No evidence for optimal fitness at intermediate levels of inbreeding in Drosophila melanogaster

Optimal outbreeding theory predicts fitness benefits to intermediate levels of inbreeding. In the present study, we test for linear (consistent with inbreeding depression) and nonlinear (consistent with optimal outbreeding) effects of inbreeding on reproductive fitness in male and female Drosophila melanogaster . We found linear declines in fitness associated with increased inbreeding for egg-to-adult viability, but not the number of eggs laid or sperm competitive ability. Egg-to-adult viability was also lower in the progeny of inbred males and females mated to unrelated individuals. However, there was no evidence for optimal fitness at intermediate levels of inbreeding for any trait. The present study highlights the importance of considering biologically realistic levels of inbreeding and cross-generational effects when investigating the costs and benefits of mating with relatives.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 501–510.     

Carbon bio‐sequestration within the phytoliths of economic bamboo species

The rates of carbon bio‐sequestration within silica phytoliths of the leaf litter of 10 economically important bamboo species indicates that (a) there is considerable variation in the content of carbon occluded within the phytoliths (PhytOC) of the leaves between different bamboo species, (b) this variation does not appear to be directly related to the quantity of silica in the plant but rather the efficiency of carbon encapsulation by the silica. The PhytOC content of the species under the experimental conditions ranged from 1.6% to 4% of the leaf silica weight. The potential phytolith carbon bio‐sequestration rates in the leaf‐litter component for the bamboos ranged up to 0.7 tonnes of carbon dioxide (CO₂) equivalents (t‐e‐CO₂) ha^?1 yr^?1 for these species. Assuming a median phytolith carbon bio‐sequestration yield of 0.36 t‐e‐CO₂ ha^?1 yr^?1, the global potential for bio‐sequestration via phytolith carbon (from bamboo and/or other similar grass crops) is estimated to be ～1.5 billion t‐e‐CO₂ yr^?1, equivalent to 11% of the current increase in atmospheric CO₂. The data indicate that the management of vegetation such as bamboo forests to maximize the production of PhytOC has the potential to result in considerable quantities of securely bio‐sequestered carbon.     

Evaluation of methods for estimating soil carbon dioxide efflux across a gradient of forest disturbance

Better understanding of variation in soil carbon dioxide (CO₂) efflux caused by measurement techniques is needed, especially over gradients of site disturbance, to accurately estimate the global carbon cycle. We present soil CO₂ efflux data from a gradient of disturbance to ponderosa pine (Pinus ponderosa C. Lawson var. scopulorum Engelm.) forests in northern Arizona, USA that were obtained using four different techniques: vented static chambers, a Licor 6400‐09, and soil CO₂ diffusion profiles using two different models (Moldrup, Millington–Quirk) to estimate soil gas diffusivity. We also compared soil CO₂ efflux measured by the Moldrup and Millington–Quirk diffusion profile methods to nighttime total ecosystem respiration (TER) data from an eddy covariance tower. We addressed four questions: (1) Does the use of a given method to measure soil CO₂ efflux bias results across a disturbance gradient? (2) Does the magnitude of difference between observed and modeled estimates of soil CO₂ differ between methods and across sites? (3) What is the spatial variability of each method at each site? (4) Which method is closest to the estimate of TER measured by the eddy covariance tower? Although soil CO₂ efflux varied significantly among methods the differences were consistent among sites. Measured and modeled total growing season fluxes were generally higher for the Licor 6400‐09 and Millington–Quirk diffusion gradient methods compared with static chamber and the Moldrup diffusion gradient methods. A power analysis showed that the larger static chamber was the most efficient method at sampling spatial variation in soil CO₂ efflux. Nighttime measurements of soil CO₂ efflux from the Moldrup diffusion gradient method were most strongly related to nighttime TER assessed with eddy covariance. The use of a single, well‐implemented method to measure soil CO₂ efflux is unlikely to create bias in comparisons across a gradient of forest disturbance.     

