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.     

Omnivory in lacertid lizards: adaptive evolution or constraint?

Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade-offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade-offs.     

Bt-maize in neotropical arthropod food webs: community-stress or lack thereof?

Although the agricultural use of genetically engineered (GE) plants has been employed extensively, its adoption is still controversial and its impact on arthropods has rarely been scrutinized at the community level. If this technology is aimed at a drastic reduction of a key community component, significant community-level impact is expected and needs to be assessed. Thus, food web analysis was used to assess the short-term impact of genetically modified maize plants, Zea mays L. (Poaceae), expressing insecticidal proteins of the bacterium Bacillus thuringiensis Berliner (i.e., Bt maize), on the associated arthropod assemblage in a neotropical scenario. Arthropods associated with winter and summer cultivations with Bt and non-Bt (isoline) maize were thus sampled using sweep nets and whole-plant collections throughout the plant phenological cycle. The collected information was used to build a plant-consumer-predator trivariate network based on data of individual arthropod body mass, numerical abundance, and biomass abundance using food web analysis. Eighty-five arthropod species were sampled, and whereas cultivation season significantly affected arthropod species richness and abundance, only marginal differences existed between maize hybrids (Bt vs. non-Bt). The recognized food webs also indicated significant differences between seasons. In contrast, Bt-maize-hosted food webs were similar to those of the non-Bt isoline indicating no significant impact on arthropod food webs. Nonetheless, Bt maize did not provide significant control of the target pest species, the fall armyworm, nor did it lead to higher crop yield, raising questions about its current usefulness in the region.     

Procreation machines: Ectogenesis as reproductive enhancement,proper medicine or a step towards posthumanism?

Full ectogenesis as the complete externalization of human reproduction by bypassing the bodily processes of gestation and childbirth can be considered the culmination of genetic and reproductive technologies. Despite its still being a hypothetical scenario, it has been discussed for decades as the ultimate means to liberate women from their reproductive tasks in society and hence finally end fundamental gender injustices generally. In the debate about the application of artificial wombs to achieve gender equality, one aspect is barely mentioned but is of crucial relevance from a medical-ethical perspective: whether and how could full ectogenesis be justified as a proper use of medicine? After characterizing the technology as a special form of human enhancement and as an extension of medical practice that goes beyond the traditional field of medicine, this paper critically assesses the theoretical possibilities of legitimizing this extension. We identify two ways of justification: either one argues that ectogenesis fulfils a proper goal of medicine (a justification we call pathologization), or one argues that the application of ectogenesis achieves a non-medical goal (which we call medicalization). Because it is important from a medical-ethical point of view to avoid an inappropriate instrumentalization or misuse of medicine and thus an undue medicalization of non-medical problems, a set of necessary conditions has to be met. It is doubtful whether full ectogenesis for non-medical purposes could fulfil these conditions. Rather, its comprehensive usage could be seen as a revolutionary modification of what it means to be human.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

The emergence of technology: A cultural step or long-term evolution?

There are two hypotheses to explain the emergence of the technical behaviour: (1) a sudden and fast appearance across the African continent; (2) a long period of emergence and consolidation before it began to spread. We defend this second hypothesis and suggest that the hominid project started around 3 Myr ago, with a ‘biofunctional’ stage. Later than 2.5 Myr, the ‘biomorphotechnical’ stage began (Mode 1), and, at around 1.7 Myr, another stage emerged and developed: the ‘biopotential’ stage (Mode 2). All these stages consist of a two-part process: innovation/emergence, and socialization/generalization of a technical mode.     

Microglia-mediated synaptic pruning as a key deficit in neurodevelopmental disorders: Hype or hope?

There is a consensus in the field that microglia play a prominent role in neurodevelopmental processes like synaptic pruning and neuronal network maturation. Thus, a current momentum of associating microglia deficits with neurodevelopmental disorders (NDDs) emerged. This concept is challenged by rodent studies and clinical data. Intriguingly, reduced numbers of microglia or altered microglial functions do not necessarily lead to overt NDD phenotypes, and neuropsychiatric symptoms seem to develop primarily in adulthood. Hence, it remains open for discussion whether microglia are truly indispensable for healthy neurodevelopment. Here, we critically discuss the role of microglia in synaptic pruning and highlight area- and age dependency. We propose an updated model of microglia-mediated synaptic pruning in the context of NDDs and discuss the potential of targeting microglia for treatment of these disorders.     

Measuring metacarpal cortical bone by digital x-ray radiogrammetry: a step forward?

