Neighborhood density and reproductive potential in harvester ants

When neighbors compete for resources, the characteristics of a neighborhood may affect fitness. We examined the relationship between reproductive success and the density and size/age characteristics of neighbors in a population of the seed-eating ant, Pogonomyrmex barbatus, in which the ages of all colonies were known. Reproductive success was estimated by trapping and counting the number of alate, reproductive ants emerging from the nest for the annual mating flight. Alate production was negatively related to neighborhood density. Decreased production of alates by more crowded colonies may be due to competition for food with surrounding colonies. Neighbor size/age was unrelated to alate production. If alate production is correlated with lifetime reproductive success, these results suggest that selection favors colonies that monopolize more space, whatever the size of neighboring colonies. Received: 12 February 1996 / Accepted: 6 September 1996     

The morphology of erythroid cells separated by density gradient centrifugation through ficoll

Summary The regenerating blood of geese injected with phenylhydrazine was subjected to large scale, zonal centrifugation through density gradients of Ficoll. In this way, erythroid cells were fractionated according to their respective stages of development. Highly enriched fractions were obtained, containing cells that were well preserved as assessed by both light and electron microscopy. The separated cells exhibited ribosome density and nucleic acid and protein staining patterns typically associated with erythrocyte differentiation. Morphometric analysis of nuclei indicated that despite an apparent net increase in the amount of compact chromatin during development, comparatively little difference existed between the volumes of condensed chromatin present in immature and mature cells. Instead, there was a three fold decrease in nuclear volume between young erythroblasts and reticulocytes, coupled with a concomitant decrease in the volume occupied by dispersed chromatin, RNP and nucleoli. These observations are discussed in relation to molecular changes associated with nuclear differentiation in erythroid cells.Supported by grants from the National Research Council of CanadaWe thank Dr. G. Setterfield for assistance with the EM data and we are grateful to the N.R.C. for use of centrifuges and the zonal rotor     

Colony age, neighborhood density and reproductive potential in harvester ants

At about age 5 years, colonies of the harvester ant, Pogonomyrmex barbatus, begin to produce winged, sexual forms (alates) that mate in large annual aggregations. We examined how colony age and neighborhood density affect the numbers, body mass, and body fat of alates produced by 172 colonies ranging in age from 4 to 17 years. Over one-third (36%) of all colonies produced no alates. Failure to reproduce was independent of colony age. Of those colonies that did produce alates, older colonies produced more alates than younger colonies. Older colonies produced lighter female alates (in dry mass), but the total biomass of additional alates produced by older colonies far outweighed the reduced allocation to female alate body mass. Body fat content was much higher in female alates (36.0% on average) than in males (3.7% on average). Alate body fat content was not related to colony age. The fitness of female alates may be related to their fresh body mass; that of females captured after mating and reared in the laboratory was positively correlated with egg-laying rate, although not with the total number of eggs in the first brood. Neighborhood density was not related to alate number, mass, or fat content, in contrast to the results of a 1995 study at the site, in which alate numbers were negatively related to neighborhood density. Thus the influence of crowding on reproductive output appears to vary from year to year, perhaps in response to variation in rainfall and food supply. Alate output by individual colonies was correlated among years. These results suggest that a few, older colonies dominate the pool of reproductives year after year. Received: 11 May 1998 / Accepted: 19 December 1998     

The reproductive potential of workers in slave-making ants

Summary Colonies of slave-making ants have been used repeatedly to test sex allocation theory. It was suggested that workers of slave-making ants are more strongly selected to reproduce than workers of related, non-parasitic species, because they are incapable of manipulating sex allocation and the sexualization of larvae in their colonies. I show here that in slave-making Formicoxenini, worker ovaries on average consist of significantly more ovarioles than in non-parasiticLeptothorax species. Similarly, whereas in mostLeptothorax species, workers form reproductive hierarchies and lay eggs only in orphaned colonies, slave-maker workers show antagonistic interactions already in the presence of the queen and at least in some species have been observed ovipositing in queen-right colonies. The significance of these results is discussed.     

