Fine Structure of Exoerythrocytic Merozoite Formation of Plasmodium berghei in Rat Liver1

The fine structure of exoerythrocytic merogony of Plasmodium berghei was studied after perfusion-fixation of rat livers from 51 h post-inoculation onwards. Meroblast formation was effected by clefts originating from the parasite plasmalemma and by fusion of vacuoles with each other. Invaginations at the periphery resulted in labyrinthine structures providing the parasites with an enormous increase in surface area, which might facilitate exchange of metabolites. When the parasitophorous vacuole membrane collapsed, the newly formed merozoites were lying free in the hepatocytic cytoplasm, which degenerated until the merozoites were sticking together by a stroma, obviously a remnant of the host hepatocyte. Groups of merozoites, still kept together by the spongy stroma, were subsequently released in the bloodstream. At 53 h most of the developmental stages leading to the release of merozoites could be found and thereafter parasite numbers decreased while large granulomas became apparent.     

Aedes polynesiensis in the Society Islands: environmental correlates of isoenzyme differentiation

Abstract Isoenzyme genetic differentiation of Aedes polynesiensis mosquitoes in Raiatea island, French Polynesia, was evaluated by two models of population structure based on seven gene-enzyme systems: Ak, Est, Got, Gpi, Hk, Mdh and Pgm. The ecological model tested whether genetic differentiation is congruent with habitat differences. The isolation model evaluated whether genetic differentiation is proportional to geographical distribution. The ecological model found no significant differentiation between populations of Ae.polynesiensis from beach and forest ecotopes, whereas the isolation model was consistent with the data. However, incipient speciation is opposed by the source-sink system of population dynamics in such small neighbouring islands, where Ae.polynensiensis extinction is readily followed by reinvasion causing considerable gene flow between island populations.     

The past history and recent decline of Badgers Meles tneles in Essex: an analysis of some of the contributory factors

The past history of the Badger in Essex is reviewed. It is shown that the population has fluctuated in the past, and that heavy gamekeeping pressure probably reduced numbers at the turn of the century, although Badgers were probably never as rare as early recorders believed. In recent years Badgers have been rare or absent in many areas of the county because they did not afford suitable sett sites, and the county as a whole is not particularly good for Badgers. Against this already low-density Badger population, in the 20 years up to the mid-1980s, 36 % of known setts had disappeared, with agricultural activities being the major cause of sett losses, and of the remaining setts there was a 14 % reduction in the number occupied by Badgers. Also, the modal sett size was reduced from six holes to three. Direct disturbance affected nearly a quarter of all viable setts in Essex. The significance of these findings is evaluated, and the effects of changing land use, sett disturbance, Badger digging, road deaths and sub-lethal levels of agricultural chemicals on Badger numbers are discussed and quantified where possible. The possible effects of a continued fragmentation of the Badger population in Essex is reviewed. The need for further research on particular aspects of the problem, and the value of such data in understanding the population pressures facing the Badger elsewhere in Europe, are highlighted.     

Use of the Pressure Bomb for Hydraulic Conductance Studies

Stem sections of alfalfa (Medicago sativa L.) were subjectedto forced flows of both water and high molecular weight dextransolutions. In either case, stems responded in accordance withthe Ohm's law analogy for flow, i.e., flow was a linear functionof pressure, at pressures ranging from 7.0–500 kPa andvacuum from 25.69 kPa. Since conductance values were the samefor both pressure and vacuum powered flows, it is possible toextrapolate conductance values determined with a pressure bombto negative pressure gradients experienced by plants. Key words: Pressure bomb, Conductance, Medicago sativa     

The Bornean Lithocarpus B1. section Synaedrys (Lindl.) Barnett (Fagaceae): its circumscription and description of a new species

The Bomean species of Lithocarpus B1. section Synaedrys edl.) Barnett (Fagaceae) are discussed in terms of their unifying characteristics, and keys to the species are provided. A novel morphological feature present in the genus, where the seed in the mature fruit is enclosed by a lignified and thickened receptacle, is illustrated. A new species, L palungensis Cannon & Manos, is described. It can be distinguished from L. pulcher (King) Markgr. by its submontane distribution, prominent reflexed cupular spines, present at all stages, and broadly oblong leaves with scattered open fasciculate trichomes on the abaxial surface. Foliar trichome types present within the section are also described. Distinctiveness of fruit wall and receptacle shape, as described by two-dimensional elliptic Fourier transformation, is demonstrated by principal components analysis.     

