Microtine ultradian rhythm of activity: an evaluation of different hypotheses on the triggering mechanism

Ultradian activity rhythms are a peculiar behavioural pattern, in which the 24-h day is divided into several short-term activity cycles. Such patterns are particularly prominent in microtine rodents. In this paper we review experimental findings and proposed hypotheses on the proximate triggering mechanism of ultradian rhythmicity. Eight different mechanisms (classified as homeostatic, pacemaker and stochastic hypotheses) were analysed within the same theoretical model-framework, considering feeding, food processing, energy turnover and activity behaviour.
Ultradian activity patterns could consistently be generated by each of the analysed models. None of the models, however, resulted in frequency dependencies in respect to body weight, metabolic rate, food quality and food deprivation, unless additional assumptions were introduced.
From our model evaluations we concluded that the stochastic model does not represent an independent hypothesis. Hence, only homeostatic and pacemaker hypotheses remained as alternative approaches to the triggering mechanism. Although the pacemaker hypothesis appeared more reasonable, a combination with some feedback mechanism to metabolism seemed even more likely. Some key experiments are suggested, which could give insight into the complex mechanism.     

Degradation of Chitotetraose to Chitobiose in the Axenic Rape Rhizosphere

In the presence of intact roots of 2-week-old axenic rape seedlings,added N, N', N', N'-tetraacetylchitotetraose was degradedto N, N'-diacetylchitobiose during 48 h of incubation. Onlyminute amounts of monomer (N-acetyglucosamine) were formed fromadded chitotetraose or chitobiose. The addition of a purifiedchitin suspension caused no measurable formation of degradationproducts. The formation of chitobiose from added chitotetraose was linear,suggesting the action of a constitutive enzyme during the incubationperiod. Key words: Brassica napus (L.) cv. Brink, rhizosphere, N, N'-diacetylchitobiose, N,N',N',N', tetraacetylchitotetraose     

Sheinwoodian (Silurian) conodonts and graptolites from NE Anti‐Atlas,Morocco

Männik, P., Loydell, D.K. & Lubeseder, S. 2010: Sheinwoodian (Silurian) conodonts and graptolites from NE Anti‐Atlas, Morocco. Lethaia, Vol. 44, pp. 410–416. Conodonts and graptolites from a limestone at the base of the Tamaghrout Formation indicate that this is of early Wenlock age. This is the first unequivocal dating of a Sheinwoodian limestone from Morocco. All of the conodonts are known also from several other regions and suggest that there was no major difference in conodont faunas in northern Gondwana, Baltica and Laurentia at this time. Biostratigraphy, conodonts, graptolites, Morocco, Silurian, Sheinwoodian.     

On the Question of Stem Polarity with Respect to Auxin Transport

The effect of section length and number of longitudinally contiguous cells upon polar transport of natural auxin from the pine stem cambial region was investigated with oat coleoptile curvature tests. Basipetal and acropetal efflux of auxin to agar declines with increasing length of the sections, but the polarity quotient varies little and is similar to the polarity of individual cells. An integrated system of cells produces a wave along the stem in the efflux of auxin from consecutive segments. The possible role of such waves in development of polarity gradients and of the morphogenic maps of orientation of cells in the stem cambial region is discussed.     

THE LOWER CAMBRIAN FOSSIL TOMMOTIA

The genera Tommotia Missarevskij 1970 (1966) and Camenella Missarevskij 1966 from the Lower Cambrian Tommotian Stage of the Siberian Platform represent different skeletal parts of the same organism and are consequently synonymous. Tommotia is selected as the valid name. Tommotia baltica n.sp. is described from the Lower Cambrian zone of Mobergella holsti of the Kalmarsund area in the southern part of the Baltic Sea. The Lower Cambrian families Tommotiidae Missarzevskij 1970 (1969) and Tannuolinidae Fonin & Smirnova 1967 show important similarities in their basic structure and are brought together in the new order Mitrosagophora, characterized by a composite outer skeleton with two types of skeletal elements, termed 'mitral' and 'sellate', each occurring in symmetrical pairs. The group is of uncertain systematic position but may have affinities with the Machaeridia.
The Scandinavian zone of Mobergella holsti is correlated with the Siberian zone of Dokidocyathus lenaicus and Majatheca tumefacta , the uppermost zone of the Tommotian Stage.     

