The evolution of brood parasitism: the role of facultative parasitism

The hypothesis that facultative brood parasitism may serve asan intermediate step in the evolutionary transition from purelyparental reproduction to obligate parasitism was investigated.The population dynamics of a host-parasite complex were computer-simulatedin a model that incorporated different intensities of parasitismand host defense and considered a simplified semelparous birdspecies living in a homogeneous habitat The individuals usetwo different breeding strategies: provide parental care orparasitize the nest of those providing parental care. Underobligate parasitism, the parasites appeared unsuccessful, drovethe host population to extinction, or coexisted with the hostin stable or oscillating proportions. The behavior of the systemdepended on both the effectiveness of the parasite and the defenseof the host. Under facultative parasitism (making the best ofa bad job), the parasites reduced host numbers but did not reducethe population size below the number of breeding sites. Thus,facultative parasitism provides a better opportunity for thedevelopment of defense in the host. The population of a hostthat shows a certain level of defense can be more successfullyinvaded by obligate parasites so that stable coexistence ofhosts and parasites is possible.     

Low‐dose linearity: The rule or the exception?

In 1976, Crump, Hoel, Langley, and Peto described how almost any dose‐response relationship for carcinogens becomes linear at low doses when background cancers are taken into account. This has been used, by the U.S. Environmental Protection Agency, USEPA, as partial justification for a regulatory posture that assumes low‐dose linearity, as is illustrated by a discussion of regulation of benzene as a carcinogen. The argument depends critically on the assumption that the pollutant and the background proceed by the same biological mechanism. In this paper we show that the same argument applies to noncancer end points also. We discuss the application to a number of situations: reduction in lung function and consequent increase in death rate due to (particulate) air pollution; reduction in IQ and hence (in extreme cases) mental deficiency due to radiation in utero; reduction of sperm count and hence increase in male infertility due to DBCP exposure. We conclude that, although the biological basis for the health effect response is different, in each case low‐dose linearity might arise from the same mathematical effect discussed by Crump et al. (1976). We then examine other situations and toxic end points where low‐dose linearity might apply by the same argument. We urge that biologists and chemists should concentrate efforts on comparing the biological and pharmacokinetic processes that apply to the pollutant and the background. Finally, we discuss some public policy implications of the possibility that low dose linearity may be the rule rather than the exception for environmental exposures.     

Use of Plant Strategy Ordination,DCA and ANOVA to elucidate relationships among habitats of Salix planifolia and Salix monticola

Abstract. Detrended Correspondence Analysis (DCA) was used on a data set of 112 species from 14 stands dominated by Salix planifolia and/or S. monticola. Environmental variables were determined which might be important to explain differences in stand vegetation composition, and willow stature (height), in willow carrs in the Rocky Mountain National Park. Correlation of environmental variables with DCA stand scores indicate that peat depth and soil redox potential are highly related to the primary DCA axis. Soils in stands of S. planifolia are more reduced in the early summer and have greater peat depths, than soils in stands of S. monticola. The second DCA axis is related to a water chemistry gradient of hydrogen ion, sulphate, and ammonium concentration. Four environmental variables selected by correlation analysis were regressed on stand scores from the first two DCA axes. Regression coefficients of August soil redox potential and soil water pH were significantly non-zero on the primary DCA axis. In addition to overall vegetation relationships elucidated by DCA, the relationships between willow stature and environmental variables were tested by simultaneous ANOVAs. ANOVA results and DCA ordinations indicate that S. planifolia and S. monticola plants achieve the greatest stature in the least reduced soils, and in shallow peat. Competitive, stress tolerant, and ruderal plant strategy theory applied to the vegetation data produced an arrangement of stands highly correlated to the DCA Axis 1 stand arrangement. These correlations indicate that the primary axis of vegetation structure can be extracted either by species composition, or species morphology/physiology relationships. Concurrent use of DCA and plant strategy theory is suggested as a tool for the prediction of community composition.     

