Genetic variability in intergenic spacers of ribosomal DNA in Pisolithus isolates associated with pine, eucalyptus and Afzelia in lowland Kenyan forests

Basidiocarps of Pisolithus associated with indigenous ( Afzelia quanzensis Welw.) and introduced ( Pinus caribaea Mor. and Eucalyptus camaldulensis Dehnh.) hosts in the lowland forests of the Coast Province of Kenya are morphologically distinct. Genetic variability among 52 Pisolithus basidiocarps, collected beneath the various host plants, was examined based on sequence polymorphism within the internal transcribed spacer (ITS) and intergenic spacer (IGS1) of ribosomal DNA genes. Variability in ITS and IGS1 sequences indicated that the three host-associated morphotypes were genetically different. Consensus trees generated by bootstrap analysis of sequence data of Pisolithus isolates from Australia and Kenya are polyphyletic and strongly suggest that the three different morphotypes/genotypes present in Kenya represent separate biological species. In addition, our data indicate that little genetic exchange occurs in silva between these species.     

Correlates of reproductive success among field colonies of Bombus lucorum: the importance of growth and parasites

Abstract.

• 1 In natural populations, colonies of bumble bees vary in many important life history traits, such as colony size and age at maturity, or the number and sex of reproductives produced. We investigated how the presence of parasites in field populations of the bumble bee Bombus lucorum L. relates to variation in life history traits and reproductive performance. A total of thirty-six colonies was placed in accessible nest sites in the field and monitored at regular intervals throughout a season.
• 2 Among the life history correlates, early nest foundation was strongly associated with large maximum colony size, old age and large size at maturity, and this in turn with successful production of males and queens, as well as with the number of sexuals produced. Overall, reproductive success was highly skewed with only five colonies producing all the queens. Sixteen colonies failed to reproduce altogether.
• 3 The social parasite Psithyrus was abundant early in the Bombus colony cycle and preferentially invaded host nests with many first brood workers and thus disproportionately large size, i.e. those colonies that would otherwise be more likely to reproduce or produce (daughter) queens rather than males. To prevent nest loss, Psithyrus had to be removed soon after invasion. Therefore, the effects reported here can only be crude estimates.
• 4 Parasitoid conopid flies are likely to cause heavy worker mortality when sexuals are reared by the colonies. Their inferred effect was a reduction in biomass that could be invested in sexuals as well as a shift in the sex ratio at the population level resulting from failure to produce queens. We suggest to group the inferred correlates into ‘early events’ surrounding colony initiation and social parasitism, and ‘late events’ surrounding attained colony size in summer and parasitism by conopid flies. Our evidence thus provides a heuristic approach to understand the factors that affect reproductive success of Bombus colonies.

     

Cytological Diversity and Triploid Frequency in a Complex Population of Ranunculus ficaria L.

An extensive mixed population of Ranunculus ficaria polyplotypeswas mapped, sampled, and examined cytologically. The presenceand relative abundance of different polyplotypes was as follows:31 per cent diploid (2n = 16), 40 per cent tetraploid (2n =32), and 29 per cent presumed intermediate triploid (2n = 24).It was demonstrated that there is no simple character for distinguishingall polyplotypes in the field and chromosome counts must beused for this purpose. The action of winter flood water on bulbildissemination and differences in ecological preference of thepolyplotypes is proposed to account for differences in distributionover the population area. There is some indication that triploidseeds may be produced under a situation of excessive numbersof tetraploid plants relative to diploids which reduces diploid/tetraploidpollen competition on diploid stigmas. Diploid plants with 1–8B-chromosomes were found to occur frequently but no consistenteffect of these B's on vigour, fertility, and meiosis was evident.B-chromosomes were entirely absent from triploid and tetraploidkaryotypes.     

Antibiotic Resistance among Escherichia coli O-serotypes from the Gut and Carcasses of Commercially Slaughtered Broiler Chickens: a Potential Public Health Hazard

Presumptive coliform counts and the distribution of Escherichia coli O-serotypes were investigated in chicken rectal contents (175) abdominal cavities (152) and on the carcasses of 44 which had been commercially raised, slaughtered and prepared for sale. Large numbers of E. coli resistant to at least one antibacterial agent were found at each site; comparison of the O-serotypes suggested heavy contamination of the carcass with strains from the gut. The range of O-serotypes was similar to that found in man and some public health implications of cross-infection particularly by handling uncooked birds in the kitchen, are discussed.     

The Recovery of Sublethally Injured Escherichia coli from Frozen Meat

Sublethal injury to Escherichia coli , measured as the inability of surviving cells to grow on media containing bile salts, was monitored during frozen storage on meat at —5, —10 and —20° C. More rapid increases in injury occurred at the higher subzero temperatures and log phase cells were more susceptible than those in the stationary phase of growth. Repair of injury in non-selective liquid media took between 2 and 6 h at 25° and was often accompanied by an increase in total viable count. Incubation for a fixed period in broth was, therefore, unsuitable for the quantitative recovery of freeze-injured Esch. coli. Resuscitation on membrane filters avoided confusing repair of injury with multiplication of uninjured or repaired cells. The mean recovery of injured cells following incubation on membranes for 4 h at 35°C on tryptone soya agar, was 94%.     

Cultivated and wild host plants supporting populations of the cabbage root fly

To determine the relative importance of different potential host plants for supporting populations of the cabbage root fly, wild and cultivated crucifers were sampled for pupae at four locations during 1971-3. In addition, eighty-three species of Cruciferae native to or naturalized in the British Isles were inoculated with cabbage root fly eggs in a glasshouse to determine which species could support the larvae. In the field, most pupae (28-7/plant) were collected from untreated cauliflowers. Fewer pupae (i-7–8-6/plant) were obtained from untreated crops of Brussels sprout, cabbage and swede. Applications of chlorfenvinphos reduced populations to two or less pupae per plant on all crops. Of five common weed species sampled, only Raphanus raphanistrum produced as many pupae as certain of the untreated brassica crops. Pupae did not occur in samples from Capsella bursa-pastoris but Sisymbrium officinale, Thlaspi arvense and Sinapis arvensis usually supported low numbers. In the glasshouse, only forty-four of the eighty-three cruciferous species tested supported larval development. Most pupae were obtained from 12-wk-old plants of Barbarea intermedia. B. stricta, Brassica napus, Cochlearia officinalis and R. raphanistrum and from 24-wk-old plants of Brassica rapa, Erysimum aureum, Cochlearia anglica and C. officinalis. Plant age considerably affected pupal production. Plants within a genus often gave similar results, pupae not being recovered from any of the Diplotaxis or Arabis species tested, or from young plants of Erysimum spp. In other families, Reseda lutea and R. luteola supported larval development, but the widely-separated Plantago major did not. Arguments for and against the removal of cruciferous weeds from the vicinity of cruciferous crops are discussed.