Sex differences in compensatory and catch-up growth in the mosquitofish Gambusia holbrooki

In many taxa, temporary nutritional shortage early in development can favour compensatory strategies that include elevated growth (‘compensatory growth’) and/or extension of the usual period of development (‘catch-up growth’) once conditions improve. The net gains from each strategy depend on the extent to which larger body size increases fitness relative to associated costs (e.g. long-term effects on adult performance, or a greater risk of juvenile mortality). These costs and benefits are likely to differ between the sexes due to sex-specific selection. We documented the responses of male and female mosquitofish (Gambusia holbrooki) to 3 weeks of low food availability (7–28 days old) that restricted subsequent growth and morphology compared to control fish continuously reared on a high food diet (N = 635 fish total). Neither sex elevated their growth rate immediately after being returned to a normal diet compared to control fish. When measured over the entire period until maturation, however, females showed compensatory growth. Males did not. Both sexes also exhibited catch-up growth but the delay until maturation was significantly longer for males. Despite early growth restriction, both sexes eventually matured at almost the same size as control fish, although males had a significantly smaller gonopodium (a sexually selected trait) than that of control males. Reasons for these sex differences are discussed.     

Testing for equal rates of cladogenesis in diverse taxa

Taxa differ widely in numbers of species, which may be due either to chance alone or to factors that cause differences in speciation and extinction rates between taxa. To test whether an observed distribution of species over taxa differs from the distribution expected from chance alone, one must take into account that neither speciation nor extinction rates are known. This paper introduces a way to estimate speciation and extinction probabilities from the distribution of extant species over families and to test whether the observed distribution is different from expected. Application of this procedure to the distributions of bird, hexapod, primate, and angiosperm species over taxa provides statistical evidence of differences in rates of cladogenesis between taxa.     

Quantitative analysis of muscle cell changes in compensatory hypertrophy and work-induced hypertrophy.

The cytological characteristics of two modes of muscle hypertrophy were studied in the extensor digitorum longus muscle of the rat. Comprensatory hypertrophy (CH) was produced by tenotomy of the tibialis anterior muscle and work-induced hypertrophy (WIH) was produced by forced swimming of the animal. While both methods produced an increase in muscle weight and cell size, these two parameters did not correlate. Morphometric analyses of the hypertrophied muscle cells demonstrated that in CH-muscle there was an increase in mitochondrial volume density, a decrease in myofibrillar volume density and no change in sarcotubular or nuclear volume density. WIH-muscle demonstrated an increase in sarcotubular volume density but no change in mitochondrial, myofibrillar or nuclear volume density. It is concluded that in CH-muscle, the cell volume increase is attributable to mitochondrial volume increase and that there is no increase in the contratile myofibrillar component of the cell. WIH-muscle, on the other hand, has a cell volume increase which is attributable to a proportional increase in these organelles.     

分子绝对进化速率与物种分歧时间之间的定量关系

通过对美国国家生物技术信息中心数据库Gen Bank提供的一些蛋白质和核苷酸序列进行比对和分析,发现生物分子绝对进化速率k与进化时间或物种分歧时间t之间存在下列定量关系:lnk=-Ea/Rt+lnK0,式中Ea为位点突变活化能,k0为分子极限绝对进化速率,R为常数,并对其生物学意义进行了初步的探讨;数据分析还揭示出物种的分子极限绝对进化速率与进化时间或物种分歧时间之间也服从相似的定量公式,也就是说生物分子进化过程可能同时受到序列位点突变和控制物种分子极限绝对进化速率进化的两个"分子钟"作用,即存在"双重分子钟"现象。     

Citrus cryopreservation: viability of diverse taxa and histological observations

Diverse citrus cultivars maintained clonally within gene banks serve as valuable resources for research and breeding programs worldwide. These critical collections are kept as trees within field, screenhouse, or greenhouse collections. Ex situ collections are at risk of being lost due to unforeseen environmental or biological disasters. Cryopreservation provides a secure method to back-up these important collections. Herein, we assessed the applicability of a vitrification-based cryopreservation method to conserve citrus collection cultivars. Shoot tips were excised from screenhouse-grown trees from the USDA-ARS National Clonal Germplasm Repository for Citrus and Dates. Shoot tips were then treated with cryoprotectants, plunged into liquid nitrogen (LN), warmed and then recovered by micrografting onto ‘Carrizo’ citrange seedling rootstocks. Of 150 cryopreserved Citrus accessions representing 32 taxa, 24 taxa had mean regrowth levels that were at least 40?%. The 36 navel orange (Citrus sinensis) accessions had an average regrowth level of 64?%. There was no decrease in viability after 3 years of LN storage for the three accessions that are part of a long-term storage experiment. Histological observations revealed high levels of cell survival after LN exposure and that cellular regrowth occurred between rootstock and shoot tips within 2 days of micrografting. We demonstrate that diverse citrus cultivars can be successfully cryopreserved within gene banks for long-term conservation.     

