Directed mutagenesis indicates that the donor to P+680 in photosystem II is tyrosine-161 of the D1 polypeptide

Photosystem II contains two redox-active tyrosines. One of these, YZ, reduces the reaction center chlorophyll, P680, and transfers the oxidizing equivalent to the oxygen-evolving complex. The second, YD, has a long-lived free radical state of unknown function. We recently established that YD is Tyr-160 of the D2 polypeptide by site-directed mutagenesis of a psbD gene in the unicellular cyanobacterium Synechocystis 6803 [Debus, R. J., Barry, B. A., Babcock, G. T., & McIntosh, L. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 427-430]. YZ is most likely the symmetry-related Tyr-161 of the D1 polypeptide. To test this hypothesis, we have changed Tyr-161 to phenylalanine by site-directed mutagenesis of a psbA gene in Synechocystis. The resulting mutant assembles PSII, as judged by its ability to produce the stable Y+D radical, but is unable to grow photosynthetically and exhibits altered fluorescence properties. The nature of the fluorescence change indicates that forward electron transfer to P+680 is disrupted in the mutant. These results provide strong support for our identification of Tyr-161 in the D1 polypeptide with YZ.     

Genetic Manipulation of the Cyanobacterium Synechocystis sp. PCC 6803 (Development of Strains Lacking Photosystem I for the Analysis of Mutations in Photosystem II)

We have taken a genetic approach to eliminating the presence of photosystem I (PSI) in site-directed mutants of photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC 6803. By selecting under light-activated heterotrophic conditions, we have inactivated the psaA-psaB operon encoding the PSI reaction center proteins in cells containing deletions of the three psbA genes. We have also introduced deletions into both copies of psbD in a strain containing a mutation that inactivates psaA (ADK9). These strains, designated D1-/PSI- and D2-/PSI-, may serve as recipient strains for the incorporation of site-directed mutations in either psbA2 or psbD1. The characterization of these cells, which lack both PSI and PSII, is described.     

A synopsis of the genus Cypholoba Chaudoir (Coleoptera, Carabidae, Anthiini) known to occur in the Republic of South Africa

Nearly one third of the described species of Cypholoba Chaudoir (Coleoptera: Carabidae) are known to inhabit the Republic of South Africa. A key and diagnostic notes are provided for their identification, as well as notes about way of life for some of the species based on observations in the Kruger National Park. Fifteen species and subspecies of the genus are recorded from the Republic of South Africa; adult specimens of each species and subspecies are illustrated and information about the distribution of each species in the Republic of South Africa is summarized and mapped: Cypholoba alstoni (Péringuey), Cypholoba alveolata (Brême), Cypholoba amatonga Péringuey, Cypholoba fritschi (Chaudoir), Cypholoba gracilis gracilis (Dejean), Cypholoba gracilis scrobiculata (Bertoloni), Cypholoba gracilis zuluana Basilewsky, Cypholoba graphipteroides graphipteroides (Guérin-Méneville), Cypholoba leucospilota semilaevis (Chaudoir), Cypholoba macilenta (Olivier), Cypholoba notata (Perroud), Cypholoba oberthueri seruana Strohmeyer, Cypholoba opulenta (Boheman), Cypholoba rutata (Péringuey), and Cypholoba tenuicollis aenigma (Dohrn).     

Preliminary investigations into a potential ant invader in Kruger National Park,South Africa

The super‐abundance of Lepisiota incisa (Forel) in settlement areas of Kruger National Park, South Africa has raised concerns that it might be exotic and could negatively impact on natural ecosystems. We documented the current distribution of this ant species around the main settlement in Kruger, assessed how ant diversity varies across habitats, and investigated potential mechanisms facilitating dominance by L. incisa. Around the main camp of Skukuza, pitfall traps were set in five habitats differing in anthropogenic influence. Baiting trails were conducted to determine whether L. incisa and native ants differed in numerical and behavioural dominance. Aggression assays were performed on L. incisa to provide information on colony structure. Although L. incisa was found in all habitats, it had a significantly higher abundance in gardens and appears confined to human‐disturbed areas. It was numerically dominant recruiting more workers to food baits than all other ant species combined. Aggression levels were low between most nests of L. incisa indicating a potential supercolony structure. More information is urgently needed on the genetics, physiology and origins of L. incisa, and monitoring of its current distribution is recommended. This species warrants attention because there may be significant potential for overseas invasion.     

Diversity and abundance of insect visitors to flowers of trees and shrubs in a South African savannah

This study presents the results of a landscape‐scale survey for insect floral visitors in the Skukuza Ranger District, Kruger National Park, South Africa. Floral visitors were sampled from flowering trees and shrubs along linear transects spanning the entire district. Six plant species were sampled in the late dry season (Acacia grandicornuta Gerstner, A. nigrescens Oliver, Cassia abbreviata Oliver, Combretum hereroense Schinz, Combretum zeyheri Sonder, Euclea divonorum Hiern), and eleven plant species were sampled during the rainy season (Acacia exuvialis Verdcourt, A. grandicornuta Gerstner, A. nilotica (L.) Willdenow, A. tortilis (Forsskal) Hayne, Dichrostachys cinerea Miquel, Flueggea virosa (Roxburgh) Baillon, Grewia bicolor Jussieu, G. flava De Candolle, G. flavescens Jussieu, G. monticola Sonder, and Peltophorum africanum Sonder). Coleoptera, Hymenoptera and Lepidoptera comprised the majority of floral visitors, while species of Blattodea, Diptera, Hemiptera and Neuroptera also occurred on flowers. Known or likely pollinators include bees (Hymenoptera: Apidae, Halictidae and Megachilidae) and scarab beetles (Coleoptera: Scarabaeidae). These plant species appear to have generalist pollination systems, with the exception of species of Grewia L., which appear to be pollinated primarily by bees. A provisional plant–pollinator food web is presented for the eleven species of trees and shrubs which flower during the rainy season.     