High density lipoprotein oxidation: in vitro susceptibility and potential in vivo consequences

Elevated levels of plasma high density lipoprotein (HDL) are strongly predictive of protection against atherosclerotic vascular disease. HDL particles likely have several beneficial actions in vivo, including the initiation of reverse cholesterol transport. The apparent importance of oxidative modification of low density lipoprotein in atherogenesis raises the question of how oxidative modification of HDL might affect its cardioprotective actions. HDL is readily oxidized using numerous models of lipoprotein oxidation. In vitro evidence suggests oxidation might impair some protective actions, but actually enhance other mechanisms induced by HDL that prevent the accumulation of cholesterol in the artery wall. This article reviews the current literature concerning the relative oxidizability of HDL, the structural changes induced in HDL by oxidation in vitro, and the potential consequences of oxidative modification on the protective actions of HDL in vivo.     

The assessment of reproductive potential in Micronesian kingfisher pairs

The Micronesian kingfisher Halcyon cinnamomina cinnamomina is now extinct in the wild and survives only in U.S. zoos. Although pairs have reproduced in captivity, the captive breeding program has been plagued with inconsistencies in reproductive success. One problem has been determining whether birds housed as reproductive pairs have really established pairbonds. The behavior of newly paired birds may provide information that could be used to predict future reproductive success. Observations conducted for 90 min immediately after introduction of five new pairs at three institutions suggest that the specific behavioral combination of high nest activity and low aggression may indicate reproductive compatibility. Pairs that ultimately produced surviving offspring were less aggressive and engaged in more nest activity than pairs that were not productive. Observations conducted on four of these pairs for an additional month after introduction failed to provide additional information relevant to the assessment of pair status. Although long-term behavioral observations are also desirable, quick assessments such as these may be useful for determining the reproductive potential of more pairs than would be possible using traditional methods. The identification of sexually compatible pairs is a critical step toward the ultimate goal of re-establishing this species in the wild. Zoo Biol 17:425–432, 1998. © 1998 Wiley-Liss, Inc.     

Pronase reduces intramembranous particle density in uterine epithelial cells in vivo

The proteolytic enzyme, pronase, was injected into the uterine lumen of rats. This treatment removed half the intramembranous particles (IMPs) from the apical plasma membrane of the uterine epithelial cells but tight junctions of these cells were unaffected. We conclude that at least some of the IMPs are proteinaceous in nature and suggest that IMPs not affected by pronase may be deeply embedded in the lipid bilayer.     

Studies on a fractionated murine fibrosarcoma: proliferative potential of the separated cells.

A transplantable methylcholanthrene-induced fibrosarcoma of female BALB/c mice (the MC-2 fibrosarcoma) was dissociated by combined mechanical and enzymatic means, then fractionated by isopycnic centrifugation in linear albumin gradients. In some experiments recovered cells were both cultured in soft nutrietn agar and inoculated subcutaneously into syngeneic recipients. In these experiments a highly significant correlation was observed between subsequtnt colony number and rapid growth phase tumor size suggesting identity of clonigenic and tumorigenic cells. It was consistently found that clonigenic cells were markedly depleted from the low density extremes of the cell density distribution profiles suggesting that the low density neoplastic cells had irreversibly left the growth fraction. With increasing tumor age, sequential studies showed that both total and clonigenic cell density distribution profiles were variable, showing no obvious trend, suggesting that in the age (13-35 days) and size (2-8 g) range studied growth fraction changes had little selective effect on cells of any specific density. These results imply that a marked selective depletion of low density clonigenic cells (or selective accumulation of low density non-proliferative cells) must mainly occur during an earlier phase of tumor growth. Studies on several other murine solid tumors also showed maximal depletion of clonigenic cells from the least dense fractions, suggesting that this situation may be common.     

Chondrogenic potential of adipose tissue-derived stromal cells in vitro and in vivo.