谈谈鱼类的补偿生长

简要介绍了鱼类的补偿生长现象,并根据补偿量的大小将鱼类的补偿生长划分为超补偿生长,完全补偿生长,部分补偿生长和不能补偿生长四类,同时根据饥饿或限食以及重喂时间的不同介绍了目前鱼类补偿生长实验设计的一般思路,最后对鱼类补偿生长在水产养殖和环境保护等方面的应用前景作了展望。     

Quantitative phenetics and taxonomy of some phlebotomine taxa

Elucidating the evolution of Phlebotominae is important not only to revise their taxonomy, but also to help understand the origin of the genus Leishmania and its relationship with humans. Our study is a phenetic portrayal of this history based on the genetic relationships among some New Word and Old Word taxa. We used both multilocus enzyme electrophoresis and morphometry on 24 male specimens of the Old Word genus Phlebotomus (with three of its subgenera: Phlebotomus, Spelaeophlebotomus and Australophlebotomus), and on 67 male specimens of the three New World genera, Warileya, Brumptomyia and Lutzomyia, (with three subgenera of Lutzomyia: Lutzomyia, Oligodontomyia and Psychodopygus). Phenetic trees derived from both techniques were similar, but disclosed relationships that disagree with the present classification of sand flies. The need for a true evolutionary approach is stressed.     

Patchiness and compensatory growth in a fungus-Collembola system

The compensatory growth potential of a grazed fungal biomass was mathematically expressed as a function of patchiness in its distribution and demonstrated in an experiment using the fungivorous collembolan Onychiurus armatus and the soil fungi Verticillium bulbillosum and Penicillium spinulosum. The model addresses the regrowth potential in relation to patch fragmentation, travelling time and consumption rate of the collembolan and the mean relative growth rate of the fungus. It suggests that the mean relative growth rate required for regrowth decreases with patch fragmentation and increases with the mean growth rate of the fungus. The experiments were performed with a system of soil-filled vials provided with fungi and collembolans. The size of the vials and the length of the tubes connecting them were varied to give different patch sizes and travelling times. The respiratory activity of fungi after grazing increased as a unit of mycelium was distributed into smaller connected vials. The slow growing species V. bulbillosum showed a greater but delayed response to grazing in comparison with the fast growing P. spinulosum. An increased travelling time delayed the growth response in both species.     

Microsatellite and mitochondrial DNA homogeneity among phenotypically diverse crossbill taxa in the UK.

Genetic differentiation within and between the three morphologically divergent crossbill species extant in the UK was assessed by comparison of allele frequencies at five unlinked microsatellite loci and DNA sequence variation across the mitochondrial control region. No significant differences in microsatellite allele frequency were found either between different populations of the same species or between the crossbill species themselves. A similar lack of genetic divergence was apparent from the mitochondrial sequence data. We resolved 33 different haplotypes, separated by low levels of sequence divergence (0-0.15%). Levels of divergence within and between species were not significantly different. Haplotypes formed a polyphyletic phylogeny, indicating that the crossbill species do not form genetically separate clades. Discordance between neutral DNA polymorphisms and adaptive morphological variation is discussed in relation to defining the systematic relationship between crossbill forms. If adaptive differences have arisen without a concomitant divergence in neutral DNA then attempting to define crossbill types from microsatellite and mitochondrial DNA without recourse to ecology and behaviour may be misleading.     

Resource allocation,hyperphagia and compensatory growth

Organisms often shown enhanced growth during recovery from starvation, and can even overtake continuously fed conspecifics (overcompensation). In an earlier paper (Ecology 84, 2777–2787), we studied the relative role played by hyperphagia and resource allocation in producing overcompensation in juvenile (non-reproductive) animals. We found that, although hyperphagia always produces growth compensation, overcompensation additionally requires protein allocation control which routes assimilate preferentially to structure during recovery. In this paper we extend our model to cover reproductively active individuals and demonstrate that growth rate overcompensation requires a similar combination of hyperphagia and allocation control which routes the part of enhanced assimilation not used for reproduction preferentially towards structural growth. We compare the properties of our dynamic energy budget model with an earlier proposal, due to Kooijman, which we extend to include hyperphagia. This formulation assumes that the rate of allocation to reserves is controlled by instantaneous feeding rate, and one would thus expect that an extension to include hyperphagia would not predict growth overcompensation. However, we show that a self-consistent representation of the hyperphagic response in Kooijman’s model overrides its fundamental dynamics, leading to preferential allocation to structural growth during recovery and hence to growth overcompensation.     

