The prevalence of antibody to infectious bovine rhinotracheitis virus in some game animals of East Africa.

Antibody to infectious bovine rhinotracheitis virus was present in the sera of 10 of 25 species of game animals from Kenya, Tanzania and Uganda during 1960-1973. Prevalence of antibody varied considerably between, but not within, species.     

Sexual showiness and parasite load: correlations without parasite coevolutionary cycles

Hamilton & Zuk (1982, Science 218, 384-387.) produced a model of sexual selection in which coevolutionary cycles of host and parasites generate consistently positive correlations between parent and offspring viability, and that animals choose mates for genetic disease resistance by scrutinizing characters whose full expression is dependent on health and vigour. They predicted a positive correlation between sexual showiness and parasite burden across species, and a negative correlation within a species. First, recent suggestions that interspecific correlations in the opposite direction to that indicated above are consistent with the mechanisms of Hamilton & Zuk's model are discussed. Second, it is shown that the model's predictions can be produced by heritable variation maintained by non-parasite fluctuating selection. In this case, the parasites associated with degree of sexual showiness are those able to amplify any initial heritable differences in vigour. Alternative sources of positive correlation between parent and offspring viability, which include the indirect effects of climatic change and exclude the need for host-parasite coevolutionary cycles, are also proposed.     

Partitioning the mechanisms by which genetic diversity of parasite infections affects total parasite load

Genetically-diverse parasite infections are common in nature, however what mechanisms influence parasite load are still under debate. Rauch et al. found consistently lower parasite loads in genetically-mixed infections compared to uniform infections. Using the additive partition of Loreau and Hector they demonstrated that this lower parasite load was due to negative complementarity effects, but they only found weak selection effects. Complementarity effects arise from differentiation among genotypes that accrue equally to all genotypes, while selection effects arise from unexpectedly high performance of certain genotypes in mixed infections. However, selection effects might arise either because genotypes with certain traits perform unexpectedly well in mixed infections at the expense of other genotypes ('dominance effects', DEs), or because genotypes with certain traits perform unexpectedly well, but not at the expense of others genotypes ('trait dependent complementarity effects', TDCEs). Here, we reanalyze the data of Rauch et al. using the tripartite partition of Fox to separate DEs, TDCEs and trait-independent complementarity effects (TICEs, corresponding to the complementarity effect of Loreau and Hector). We found significantly negative TDCEs that contribute strongly to the low parasite loads in mixed infections. We suggest novel, testable hypotheses to explain negative TDCEs. Ours is the first study to demonstrate consistently-strong TDCEs, which are rare in studies of the productivity of plant mixtures. Our results highlight the importance of testing for TDCEs, rather than assuming them to be small. We discuss the interpretation and value of the tripartite partition as an analytical tool complementary to more mechanistic approaches.     

Suppression of parasite antigen-specific lymphoid blastogenesis in African trypanosomiasis

Inbred C57BL/6J mice were infected with either Trypanosoma rhodesiense organisms of Walter Reed Army Trypanozoon antigenic type 3 or 5 (WRATat 3 or WRATat 5) or were immunized with soluble trypanosomal antigens. Spleen cells obtained from immunized hosts undergo blastogenesis, measured by thymidine incorporation, when exposed to trypanosomal antigens in vitro. Spleens obtained from mice infected with T. rhodesiense organisms do not respond or respond only minimally to trypanosomal antigens in vitro. Spleen cells of infected mice suppress the trypanosomal antigen-induced proliferative response of spleen cells from immunized mice in co-culture experiments. The suppressive activity was found in both the plastic adherent and plastic nonadherent spleen cell populations. The in vitro responses of normal spleen cells to LPS and Con A were also suppressed by spleen cells obtained from infected mice.     

