Origin of glutaminyl-tRNA synthetase: An example of palimpsest?

Sequence data and evolutionary arguments suggest that a similarity may exist between the C-terminal end of glutaminyl-tRNA synthetase (GlnRS) and the catalytic domain of glutamine amidotransferases (GATs). If true, this would seem to imply that the amidation reaction of the Glu-tRNA^GIn complex was the evolutionary precursor of the direct tRNA^GIn aminoacylation pathway. Since the C-terminal end of GlnRS does not now have an important functional role, it can be concluded that this sequence contains vestiges that lead us to believe that it represents a palimpsest. This sequence still conserves the remains of the evolutionary transition: amidation reaction aminoacylation reaction. This may be important in deciding which mechanism gave origin to the genetic code organization. These observations, together with results obtained by Gatti and Tzagoloff [J. Mol. Biol. (1991) 218: 557–568], lead to the hypothesis that the class I aminoacyl-tRNA synthetases (ARSs) may be homologous to the GATs of the trpG subfamily, while the class Il ARSs may be homologous to the GATs of the purF subfamily. Overall, this seems to point to the existence of an intimate evolutionary link between the proteins involved in the primitive metabolism and aminoacyl-tRNA synthetases.     

Paranthropus boisei: An example of evolutionary stasis?

Of the presently recognised early hominid species, Paranthropus boisei is one of the better known from the fossil record and arguably the most distinctive; the latter interpretation rests on the numbers of apparently derived characters it incorporates. The species as traditionally diagnosed is distributed across approximately one million years and is presently confined to samples from East African sites. The hypodigm has been examined for evidence of intraspecific phyletic evolution, with particular emphasis on the areas best represented in the fossil record, namely the teeth and mandible. The results of this examination of 55 mandibular and dental variables, which uses the Γ test statistic for the detection of trend, and nonparametric spline regression (Loess regression) for investigating pattern and rate of temporal change, show that within Paranthropus boisei sensu stricto most evidence of temporally related morphological trends relates to the morphology of the P₄ crown. There is little or no evidence of any tendency to increase in overall size through time. Fossils from the Omo Shungura Formation and West Turkana which have been recovered from a time period earlier than the P. boisei sensu stricto hypodigm resemble the latter taxon in some features, but differ from it in aspects of cranial morphology. There is insufficient fossil evidence of the earlier taxon to tell whether it changes through time, but when trends of 47 mandibular and dental variables are assessed across the combined East African “robust” australopithecine sample, there is evidence for a relatively abrupt change around 2.2–2.3 Myr in approximately 25% of the dental and mandibular remains. Some of these changes correspond with the temporal trends within P. boisei sensu stricto, but others, such as mandible height, do not. If the earlier material is ancestral to P. boisei sensu stricto, evidence from the teeth and jaws is consistent with a punctuated origin for the latter taxon. © 1994 Wiley-Liss, Inc.     

Flowering phenology: An example of relaxation of natural selection?

Flowering phenology has normally been viewed as fundamental to a plant species' reproductive ecology. Researchers in the field have emphasized the adaptive importance of flowering at a particular time relative to other individuals in the population, or other species in the community. An alternative view, however, is that flowering phenology is a trait that may not be under strong selection, and this may have allowed some variation to appear in populations by chance.     

Do predators prefer toxic animals? A case of chemical discrimination by an Asian snake that sequesters firefly toxins

Several Asian natricine snakes of the genus Rhabdophis feed on toads and sequester steroidal cardiac toxins known as bufadienolides (BDs) from them. A recent study revealed that species of the Rhabdophis nuchalis Group ingest lampyrine fireflies to sequester BDs. Although several species of fireflies are distributed in the habitat of the R. nuchalis Group, only lampyrine fireflies, which have BDs, are included in the diet of these snakes. Thus, we hypothesized that the R. nuchalis Group chemically distinguishes fireflies that have BDs from those that do not have BDs. We also predicted that the R. nuchalis Group detects BDs as the chemical cue of toxin source. To test these predictions, we conducted 3 behavioral experiments using Rhabdophis chiwen, which belongs to the R. nuchalis Group. In the first experiment, R. chiwen showed a moderate tongue flicking response to cinobufagin, a compound of BDs. On the other hand, the snake showed a higher response to the chemical stimuli of lampyrine fireflies (BD fireflies) than those of lucioline fireflies (non-BD fireflies). In the second experiment, in which we provided live BD and non-BD fireflies, the snake voluntarily consumed only the former. In the third, a Y-maze experiment, the snake tended to select the chemical trail of BD fireflies more frequently than that of non-BD fireflies. These results demonstrated that R. chiwen discriminates BD fireflies from non-BD fireflies, but the prediction that BDs are involved in this discrimination was not fully supported. To identify the proximate mechanisms of the recognition of novel toxic prey in the R. nuchalis Group, further investigation is necessary.     