Renal glutathione homeostasis in compensatory renal growth

Glutathione homeostasis was investigated in unilaterally nephrectomized and sham-operated rats. Following twelve days of compensatory renal growth, it was found that the concentrations of glutathione and glutathione disulfide in representative samples of the entire remnant right kidney from the nephrectomized rats were similar to those found in corresponding samples of the right kidneys from the sham-operated rats. However, since the mass of the remnant right kidneys in the nephrectomized rats was greater than that of the right kidneys from the sham-operated rats, the absolute content of glutathione and glutathione disulfide was greater in the remnant right kidneys of the nephrectomized rats than in the right kidneys of the sham-operated rats. In general, the findings from the present study indicate that the absolute content of glutathione and glutathione disulfide in renal epithelial cells increases in proportion to the increase in mass that results from compensatory renal cellular hypertrophy.     

Long-term consequences of compensatory lung growth

Left pneumonectomy or left nephrectomy was performed on 10-wk-old littermate male New Zealand White rabbits, and they were killed at 30 wk of age. Thirty-week-old male littermates served as controls. Nephrectomy was done to produce major tissue loss and trauma and to assess blood somatomedin C. At the end of the experiment, the right lungs of the pneumonectomy animals had a greater lung volume, weight, gas-exchanging surface area, and alveolar number than the nephrectomy animals and the controls, and their air spaces were the same size. When compared with both lungs of the nephrectomy group and the controls, lung weight was the same; lung volume, alveolar number, and protein were not significantly less in the pneumonectomy group, but gas-exchanging area (compared with controls only), DNA, and RNA were. After left nephrectomy, the right kidney increased in weight; nephrectomy had no effect on lung size or structure. We conclude that pneumonectomy at age 10 wk in male rabbits results in significant compensatory lung growth, including alveolar multiplication, and this persists to age 30 wk. Compensatory lung growth, however, was incomplete; that is, it did not reconstitute (equal) in all respects that of both lungs of the nephrectomy animals or the controls.     

Increase in pulsatile secretion of growth hormone during failure of catch-up growth following glucocorticoid-induced growth inhibition

The pattern of growth hormone (GH) secretion was determined in rats injected with cortisone acetate, 5 mg/rat/day subcutaneously, or with an equivalent volume of saline for 4 days from age 40 days. Cortisone injections resulted in inhibition of growth of body weight and tail length. During recovery the rats resumed a normal rate of growth but failed to show catch-up growth acceleration. From 17 to 27 days of recovery, plasma was sampled at 15-min intervals through the lights-on period, 06:00 to 18:00, via a catheter chronically implanted in the superior vena cava. During sampling each rat was housed singly in an insulated chamber, unrestrained, and with food and water ad lib. Cortisone-treated animals had a normal periodicity of GH plasma concentration, but they showed a reduction in values in the range of 50 to 99 ng/ml (P less than 0.01) and an increase of values in the range of 200 to 499 ng/ml (P less than 0.025) and above 1000 ng/ml (P less than 0.05). The area under the GH concentration curve of the cortisone-treated rats was significantly greater than that of the controls, 100.9 +/- 18.7 (mean +/- SE) units vs 55.3 +/- 7.4 (P less than 0.025). Thus, increased growth hormone secretion during the light phase persisted in spite of failure of catch-up growth acceleration. The findings indicate that the mechanism involved in GH release is linked to the catch-up growth control.     

Substrate specificity of a maize ribosome-inactivating protein differs across diverse taxa.

The superfamily of ribosome-inactivating proteins (RIPs) consists of toxins that catalytically inactivate ribosomes at a universally conserved region of the large ribosomal RNA. RIPs carry out a single N-glycosidation event that alters the binding site of the translational elongational factor eEF1A and causes a cessation of protein synthesis that leads to subsequent cell death. Maize RIP1 is a kernel-specific RIP with the unusual property of being produced as a zymogen, proRIP1. ProRIP1 accumulates during seed development and becomes active during germination when cellular proteases remove acidic residues from a central domain and both termini. These deletions also result in RIP activation in vitro. However, the effectiveness of RIP1 activity against target ribosomes remains species-dependent. To determine the potential efficiency of maize RIP1 as a plant defense protein, we used quantitative RNA gel blots to detect products of RIP activity against intact ribosomal substrates from various species. We determined the enzyme specificity of recombinant maize proRIP1 (rproRIP1), papain-activated rproRIP1 and MOD1 (an active deletion mutant of rproRIP1) against ribosomal substrates with differing levels of RIP sensitivity. The rproRIP1 had no detectable enzymatic activity against ribosomes from any of the species assayed. The papain-activated rproRIP1 was more active than MOD1 against ribosomes from either rabbit or the corn pathogen, Aspergillus flavus, but the difference was much more marked when rabbit ribosomes were used as a substrate. The papain-activated rproRIP1 was much more active against rabbit ribosomes than homologous Zea mays ribosomes and had no detectable effect on Escherichia coli ribosomes.     

