Biology and host preference of Selitrichodes neseri: A potential biological control agent of the Eucalyptus gall wasp,Leptocybe invasa

Selitrichodes neseri (Hymenoptera: Eulophidae) is a parasitoid of the invasive gall-forming wasp Leptocybe invasa (Hymenoptera: Eulophidae), which has caused serious damage to Eucalyptus plantations in many parts of the world. S. neseri is a recently discovered parasitoid considered to be a potentially important biological control agent of L. invasa. The aim of this study was to provide the first basic data on the biology of S. neseri, which is essential for its application in biological control. S. neseri was shown to be a biparental ectoparasitoid. Observation from dissected galls indicated that the parasitoid developed on late larvae, pupae and callow adults, although development did occur in a range of gall ages. Observed nominal parasitism in captivity ranged from 9.7% to 71.8%. Adult S. neseri specimens, fed with honey-water and galled Eucalyptus leaves, survived an average of 26 days at 26 °C. The average developmental time from oviposition to emergence was 19.3 days ± 0.2 days. There was no pre-oviposition period. A single female produced a maximum of thirty-nine offspring, with a maximum of ten per day. Dissection of the ovaries showed that twelve ovarioles were present. The sex ratio of S. neseri observed in this study was 1:3.43 males:females. Galls of native insects most closely related to L. invasa and to galls of similar morphology to L. invasa-induced galls, were not suitable for S. neseri oviposition. S. neseri showed considerable potential as a biological control agent of L. invasa due to its relatively short developmental time, long adult life span when supplemented with carbohydrates, ability to utilize a range of gall ages and the fact that it has a high level of host specificity.     

A search for quantitative trait loci for ovulation rate in cattle

Seventy-seven polymorphic microsatellites were analysed in offspring of three elite sires that were part of the foundation of an experimental population selected for twinning rate at the US Meat Animal Research Center, Clay Center, Nebraska. All females were assessed for ovulation rate by rectal palpation of corpora lutea over 8–10 consecutive oestrous cycles from approximately 12 to 18 months of age, and associations between ovulation rate and sire allele were examined in each of the three sire groups. A preliminary analysis was performed using selectively genotyped daughters of each sire. Markers found significant or approaching significance were also genotyped in all daughters, sons and granddaughters of these sires. A test of marker associations limited to the granddaughter data provided an independent confirmation of marker effect and significance relative to the initial test with daughter data. Putative ovulation rate quantitative trait loci were detected on chromosomes 7 and 23. Marker UWCA20 on chromosome 7 was associated with an effect in excess of one phenotypic standard deviation and accounted for approximately 10% of phenotypic variation ovulation rate. Marker CYP21 (steroid 21-hydroxylase) on chromosome 23 was associated with an effect of slightly less than half a phenotypic standard deviation and accounted for approximately 4% of phenotypic variation.     

Biogenic Iron Preserves Structures during Fossilization: A Hypothesis

It is hypothesized that iron from biological tissues, liberated during decay, may have played a role in inhibiting loss of anatomical information during fossilization of extinct organisms. Most tissues in the animal kingdom contain iron in different forms. A widely distributed iron-bearing molecule is ferritin, a globular protein that contains iron crystallites in the form of ferrihydrite minerals. Iron concentrations in ferritin are high and ferrihydrites are extremely reactive. When ancient animals are decaying on the sea floor under anoxic environmental conditions, ferrihydrites may initialize the selective replication of some tissues in pyrite FeS₂. This model explains why some labile tissues are preserved, while other more resistant structures decay and are absent in many fossils. A major implication of this hypothesis is that structures described as brains in Cambrian arthropods are not fossilization artifacts, but are instead a source of information on anatomical evolution at the dawn of complex animal life.     

On the Information Matrix of Exponential Mixture Models with Long-term Survivors

The aim of this paper is to study the properties of the asymptotic variances of the maximum likelihood estimators of the parameters of the exponential mixture model with long-term survivors for randomly censored data. In addition, we study the asymptotic relative efficiency of these estimators versus those which would be obtained with complete follow-up. It is shown that fixed censoring at time T produces higher precision as well as higher asymptotic relative efficiency than those obtainable under uniform and uniform-exponential censoring distributions over (0, T). The results are useful in planning the size and duration of survival experiments with long-term survivors under random censoring schemes.     