Familial transmission of a dysmorphic syndrome: a variant example of Kabuki syndrome?

Familial transmission of a dysmorphic syndrome: a variant example of Kabuki syndrome?: We report a Romanian family with a dysmorphic syndrome in three generations: a boy, his mother and maternal grandfather, who all presented with the typical facial appearance, characteristic skeletal and dermatoglyphic findings of Kabuki syndrome, but no mental retardation, short stature and visceral abnormalities. The phenotype observed in this family may represent the mild end of a spectrum of clinical manifestations described in this condition. This report provides a further evidence for autosomal dominant transmission of the disorder.     

Selection of aphid prey by a generalist predator: do prey chemical defences matter?

1. For predators, prey selection should maximise nutrition and minimise fitness costs. In the present study, it was investigated whether a generalist predator [Chrysoperla carnea (Stephens) lacewing larvae] rejected harmful, chemically‐defended prey [Brevicoryne brassicae (Linnaeus) aphids] when non‐defended prey [Myzus persicae (Sulzer) aphids] were available. 2. It was tested: (i) whether consuming different prey species affects predator mortality; (ii) whether naïve predators reject chemically‐defended prey while foraging when non‐defended prey are available; (iii) whether the relative abundance of each prey affects the predator's prey choice; and (iv) whether predators learn to avoid consuming chemically‐defended prey after exposure to both prey species. 3. Consumption of B. brassicae yielded greater C. carnea mortality than M. persicae consumption, but naïve C. carnea did not reject B. brassicae in favour of M. persicae during foraging. When presented at unequal abundances, naïve predators generally consumed each aphid species according to their initial relative abundance, although, predation of non‐defended prey was less than expected when defended prey were initially more abundant, indicating a high consumption of B. brassicae impeded M. persicae consumption. With experience, C. carnea maintained predation of both aphid species but consumed more M. persicae than B. brassicae, indicating a change in behaviour. 4. Although prey choice by C. carnea may change with experience of available prey, prey chemical defences do not appear to influence prey choice by naïve predators. This inability to avoid harmful prey could facilitate wider, indirect interactions. Myzus persicae may benefit where high consumption of B. brassicae hinders predators in the short term, and in the long term, increases predator mortality.     

Is the firefly flash regulated by calcium?

The very different courtship flashes of Photuris versicolorand Photuris lucicrescens males mirror the pattern of neuralimpulses produced by their brain. Their lanterns luminescencevery differently, however, in response to direct, electricalstimulation. Whereas P. lucicrescens lanterns glow in responseto high frequency, continuous electrical stimulation, thoseof P. versicolor produce only rapid, triple-pulsed flashlettesthat resemble, but are not identical to, their courtship flashes.In addition, the exposed lantern tissue of P. versicolor males,when immersed in firefly saline high in potassium and calciumions, scintillates with hundreds of photocytes flashing in randomfashion. P. lucicrescens male lanterns, so treated, only glow.Tests of P. versicolor lanterns with salines of different compositionsuggest that calcium ions are essential in producing this intense,long lasting scintillation response and are therefore possiblyimplicated in the final stages of flash control in this species.     

Calcium: just a chemical switch?

The calcium-signature hypothesis has evolved as a concept to explain specificity in signaling pathways that utilise calcium as a second messenger. In plant biology, this hypothesis was purely conceptual and based only upon correlative observations until recently. In the past few years, however, empirical data have emerged from experiments that were specifically designed to tackle the question of how specificity is encoded by calcium. In light of the attractive calcium-signature hypothesis, other potential explanations for signalling specificity have been overshadowed and ignored: it has been assumed that the calcium-signature dogma will explain all plant calcium signaling. However, there is a good deal of evidence supporting a counter-hypothesis in which calcium does not itself encode specificity but is merely an essential 'switch' in signaling. At the very least, both hypotheses are likely to be true in different situations, and it may well be that the calcium-signature hypothesis describes the exception rather than the rule.     

Is abundance a species attribute? An example with haematophagous ectoparasites

Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that differ among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of fleas ectoparasitic on small mammals. The data included samples of 548 flea populations, representing 145 flea species and obtained from 48 different geographical regions. Abundances of the same flea species on the same host species, but in different regions, were more similar to each other than expected by chance, and varied significantly among flea species, with 46% of the variation among samples accounted by differences between flea species. Thus, estimates of abundance are repeatable within the same flea species. The same repeatability was also observed, but to a lesser extent, across flea genera, tribes and subfamilies. Independently of the identity of the flea species, abundance values recorded on the same host species, or in the same geographical region, also showed significant statistical repeatability, though not nearly as strong as that associated with abundance values from the same flea species. There were also no strong indications that regional differences in abiotic variables were an important determinant of variation in abundance of a given flea species on a given host species. Abundance thus appears to be a true species trait in fleas, although it varies somewhat within bounds set by species-specific life history traits.     

