The Late Palaeozoic phytoplankton blackout — Artefact or evidence of global change?

The fossil record of the Palaeozoic documents one of the most dramatic changes in Phanerozoic marine primary production, although causes and effects of these changes have been the subject of rather controversial discussions. During the early Palaeozoic the marine phytoplankton experienced an enormous radiation and diversification of taxa especially among acritarchs, which was punctuated by a few extinction events possibly associated with climate changes. Phytoplankton diversity was drastically reduced at the Devonian/Carboniferous boundary, a phenomenon here designated as the “Phytoplankton Blackout”.After a lapse of about 130 million years phytoplankton diversity was gradually restored during the Late Triassic with the appearance of dinoflagellates and somewhat later of coccolithophorids and diatoms. Evidence from recent phytoplankton suggests that the dominant groups of phytoplankton differ from those of the Palaeozoic in their nutritional requirements and that fundamental changes in ocean chemistry have played an important role.The remarkable temporal coincidence of the Phytoplankton Blackout with plate tectonic processes during the assembly and breakup of Pangaea and the concomitant rise of land plants towards the end of the Devonian provide arguments that nutrient depletion in the ocean may have played a decisive role in controlling the phytoplankton blackout. Contrary arguments in favour of oceanic eutrophication, changes in life cycles of dominant phytoplankton groups or selective preservation are discussed and weighed against the scenario presented here. Metazoan evolution seems only loosely linked with the phytoplankton blackout. However, there is good agreement between phytoplankton and reef evolution throughout the Phanerozoic.     

The telomere lengthening conundrum—artifact or biology?

Recent longitudinal studies of age-dependent leukocyte telomere length (LTL) attrition have reported that variable proportions of individuals experience LTL lengthening. Often, LTL lengthening has been taken at face value, and authors have speculated about the biological causation of this finding. Based on empirical data and theoretical considerations, we show that regardless of the method used to measure telomere length (Southern blot or quantitative polymerase chain reaction-based methods), measurement error of telomere length and duration of follow-up explain almost entirely the absence of age-dependent LTL attrition in longitudinal studies. We find that LTL lengthening is far less frequent in studies with long follow-up periods and those that used a high-precision Southern blot method (as compared with quantitative polymerase chain reaction determination, which is associated with larger laboratory error). We conclude that the LTL lengthening observed in longitudinal studies is predominantly, if not entirely, an artifact of measurement error, which is exacerbated by short follow-up periods. We offer specific suggestions for design of longitudinal studies of LTL attrition to diminish this artifact.     

The cell: locus or object of inquiry?

Research in many fields of biology has been extremely successful in decomposing biological mechanisms to discover their parts and operations. It often remains a significant challenge for scientists to recompose these mechanisms to understand how they function as wholes and interact with the environments around them. This is true of the eukaryotic cell. Although initially identified in nineteenth-century cell theory as the fundamental unit of organisms, researchers soon learned how to decompose it into its organelles and chemical constituents and have been highly successful in understanding how these carry out many operations important to life. The emphasis on decomposition is particularly evident in modern cell biology, which for the most part has viewed the cell as merely a locus of the mechanisms responsible for vital phenomena. The cell, however, is also an integrated system and for some explanatory purposes it is essential to recompose it and understand it as an organized whole. I illustrate both the virtues of decomposition (treating the cell as a locus) and recomposition (treating the cell as an object) with recent work on circadian rhythms. Circadian researchers have both identified critical intracellular operations that maintain endogenous oscillations and have also addressed the integration of cells into multicellular systems in which cells constitute units.     

The evolution of regeneration: adaptive or inherent?

If regeneration were adaptive, it would have arisen autonomously by natural selection from non-regenerative antecedents. Unless each episode coincidentally reinvented the same method of regeneration independently, one would expect the various lineages to differ basically from each other, which they do not. On the other hand, if regeneration were inherent to metazoan life, a derivative of embryogenesis, its various expressions should be as much like each other as they resemble the development of embryonic appendage buds, which they do. It follows that the uneven distribution of regeneration must have been due to its extinction here and there, not as a negative adaptation by natural selection but as a pleiotropic epiphenomenon linked to more useful adaptations with which it was incompatible. In vertebrate evolution, these adaptations have included the transition from aquatic to terrestrial habitats and the modification of poikilothermic to homeothermic metabolism. The former advance rendered the regeneration of weight-bearing limbs impractical; the latter favored rapid wound healing and scar formation which effectively precluded blastema formation. If the latent capacity for regeneration persists in non-regenerative appendages, as would seem to be the case, then the restoration of its overt expression should be possible if the mechanisms of its inhibition could be discovered and eventually rendered ineffectual.     

The Puzzle of Chuukese Mobility Patterns—Contradictory,Dualistic, or Pluralistic?

