Ultrastructural Histopathology of Infection and Colonization of Maize by Stenocarpella maydis (= Diplodia maydis)

The mode of penetration and colonization of stalk, shank and leaf sheath tissues of maize by Stenocarpella maydis (=Diplodia maydis) was determined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Detached plant tissues, inoculated with a conidial suspension and examined by SEM at various intervals, showed that S. maydis conidia germinated on all plant material types after 5 h incubation at 30 °C. After 72 h incubation, appressoria had formed at the hyphal tips. Similar observations were recorded on plants inoculated in the glasshouse except that germination was delayed by 7 days after inoculation. TEM studies showed that penetration was affected by a penetration hypha which resulted in the inter- and intracellular colonization of the plant tissues. Colonization was accompanied by degradation of cell walls suggesting that host colonization is facilitated by enzyme activity.     

The Relation between Protein Synthesis and Lipide Accumulation in L Strain Cells and Ehrlich Ascites Cells

It has long been known that fat accumulates in old injured cells both in tissue culture and in many mammalian disease states. The use of L cells grown in suspension tissue culture permitted the opportunity to study conditions in which lipide accumulation could be retarded or accelerated. These cultures exhibit a three-phase growth curve which is similar to that previously found with bacteria and consists of a lag period, logarithmic growth period, and stationary period. Daily aliquots were removed from cultures going through these phases and protein and cholesterol content correlated with cell division. It was found that L cells gradually accumulated lipide in the cell concurrent with retardation of cell division and protein synthesis. Conversely old lipide-laden cells, placed in fresh media and encouraged to active division with net protein synthesis progressed from a high to a low lipide/cell ratio over a period of 2 to 4 days. An amino acid analogue p-fluorophenylalanine and a mitotic inhibitor, colchicine, also markedly increased the lipide/cell ratio. Similar results were found in in vitro experiments with Ehrlich ascites cells.     

STUDIES ON THE INTRACELLULAR DIGESTIVE PROCESS IN MAMMALIAN TISSUE CULTURE CELLS

DNA-protein coacervates containing colloidal gold particles were readily phagocytized by strain L fibroblasts. During the subsequent digestion process, the gold particles served as markers which permitted the demonstration of the evolution of digestive vacuoles to multivesicular bodies and finally to dense bodies. Acid phosphatase and esterolytic activity was present in these structures. The hydrolytic enzymes were apparently brought to the phagocytotic vacuoles in small vesicles originating in the Golgi region. These vesicles entered the vacuoles prior to the digestion of the coacervates and the appearance of positive cytochemical reactions. The cytoplasmic dense bodies frequently merged with the phagocytotic vacuoles. This was demonstrated by prelabeling the dense bodies with colloidal iron prior to phagocytosis of the coacervates. In addition, evidence is presented for the interrelationship of the phagocytotic and autophagic pathways.     

THE FATE OF DNA-CONTAINING PARTICLES PHAGOCYTIZED BY MAMMALIAN CELLS

Particulate DNA protein coacervates were digested immediately after being phagocytized by L strain fibroblasts in suspension culture. Enlargement of the phagocytotic vacuoles occurred simultaneously with a loss of the electron opacity of the phagocytized particles. Cytochemical reactions positive for non-specific esterase, acid phosphatase, and nucleoside phosphatase in the phagocytotic vacuoles provided additional evidence for the probability of complete hydrolysis of the phagocytized nucleoprotein.     

THE SOURCE OF LIPID ACCUMULATION IN L CELLS

Strain L cells accumulate lipid, concurrent with cessation of protein synthesis, in the stationary phase of growth from the extracellular medium and as a result of de novo synthesis. Cells which have been more severely damaged with an amino acid analogue also accumulate lipid from the extracellular medium, but synthesize very little lipid from labeled acetate. The possible roles which lipid accumulation may play in the cell are discussed.     

HIGHER FITNESS FOR PHILOPATRIC THAN FOR IMMIGRANT MALES IN A SEMI-ISOLATED POPULATION OF GREAT REED WARBLERS

To compare the fitness of philopatric and immigrant individuals we examined the lifetime reproductive success of 116 male and 137 female great reed warblers. The study was carried out in a semi-isolated population in Sweden and covered breeding adults hatched between 1985 and 1993. Lifetime fitness, measured as life time number of fledglings and offspring recruits, was lower for immigrant than for philopatric males. We found no such relationships for females. The difference in reproductive success could not be explained by immigrant males having lower phenotypic quality because they had similar life span, spring arrival date, and territory quality as philopatric males. The lower lifetime fitness among immigrant than philopatric males appeared to result from reduced mating success. This suggests that females are reluctant to mate with immigrant males despite their apparently similar phenotypic quality. Though it is not known whether females gain in fitness by avoiding matings with immigrant males, it is notable that immigrant males have smaller song repertoires than philopatric males. Large repertoires, previously shown to sexually arouse great reed warbler females, correlate with the occurrence of extrapair paternity and postfledging survival of offspring in our population.     