Phylogenetic utility of the first two introns of the S7 ribosomal protein gene in African electric fishes (Mormyroidea: Teleostei) and congruence with other molecular markers

A series of recent molecular systematic studies of the African electric fishes (Mormyroidea) have challenged many aspects of their traditional taxonomy and precladistic hypotheses of their phylogeny. However, poor resolution of some interrelationships within the subfamily Mormyrinae in these studies highlights the need for additional data and analyses. Here we evaluate the phylogenetic information content of nucleotide sequences from the first two introns of the low‐copy nuclear S7 ribosomal protein gene in 40 mormyroid species. Alignment of S7 sequences from 38 taxa within the subfamily Mormyrinae is non‐problematic, but these are difficult to align with sequences of Petrocephalus bovei (Petrocephalinae) and Gymnarchus niloticus (Gymnarchidae), which we exclude from our analysis. There are no significant differences in base frequencies among these sequences and base compositional bias is low. Maximum parsimony (MP) analysis on the S7 dataset, designating Myomyrus macrops as the outgroup, generates a phylogenetic hypothesis for these taxa with a low level of homoplasy (RI = 0.87). We examine agreement between the S7 data with previously published mitochondrial (12S/16S, cytochrome b) and nuclear (rag 2) datasets for the same taxa by means of incongruence length difference tests and partitioned Bremer support (decay) analysis. While we find significant agreement between the S7 dataset and the others, MP analysis of the S7 data alone and in combination with the other datasets indicates two novel relationships within the Mormyrinae: (1) Mormyrus is the sister group to Brienomyrus brachyistius and Isichthys henryi, and (2) Hippopotamyrus pictus is the sister group of a clade, previously recovered, containing Marcusenius senegalensis. S7 data provide additional support for a number of clades recovered in the earlier molecular studies, some of which conflict with current mormyrid taxonomy. Inferred indels and a single inversion in the S7 fragment provide supplemental character support for many of these relationships. These phylogenetic results strengthen recent hypotheses concerning the evolution of electric organ structure in these fishes. The evolutionary characteristics of this nuclear marker and its phylogenetic utility in this group suggests that it could be widely useful for systematic studies at the subfamilial level in teleost fishes. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society, 2003, 78 , 273–292.     

Isolation and characterization of 27 polymorphic microsatellite loci for the common snook,Centropomus undecimalis

Here we describe 32 di‐, tri‐ and tetranucleotide microsatellite loci isolated by PIMA, a polymerase chain reaction (PCR)‐based procedure, for the common snook (Centropomus undecimalis). Five loci were monomorphic, and the remaining loci averaged 6.7 alleles per locus in a sample of 45 common snook. For polymorphic loci, expected heterozygosities ranged from 0.02 to 0.91 (mean = 0.538). Significant departures from Hardy–Weinberg equilibrium expectations occurred in two loci. Exact tests for genotype disequilibrium gave evidence for linkage at one pair of loci. Many cross‐species primer assays yielded PCR fragments of the expected size for 11 species of Centropomus and two species of the confamilial genus Lates.     

Microsatellite evidence for monogamy and sex-biased recombination in the Western Australian seahorse Hippocampus angustus

Four polymorphic microsatellite loci were used to assess biological parentage of 453 offspring from 15 pregnant males from a natural population of the Western Australian seahorse Hippocampus angustus . Microsatellite genotypes in the progeny arrays were consistent with a monogamous mating system in which both females and males had a single mate during a male brooding period. Multilocus genotypes implicated four females in the adult population sample as contributors of eggs to the broods of collected males, but there was no evidence for multiple mating by females. Based on genotypic data from the progeny arrays, two loci were linked tightly and the recombination rate appeared to be ≈ 10-fold higher in females than in males. The utility of linked loci for parentage analyses is discussed.     