Tropical dry and wet season polyphenism in the butterfly Melanitis leda (Satyrinae): Phenotypic plasticity and climatic correlates

Changes in wing pattern, colour, shape and size associated with seasonal polyphenism in Melanitis leda were quantified using a series of 155 butterflies collected by N. Manders on Mauritius in 1905. Butterflies of the wetter period were predominantly of the wet season form with large, well differentiated eyespots, short tails, smaller wings and a characteristic background colour. The dry season form occurred only in the drier period and has much smaller eyespots, longer tails, larger wings and a variable background. Many intermediates occurred, mainly in the drier period. These are associated with an absence of extreme seasonal change in Mauritius. The first principal component (PCI) describing the morphometric and colour data is closely related to the wing form (r = 0.80). Regression analyses using temperature and rainfall data for the 8 weeks before each capture showed that about 40% of variation in PCI could be accounted for by temperature in weeks 2–3 before capture. Many of the characters measured are redundant; a subset of seven morphometric characters yields a closely similar PCI. Analysis of is subset in an additional sample of 70 M. leda from Kenya showed that the seasonal polyphenism overrides a small degree of sexual dimorphism. The results are discussed with regard to seasonal changes in adult activity, resting backgrounds and visual predation. Wing phenotype characters are part of an array of coordinated morphological and life history traits which include ovarian dormancy and fat body development in dry season adults. A partial independence occurs in the proximal control of these traits as indicated, for example, by the larger wing and tail size, and smaller eyespots of the small number of the wet season form captured in the drier period in comparison to those of the wetter months.     

Behavioural studies on the peppered moth Biston betularia and a discussion of the role of pollution and lichens in industrial melanism

We examined the resting behaviour during pairing and egg-laying of bred female Biston betularia (L.) after they were set free at wooded sites in Somerset and Cardiff. Moths were not released immediately on emergence but were held for three nights to overcome an initial period of flight activity. Females (N= 257) were placed on trunks, and on large and small branches of trees, especially oaks, over periods of several weeks in 1984, 1985 and 1986. Releases were not made within 50 m of any known survivor. One hundred and thirty-one pairings were observed. We also examined oviposition behaviour in a cage experiment using different types of branches. Our observations support Mikkola's earlier conclusion from cage experiments with male moths that the species rests predominantly on branches and shows an appropriately specialized resting attitude, demonstrated here in a series of photographs. Many moths will rest underneath, or on the side of, narrow branches in the canopy. Once released females had settled and paired they only moved quite short distances, but positioning and egg-laying were profoundly influenced by the presence of foliose lichens. Females of all phenotypes show a strong preference to oviposit beneath a thallus of foliose lichens. Their tendency to rest against or close to the lichen during the day could markedly influence their crypsis. In the absence of foliose lichens, eggs are laid in cracks in the bark. The survivorship of released females both in different pairing combinations and during their whole reproductive life-span is analysed. These preliminary data suggest that bird predation can give rise to differential mortality of different pairing combinations and of the phenotypes. This technique provides a powerful method of measuring the relative crypsis and differential mortality of phenotypes with living females in natural resting sites. The significance of our observations on resting behaviour is discussed with regard to the role of air pollution and epiphytes in industrial melanism. Particular attention is given to the causal mechanisms underlying recent declines in the frequency of carbonaria melanics in parts of Britain. One important factor is the new growth made by trees since the marked reduction in particulate air pollution in the 1960s. It is emphasized that we need to know much more about the interactions between pollution, epiphytes and resting backgrounds, especially in the canopy, before we can be confident of our understanding of the evolution of industrial melanism.