A new species of Dyrosaurus (Crocodylomorpha, Dyrosauridae) from the early Eocene of Morocco: phylogenetic implications

A new dyrosaurid is described from the Ypresian of the phosphatic deposits of the Oulad Abdoun Basin of Morocco. It is based on numerous cranial and postcranial remains, allowing an almost complete reconstruction. This new Dyrosaurus species, Dyrosaurus maghribensis sp. nov. , is currently only known from Morocco. It differs from D. phosphaticus , present in contemporaneous levels of Algeria and Tunisia, by several autapomorpies, including a smooth dorsal margin of the parietal and widely opened choanae. A phylogenetic analysis, using 47 taxa and 234 morphological characters, shows the dyrosaurids as the sister taxon of pholidosaurids, which include Elosuchus , Sarcosuchus , Terminonaris and Pholidosaurus , and the thalattosuchians. Goniopholididae is a non-monophyletic group; however, if dyrosaurids are not included in the analysis, the result differs and the goniopholidids form a distinct clade. If Thalattosuchia is excluded, both Goniopholididae and Pholidosauridae become paraphyletic assemblages. Thus, phylogenetic problems remain with respect to longirostrine clade, and more attention should be paid to resolving their evolutionary relationships amongst the crocodyliforms.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 148 , 603–656.     

Factors Mediating the Vitamin B12 Requirement of Euglena

SYNOPSIS. Deprived of vitamin B₁₂, Euglena gracilis strain Z ceases to divide which we believe to be a function of the light regime: division inhibition occurs more quickly in continuous light than in alternating (6L : 6D) light and not at all in total darkness. This phenomenon is dependent on the carbon source; cells grown in glutamate-malate medium do not divide regardless of the culture conditions while dl -lactate as carbon source permits growth in darkness in the absence of B₁₂. Conditions which lead to an increased O₂ or decreased CO₂ tension in the medium, such as agitation in darkness or incubation in red or white light, result in inhibition of division. This inhibition can be reversed by re-transferring the cells to still culture in the dark or, in the case of light-induced blockage, by the addition of DCMU.     

Deconvolution of pigment and physiologically related photochemical reflectance index variability at the canopy scale over an entire growing season

The sensitivity of the photochemical reflectance index (PRI) to leaf pigmentation and its impacts on its potential as a proxy for light‐use efficiency (LUE) have recently been shown to be problematic at the leaf scale. Most leaf‐to‐leaf and seasonal variability can be explained by such a confounding effect. This study relies on the analysis of PRI light curves that were generated at the canopy scale under natural conditions to derive a precise deconvolution of pigment‐related and physiologically related variability in the PRI. These sources of variability were explained by measured or estimated physiologically relevant variables, such as soil water content, that can be used as indicators of water availability and canopy chlorophyll content. The PRI mainly reflected the variability in the pigment content of the canopy. However, the corrected PRI, which was obtained by subtracting the pigment‐related seasonal variability from the PRI measurement, was highly correlated with the upscaled LUE measurements. Moreover, the sensitivity of the PRI to the leaf pigment content may mask the PRI versus LUE relationship or result in an artificial relationship that reflects the relationship of chlorophyll versus LUE, depending on the species phenology.     

Role of Aromatic Amino-acid Residues in the Binding of Enzymes and Proteins to Nucleic Acids

MANY studies have been made of the specificity of interaction between nucleic acids and polypeptides, proteins and enzymes^1,2. Electrostatic forces between basic amino-acids and phosphate groups contribute to the stability of the complexes, but selective recognition requires more specific interactions which are not yet understood. The recognition of a specific region of a nucleic acid could be explained if this region has some particular conformation or if there are specific interactions between a few amino-acid residues and the bases of this region. We wish to report results which show that the aromatic amino-acids tryptophan and tyrosine can interact with nucleic acid bases in double stranded nucleic acids. They suggest that aromatic amino-acid residues of enzymes and proteins could participate in the binding to nucleic acids by intercalating between the bases and thus constraining the nucleic acid molecule to adopt a definite position with respect to the protein molecule.     

