Whatever happened to the ‘microtrabecular concept’?

Keith Porter culminated his stellar career as the founding father of biological electron microscopy by acquiring, in the late 1970s, a high-voltage electron microscope (HVEM). With this magnificent instrument he examined whole-mounts of cultured cells, and perceived within them a structured cytoplasmic matrix he named the "microtrabecular lattice". Over the next decade Porter published a series of studies, together with a team of outstanding young colleagues, which elaborated his broader "microtrabecular concept." This concept posited that microtrabeculae were real physical entities that represented the fundamental organization the cytoplasm, and that they were the physical basis of cytoplasmic motility and of cell-shape determination. The present review presents Porter's original images of microtrabeculae, after conversion to a more interpretable "digital-anaglyph" form, and discusses the rise and fall of the microtrabecular concept. Further, it explains how the HVEM images of microtrabeculae finally came to be considered as an artifact of the preparative methods Porter used to prepare whole cells for HVEM. Still, Keith's "microtrabecular concept" foretold of our current appreciation of the complexity and pervasiveness of the cytoskeleton, which has now been found by more modern methods of EM to actually be the fundamental organizing principle of the cytoplasmic matrix. During the impending eclipse of Porter's microtrabecular concept in the late 1980s, many of Keith's colleagues fondly described the cell as being filled, not with protoplasm, but with "Porterplasm." Despite the fact that Keith's view was clouded by the methods of his time, it would be fitting and apt to retain this name, still today, for the ordered matrix of cytoskeletal macromolecules that exists in the living cell. In the end, the story of what happened to Porter's microtrabecular concept should be an object lesson in scientific hubris that should humble and inform all of us in cell biology, even today--particularly when we begin to think that our most recent methods and observations are achieving "the last word".     

Mitochondria and peroxisomes: Are the ‘Big Brother’ and the ‘Little Sister’ closer than assumed?

Mitochondria and peroxisomes are essential subcellular organelles in mammals. Despite obvious differences, both organelles display certain morphological and functional similarities. Recent studies have elucidated that these highly dynamic and plastic organelles share components of their division machinery. Mitochondria and peroxisomes are metabolically linked organelles, which are cooperating and cross-talking. This review addresses the dynamics and division of mitochondria and peroxisomes as well as their functional similarities to provide insight as to why these organelles share the fission machinery in evolutionary aspects.     

Competitive exclusion: phylogeography’s ‘elephant in the room’?

Phylogeographic and evolutionary research programmes have successfully elucidated compelling genetic signatures of earth history. Particularly influential achievements include the demonstration of postglacial recolonization patterns for high-latitude taxa and phylogenetic demonstration of the 'progression rule' along oceanic island chains such as Hawaii. While both of these major biogeographic patterns clearly rely on rapid dispersal over long distances, their phylogeographic detection also apparently relies on the competitive exclusion of secondary dispersers. Such exclusion could occur either between or within species and might reflect fitness differences between lineages or, alternatively, neutral demographic processes (e.g. 'high-density blocking'). Regardless, such spatial genetic patterns would be rapidly eroded were it not for the failure of subsequent dispersers to contribute genetically to newly colonized populations. In addition to its role in revealing colonization patterns, competitive exclusion may also explain the maintenance of historic phylogeographic disjunctions long after the original physical barriers to dispersal have ceased to exist. Additionally, some of the most persuasive evidence of competitive exclusion comes from studies of anthropogenic extinction, where surviving lineages have subsequently expanded their ranges, apparently benefitting from the demise of their prehistoric sisters. Broadly, these biogeographic paradigms are united by the 'disconnect' between dispersal and colonization success, the latter being heavily influenced by inter- and intraspecific competition. Despite its apparent importance, such exclusion (especially within species) has received virtually no attention in the phylogeographic literature. Future studies should aim to test directly for the role of competitive exclusion in constraining the biogeography of highly dispersive taxa.     

Quantitative floral phenology at the landscape scale: Is a comparative spatio-temporal description of ‘‘flowering landscapes’’ possible?

Entomophilous flowers form the food resources for insect pollinators. Many pollinator species forage at the landscape scale and depend on floral resources that are highly variable in space and time. We present a general model approach in which the floral resources of plant communities are estimated by the floral phenology and the cover of entomophilous plant species. We applied this landscape model in a case study for three landscape sections (1.5–2.2 km²) with strongly differing land-use patterns. The comparison between a conservation area and two agricultural landscapes shows extreme differences in the quantities and in the course of floral resources.

In a stepwise simplification of the landscape model we tested the effects of input data with lower spatio-temporal resolution. Even if input data for floral phenology and vegetation have a low resolution, the landscape model allows a ranking of landscape-specific floral resource potentials. The results of the case study encourage the use of landscape models to estimate floral resource potentials. The assessment of floral resource potentials may help to define this essential landscape quality for evaluation in practical nature conservation.     