Female polymorphism, condition differences, and variation in male harassment and ambient temperature

Female polymorphism is considered to be maintained through negative frequency-dependent selection imposed by costly male harassment. However, few studies have questioned whether male harassment negatively affects female morph success and does so differently for female morphs, especially in the wild. In the present study, we quantified female morph condition (relative body mass and energy reserves) for a colour polymorphic damselfly under natural conditions and evaluated these measures against variation in proxies of male harassment (population density and operational sex ratio) and ambient temperature. Differences in protein content between female morphs were detected and the variation in condition could partly be explained from concomitant variation in proxies of male harassment. Specifically, the relationship between protein content and operational sex ratio differed between morphs in that the negative effect of male harassment was more pronounced in gynomorphs than in andromorphs. In addition, ambient temperature affected the body mass and protein content of female morphs differently, with andromorphs having higher condition values in favourable weather conditions, whereas, for gynomorphs, the patterns tended to be opposite. In conclusion, the results obtained in the present study suggest that male harassment negatively and differentially affects female morph success. Future studies should aim to elucidate whether the observed effects of ambient temperature contribute to the maintenance of the polymorphism.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 545–554.     

Antigenic Analysis of Virulent and Avirulent Strains of Trichomonas gallinae by Gel Diffusion Methods*

SYNOPSIS. Antigenic constitution of 5 Trichomonas gallinae strains and substrains was analyzed by gel diffusion technics. Fresh isolates of the very virulent JB and of an avirulent SG strain as well as avirulent substrains JBC and SGC, derived from JB and SG respectively by prolonged in vitro cultivation, were used in the experiments. An originally avirulent AG strain that was attenuated still further and lost its infectivity for pigeons during many years of serial transfers in nonliving media also was analyzed. Two major groups of antigens, A and B, were differentiated on the basis of precipitin line patterns formed in gel diffusion reactions involving the 5 strains and substrains and antisera prepared in rabbits against each of these trichomonad stocks. Group A was subdivided further into subgroups [A] and (A). JB, JBC, AG, and SGC trichomonads appeared to share all or nearly all antigens of both these subgroups, but AG strain contained some unique [A] and (A) antigens in addition to those which it had in common with the remaining 4 strains and substrains. Group B antigens were divided into 5 subgroups, B₁ to B₅. The complete B₁ antigenic complex was found in JB and JBC trichomonads and part of this complex was present also in SG strain and SGC substrain. In all instances, subgroup B₁ antigens stimulated production of specific antibodies in rabbits and combined with these antibodies present in immune sera. The complete B₂ antigenic complex was found only in JBC substrain. Some subgroup B₂ antigens were present also in JB trichomonads. Very few of these, however, were capable of stimulating antibody production in rabbits. The more numerous B₂ elements of JB strain that did not stimulate immunologic responses in rabbits, might be in the form of incomplete hapten-like antigens. All subgroup B₂ antigens found in JB strain represented only a portion of the B₂ complex associated with JBC substrain. Subgroup B₂ was characteristic of SG and SGC trichomonads, the latter substrain differing from the parental SG strain in the levels of both B₂ and B₁ antigens; these differences, however, were purely quantitative. JB strain reacted with some of subgroup B₃ antibodies present in SG and SGC antisera, but failed to stimulate antibody formation against any of these antigens in rabbits. The B₃ elements of JB trichomonads might be incomplete antigens. AG strain was characterized by having B₄ and B₅ antigenic complexes. The very small part of subgroup B₄, represented by a weak precipitin line in reactions between JB strain or JBC substrain and anti-AG serum, suggested the presence of some incomplete B₄ antigens in these trichomonads. Irrespective of whether freshly isolated avirulent strains or substrains attenuated by prolonged in vitro cultivation are examined by gel diffusion, such organisms are found richer in subgroup B antigens than the fully virulent JB trichomonads. All the results suggest that there may be a direct relationship between antigenic constitution and virulence of T. gallinae strains.     

Protein Targeting into Secondary Plastids1

ABSTRACT. Most of the coding capacity of primary plastids is reserved for expressing some central components of the photosynthesis machinery and the translation apparatus. Thus, for the bulk of biochemical and cell biological reactions performed within the primary plastids, many nucleus‐encoded components have to be transported posttranslationally into the organelle. The same is true for plastids surrounded by more than two membranes, where additional cellular compartments have to be supplied with nucleus‐encoded proteins, leading to a corresponding increase in complexity of topogenic signals, transport and sorting machineries. In this review, we summarize recent progress in elucidating protein transport across up to five plastid membranes in plastids evolved in secondary endosymbiosis. Current data indicate that the mechanisms for protein transport across multiple membranes have evolved by altering pre‐existing ones to new requirements in secondary plastids.