Evaluation of X-ray densitometry to identify tree-ring boundaries of two deciduous species from semi-arid forests in Brazil

The presence of visible annual rings in semi-arid tropical trees may allow the application of dendrochronological methods. However, variation in water availability may cause the formation of narrow, irregular ill- or non-defined annual rings hindering the correct dating of tree-ring series. We aimed to evaluate X-ray densitometry as a method to identify tree rings of two deciduous tree species from the Caatinga forest, a semi-arid region in the northeast of Brazil, and compare with two other methods commonly used in dendrochronology, the sliding-stage micrometer and image analysis. Xylem was observed macro- and microscopically and wood anatomical features were assessed in Aspidosperma pyrifolium and Poincianella pyramidalis trees. In both species, tree-ring boundaries were identified considering intra-annual density patterns and wood anatomical features. No significant differences in tree-ring widths were found among methods. X-ray densitometry measurements showed a positive correlation with the measurements obtained with image analysis and sliding-stage micrometer in A. pyrifolium and P. pyramidalis, revealing the high reliability of the methods used. However, inter-correlation of tree-ring width series showed differences in the accuracy of crossdating across measuring methods. The maximum, mean and minimum density values were species-dependent, with mean wood density of A. pyrifolium lower than P. pyramidalis. Our results highlight X-ray densitometry as an important and complementary tool to identify tree-rings boundaries in semi-arid tree species, especially in A. pyrifolium. Along with other measuring methods, it may provide higher accuracy in dendrochronological studies in semi-arid or subtropical environments.     

A comparison of indices and measured values of eggshell thickness of different shell regions using museum eggs of 230 European bird species

The thickness of avian eggshells is used to assess shell quality in wild and domestic species, as an indicator of environmental pollution and as an adaptive explanation for shell maculation. Both direct measurements and calculated eggshell thickness indices (ETI) are used in such research, yet this is the first study to quantify, across a large spectrum of bird families (and thus egg shapes), the correlation between measured thicknesses and ETI. Furthermore, few studies have quantified thickness variation across the entire length of the shell, although this variation may influence both gas transfer and embryonic development. We measured the thickness of 942 eggshells of 230 European bird species from the Class II material at the Natural History Museum, Tring, UK, both in the conventional manner, at the equator through the blowhole and, uniquely, after a single longitudinal, cut at its equator at the blunt and pointed ends. Over half of the samples revealed shell defects, cautioning against the indiscriminate use of museum specimens. Strong positive associations were found between species‐specific means of shell thickness with each other and also with ETI, especially those derived from Schönwetter's ‘Handbuch der Oologie’ method, validating the interspecific comparative use of ETI. Thickness measurements and ETI factors are provided for all 230 species. Eggshells were usually thinner at the blunt end (the location of the air sac) than at the equator, but of equal thickness in passerine eggs. This difference was greatest in species producing elongate eggs and suggests that there is a functional significance of shell thickness variation among species that requires further investigation.     

Comparative whole genome analysis of six diagnostic brucellaphages

Whole genome sequencing of six diagnostic brucellaphages, Tbilisi (Tb), Firenze (Fz), Weybridge (Wb), S708, Berkeley (Bk) and R/C, was followed with genomic comparisons including recently described genomes of the Tb phage from Mexico (Tb_M) and Pr phage to elucidate genomic diversity and candidate host range determinants. Comparative whole genome analysis revealed high sequence homogeneity among these brucellaphage genomes and resolved three genetic groups consistent with defined host range phenotypes. Group I was composed of Tb and Fz phages that are predominantly lytic for Brucella abortus and Brucella neotomae; Group II included Bk, R/C, and Pr phages that are lytic mainly for B. abortus, Brucella melitensis and Brucella suis; Group III was composed of Wb and S708 phages that are lytic for B. suis, B. abortus and B. neotomae. We found that the putative phage collar protein is a variable locus with features that may be contributing to the host specificities exhibited by different brucellaphage groups. The presence of several candidate host range determinants is illustrated herein for future dissection of the differential host specificity observed among these phages.     

Entamoeba histolytica mitosomes: organelles in search of a function

It has been more than eight years since the discovery of mitosomes (mitochondrial remnant organelles) in the intestinal human pathogen Entamoeba histolytica. Despite detailed knowledge about the biochemistry of this parasite and the completion of the E. histolytica genome sequencing project no physiological function has yet been unequivocally assigned to these organelles. Entamoeba mitosomes seem to be the most degenerate of all endosymbiosis-derived organelles studied to date. They do not appear to participate in energy metabolism and may have dispensed completely with the proteins required for iron-sulphur cluster biosynthesis. However, the large number of mitosomes found in E. histolytica trophozoites hints at a significant biological role for these organelles in their natural environment. Identifying the protein complement of mitosomes will provide answers as to their biological significance and the reason(s) for their retention in this parasite.     

单神经元分辨水平的小鼠全脑网络可视化

脑科学是当今国际科技研究的前沿领域。脑是最复杂的器官,其中尚有诸多重大的基础科学问题有待解决。开展脑科学研究需多学科人员协同攻关,对于建立新学科将有极大的促进作用,对于人类健康和社会发展具有巨大的推动作用。简述了神经科学在结构成像方面的基础性需求,介绍了小鼠全脑可视化的发展历程以及近几年的代表性研究,并展望了全脑可视化研究的发展趋势,对可能存在的难点予以说明。