Ethnicity and factionalism in Zimbabwe nationalist politics 1957–79

Four explanations of xenophobia and racism will be reviewed by confronting them with the results of empirical studies. I try to show that xenophobic and racist views of the social world are not instrumental to a fight for scarce jobs or housing. Neither is it appropriate to interpret them as a result of a culture clash that is caused by migratory movements across countries and continents. They are not mere radicalizations of the discourse of exclusion and devaluation which political and administrative elites generate and institutionalize, for example, in immigration policies. Starting from the insights of this critical review, I shall develop the hypothesis that xenophobia and racism should be seen as appeals to the pact of solidarity into which state and society have entered in modern nation‐states and which in times of intensified social conflicts seems fragile in the eyes of downwardly mobile groups. The xenophobic discourse serves not only to reassure identity when nationalistic self‐images run into crisis but is an element of a political struggle about who has the right to be cared for by the state and society: a fight for the collective goods of the modern state.     

The classification of wetlands: integration of top-down and bottom-up approaches and their significance for ecosystem service determination

The typology of wetlands provides important information for both water resource managers and conservation planners. One of the most important aims of allocating wetlands to a certain type or class is to provide information about the ecosystem services that the wetland provides. There are two main approaches towards wetland classification. Firstly, there are top-down approaches whereby wetlands are divided into several categories based on a conceptual understanding of how the wetland functions (mostly with regards to water flows). Secondly there are bottom-up approaches whereby the classification of wetlands is based on the collection of data in the wetland that is then subjected to various clustering techniques (mostly with regards to biodiversity). The most utilized system of top-down classification assigns wetlands into hydrogeomorphic units, which function as a single unit in terms of hydrology and geomorphology. This type of classification is most useful for water resource planning, as it provides information about how the wetland is connected to the drainage network and what are the water inflows, throughflows and outflows of the wetland. The bottom-up classification approach typically focusses on the classification of wetland habitats rather than complete wetlands, where wetland habitat represents a spatial unit delineated on the basis of vegetation, embedded within the (complete) hydrogeomorphic unit, and defined as an area of wetland that is homogeneous in terms of opportunities for plant growth. At a broad scale, most ecosystem services can be superficially derived from the hydrogeomorphic unit type and the way water moves through a wetland, but habitat units and the plant species that define them would have a specific effect on the delivery of ecosystem services, for example, with different assemblages providing different resistance to flow. Some types of ecosystem services are exclusively linked to specific wetland habitats, especially provisioning services. For this reason, it is proposed that a combined approach of hydrogeomorphic classification together with a vegetation map, offers the maximum information value for ecosystem service determination. In order to account for the potential pitfall of “double counting” when combining the top-down and bottom-up approaches, each service needs to be considered individually with reference to the degree to which a service is either: (a) primarily determined by HGM class/attributes and modified by the vegetation class/attributes; or (b) primarily determined by the vegetation class/attributes.     

Effects of host larval stage preferences and diet on life history traits of Diadegma mollipla,an African parasitoid of the Diamondback Moth

Knowledge of the biological attributes of parasitoids plays a fundamental role in improved management of their pest hosts. Diadegma mollipla is a major indigenous parasitoid of the Diamondback Moth (DBM), Plutella xylostella (Linnaeus), in Eastern Africa. Two laboratory experiments were conducted to determine the DBM larval stage preferences of D. mollipla and their influence on life history traits and the effect of different diets (20% honey, 20% sugar solution, water or nothing) on adult parasitoid longevity. In the first study, 60 DBM larvae (15 each of larval stages L1–L4) were exposed to either one adult parasitoid female or four competing females in choice experiments. When DBM larvae were exposed to one parasitoid, in terms of parasitism, L1 and L2 were found to be the most preferred stages, followed by L3 and then L4. Sex ratio (females/males) increased with host larval stage from 1.3 to 3.1. Pre-imaginal development time was longer in L1 than in the other three stages. When exposed to four parasitoids, no significant differences in parasitism rates and progeny production were obtained between DBM larval stages. However, sex ratio increased from 0.8 in L1 to 4.1 in L4. Developmental time was longest in L4, intermediate in L1 and L3, and shortest in L2. In the diet experiment, honey and sugar were found to significantly increase longevity for D. mollipla adults of both sexes. Overall, combined adult male and female longevity was 24.5, 9.9, 2.2 and 1.9 days when fed on honey, sugar, water or nothing, respectively.