Factors associated with height catch-up and catch-down growth among schoolchildren

In developed countries, children with intrauterine growth restriction (IUGR) or born preterm (PT) tend to achieve catch-up growth. There is little information about height catch-up in developing countries and about height catch-down in both developed and developing countries. We studied the effect of IUGR and PT birth on height catch-up and catch-down growth of children from two cohorts of liveborn singletons. Data from 1,463 children was collected at birth and at school age in Ribeirão Preto (RP), a more developed city, and in São Luís (SL), a less developed city. A change in z-score between schoolchild height z-score and birth length z-score≥0.67 was considered catch-up; a change in z-score≤−0.67 indicated catch-down growth. The explanatory variables were: appropriate weight for gestational age/PT birth in four categories: term children without IUGR (normal), IUGR only (term with IUGR), PT only (preterm without IUGR) and preterm with IUGR; infant''s sex; maternal parity, age, schooling and marital status; occupation of family head; family income and neonatal ponderal index (PI). The risk ratio for catch-up and catch-down was estimated by multinomial logistic regression for each city. In RP, preterms without IUGR (RR = 4.13) and thin children (PI<10^th percentile, RR = 14.39) had a higher risk of catch-down; catch-up was higher among terms with IUGR (RR = 5.53), preterms with IUGR (RR = 5.36) and children born to primiparous mothers (RR = 1.83). In SL, catch-down was higher among preterms without IUGR (RR = 5.19), girls (RR = 1.52) and children from low-income families (RR = 2.74); the lowest risk of catch-down (RR = 0.27) and the highest risk of catch-up (RR = 3.77) were observed among terms with IUGR. In both cities, terms with IUGR presented height catch-up growth whereas preterms with IUGR only had height catch-up growth in the more affluent setting. Preterms without IUGR presented height catch-down growth, suggesting that a better socioeconomic situation facilitates height catch-up and prevents height catch-down growth.     

Catch-up growth and endocrine changes in childhood celiac disease. Endocrine changes during catch-up growth

Childhood celiac disease may lead to a failure of statural growth. After institution of a gluten-free diet most patients exhibit catch-up growth. Catch-up growth is a remarkable phenomenon characterized by a supranormal height velocity. One of the hypothetical mechanisms of catch-up growth is that an increased activity of the somatotrophic axis is involved. In order to provide further insight in the physiology of catch-up growth, auxological and endocrine changes were prospectively studied in 28 children with newly diagnosed celiac disease. The results demonstrate a malnutrition-like state of the somatotrophic axis at the time of diagnosis and a rapid recovery of this axis towards normal functioning after institution of the gluten-free diet. Although several correlations between these endocrine alterations and auxological parameters were detected, it is questionable whether the endocrine changes are the driving force behind catch-up growth.     

Signals and mechanisms of compensatory lung growth.

Growth of the lung involves unique structure-function interactions not seen in solid organs. Mechanical feedback between the lung and thorax constitutes a major signal that sustains developmental as well as compensatory lung growth. After the loss of lung units as by pneumonectomy (PNX), increased mechanical stress and strain on the remaining units induce adaptive responses to augment oxygen transport, including 1) recruitment of alveolar-capillary reserves, 2) remodeling of existing tissue, and 3) regenerative growth of acinar tissue when strain exceeds a critical threshold. Alveolar hypoxia, hormones, and growth factors may feed into the mechanical feedback system to modify an existing growth response but are unlikely to initiate compensatory growth in the absence of sufficient mechanical signals. Whereas endogenous post-PNX alveolar growth preserves normal structure-function relationships, experimental manipulation of selected metabolic pathways can distort these relationships. Finally, PNX widens the disparity between the rapidly adapting acini and slowly adapting conducting airways and blood vessels, leading to disproportionate airflow and hemodynamic dysfunction and secondary hypertrophy of the right ventricle and respiratory muscles that limits overall organ function despite regeneration of gas exchange tissue. These are key concepts to consider when formulating approaches to stimulate or augment compensatory growth in chronic lung disease.