Concentrations of Vacuolar Inorganic Ions in Individual Cells of Intact Wheat Leaf Epidermis

A method is described for quantitative determination of themajor inorganic constituents of individual cells of higher plants.The approach utilizes a modified pressure probe to extract samplesof undiluted vacuolar sap from single cells. Subsamples of constantvolume are taken from these sap samples and are freeze-driedon to thin films along with similarly-sized droplets of standards.The films are placed in a scanning electron microscope and elementalcontent of the freeze-dried material is determined by X-raymicroanalysis. The method has been used to compare levels ofa range of ions in two distinct types of epidermal cell froma young wheat leaf and, in association with nanolitre osmometry,was used to assess the relative importance of the inorganicions in the generation of turgor pressure in these cells. Itwas found that the concentrations of the major inorganic ionswithin the vacuole was constant both within and between twoanatomically distinct groups of epidermal cells on a leaf. Key words: Pressure probe, vacuolar ion levels, single cell sampling, wheat     

A Comparison of Methods for Measuring Turgor Pressures and Osmotic Pressures of Cells of Red Beet Storage Tissue

Two methods for measuring the turgor pressures of cells in discsof storage tissue of red beet (Beta vulgaris L.) were compared,and a centrifugation method for extracting sap from frozen andthawed tissue was evaluated. Turgor pressures were measureddirectly using a pressure probe, or indirectly using a vapourpressure osmometer. With the latter, discs were placed directlyin the osmometer chamber and turgor was calculated as the differencein osmotic pressure before and after freezing and thawing. Turgorin freshly cut discs, measured with the pressure probe, wasbetween 0-012 MPa and 0.118 MPa with a mean ±s.d. of0.092±;0.032 MPa (n = 24). That measured with the osmometervaried between 0.08 MPa and 0.12 MPa with a mean ±s.d.of 0.09±0.10 MPa (n = 54). After vacuum infiltrationof discs with distilled water, the turgor measured with thepressure probe increased to 1.05–1.12 MPa. Turgor measuredwith the osmometer also increased after vacuum infiltrationbut was, on average, 12% lower than that measured with the pressureprobe. Overall, the results suggest that for routine measurements,the osmometer can provide reasonable estimates of the turgorof cells in beet discs. This is because a number of factorsthat, potentially, could interfere with this method have onlya small effect in this tissue. None of the measured turgorsis indicative of that occurring in intact storage roots becauseboth excision and vacuum infiltration of discs alter the concentrationsof solutes in the extracellular space. The osmotic pressureof sap extracted by centrifugation from frozen and thawed discswas not significantly different from that measured by placingfrozen and thawed discs directly in the osmometer. Solute concentrationsin the sap were not significantly different from those measuredby chemical extraction of discs. Key words: Beta vulgaris, Osmotic pressure, Turgor pressure     

冠龙手部三维数字建模与初步功能分析*

冠龙是一种生活于侏罗纪晚期的基干暴龙类,现已发现的化石皆产于中国新疆准噶尔盆地的石树沟组。本次研究使用激光非接触数据化仪对冠龙标本IVPP V14531的左手进行扫描,用RapidformXOV2软件建立单块骨骼三维数字模型,然后用AutodeskMaya软件关联手部各块骨骼,建立整个手部的功能性三维数字模型。尽管基于骨骼化石对兽脚类恐龙手指活动范围进行推测受制于一些不确定性因素,但我们还是能够给出手指的可能活动范围,来测算兽脚类恐龙手指的背展和屈曲度。对模型的分析显示,冠龙手指Ⅱ和Ⅲ的有限背展度介于基干僵尾龙高棘龙和虚骨龙类当中的恐爪龙之间,有限屈曲度变化范围很大,但在高棘龙和恐爪龙变化范围之内;手指Ⅳ的掌骨和指节间关节几乎没有活动性,第一个指节间关节背展度很大,甚至强于高棘龙,第二个指节间关节活动性和高棘龙相当,第三个指节间关节活动性和恐爪龙相当。这也许暗示兽脚类恐龙在演化过程中,手指背展能力逐渐减弱,而屈曲能力逐步加强。这一演化趋势是否存在还需要更多相关数据来检验。