Variable discrimination and asymmetric preferences in laboratory tests of reproductive isolation between cichlid colour morphs

Mating behaviour affects reproductive isolation and phenotypic differentiation. In Lake Tanganyika, the cichlid fish Tropheus moorii diversified into numerous, currently allopatric colour variants. Allopatric isolation is periodically interrupted by dispersal and secondary contact during lake level fluctuations, making long‐term differentiation partly dependent on assortative mating. Laboratory experiments with two moderately distinct morphs revealed assortative female preferences in one (Nakaku), but random mate choice in the other morph (Mbita). No discrimination was apparent between two subtly differentiated morphs (Chimba and Moliro). Tested against each other in a previous study, the highly distinct Moliro and Nakaku exhibited strong assortative preferences. The correlation between colour pattern similarity and mate discrimination suggests that allopatry and philopatric behaviour are less crucial for the maintenance of differentiation between highly distinct morphs than for more similar morphs. Interestingly, the asymmetric isolation in one pair of morphs is congruent with a pattern of unidirectional mitochondrial introgression between populations.     

On the food of Chironomus costatus (Chironomidae: Diptera) from a shallow freshwater pond in South India

A study has been made of the feeding of Chironomus costatus in a temporary fresh-water pond in South India. It was found that, irrespective of the size of the larvae, the food composition was the same. The larvae were non-selective feeders in that the organisms enumerated in the water were also found in the gut.     

Dinoflagellate Evolution: Speculation and Evidence*†

SYNOPSIS. Nuclear features of dinoflagellates that were used originally to support the Mesocaryota concept are reviewed. The fibrillar diameter of dinoflagellate chromatin, low level of chromosomal basic proteins, membrane attachment of chromosomes and swirl pattern observed in sectioned chromosomes are features that support a prokaryotic affinity. The presence of repeated and highly complex DNA, a S-phase of DNA synthesis in the cell cycle, presence of basic proteins, and the reinterpretation of extranuclear microtubules as a spindle support the contention that dinoflagellates are eukaryotes. This combination of prokaryotic and eukaryotic features suggests that dinoflagellates are a geologically old group and that perhaps they diverged from the higher eukaryotic lineage before evolution of eukaryotic chromatin but after the evolution of repeated DNA. The 2 patterns of carotenoid composition exemplified by the presence of peridinin or fucoxanthin suggest separate origins of dinoflagellate plastids, perhaps by prokaryotic and eukaryotic capture. It is suggested that the species possessing fucoxanthin obtained their plastids by capture of photosynthetic eukaryotes. A new class and order, Syndiniophyceae and Syndiniales, are proposed for the dinoflagellates with low chromosome numbers, V-shaped chromosomes, chromosomes containing a sufficient quantity of basic proteins detectable histochemically, possession of centrioles associated with mitosis, intracellular parasitism as a mode of nutrition, and lack of a cellular covering containing plates. Ultrastructural and paleontologic evidence indicates that the thecate is more primitive than the nonthecate condition. The Prorocentrales are considered to be primitive and their thecal construction is reinterpreted as having epithecal and hypothecal regions surrounding a flagellar pore region containing 7 plates. Acritarchs resemble cysts of modern dinoflagellates in size, structure, and chemical composition except for the absence of a polygonal excystment aperture and lack of any indication of transverse and longitudinal flagellar grooves on the acritarchs. The suggestion that some acritarchs may have dinoflagellate affinities is supported by the occurrence of modern dinoflagellates (Prorocentrales) which lack a theca of numerous polygonal plates and lack transverse and longitudinal flagellar arrangement. The Prorocentrales, as opposed to the more typical Dinophyceae, perhaps represent the type of organism that produced some acritarchs.     

Efficacy of Esbiothrin mosquito coils at community level in northern Tanzania

Field trials with mosquito coils containing 0.15% Esbiothrin at Usa River settlement, northern Tanzania, during 1986 achieved a 52% reduction in biting rates of Anopheles arabiensis Patton and a 73% reduction of Culex quinquefasciatus Say mosquitoes. No mosquito biting activity occurred during the coil burning period which started at 20.00 hours daily and lasted for an average of 8.6 h. A sociological survey indicated that the coils were favourably accepted and produced no serious side-effects.     