Rank and age related feeding strategy observed through field experiments in the Koshima group of Japanese macaques

The feeding process of Japanese monkeys on soy beans which were scattered over a sandy beach on Koshima islet was studied. Younger monkeys were able to pick up more beans when 8 kg of beans were divided and given two times (“two times feeding”) than when the whole amount (8 kg) of beans was given at one time (“one time feeding”). The effect of saturation of the food intake capacity in younger monkeys at the first feeding in “two times feeding” did not appear at the second feeding one hour later. The minutely intake of soy beans (feeding speed) for each age class was analyzed. The decline of feeding speed in adult females after the peak in “one time feeding” was not related to the decline in density of beans on the ground, and this decline was caused by saturation of their food intake capacity. Adult females were divided into four classes according to their dominance rank order: high, lower-high, higher-low, and low classes. The total amount of intake in “one time feeding” was far larger in the high class than in any of the other classes. The total amount of feeding in the first feeding of “two times feeding” increased in accordance with rise in the dominance rank class, and there was no relation to rank and total feeding amount in the second feeding of “two times feeding.” Differences existed in the process of feeding between the rank classes. The feeding speed of the low class was as high as that of the high class on the curve of minutely intake, while the low class stopped feeding much earlier than the high class. The lower-high class displayed a low feeding speed, and stopped feeding the latest. The order of the duration to stay and to feed in the feeding area was lower-high > high > higher-low > low, and this order did not change under the three different feeding conditions, “one time feeding,” and the first and second feedings of “two times feeding.” Adolescent females tended to stay the longest duration in the feeding area among all age classes. Both the lower-high class females and adolescent females had an unstable social status in the Koshima group, and their social status affected their feeding behaviors. The feeding behaviors were similar in attitude depending on social status, and are considered to be maintained for a fairly long time. The feeding strategy of the lower-high class, in staying a longer duration in the artificial feeding area, and departing later, may be effective under the artificial feeding conditions, but it may be a bad strategy in a natural habitat where the food is not so clumped as in artificial feeding, and where choice of other food patches is possible. The above results agree well with previous reports for the Koshima group, indicating that the rank of the lower-high class females was unstable (Mori et al., 1989), and that their reproductive success was low (Watanabe et al., 1992).     

Involvement of plasma membrane potential in the tolerance mechanism of plant roots to aluminium toxicity

H⁺-ATPase activity of a plasma membrane-enriched fraction decreased after the treatment of barley (Hordeum vulgare) seedlings with Al for 5 days. A remarkably high level of Al was found in the membrane fraction of Al-treated roots. A long-term effect of Al was identified as the repression of the H⁺-ATPase of plasma membranes isolated from the roots of barley and wheat (Triticum aestivum) cultivars, Atlas 66 (Al-tolerant) and Scout 66 (Al-sensitive). To monitor short-term effects of Al, the electrical membrane potentials across plasma membranes of both wheat cultivars were compared indirectly by measuring the efflux of K⁺ for 40 min under various conditions. The rate of efflux of K⁺ in Scout was twice that in Atlas at low pH values such as 4.2. Vanadate, an inhibitor of the H⁺-ATPase of the plasma membrane, increased the efflux of K⁺. Al repressed this efflux at low pH, probably through an effect on K⁺ channels, and repression was more pronounced in Scout. Al strongly repressed the efflux of K⁺ irrespective of the presence of vanadate. Ca²⁺ also had a repressive effect on the efflux of K⁺ at low pH. The effect of Ca²⁺, greater in Scout, might be related to the regulation of the net influx of H⁺, since the effect was negated by vanadate. The results suggest that extracellular low pH may cause an increase in the influx of H⁺, which in turn is counteracted by the efflux of K⁺ and H⁺. These results suggest that the ability to maintain the integrity of the plasma membrane and the ability to recover the electrical balance at the plasma membrane through a net influx of H⁺ and the efflux of K⁺ seem to participate in the mechanism of tolerance to Al stress under acidic conditions.     