Education, employment, and health care are the three main reasons given by Micronesians for the ongoing flow of migrants to the USA. In many families, remittances constitute the only source of steady cash income. Therefore, migration is seen as part of the islanders’ subsistence strategy. Emotional implications for the individual are subsumed under the collective good. This paper will review migration motifs as experienced by chóón (people of) Chuuk, Federated States of Micronesia. With regard to kin relations, the value of family and notions of the self, focus is put on those who leave and/or come back as well as on those who make the decisions. Western spectators are often puzzled by the apparent contradictions between the adherence to traditional culture and the practices of modern life, between love for land and kin and the perceived necessity to nevertheless leave both behind. This paper thus aims to explore whether these dynamics are really in contradiction or rather parallel and interlocking dimensions of cultural concepts of locality and mobility that are connected to ideas of belonging.     

Mutualism or parasitism? The variable outcome of cleaning symbioses

The exact nature of many interspecific interactions remains unclear, with some evidence suggesting mutualism and other evidence pointing to parasitism for the same pair of interacting species. Here, we show spatial variation in the outcome of the cleaning relationship between Caribbean cleaning gobies (Elacatinus evelynae) and longfin damselfish (Stegastes diencaeus) over the distribution range of these species, and link this variation to the availability of ectoparasites. Cleaning interactions at sites with more ectoparasites were characterized by greater reductions in ectoparasite loads on damselfish clients and lower rates of removal of scales and mucus (i.e. cheating) by cleaning gobies, whereas the opposite was observed at sites where ectoparasite abundance was lower. For damselfish clients, cleaning was therefore clearly mutualistic in some locations, but sometimes neutral or even parasitic in others. Seasonal variability in ectoparasite abundance may ensure that locally low parasite availability, which promotes cleanerfish cheating, may be a transient condition at any given site. Conflicting conclusions about the nature of cleaning symbioses may, therefore, be explained by variation in ectoparasite abundance.     

Selfish or selfless? The role of empathy in economics

Empathy is a longstanding issue in economics, especially for welfare economics, but one which has faded from the scene in recent years. However, with the rise of neuroeconomics, there is now a renewed interest in this subject. Some economists have even gone so far as to suggest that neuroscientific experiments reveal heterogeneous empathy levels across individuals. If this were the case, this would be in line with economists'' usual assumption of stable and given preferences and would greatly facilitate the study of prosocial behaviour with which empathy is often associated. After reviewing some neuroscientific psychological and neuroeconomic evidence on empathy, we will, however, criticize the notion of a given empathy distribution in the population by referring to recent experiments on a public goods game that suggest that, on the contrary, the degree of empathy that individuals exhibit is very much dependent on context and social interaction.     

The antigenic evolution of influenza: drift or thrift?

It is commonly assumed that antibody responses against the influenza virus are polarized in the following manner: strong antibody responses are directed at highly variable antigenic epitopes, which consequently undergo ‘antigenic drift’, while weak antibody responses develop against conserved epitopes. As the highly variable epitopes are in a constant state of flux, current antibody-based vaccine strategies are focused on the conserved epitopes in the expectation that they will provide some level of clinical protection after appropriate boosting. Here, we use a theoretical model to suggest the existence of epitopes of low variability, which elicit a high degree of both clinical and transmission-blocking immunity. We show that several epidemiological features of influenza and its serological and molecular profiles are consistent with this model of ‘antigenic thrift’, and that identifying the protective epitopes of low variability predicted by this model could offer a more viable alternative to regularly update the influenza vaccine than exploiting responses to weakly immunogenic conserved regions.     

The mitochondrial theory of aging: dead or alive?

The mitochondrial theory of aging is based around the idea of a vicious cycle, in which somatic mutation of mtDNA engenders respiratory chain dysfunction, enhancing the production of DNA-damaging oxygen radicals. In turn, this is proposed to result in the accumulation of further mtDNA mutations. Finally, a bioenergetic crisis leads to overt tissue dysfunction and degeneration. A substantial body of circumstantial evidence seems to support this idea. However, the extent of detectable mtDNA mutation is far less than can easily be reconciled to this hypothesis, unless it is assumed that a subset of cells with much higher than average mtDNA mutation load is systematically lost by apoptosis. A rigorous test of the hypothesis remains to be undertaken, but would require a direct manipulation of the rate of mtDNA mutagenesis, to test whether this could alter the kinetics of aging.     

TRICHOMONAL VAGINITIS—The Problem of Chronic or Recurring Infection

In general practice and in gynecology, vaginal trichomoniasis is a frequent and troublesome problem. However, the trichomonas vaginalis organism is frequently found in an apparently healthy vagina, indicating that symptoms, recurrences, or exacerbations may depend on local changes in secretions, probably due in part to emotional stress. Therapy must, therefore, include not only the topical use of an effective trichomonacidal drug, but also sympathetic and considerate listening by the physician.The combination of furazolidone and nifuroxime in vaginal suppositories and vaginal insufflation powder was found to be an effective trichomonacidal compound. A total of 56 patients with trichomonal, monilial and nonspecific bacterial vaginitis was treated with this nitrofuran combination with good results.In topical therapy, powders seem more effective, probably because a dry environment is unfavorable to the flagellates. The patient should be instructed to insert two vaginal suppositories daily for the first week, then to decrease the dosage gradually as indicated by the physician after clinical examination and microscopic examination of vaginal secretions each week. Of great importance is the fact that some patients may need long-term maintenance therapy—one or two suppositories weekly—especially if the emotional difficulties appear to be insurmountable.