The concepts of ‘plant functional types’ and ‘functional diversity’ in lake phytoplankton – a new understanding of phytoplankton ecology?

1. This is a discussion of the applicability to the phytoplankton of the concepts of ‘plant functional types’ (PFTs) and ‘functional diversity’ (FD), which originated in terrestrial plant ecology. 2. Functional traits driving the performance of phytoplankton species reflect important processes such as growth, sedimentation, grazing losses and nutrient acquisition. 3. This paper presents an objective, mathematical way of assigning PFTs and measuring FD. Ecologists can use this new approach to investigate general hypotheses [e.g. the intermediate disturbance hypothesis (IDH), the insurance hypothesis and synchronicity phenomena] as, for example, in its original formulation the IDH makes its predictions based on FD rather than species diversity.     

Do leaves contribute to the abscisic acid present in the xylem sap of ‘draughted’ sunflower plants?

Abstract. The root systems of 30-d-old sunflower plants were treated with polyethylene glycol (PEG; osmotic potential - 1.0MPa) for 2h, causing mild and transient wilting. Ten minutes before this treatment was applied, half the plants were defoliated. At varying times after the imposition of the PEG 'drought stimulus', the plant stems were cut and the sap exudate was collected and analysed for abscisic acid (ABA), using an elisa method. When stems were cut 2.25h after the treatments were applied, the ABA concentration in the sap of the controls did not vary with time: the mean concentration was 10.7 ± 1.0μ, mol m⁻³. However, in the treated plants, the first sample contained 78.1 ± 10.1 μmol m⁻³, decreasing to 13.6 ± 2.8 μmol m⁻³ over 8.75h. Defoliation did not affect the ABA concentration in the sap. When stems were cut at varying times (up to 25h) after treatment, the PEG treatment again caused an immediate increase in the ABA concentration in the sap, from 20 ± 1 to 136 ± 21 μmol m⁻³. However, defoliation reduced this increase, but only in plants sampled 4–25h after treatment. We conclude that, after the PEG treatment to the roots, the initial increase of the ABA content of sap, and its attenuation with time, may be ascribed to synthesis in the roots whereas, thereafter, ABA derived from the leaves makes a major contribution to the ABA found in the xylem sap.     

Does acoustic priming ‘sweeten the pot’ of floral nectar?

A recent claim that evening primrose flowers adaptively secrete nectar in response to vibrations from hovering bees lacks supporting evidence. The authors fail to demonstrate that bees can access the concealed nectar and that their visits enhance plant fitness. Reanalysis of the authors’ data raises additional concerns about their conclusions.     

Omarakana revisited,or ‘do dual organizations exist?’ in the Trobriands

Omarakana is arguably the most renowned village in the Trobriand and anthropological worlds. It is the very centre and wellspring of the North Kiriwinan universe and thus a sacred site, serving as the home of the Tabalu chiefly paramountcy. For us anthropologists, it is ground zero for our field methodology, thanks to Malinowski's pioneering research, and probably Melanesia's most hierarchical polity. Ironically, though, very little is actually known ethnographically about Omarakana's spatial layout. In this article I seek to compensate for that deficiency, arguing that Omarakana's seemingly concentric contours encode transformations of indigenous symbolism involving recurrent metaphors drawn from at least three conjoined semantic contexts of wide distribution across the Austronesian sphere and beyond: the double bisection of ‘male’ versus ‘female’; the botanical imagery of ‘base’, ‘body’, ‘tip’, and ‘fruit’; and various elements of ‘canoe’ symbolism. This alternative view of Omarakana's spatio‐temporal plan sheds new light on various additional dimensions of Trobriand sociality and cosmology while elaborating classic and contemporary anthropological theories of dualism.     

Herb endozoochory by cockatoos: Is ‘foliage the fruit’?

Establishing whether herb seed endozoochory is accidental or has evolved independently or in combination with other dispersal mechanisms may be valuable in the study of plant–animal interactions, but it remains unexplored for birds. We tested whether an Australian cockatoo, the galah (Eolophus roseicapilla), swallows entire seeds when feeding on other tissues without subsequent seed digestion, thus enhancing seed dispersal (the ‘foliage is the fruit’ hypothesis). Our preliminary sampling provides strong evidence supporting that this seed predator also acts as a legitimate endozoochorous disperser. A large proportion of droppings contained numerous seeds of six herb species of three plant families, surviving gut passage to be dispersed as viable propagules. The wide range in the number of seeds found in combinations with up to five species in particular droppings suggests both simultaneous and sequential passive ingestion without seed digestion and/or focused seed predation and digestion. As expected for inadvertent ingestion and inefficient digestion, our findings suggest that seed number and richness of dispersed plants are associated traits in this particular mutualistic interaction. This relationship can have important implications in community‐wide processes, favouring herbs whose seeds are disseminated in a viable state over those predated or negatively affected by gut transit.     