Agroforestry: a refuge for tropical biodiversity?

As rates of deforestation continue to rise in many parts of the tropics, the international conservation community is faced with the challenge of finding approaches which can reduce deforestation and provide rural livelihoods in addition to conserving biodiversity. Much of modern-day conservation is motivated by a desire to conserve 'pristine nature' in protected areas, while there is growing recognition of the long-term human involvement in forest dynamics and of the importance of conservation outside protected areas. Agroforestry -- intentional management of shade trees with agricultural crops -- has the potential for providing habitats outside formally protected land, connecting nature reserves and alleviating resource-use pressure on conservation areas. Here we examine the role of agroforestry systems in maintaining species diversity and conclude that these systems can play an important role in biodiversity conservation in human-dominated landscapes.     

Do aquatic macrophytes co-occur randomly? An analysis of null models in a tropical floodplain

One of the main issues in community ecology is the detection of structure and the identification of its related causes. In this study, co-occurrence null models were used to identify possible spatio-temporal patterns in the assemblage of aquatic macrophytes in the Upper Paraná River floodplain. The samples were obtained through the Long Term Ecological Research (LTER) Program at two different grains: (1) a coarser spatial grain in January and August 2001 (entire floodplain lagoons); (2) and a finer spatial grain in November 2006 (1 m² quadrats). The study was conducted in 36 lagoons, both connected and disconnected to the main river channel, located in the sub-basins of the Baía, Ivinheima and Paraná rivers. Two null models of species co-occurrence, the C-Score and Checkerboard indices, were used to test the null hypothesis of random structure of the aquatic macrophyte assemblages. The null models showed that the aquatic macrophyte assemblages were spatially structured in the distinct spatial grains. However, despite this general pattern, macrophyte assemblages are organized differently depending on the degree of connectivity, seasonal period and, at a finer grain, depth. Species co-occurrences were random in the disconnected lagoons during flood periods, in deep zones of the lagoons of the Baía River and in the shallow littoral zone in the lagoons of the Paraná River. Analysis of the patterns of co-occurrence indicated that competition and/or habitat preferences are probably important influences on the nonrandom structure of assemblages. However, we suppose that at least three important factors (disturbances by water level fluctuation, dispersion and facilitation) counteract potential effects of competition in specific situations, leading macrophyte assemblages to assume random structure.     

Schinzel acrocallosal syndrome: a variant example of the Greig syndrome?

A 5-month-old male is reported with clinical and radiological findings identical to those present in the Schinzel acrocallosal syndrome. The similarity with the Greig syndrome is discussed and the question is raised whether both syndromes are variant examples of the same autosomal dominant condition.     

Parasite diversity as an indicator of environmental change? An example from tropical grouper (Epinephelus fuscoguttatus) mariculture in Indonesia

Fish parasites are used to monitor long-term change in finfish grouper mariculture in Indonesia. A total of 210 Epinephelus fuscoguttatus were sampled in six consecutive years between 2003/04 and 2008/09 and examined for parasites. The fish were obtained from floating net cages of a commercially run mariculture facility that opened in 2001. The fauna was species rich, consisting of ten ecto- and 18 endoparasite species. The ectoparasite diversity and composition was relatively stable, with the monogeneans Pseudorhabdosynochus spp. (83-100% prevalence, Berger-Parker Index of 0·82-0·97) being the predominant taxon. Tetraphyllidean larvae Scolex pleuronectis and the nematodes Terranova sp. and Raphidascaris sp. 1 were highly abundant in 2003/04-2005/06 (max. prevalence S. pleuronectis 40%, Terranova sp. 57%, Raphidascaris sp. 1 100%), and drastically reduced until 2008/09. These parasites together with the prevalence of Trichodina spp., ecto-/endoparasite ratio and endoparasite diversity illustrate a significant change in holding conditions over the years. This can be either referred to a definite change in management methods such as feed use and fish treatment, or a possible transition of a relatively undisturbed marine environment into a more affected habitat. By visualizing all parameters within a single diagram, we demonstrate that fish parasites are useful bioindicators to monitor long-term change in Indonesian grouper mariculture. This also indicates that groupers can be used to monitor environmental change in the wild. Further taxonomic and systematic efforts in less sampled regions significantly contributes to this new application, supporting fish culture and environmental impact monitoring also in other tropical marine habitats.     