Estimating heritabilities and genetic correlations: comparing the 'animal model' with parent-offspring regression using data from a natural population

Quantitative genetic parameters are nowadays more frequently estimated with restricted maximum likelihood using the 'animal model' than with traditional methods such as parent-offspring regressions. These methods have however rarely been evaluated using equivalent data sets. We compare heritabilities and genetic correlations from animal model and parent-offspring analyses, respectively, using data on eight morphological traits in the great reed warbler (Acrocephalus arundinaceus). Animal models were run using either mean trait values or individual repeated measurements to be able to separate between effects of including more extended pedigree information and effects of replicated sampling from the same individuals. We show that the inclusion of more pedigree information by the use of mean traits animal models had limited effect on the standard error and magnitude of heritabilities. In contrast, the use of repeated measures animal model generally had a positive effect on the sampling accuracy and resulted in lower heritabilities; the latter due to lower additive variance and higher phenotypic variance. For most trait combinations, both animal model methods gave genetic correlations that were lower than the parent-offspring estimates, whereas the standard errors were lower only for the mean traits animal model. We conclude that differences in heritabilities between the animal model and parent-offspring regressions were mostly due to the inclusion of individual replicates to the animal model rather than the inclusion of more extended pedigree information. Genetic correlations were, on the other hand, primarily affected by the inclusion of more pedigree information. This study is to our knowledge the most comprehensive empirical evaluation of the performance of the animal model in relation to parent-offspring regressions in a wild population. Our conclusions should be valuable for reconciliation of data obtained in earlier studies as well as for future meta-analyses utilizing estimates from both traditional methods and the animal model.     

Population structure and migratory directions of Scandinavian bluethroats Luscinia svecica– a molecular, morphological and stable isotope analysis

Many species of birds show evidence of secondary contact zones and subspeciation in their Scandinavian distribution range, presumably resulting from different post-glacial recolonization routes. We investigated whether this is the case also in the Scandinavian bluethroat Luscinia svecica , a species that has been suggested to consist of two separate populations: one SW-migrating and long-winged ( L. s. gaetkei ) breeding in southern Norway, and one shorter-winged ESE-migrating ( L. s. svecica ) in northern Scandinavia. We sampled males at eleven breeding sites from southern Norway to northernmost Sweden. There were no morphological differences or latitudinal trends within the sample, neither were there any genetic differences or latitudinal trends as measured by variation in AFLP and microsatellite markers. Stable isotope ratios of throat feathers moulted on the wintering grounds showed no, or possibly marginal differences between birds from southern Norway and northern Sweden. We also re-measured old museum skins that in previous studies were classified as L. s. gaetkei , and found marginally longer wings in birds from the southern part of the Scandinavian breeding range. The difference, however, was much smaller than proposed in earlier studies. We conclude that there is no evidence of a genetic population structure among Scandinavian bluethroats that would suggest the presence of a zone of secondary contact. Finally we discuss whether the presumed subspecies gaetkei ever existed.     

Haemosporidian blood parasites in European birds of prey and owls

Avian blood parasites have been intensively studied using morphological methods with limited information on their host specificity and species taxonomic status. Now the analysis of gene sequences, especially the mitochondrial cytochrome b gene of the avian haemosporidian species of Haemoproteus, Plasmodium, and Leucocytozoon, offers a new tool to review the parasite specificity and status. By comparing morphological and genetic techniques, we observed nearly the same overall prevalence of haemosporidian parasites by microscopy (19.8%) and polymerase chain reaction (PCR) (21.8%) analyses. However, in contrast to the single valid Leucocytozoon species (L. toddi) in the Falconiformes we detected 4 clearly distinctive strains by PCR screening. In the Strigiformes, where the only valid Leucocytozoon species is L. danilewskyi, we detected 3 genetically different strains of Leucocytozoon spp. Two strains of Haemoproteus spp. were detected in the birds of prey and owls examined, whereas the strain found in the tawny owl belonged to the morphospecies Haemoproteus noctuae. Three Plasmodium spp. strains that had already been found in Passeriformes were also detected in the birds of prey and owls examined here, supporting previous findings indicating a broad and nonspecific host spectrum bridging different bird orders.     

A comparative analysis of microscopy and PCR-based detection methods for blood parasites

We compared information obtained by both microscopy and nested mitochondrial cytochrome b PCR in determining prevalence of haemosporidian infections in naturally infected birds. Blood samples from 472 birds of 11 species belonging to 7 families and 4 orders were collected in Europe, Africa and North America. Skilled investigators investigated them using the PCR-based screening and microscopic examination of stained blood films. The overall prevalence of haemosporidian infections, which was determined combining results of both these methods, was 60%. Both methods slightly underestimated the overall prevalence of infection, which was 54.2% after the PCR diagnostics and 53.6% after microscopic examination. Importantly, both these tools showed the same trends of prevalence of Haemoproteus spp. (21% by PCR and 22% by microscopy), Plasmodium spp. (17% and 22%) and Leucocytozoon spp. (30% and 25%) in the same sample, testifying that microscopy is a reliable tool in determining patterns of distribution of blood haemosporidian parasites in naturally infected birds. We encourage using optical microscopy in studies of blood parasites in parallel to the now widely employed molecular methods. Microscopy is relatively inexpensive and provides valuable information about directions how molecular methods can be further improved and most effectively applied, especially in the field studies of parasites. Importantly, blood films, which are used for microscopic examination, should be of good quality; they should be examined properly by skilled investigators. In spite of relatively long duration of microscopy of each sample, such examination provides opportunities for simultaneous determination and verification of taxonomically different parasites. Presently, different PCR protocols must be used for the detection of parasites belonging to different genera; this is expensive and time-consuming.