‘Do you have a mobile?’ Mobile phone practices and the refashioning of social relationships in Port Vila Town

Mobile phones have quickly become an important part of young people's social relationships in Port Vila Vanuatu. In particular, young people embrace the new technology's capacity to broaden the breadth of their sociality. They use the mobile phone to facilitate private and secretive communication, engage in unsanctioned relationships, pre‐marital sexual relationships, and also multiple concurrent intimate relationships. Literature on mobile phone use often either takes the approach that mobile phone technology becomes purely incorporated into pre‐existing social practices, or that it dramatically reshapes social ontologies. The present article argues for an alternative view, one that takes into account the nuances between these two analytical poles. This article suggests that young people use the mobile phone in practices informed by previous models of social relationships, yet the specific materiality of the mobile phone technology is influencing the direction in which models of social relationships are changing. In demonstrating this point, I pay particular attention to two material aspects of the mobile phone technology ‐ the mobile phone as a repository of a particular kind of information ‐ ‘evidence’, and the capacity of the mobile phone to ‘disconnect’ people from their relationships by switching off the mobile. This article argues that these practices are influencing the emergence of a radically altered kinship and gender landscape in the urban context.     

Spermatogenic ultrastructure in the anomalodesmatan bivalve Myochama anomioides (Mollusca: Myochamidae) – does the nucleus help position the ‘temporary’ acrosome?

Spermatogenic ultrastructure in the marine bivalve mollusc Myochama anomioides (Myochamidae) is described and contrasted with other bivalves, especially other euheterodonts. Small (0.1 μm diameter), primary proacrosomal vesicles produced in spermatocytes give rise to much larger (0.4 μm diameter) secondary proacrosomal vesicles in early spermatids, which in turn form the dished‐shaped, definitive acrosomal vesicle (diameter 1.0 μm) of later spermatids. The acrosomal vesicle acquires a deposit of subacrosomal material and comes to lie close to or in contact with the plasma membrane. The acrosomal complex (acrosomal vesicle + subacrosomal material) initially positions itself at the apex of the condensing, fibrous nucleus (the so‐called temporary acrosome position), but subsequently begins to move posteriorly. The condensing nucleus becomes markedly folded so that its apex is posteriorly orientated towards the migrating acrosomal complex and the midpiece (mitochondria and centrioles). The close spatial relationship of nuclear apex to acrosomal complex during this folding strongly suggests that acrosomal migration in M. anomioides is assisted, at least in part, by movement of the late spermatid nucleus. Similar nuclear folding has previously been demonstrated in an early stage of fertilization in another anomalodesmatan (Laternula limicola) raising the possibility that one event might be a reversal of the other.     

The ‘kinetochore maintenance loop’—The mark of regulation?

Kinetochores can form and be maintained on DNA sequences that are normally non‐centromeric. The existence of these so‐called neo‐centromeres has posed the problem as to the nature of the epigenetic mechanisms that maintain the centromere. Here we highlight results that indicate that the amount of CENP‐A at human centromeres is tightly regulated. It is also known that kinetochore assembly requires sister chromatid cohesion at mitosis. We therefore suggest that separation or stretching between the sister chromatids at metaphase reciprocally determines the amount of centromere assembly in the subsequent interphase. This reciprocal relationship forms the basis of a negative feedback loop that could precisely control the amount of CENP‐A and faithfully maintain the presence of a kinetochore over many cell divisions. We describe how the feedback loop would work, propose how it could be tested experimentally and suggest possible components of its mechanism.     

Was the Oligo‐Miocene Australian metatherian Yalkaparidon a ‘mammalian woodpecker’?

One of the most striking examples of convergent evolution within mammals is the suite of anatomical specializations shared by the primate Daubentonia of Madagascar and the marsupial Dactylopsila of Australia and New Guinea. Having last shared a common ancestor over 125 million years ago, these two genera have independently evolved extremely similar adaptations for feeding on xylophagous (wood-boring) insect larvae. These include enlarged incisors to gouge holes in wood, cranial modifications to strengthen the skull against the stresses generated by wood gouging and elongate manual digits that are used as probes to extract the larvae. Elsewhere in the world, the same ecological niche is filled by birds (woodpeckers or morphologically convergent forms) that use their beaks for wood gouging. An extinct group of eutherian mammals, the apatemyids, exhibit very similar craniodental and postcranial adaptations to Daubentonia and Dactylopsila and presumably also occupied the woodpecker niche. A qualitative analysis of characters of the skull and dentition of the enigmatic Oligo-Miocene Australian metatherian Yalkaparidon – specifically its combination of very large, open-rooted incisors, zalambdodont molars and features to strengthen the skull against rostral bending – supports the hypothesis that it is probably a fourth 'mammalian woodpecker'. Discovery of the (as yet unknown) manus of Yalkaparidon will test this hypothesis by revealing whether any of its digits are elongate.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 1–17.