The pulmonary circulation of some domestic animals at high altitude

Pulmonary haemodynamics and the histology of the pulmonary vasculature have been studied at high altitude in the yak, in interbreeds between yaks and cattle, and in domestic goats and sheep indigenous to high altitudes together with crosses between them and low-altitude strains. Cattle at high altitude had a higher pulmonary arterial pressure than cattle at low altitude. The yak and two interbreeds with cattle (dzos and stols) had a low pulmonary arterial pressure compared with cattle, while the medial thickness of the small pulmonary arteries was less than would be expected in cattle, suggesting that the yak has a low capacity for hypoxic pulmonary vasoconstriction and that this characteristic is transmitted genetically. Goats and sheep showed haemodynamic evidence of a limited response of the pulmonary circulation to high altitude, but no evidence that the high altitude breeds had lost this response. There were no measurable differences in the thickness of the media of the small pulmonary arteries between high- and low-altitude breeds of goats and sheep. All these species showed prominent intimal protrusions of muscle into the pulmonary veins but no specific effect of high altitude in this respect.     

The biomass of game animals in Nairobi National Park, 1960–66

The large animals of Nairobi National Park have been censused intermittently once a month from mid-1960 until the end of 1966. Of the 23 species discussed, the density per kilometre has been determined accurately for the following: Grant's gazelle, Thomson's gazelle, water-buck, impala, wildebeest, hartebeest, eland, buffalo, warthog, giraffe, zebra and ostrich. From these figures the biomass has been calculated for each species each year. After a peak biomass of 12,775 kg/sq. km during the drought of 1960–61 the population declined to and remained fairly level at about 5690 kg/sq. km from 1962 to 1966. This figure includes about 1050 kg/sq. km of cattle and sheep. The large predators account for only about 1.4 % of the total biomass of wild animals while removing about 15.5% from this group annually.     

Malaria: some considerations regarding parasite productivity

The complicated life cycle of Plasmodium is characterized by proliferative stages in each of its hosts--mosquito and vertebrate--that are interrupted by restrictive steps as it moves from one to the other. Productivity at each stage affects not only pathology but also the probability for successful transmission. This Opinion article briefly assesses what is known about productivity at each step and attempts, with limited success, to put each in the context of an entire cycle, sporozoite to sporozoite.     

Genetic variation within social insect colonies reduces parasite load

In colonies of social Hymenoptera (ants, bees and wasps), workers are often not very closely related to each other, because queens mate with several different males (polyandry) or because several functional queens are present (polygyny). Both characteristics increase genetic variation among the queens'' reproductive and worker offspring, but the benefits of this increased variation remain obscure. Here we report an experiment where genetically homogeneous and genetically heterogeneous colonies of the bumble bee, Bombus terrestris, have been exposed to parasitism under field conditions. Colonies of high or low genetic variation were achieved by adding and removing brood from donor colonies. The results showed a consistent effect in that genetically variable colonies experienced reduced parasite loads, i.e. lower prevalence, intensity and parasite species richness, for a range of protozoa, nematodes, mites or parasitoids affecting the workers. We therefore propose that polyandry and/or polygyny of social insects may be beneficial under parasitism.     

Human African trypanosomiasis: connecting parasite and host genetics

In West and Central Africa, the protozoan parasite Trypanosoma brucei (T. b.) gambiense causes a chronic form of Human African trypanosomiasis (HAT) that might last several years, whereas T. b. rhodesiense refers to an acute form in East Africa that lasts weeks to months. Without treatment, both forms can cause death. Diagnosis relies on detecting parasites in blood, lymph or cerebrospinal fluid. HAT was no longer considered a public health problem in the 1960s, but it returned to alarming levels in the 1990s. After intensifying case detection and treatment, WHO recently declared the situation is under control. However, research based on host and trypanosome interactions should be encouraged to help develop innovative tools for HAT diagnosis and treatment to prevent re-emergence.     

