Variation in the Long-tailed field-mouse (Apodemus sylvaticus) in south-west england

Measurements of four skull and five external characters were made on each of 277 specimens of Apodemus sylvaticus (L.) from the two Isles of Scilly (Tresco and St Mary's) on which it occurs and from six localities in mainland Cornwall. The skull characters were greatest length of skull, maxillary tooth row, cranial breadth and length of palatal foramen. Lengths of the pectoral stripe, tail, hindfoot and ear were obtained, as well as the weight of each animal. The age of each individual was assessed by means of a tooth wear character and a regression adjustment was used to bring all the characters to a uniform age class. The adjusted and unadjusted means have been calculated of each character for every locality. The sexes were separate throughout the analysis.
The island mice are slightly larger than those from the mainland, the latter forming a fairly homogeneous group. In addition to overall size the most distinctive sign for the Tresco mice is the particularly small pectoral stripe. The St Mary's mice have a long tooth row, large pectoral stripe and large palatal foramen. The females were usually slightly smaller than the males.
A canonical analysis was made in an attempt to account for as much variation as possible between groups using a limited number of linear combinations of the original measurements. The greater part of the variance was contained in the first two canonical variates. From these, the populations separated into three groups, i.e. the mainland group, the mice from Tresco and those from St Mary's. The two Scilly Island populations are as distinct from each other as they are from the mainland populations. Separate introductions from different sources and, possibly, slightly different genetic composition of the original immigrants may have accounted, in part, for the divergence shown by these two island stocks. It is not proposed that the island races should be given subspecific status.     

Molecular characterization of ribosomal gene variation within and among NORs segregating in specialized populations of chicken.

The molecular organization of the 18S, 5.8S, and 28S ribosomal RNA gene repeat units, located at the single nucleolus organizer region (NOR) locus in the chicken, was investigated in genetically distinct populations of research and commercial chickens. Substantial gene repeat variation within and among NORs was documented. Intact ribosomal gene repeat size ranged from 11 kb to over 50 kb. Unique combinations of ribosomal genes, of different size, were specific to particular populations. It was determined that the basis for the ribosomal gene repeat size variation was intergenic spacer (IGS) length heterogeneity. Interestingly, in different populations, the location of the variation that contributes to length heterogeneity was specific to particular IGS subregions. In addition to IGS variation, an inbred line of Red Jungle Fowl exhibited coding region variation. Ribosomal gene copy number variation was also studied, and line averages ranged from 279 to 368. Average rDNA array size (a function of copy number and gene repeat length) was calculated for each of the populations and found to vary over a range of two megabases, from 5 to 7 Mb.     

A subset of CD16-natural killer cells without antibody-dependent cellular cytotoxicity function

The low affinity IgG receptor, CD16 (Fc gamma RIII), is expressed on almost all peripheral blood natural killer (NK) cells. A small subset of CD3- CD16- CD56+ NK cells, representing less than 1% of peripheral blood lymphocytes, expands during in vivo IL-2 treatment. To analyze this CD16- NK cell subset in more detail, NK clones have been generated. One of them (TNK2) has been used to study the function of these cells in more detail. It is demonstrated that TNK2 exerts normal NK activity and displays large granular lymphocyte morphology. Since this clone lacks CD16 expression, antibody-dependent cellular cytotoxicity cannot be exerted. CD16 monoclonal antibodies fail to induce cytotoxic activity against NK-resistant target cells. These studies reveal that the lack of CD16 detection is not due to the modulation or the stage of activation of these NK cells. TNK2 is representative of this small subset of peripheral blood NK cells, expanded during IL-2 treatment, which does not express Fc gamma RIII and therefore cannot perform antibody-dependent cellular cytotoxicity.     

The population dynamics of small rodents in a tropical African grassland

Monthly estimates were obtained of the density of small rodents in tropical grassland in Rwenzori Park, Uganda between April 1972 and September 1973. Of the 12 species of rodents present, the most numerous were Lemniscomys striatus, Lophuromys sikapusi, Mus triton, Mylomys dybowskii and Praomys natalensis . In a live trapping grid estimates were obtained using direct enumeration, numbers caught, Hayne's Lincoln Index and Jolly's method. Monthly estimates ranged between 16·67 and 63·32 animals per hectare. Intensive removal trappings were also undertaken and these gave estimates of 6·45 to 27·24 per hectare. The inconsistency of the two estimates may be accounted for by small microhabitat and vegetational differences.
Breeding occurs in Lemniscomys and Praomys during the wet season whilen Lophuromys it is more extended but nevertheless seasonal. There is considerable evidence of rapid population turnover as the five species examined in detail had a mean duration of residence between two and three months. Few animals were resident for more than eight months.
The monthly standing crop biomass ranged from 672 to 2221 g/ha on the live trapping grid and from 348 to 1126 g/ha on the intensive removal grids. Estimates of net annual production on the live trapping grid rely on a number of assumptions but are nevertheless relatively high ranging from 5897 to 7072 g/ha.
Fires had a significant indirect effect on the composition of the fauna. Mus triton and Lemniscomys increased their numbers in the five months following the burn to levels not previously attained whereas Mylomys and Lophuromys were less frequent during this period. Several species of avian, reptilian and mammalian predators are recorded.     

Teratogenic development in chicken embryos associated with a major deletion in the rRNA gene cluster

A new strain of chickens (mPNU) that segregates a severely deleted rDNA cluster was studied. Individuals heterozygous (+/p²) and homozygous (p²/p²) for the deletion were found to have 56 and 27%, respectively, of the normal complement of rRNA genes (290 copies/cell). Morphogenesis, cellular rRNA levels, and nucleolar sizes, were investigated and compared in normal +/+, +/p², and p²/p² embryos. Cellular rRNA contents were similar among the three genotypes at stage X, but subsequently during gastrulation, p²/p² levels were reduced to 56% and eventually to 43% of +/+. Viability and morphogenesis were normal in p²/p² embryos until the initial primitive streak stage of gastrulation. However, further development was abnormal and characterized by disrupted axis formation. In +/+ and +/p² embryos, rRNA levels and nucleolar sizes increased during early development; however, the profile of these increases differed temporally and quantitatively between the genotypes. The +/p² embryos, at the full streak stage of gastrulation, exhibited reduced rRNA levels and nucleolar sizes (80% of +/+), yet the +/p² embryos developed normally. These studies establish a minimum copy number requirement lower than previously demonstrated, that is, a rDNA genotype with only 56% of the normal gene complement (～160 genes) is compatible with early embryonic viability. Also, a rRNA threshold was detected: rRNA levels that were 56% of +/+ failed to support normal gastrulation; however, even under the circumstance of reduced rRNA levels (43% of control), some aspects of gastrulation apparently continue (cell migration and invagination). The teratogenic development of p²/p² embryos is a biological consequence unique from that found in other metazoan models of rDNA-deficiency, and will be useful as a model to investigate mechanisms of vertebrate gastrulation and axis formation.