Testing parameter sensitivities and uncertainty analysis of Biome-BGC model in simulating carbon and water fluxes in broadleaved-Korean pine forests

生态过程模型的发展为研究者在长时间序列和区域尺度的研究提供了便利, 但模型模拟的准确性受到模型自身结构、模型参数估计合理性的影响。敏感性分析能够定量或定性筛选出对模型模拟结果影响较大的敏感参数, 是模型参数校准过程中的重要工具, 也是建模和应用的先决条件。该文以阔叶红松林为研究对象, 采用全局敏感性分析方法——傅里叶幅度灵敏度检验扩展法(EFAST)对Biome-BGC模型的生理生态参数进行了敏感性分析, 分别分析了红松(Pinus koraiensis)和阔叶树的净初级生产力(NPP)、蒸散(ET)对参数变化的敏感性。结果表明: (1)模拟红松NPP的不确定性高于阔叶树, 但二者的模拟ET的不确定性均较小。阔叶树的NPP和ET对生理生态参数的敏感性总体上都小于红松。(2)无论是红松、阔叶或其他植被类型, 模拟NPP均表现出对叶片碳氮比、细根碳氮比、比叶面积(SLA)和冠层截留系数的敏感性, 这4个参数的高敏感性主要是由模型自身结构所决定的, 与植被类型和研究地区的关系较小。对模拟ET而言, 细根与叶片碳分配比、新茎与新叶碳分配比和SLA均是影响红松和阔叶树ET的敏感参数, 但红松ET主要受参数与参数间的二阶或多阶交互作用的间接影响, 而阔叶树ET则主要是受到敏感参数直接效应的影响。(3)除了上述影响红松和阔叶树碳水通量的共性参数外, 诸如核酮糖-1,5-二磷酸羧化酶中叶氮含量、叶片与细根周转率、所有叶面积与投影叶面积之比等也是对模拟结果有影响的重要参数, 但是其敏感程度随物种不同和研究区不同而不同, 所以这类参数可以根据具体情况进行参数本地化, 对于其他不敏感参数则可以采用模型缺省值。     

Tradeoff between height and relative growth rate in a dominant grass from the Serengeti ecosystem

We determined the relationship between plant height and whole-plant relative growth rate (g g^-1 day^-1) for ten genotypes of Sporobolus kentrophyllus collected from an intensively grazed site on the Serengeti Plains, Tanzania. Plants were grown for 7 weeks in a greenhouse in Syracuse, N.Y., and harvested weekly. Plants that received simulated bovine urine showed a negative relationship between plant height and growth rate, suggesting a genetic tradeoff between competitive ability if ungrazed (height) and ability to recover from grazing (growth rate). There was no height-growth rate relationship under nitrogen addition rates similar to field mineralization rates. In addition, faster-growing, shorter plants tended to have relatively higher above-ground growth rates than slower-growing, taller plants. These results suggest that natural selection has maintained a gradient of morphologies within this species ranging from short, rapidly growing genotypes adapted to intense grazing conditions to tall, slow-growing, grazer-susceptible genotypes that are superior light competitors in absence of herbivory.     

ESTIMATING NATURAL MORTALITY RATE IN REPRODUCTIVELY ACTIVE FEMALE SOUTHERN RIGHT WHALES, EUBALAENA AUSTRALIS

Cow-calf pairs of southern right whales on the South African coast have been photographed in aerial surveys in October each year since 1979. In this paper 469 resightings of 177 individually identified cows photographed in the first six years of surveys have been analyzed in two ways to produce estimates of natural mortality rate. Both methods assume that all females calve either two, three, or four years after their previous calf. In Method A there is assumed to be no systematic trend with time in the probability of a female being photographed on each calving occasion. Natural logarithms of the numbers photographed 2-4, 5-7, 8-10, etc. yr after being first seen are regressed against time, the slope of which provides an estimate of natural mortality rate of 0.0255 ± 0.0071. The intercept value for this regression provides an estimate of the detection probability, or 0.769 ± 0.011. In Method B it is assumed that if a female has not been photographed for at least nine years then it is dead. Annual mortality estimates are obtained from the proportional reduction in the numbers of females known to be alive at each three-year interval after being first photographed, up to at least 6-8 yr from the present. Method B produces an estimate of natural mortality of 0.0260 ± 0.0190 (corrected to 0.0227 ± 0.0192 using the average detection probability). Both methods may be subject to various biases that tend to inflate estimates of natural mortality.