Indirect facilitation of a native mesopredator by an invasive species: are cane toads re-shaping tropical riparian communities?

Top predators can suppress mesopredators both by killing them and by motivating changes in their behavior, and there are numerous examples of mesopredator release caused by declines in top predator populations. Demonstrated cases of invasive species triggering such releases among vertebrate trophic linkages (indirect facilitation), however, are rare. The invasive cane toad, Bufo marinus, has caused severe population-level declines in some Australian predators via lethal toxic ingestion. During a long-term study of the direct impacts of cane toads on predatory monitor lizards in tropical Australia, we documented significant, marked increases in annual counts of a mesopredator, the common tree snake (Dendrelaphis punctulatus). Mean snake counts during surveys of 70-km river transects at two sites increased from <1 individual per survey during 2001–2006, to 8–18 per survey in 2007. These increases occurred approximately 3 years following the arrival of cane toads, and 1–3 years after 71–96 % population declines in three species of predatory monitor lizards (Varanus panoptes, V. mertensi, and V. mitchelli). These data suggest a mesopredator release: the dramatic reduction of predatory monitor lizards caused increases in the tree snake by decreasing predation risk. The increases in tree snake counts were not attributable to either abiotic factors, or a trophic subsidy. The severe declines of predatory monitor lizards, coupled with recent evidence of cascading effects on their prey, suggest that cane toads are re-shaping riparian communities in tropical Australia through both direct negative effects and indirect facilitation.     

Butterfly host plant range: an example of plasticity as a promoter of speciation?

Mary Jane West-Eberhard has suggested that plasticity may be of primary importance in promoting evolutionary innovation and diversification. Here, we explore the possibility that the diversification of phytophagous insects may have occurred through such a process, using examples from nymphalid butterflies. We discuss the ways in which host plant range is connected to plasticity and present our interpretation of how West-Eberhard’s scenario may result in speciation driven by plasticity in host utilization. We then review some of the evidence that diversity of plant utilization has driven the diversification of phytophagous insects and finally discuss whether this suggests a role for plasticity-driven speciation. We find a close conceptual connection between our theory that the diversification of phytophagous insects has been driven by oscillations in host range, and our personal interpretation of the most efficient way in which West-Eberhard’s theory could account for plasticity-driven speciation. A major unresolved issue is the extent to which a wide host plant range is due to adaptive plasticity with dedicated modules of genetic machinery for utilizing different plants.     

Can receiver psychology explain the evolution of aposematism?

The evolution of aposematism is difficult to explain because: (1) new aposematic morphs will be relatively rare and thus risk extinction during predator education; and (2) aposematic morphs lack the protection of crypsis, and thus appear to invite attacks. I describe a simple method for evaluating whether rare aposematic morphs may be selectively advantaged by their effects on predator psychologies. Using a simulated virtual predator, I consider the advantages that might accrue to dispersed and aggregated morphs if aposematic prey can cause neophobic avoidance, accelerate avoidance learning and decelerate predator forgetting. Simulations show that aposematism is very hard to explain unless there are particular combinations of ecological and psychological factors. If prey are dispersed throughout a locality then aposematism will be favoured only if (1) there is neophobia, learning effects and forgetting or if (2) there are learning effects and warning signals reduce forgetting rates. However, the best scenario for aposematic advantage involves learning rates, forgetting and neophobia when prey are aggregated. Prey aggregation has two important effects. First, it is a highly effective way to maximize the per capita benefits of the neophobia. Second, after an attack on a single prey the benefits of learnt aversions will be immediately conferred on the surviving members of an aggregation without the diluting effects of forgetting. Aggregation therefore provides good protection against forgetting. The simulations thus provide new insights into the complexities of aposematic protection and suggest some important directions for empirical work. Copyright 2001 The Association for the Study of Animal Behaviour.     

An example of enzymatic promiscuity: the Baylis–Hillman reaction catalyzed by a biotin esterase (BioH) from Escherichia coli

Ten lipases and esterases have been examined to catalyse the reaction between p-nitrobenzaldehyde and methyl vinyl ketone, the Baylis–Hillman reaction, to form 3-[hydroxyl-(4-nitrophenyl)-methyl]-but-3-en-2-one. Among these enzymes, Escherichia coli BioH esterase had the best activity. Optimal conditions for this reaction were: 0.1 mmol aldehyde, 0.1 mmol activated alkene, 30 mg E. coli BioH, 1 ml acetonitrile at 30 °C for 96 h. In addition to the named substrates, four other aldehydes and three activated alkenes were also investigated to determine the substrate range of the enzyme. The structures of nine products were confirmed by NMR and yields of the corresponding products ranged from 21 to 46 %.