Articular cartilage exhibits little intrinsic repair capacity, and new tissue engineering approaches are being developed to promote cartilage regeneration using cellular therapies. The goal of this study was to examine the chondrogenic potential of adipose tissue-derived stromal cells. Stromal cells were isolated from human subcutaneous adipose tissue obtained by liposuction and were expanded and grown in vitro with or without chondrogenic media in alginate culture. Adipose-derived stromal cells abundantly synthesized cartilage matrix molecules including collagen type II, VI, and chondroitin 4-sulfate. Alginate cell constructs grown in chondrogenic media for 2 weeks in vitro were then implanted subcutaneously in nude mice for 4 and 12 weeks. Immunohistochemical analysis of these samples showed significant production of cartilage matrix molecules. These findings document the ability of adipose tissue-derived stromal cells to produce characteristic cartilage matrix molecules in both in vitro and in vivo models, and suggest the potential of these cells in cartilage tissue engineering.     

Hormonally stimulated adenylate cyclase and cAMP dependent protein kinase in membranes of rabbit erythroid cells separated according to density

Plasma membranes were prepared after density gradient separation of erythroid cells obtained from bled animals. In a fraction enriched in young reticulocytes (lowest density), the basal and the prostaglandin stimulated adenylate cyclase were greatly augmented if compared with the membranes from unfractionated cells or from the layers of higher densities. Potentiation by GTP or soluble factor(s) of the prostaglandin stimulated adenylate cyclase was found solely in the fractions containing the youngest cells (lowest density). A very significant augmentation of both the basal and the effectors stimulated adenylate cyclase was obtained when the white blood cells and the platelets were removed by filtration through alpha-cellulose prior to density separation. A small population of probably very young reticulocytes was shown to contain a very active adenylate cyclase coupled to the hormonal receptor. Upon short time of maturation this coupling could no longer be detected. The cAMP generated in the fraction enriched in young reticulocytes increased the phosphorylation of some membrane proteins. The presence of a hormonally regulated adenylate cyclase and eventually the phosphorylation of some specific membrane proteins by the cAMP generated in situ permit to envisage possible functions of this system in young reticulocytes.     

Characterization of subpopulated articular chondrocytes separated by Percoll density gradient

The aim of this study was to develop a method for fractionation of articular chondrocytes from the entire thickness of the tissue. Isolated chondrocytes from rabbit articular cartilage fractionated by centrifugation in a discontinuous Percoll gradient resulted in four cell fractions with two differing properties. The lowest-density fraction consisted mainly of large cells with small nuclei proliferated actively, maintained the chondrocytic phenotype, and secreted larger amounts of proteoglycan. In contrast, the highest-density fraction consisted of small cells with large nuclei proliferated slowly, did not express the chondrocytic phenotype, and produced larger amounts of interleukin 1-induced nitric oxide. Comparing our results with other previous reports, we find that fraction 1 cells are likely originated from the deep layer of the articular cartilage, whereas fraction 4 cells are tentatively categorized as chondrocytes from the superficial layer of cartilage. Centrifugal fractionation of articular chondrocytes via Percoll density gradient permits clear separation of these heterogeneous cells into different phenotypic populations and allows distinguishing of cells from the different layers of articular cartilage. This simple novel method will provide ready separation of articular chondrocytes for the investigation of the pathogenesis of articular cartilage.     

Two-dimensional impedance studies of BSA buoyant density separated human erythrocytes

Combined DC (Coulter Volume) and radio frequency impedance studies were performed on human erythrocytes which had been separated by buoyant density in linear, neutral, isotonic bovine serum albumin gradients. The individual buoyant density fractions showed no reproducible shift in volume with buoyant density but did show a shift with opacity, radio frequency impedance divided by dc impedance. This new electronic parameter of opacity can be related to cell age, since both it and cell age are directly related to buoyant density. This increase in opacity with buoyant density is correlated with a change in shape.     