Changes in metacarpal cortical bone mineral density (BMD) using digital x-ray radiogrammetry were studied in patients with early rheumatoid arthritis. After 1, 2, and 5 years, large BMD losses were found: -1.7%, -2.8%, and -5.6%, respectively. Elevated erythrocyte sedimentation rate and anti-cyclic citrullinated peptide levels were independent predictors of bone loss, indicating that the largest amount of bone loss was found in patients with severe inflammation and high production of auto-antibodies, who are known to be at the highest risk of developing radiological bone damage. Studies are needed about the spatial and time relationship between erosions and juxta-articular and metacarpal bone loss.     

Assimilation efficiency in birds: A function of taxon or food type?

• 1.1. We review the available measurements of assimilation efficiency in birds and find a strong dependence upon food ingested, regardless of bird taxa.
• 2.2. Assimilation efficiency in birds is about 75% for most food types, except plants (36.9%) and fruits (41%).

     

Genome evolution: extinction,continuation or explosion?

Darwin recognised the processes of speciation and the frequent extinction of species. We now understand many of the genome-scale processes occurring during evolution involving mutations, amplification, loss or homogenisation of DNA sequences; rearrangement, fusion and fission of chromosomes; and horizontal transfer of genes or genomes, including processes involving hybridisation and polyploidy. DNA sequence information, combined with appropriate informatic tools and experimental approaches such as generation of synthetic hybrids, comparison of genotypes across environments, and modelling of genomic responses, is now letting us link genome behaviour with its consequences. The understanding of genome evolution will be of critical value both for conservation of the biodiversity of the plant kingdom and addressing the challenges of breeding new and more sustainable crops to feed the human population.     

The staminal lever mechanism in Salvia L. (Lamiaceae): a key innovation for adaptive radiation?

Floral key innovations play a significant role in the discussion of adaptive radiation in plants. The paper brings together a brief review of morphological key innovations in plants, elucidating their evolutionary significance in flower–pollinator interactions, and new data on Salvia, a genus being examined as an example for presumed adaptive radiation. We hypothesize that the characteristic staminal lever mechanism functions as a key innovation. It is defined as a functional unit including the modification of stamens to lever-like structures, their reversible movement, and the organization of the remaining floral structures involved in the process of pollen transfer. We follow the assumption that structure and functioning of the staminal levers play a major role in the process of pollen deposition on the pollinator's body, and that minute changes of both their proportions and their interactions with pollinators may have significant consequences for the pollination system. The functioning of the staminal lever mechanism is tested by field investigations, biomechanical experiments and pollination simulations. First results are presented, and possible modes of allopatric and sympatric speciation are discussed, based on morphometry of Salvia flowers and pollinators as well as on the operating mode of the staminal lever mechanism. Special attention is given to species-specific patterns of pollen deposition on the pollinator's body. We assume that, depending on the precision of the lever movement, sympatric Salvia species flowering during overlapping periods and sharing the same pollinating species may be either mechanically isolated from each other or able to hybridize. The latter may result in speciation, as may spontaneous mutations influencing the flower-pollinator interaction, e.g. by significant changes in morphometry of the staminal lever system and/or other flower structures. As a consequence, Salvia individuals may deposit pollen on a different part of the pollinator's body, or even adapt to a new pollinator species, both resulting in reproductive isolation from the parental population.     

Haemoglobin C and S in natural selection against Plasmodium falciparum malaria: a plethora or a single shared adaptive mechanism?

Conclusive evidence exists on the protective role against clinical Plasmodium falciparum malaria of Haemoglobin S (beta 6Glu-->Val) and HbC (HbC; beta 6Glu-->Lys), both occurring in sub-Saharan Africa. However, the mechanism/s of the protection exerted remain/s debated for both haemoglobin variants, HbC and HbS. Recently, an abnormal display of PfEMP1, an antigen involved in malaria pathogenesis, was reported on HbAC and HbCC infected erythrocytes that showed reduced cytoadhesion and impaired rosetting in vitro. On this basis it has been proposed that HbC protection might be attributed to the reduced PfEMP1-mediated adherence of parasitized erythrocytes in the microvasculature. Furthermore, impaired cytoadherence was observed in HbS carriers suggesting for the first time a convergence in the protection mechanism of these two haemoglobin variants. We investigated the impact of this hypothesis on the development of acquired immunity against P. falciparum variant surface antigens (VSA) encoding PfEMP1 in HbC and HbS carriers in comparison with HbA of Burkina Faso. Higher immune response against a VSA panel and several malaria antigens were observed in all adaptive genotypes containing at least one allelic variant HbC or HbS in the low transmission urban area whereas no differences were detected in the high transmission rural area. In both contexts the response against tetanus toxoid was not influenced by the beta-globin genotype. Thus, these findings suggest that both HbC and HbS affect the early development of naturally acquired immunity against malaria. We reviewed the hypothesized mechanisms so far proposed in light of these recent results.     