Photosynthesis, Ribulose-1,5-bisphosphate Carboxylase and Leaf Characteristics of Nicotiana tabacum L. Genotypes Selected by Survival at Low CO2 Concentrations

The photosynthetic characteristics (responses to CO₂ and light),ribulose-1,5-bisphosphate carboxylase (Rubisco) properties,and the size and number of cells of the mesophyll of Nicotianatabacum L. leaves of genotypes selected for survival at lowatmospheric CO₂ concentrations are described. When grown inthe greenhouse with nutrient solutions, the total dry matterproduction of the selected genotypes was 23% greater than thatof the parent genotype; this increase was related to a greaternumber of mesophyll cells of smaller size in the selected plantscompared to the parent. However, it was not related to changesin the photosynthetic characteristics nor to Rubisco properties.These results suggest that the increased dry matter accumulationof the selected genotypes is not due to a reduction in photorespirationnor an increase in the CO₂ assimilation rates. Rather, the selectionof haploid tobacco plantlets in low CO₂ has resulted in plantswith greater leaf area (shown in previous work), due to theproduction of more cells of smaller size and to lower respirationrates per unit of leaf dry mass (previous work), thus increasinglight capture, reducing the loss of assimilates and increasingtotal plant dry matter production. Key words: Photosynthesis, ribulose-1,5-bisphosphate carboxylase, leaf anatomy, tobacco, genotypes     

Pectolytic Activity by the Haustorium of the Parasitic PlantOrobancheL. (Orobanchaceae) in Host Roots

The possible involvement of enzymes in the penetration of intrusivecells of the parasitic angiospermOrobancheinto host root tissueswas studied using cytochemical and immunocytochemical methods.Pectin methyl esterase (PME) was detected, with specific antibodies,in the cytoplasm and cell walls ofOrobancheintrusive cells andin adjacent host apoplast. Depletion and chemical changes ofpectins in host cell walls were shown by histochemical stainingwith PATAg, which detects carbohydrates that are sensitive toperiodic acid, especially pectins, and with the monoclonal antibodiesJIM 5 and JIM 7 that label pectins with low and high rates ofesterification, respectively. Galacturonic sequences with lowrates of esterification were more abundant in host cell wallsadjacent to the parasite, which is consistent with pectin de-methylationby PME release from the parasite. Pectins were absent in middlelamellae and in host cell walls neighbouring mature intrusivecells of the parasite, consistent with further degradation ofpectins by other enzymes. These results provide the first directevidence for the presence and activity of a pectolytic enzymein the infection zone of the haustorium of a parasitic angiosperminsitu.Copyright 1998 Annals of Botany Company Broomrape;Orobanche; parasitic weed; haustorium; pectin methyl esterase; pectin; cell wall.     

The Location of Glutamine Synthetase in Leaf Cells and its Role in the Reassimilation of Ammonia Released in Photorespiration

The localization of glutamine synthetase within the cells ofbarley and pea leaves has been reinvestigated using either amechanical technique or rupturing of isolated protoplasts torelease the cellular organelles, and both differential and densitygradient centrifugation to separate them. In no case could wefind evidence for any significant association between glutaminesynthetase and the mitochondria; our results suggest that theenzyme is present in the chloroplast and the cytoplasm of bothspecies. Experiments with isolated mitochondria from spinachalso failed to provide any suggestion that these organellesmight contain glutamine synthetase. Thus there is no evidenceto support the hypothesis, published by others, that mitochondriareassimilate ammonia, released from glycine oxidation, by meansof their own glutamine synthetase. Further experiments werecarried out to see if glutamate dehydrogenase present in themitochondria could reassimilate ammonia under conditions inwhich the electron transport chain to oxygen was blocked. Althoughthere was some evidence for a small amount of assimilatory glutamatedehydrogenase activity under these conditions it was dependenton adding relatively high concentrations of ammonia and wasinsufficient to sustain the rate of recycling of NAD requiredfor glycine oxidation. The results were thus considered to becompatible with the operation of the photorespiratory nitrogencycle as previously published.