Correlates of parasite load in bumblebees in an Alpine habitat

Essentially, all animals face parasites, but little data are available on the rate of parasitism in wild animals, particularly in insects. Here, we report observations of more than 400 bumblebee workers collected at an Alpine site, including the parasites observed (Crithidia bombi, Nosema bombi, conopid parasitoid fly larvae and tracheal mites), as well as date of collection, bumblebee species and body variables (size, fat content, egg development and antibacterial activity). Among the 14 bumblebee species collected, C. bombi and tracheal mites reached a prevalence of approximately 10 and 6%, respectively, while conopids and N. bombi were almost absent. Correlations among the measured parameters suggest that larger workers are more likely to develop eggs and contain more tracheal mites. Across the season, we found a decrease in fat content but an increase in C. bombi and mite prevalence. Mites’ fitness was higher in fatter bees and lower in bees with more tracheal mites. Antibacterial activity was found in approximately 10% of the workers, suggesting at least sporadic infection with bacteria.     

The distribution of phytoplankton in some Central East African waters

Summary Observations of the distribution of phytoplankton were made in Pilkington Bay, Lake Victoria and in Lake Kyoga. For Pilkington Bay, series of samples were taken along an east-west line in the north-west corner of the bay and along a north-south line through the mouth of the bay. For Lake Kyoga, the main series of samples was taken from the north-east arm to the point of inflow of the Victoria Nile.Counts of algae were made by the sedimentation technique and it was found that for Pilkington Bay Melosira was the dominant genus during the period of the investigation. For the north-east arm of Lake Kyoga the dominant alga in mid-August was Lyngbya limnetica.At times, marked changes not only in density of phytoplankton but also in vertical distribution were observed from station to station in Pilkington Bay.During May an increase of Melosira occurred in the north-west corner of Pilkington Bay and this increase is as likely to have been due to water movements as to growth.Water movements have an important effect on phytoplankton distribution and it is possible that surface water movements bring about inoculation of relatively dense concentrations of phytoplankton, especially Melosira, into the Buvuma Channel from Pilkington Bay.The contribution of the north-east arm of Lake Kyoga to the Victoria Nile system was found to be markedly different chemically and biologically from that of Lake Victoria.A number of new records of algae from Lake Kyoga are listed.

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Résumé Des recherches sur la distribution du phytoplancton furent poursuivies dans la baie de Pilkington, dans le lac Victoria et dans le lac Kyoga. A la baie de Pilkington, des séries d'échantillons furent prélevées sur une ligne allant de l'est à l'ouest et située dans la partie nord-ouest de la baie, ainsi que sur une ligne traversant du nord au sud l'entrée de la baie. Au lac Kyoga, la principale série d'échantillons fut prélevée à partir de sa pointe nord-est jusqu'à l'arrivée des eaux de la branche mère du Nil.Le dénombrement des algues fut fait selon le procédé de la sédimentation et les résultats de l'enquête indiquent que, dans la baie de Pilkington, Melosira était le genre le plus répandu pendant la durée des recherches. Quant à la pointe nord-est du lac Kyoga, l'algue la plus répandue, à la mi-août, était Lyngbya limnetica.A certains moments, des variations marquèes, non seulement dans la densité du phytoplancton mais encore dans sa distribution verticale, furent constatées de divers postes d'observation sur la baie de Pilkington.Pendant le mois de mai, il se produisit une augmentation de la quantité de Melosira dans la partie nord-ouest de la baie de Pilkington, augmentation qui semble provenir des mouvements de l'eau ainsi que de la croissance.Le mouvement de l'eau exerce une influence importante sur la distribution du phytoplancton et il est possible que les mouvements de surface de l'eau produisent l'augmentation dans la canal de Buvuma de concentrations assez denses de phytoplancton, de Melosira surtout, provenant de la baie de Pilkington.L'apport de la pointe nord-est du lac Kyoga au réseau de la branche mère du Nil se révéla de composition chimique et biologique sensiblement differente de celle du lac Victoria.Un certain nombre d'observations nouvelles des algues du lac Kyoga ont été notées.