Vertebrate genome evolution: a slow shuffle or a big bang?

In vertebrates it is often found that if one considers a group of genes clustered on a certain chromosome, then the homologues of those genes often form another cluster on a different chromosome. There are four explanations, not necessarily mutually exclusive, to explain how such homologous clusters appeared. Homologous clusters are expected at a low probability even if genes are distributed at random. The duplication of a subset of the genome might create homologous clusters, as would a duplication of the entire genome. Alternatively, it may be adaptive for certain combinations of genes to cluster, although clearly the genes must have duplicated prior to rearrangement into clusters. Molecular phylogenetics provides a means to examine the origins of homologous clusters, although it is difficult to discriminate between the different explanations using current data. However, with more extensive sequencing and mapping of vertebrate genomes, especially those of the early diverging chordates, it should soon become possible to resolve the origins of homologous clusters. BioEssays 21:697–703, 1999. © 1999 John Wiley & Sons, Inc.     

Phylogenetic,ontogenetic and adult adaptive plasticity of rhythmic neural networks: a common neuromodulatory mechanism?

Neuromodulatory inputs are known to play a major role in the adaptive plasticity of rhythmic neural networks in adult animals. Using the crustacean stomatogastric nervous system, we have investigated the role of modulatory inputs in the development of rhythmic neural networks. We found that the same neuronal population is organised into a single network in the embryo, as opposed to the two networks present in the adult. However, these adult networks pre-exist in the embryo and can be unmasked by specific alterations of the neuromodulatory environment. Similarly, adult networks may switch back to the embryonic phenotype by manipulating neuromodulatory inputs. During development, we found that the early established neuromodulatory population display alteration in expressed neurotransmitter phenotypes, and that although the population of modulatory neurones is established early, with morphology and projection pattern similar to adult ones, their neurotransmitter phenotype may appear gradually. Therefore the abrupt switch from embryonic to adult network expression occurring at metamorphosis may be due to network reconfiguration in response to changes in modulatory input, as found in adult adaptive plasticity. Strikingly, related crustacean species express different motor outputs using the same basic network circuitry, due to species-specific alteration in neuromodulatory substances within homologous projecting neurones. Therefore we propose that alterations within neuromodulatory systems to a given rhythmic neural network displaying the same basic circuitry may account for the generation of different motor outputs throughout development (ontogenetic plasticity), adulthood (adaptive plasticity) and evolution (phylogenetic plasticity).Abbreviations CoG Commissural ganglion - OG Oesophageal ganglion - STG Stomatogastric ganglion - STNS Stomatogastric nervous system     

Accelerated communciation: Constitutive μ opioid receptor activation as a regulatory mechanism underlying narcotic tolerance and dependence

Chronic administration of narcotic μ opioid agonists results in tolerance and dependence. We propose that agonist stimulation causes a gradual conversion of μ receptors to a constitutively active state μ¹ as a key step in tolerance and physical dependence. We provide evidence in support of the existence of μ¹ in human neuroblastoma cells, SH-SY5Y, and μ¹ upregulation during morphine treatment. Naloxone blocked μ¹ activity, acting as an antagonist with negative intrinsic activity which accounts for its high potency in eliciting withdrawal. In contrast, the μ selective antagonist CTAP did not affect μ¹ activity but inhibited naloxone's effect. The protein kinase inhibitor H7 was found to suppress μ¹ formation, suggesting that μ¹ is phosphorylated. In a model of acute morphine tolerance/dependence in mice, H7 prevented naloxone induced withdrawal jumping and reversed morphine (antinociceptive) tolerance. CTAP cause only mild withdrawal and attenuated naloxone induced withdrawal, as predicted for an antagonist without negative activity. These results support a role for constitutive μ receptor activation in narcotic tolerance and dependence, affording potential separation of acute and chronic narcotic effects.     

Was monogamy a key step on the hominin road? reevaluating the monogamy hypothesis in the evolution of cooperative breeding

Because human mothers routinely rely on others to help raise their young, humans have been characterized as cooperative breeders.^1–9 Several large‐scale phylogenetic analyses have presented compelling evidence that monogamy preceded the evolution of cooperative breeding in a wide variety of nonhuman animals.^10–14 These studies have suggested that monogamy provides a general rule (the monogamy hypothesis) for explaining evolutionary transitions to cooperative breeding.¹⁵ Given the prevalence of cooperative breeding in contemporary human societies, we evaluate whether this suggests a monogamous hominin past.