Protein synthesis in different populations of rat hepatocytes separated according to density

Hepatocytes were isolated from fasted rats by a two-step Ca⁺⁺-free/collagenase perfusion method. The cells were subjected to centrifugation under mild conditions at 12°C in a linear metrizamide gradient (1.075–1.12 gm/cm³). The cells were distributed in the gradient a bell-shaped manner. According to their position in the gradient the cells were divided in five different population. The heaviest population was omitted from the subsequent evaluation because it contained a high proportion of dead cells. The activity of alanine aminotransferase increased with increasing cell density indicating that the lightest cell population was enriched in perivenous cells, whereas the heaviest cell population had an excess of periportal cells. Protein synthesis was more rapid in the light (perivenous) cell population than in the heavy (periportal) cell population as measured by means of incoporation of radioactively labeled valine into protein. The distribution measured in vitro indicated approximately 80% higher rates in perivenous cells. On the other hand, the synthesis and secretion of export proteins were similar in all cell populations regardless of their density. Protein degradation measured as appearance of free valine in cell media was higher in the light (perivenous) cell population than in the other populations. Thus protein metabolism seemed to be faster in the light cell population.     

The neuroprotective potential of carotenoids in vitro and in vivo

BackgroundDespite advances in research on neurodegenerative diseases, the pathogenesis and treatment response of neurodegenerative diseases remain unclear. Recent studies revealed a significant role of carotenoids to treat neurodegenerative diseases. The aim of this study was to systematically review the neuroprotective potential of carotenoids in vivo and in vitro and the molecular mechanisms and pathological factors contributing to major neurodegenerative diseases (Alzheimer's disease, Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, and stroke).HypothesisCarotenoids as therapeutic molecules to target neurodegenerative diseases.ResultsAggregation of toxic proteins, mitochondrial dysfunction, oxidative stress, the excitotoxic pathway, and neuroinflammation were the major pathological factors contributing to the progression of neurodegenerative diseases. Furthermore, in vitro and in vivo studies supported the beneficiary role of carotenoids, namely lycopene, β-carotene, crocin, crocetin, lutein, fucoxanthin and astaxanthin in alleviating disease progression. These carotenoids provide neuroprotection by inhibition of neuro-inflammation, microglial activation, excitotoxic pathway, modulation of autophagy, attenuation of oxidative damage and activation of defensive antioxidant enzymes. Additionally, studies conducted on humans also demonstrated that dietary intake of carotenoids lowers the risk of neurodegenerative diseases.ConclusionCarotenoids may be used as drugs to prevent and treat neurodegenerative diseases. Although, the in vitro and in vivo results are encouraging, further well conducted clinical studies on humans are required to conclude about the full potential of neurodegenerative diseases.     

The origin of helping: the role of variability in reproductive potential

We investigate the relationship between variation in reproductive potential among members of a family and genetic relatedness to determine which combinations favor natural selection for helping behavior. Conditions favoring helping are derived for the helper, the recipient, and the parents of these individuals. Our analysis reveals that a factor of general significance in the evolution of social organisms is variability in reproductive potential among offspring of a parent. To a limited extent this factor has already been appreciated because of its implicit role in "facultative altruism" and "parental manipulation", or suppression of offspring or sibs; however, the unifying role of variance per se and the ways by which it may act have not been widely appreciated. We show that suppression as a source of intra-brood variance is less powerful in the evolution of sociality than other, natural, sources of variance. The facts of natural history appear to be more consistent with a model utilizing natural variance than with a variance-enhancement model for most vertebrates. We present models for discrete and for overlapping generations. Fecundity of young potential helpers relative to adults is an important source of variance for the origin of helping.     

凹唇壁蜂的耐寒性及生殖潜力研究

在滞育期和滞育结束后 (成虫出茧之前 ) ,分别测定凹唇壁蜂越冬成虫的耐寒性 ,结果表明 :滞育期成虫的过冷却点和体液冰点分别为 -2 6 4 8℃和 -2 0 91℃ ,解除滞育后分别为 -1 8 4 0℃和-1 1 78℃。自然条件下 ,凹唇壁蜂在我国北方大部分地区可安全越冬。在筑巢前期 ,对雌蜂的生殖系统解剖观察发现 ,卵巢由 6根卵巢管组成 ,卵母细胞总数平均为 55 9± 4 4 6个 ,卵原区在成虫筑巢期不再产生卵母细胞。