Genetic structure of the endangered perennial plant Eryngium alpinum (Apiaceae) in an alpine valley

We investigated the genetic structure of Eryngium alpinum (Apiaceae) in an Alpine valley where the plant occurs in patches of various sizes. In a conservation perspective, our goal was to determine whether the valley consists of one or several genetic units. Habitat fragmentation and previous observations of restricted pollen/seed dispersal suggested pronounced genetic structure, but gene dispersal often follows a leptokurtic distribution, which may lead to weak genetic structure. We used nine microsatellite loci and two nested sampling designs (50 × 50 m grid throughout the valley and 2 × 2 m grid in two 50 × 10 m quadrats). Within the overall valley, F -statistics and Bayesian approaches indicated high genetic homogeneity. This result might be explained by: (1) underestimation of long-distance pollen/seed dispersal by in situ experiments and (2) too recent fragmentation events to build up genetic structure. Spatial autocorrelation revealed isolation by distance on the overall valley but this pattern was much more pronounced in the 50 × 10 m quadrats sampled with a 2-m mesh. This was probably associated with limited primary seed dispersal, leading to the spatial clustering of half-sibs around maternal plants. We emphasize the interest of nested sampling designs and of combining several statistical tools.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 667–677.     

黑龙江东部双鸭山、集贤煤田中生代含煤地层研究*

本文系统地讨论了黑龙江双鸭山、集贤两煤田的中生代含煤地层序列,综合各门类化石研究结果,认为海相的绥滨组和东荣组属晚侏罗世卡洛夫晚期至伏尔加期,非海相的城子河组和穆棱组属早白垩世尼坎期。文内提供11条详细的钻探剖面的生物地层资料。     

Costly sexual harassment in a beetle

Abstract The optimal number of mating partners for females rarely coincides with that for males, leading to sexual conflict over mating frequency. In the bruchid beetle Callosobruchus maculatus, the fitness consequences to females of engaging in multiple copulations are complex, with studies demonstrating both costs and benefits to multiple mating. However, females kept continuously with males have a lower lifetime egg production compared with females mated only once and then isolated from males. This reduction in fitness may be a result of damage caused by male genitalia, which bear spines that puncture the female’s reproductive tract, and/or toxic elements in the ejaculate. However, male harassment rather than costs of matings themselves could also explain the results. In the present study, the fitness costs of male harassment for female C. maculatus are estimated. The natural refractory period of females immediately after their first mating is used to separate the cost of harassment from the cost of mating. Male harassment results in females laying fewer eggs and this results in a tendency to produce fewer offspring. The results are discussed in the context of mate choice and sexual selection.     

Thermal and hydric implications of diurnal activity by a small tropical frog during the dry season

Amphibians are typically intolerant of high temperatures and dehydrating conditions, and small species are particularly susceptible to desiccation. The rockhole frog, Litoria meiriana (Hylidae), is diurnal and is often observed on rocks in the sun near streams in tropical Australia. These hot, desiccating conditions are avoided by most frog species. We measured the microclimate in the areas used by frogs and the activity, body temperatures and hydric state of free‐ranging individuals of this small frog. We also used plaster models to further explore the dynamic nature of hydric state by combining estimates of water loss and water uptake with behavioural observations of activity and microhabitat selection. Both direct measures and estimates of dynamic hydric state indicated that free‐ranging frogs generally maintained a hydric state above 95% of full hydration, but occasionally, particularly during the afternoon, frogs allowed their hydric state to fall as low as 85%. Body temperatures of frogs remained below the critical thermal maximum (CT_max) even when the frogs were in the sun, because this species has no cutaneous resistance to evaporative water loss and so they cool by evaporation. However, during the hotter part of the day, on dry sunny substrates, the hydric state of the frogs could fall to near lethal hydration states (approximately 70% of full hydration) within a short period (approximately 20 min). Thus, the threat of desiccation appears to be more limiting than the threat of overheating. These diurnal frogs rely on frequent bouts of rehydration to support their ability to venture onto hot, dry rocks during the day.     

Soil [N] modulates soil C cycling in CO2‐fumigated tree stands: a meta‐analysis

Under elevated atmospheric CO₂ concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO₂ effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta‐analysis to test the hypotheses that: (1) elevated atmospheric CO₂ stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO₂ induces a C allocation shift towards below‐ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO₂. Soil N concentration strongly interacted with CO₂ fumigation: the effect of elevated CO₂ on fine root biomass and –production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO₂ are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.