancement) gave a detectable quantity of DNA and were successfully profiled. Out of the 45 samples processed for DNA profiling, 44 gave full profiles, while the remaining showed allele drop out in one or two loci.

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The soils in Cwmcadian, Merionethshire, have developed in uniform Silurian mudstones. This rock consists of fundamental primary particles of silt and clay size. These are released on weathering in the same ratio as they occur in the rock. Because of the simple mode of weathering, silt may be used as an internal standard against which to assess gains and losses of mobile soil constituents during pedogenesis.THIS series of apers will describe variations in podzolic soils formed in tive evidence of the pedological changes which have taken place.Quantitative assessments of changes involved in the divergent development of different soil profiles on the same parent material or conver ent development on different parent materials, are often hampered by a % ck of precise information on the initial state of the mineral skeleton. In

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