Improved correlation between soil exchangeable K and plant K contents on a tissue water basis

In acid volcanic soils, plant roots are thought to be injured by acidity (low pH) and/or solubilized aluminium (Al) ions. An attempt was made to separate the effects of low pH from those of Al on the elongation and viability of alfalfa (Medicago sativa L.) radicles in water culture. Root elongation was irreversively curtailed by 20 hours treatment at pH 4.0 without Al or 20 mmol m^-3 Al at pH 5.0. Viability of surface cells of root tips was detected as a degrading activity of fluorescein diacetate (FDA) by cellular esterases and subsequent accumulation of derived fluorescein within cells. Large numbers of the surface cells lost their viability after four hours exposure at the low pH. In contrast, surface cells maintained both FDA degrading activity and ability to accumulate fluorescein 20 h after initial exposure to the Al solution (20 mmol Al m^-3, pH 5.0). These results suggest that there are some significant differences in the mechanisms of phytotoxicity to alfalfa root between the two stress factors.     

Operational patterns affecting lactic acid production in ultrafiltration cell recycle bioreactor

Lactic acid production with cell recycling on an ultrafiltration tubular membrane reactor was studied; higher lactic acid concentrations as well as productivities were obtained under long-term fermentations compared with other high cell density systems. Different operational conditions, namely dilution rates and start-up modes, were assessed. Performances were very different at the three different dilution rates tested (D = 0.20 h(-1), D = 0.40 h(-1), or D = 0.58 h(-1)). The different behaviours are discussed and factors responsible for them are presented. The best way to operate for lactic acid production is chosen, the dilution rate of D = 0.40 h(-1) being the one providing the best overall performance. On the other hand, results show that of the two start-up modes tested, continuous start (membrane open) permits higher permeabilities throughout the operational runs than batch start (membrane closed). Operational stability was found to be directly associated with membranes that work at "steady state," the membrane permeability being kept around 15 L/m(2) h. Optimized cell bleed can improve time of operation if such membrane permeability can be maintained for a longer time. A comparison of results with those obtained in other lactic acid production systems is presented; such comparison shows that this tubular ultrafiltration membrane cell recycle reactor presents three important advantages: (1) concomitant lactic acid concentrations and productivities; (2) long periods of operation at reasonable permeabilities; and (3) good mechanical stability permitting the use of steam sterilization. (c) 1995 John Wiley & Sons, Inc.     

Changes associated with tyrosine phosphorylation during short-term hypoxia in retinal microvascular endothelial cells in vitro

The occlusion of capillary vessels results in low oxygen tension in adjacent tissues which triggers a signaling cascade that culminates in neovascularization. Using bovine retinal capillary endothelial cells (BRCEC), we investigated the effects of short-term hypoxia on DNA synthesis, phosphotyrosine induction, changes in the expression of basic fibroblast growth factor receptor (bFGFR), protein kinase C (PKCα), heat shock protein 70 (HSP70), and SH2-containing protein (SHC). The effect of protein tyrosine kinase (PTK) and phosphatase inhibitors on hypoxia-induced phosphotyrosine was also studied. Capillary endothelial cells cultured in standard normoxic (pO₂ = 20%) conditions were quiesced in low serum containing medium and then exposed to low oxygen tension or hypoxia (pO₂ = 3%) in humidified, 5% CO₂, 37°C, tissue culture chambers, on a time-course of up to 24 h. DNA synthesis was potentiated by hypoxia in a time-dependent manner. This response positively correlated with the cumulative induction of phosphotyrosine and the downregulation of bFGFR (M_r ～ 85 kDa). Protein tyrosine kinase inhibitors, herbimycin-A, and methyl 2,5-dihydroxycinnamate, unlike genistein, markedly blocked hypoxia-induced phosphotyrosine. Prolonged exposure of cells to phosphatase inhibitor, sodium orthovanadate, also blocked hypoxia-induced phosphotyrosine. The expression of HSP70, PKCα, and SHC were not markedly altered by hypoxia. Taken together, these data suggest that short-term hypoxia activates endothelial cell proliferation in part via tyrosine phosphorylation of cellular proteins and changes in the expression of the FGF receptor. Thus, endothelial cell mitogenesis and neovascularization associated with low oxygen tension may be controlled by abrogating signaling pathways mediated by protein tyrosine kinase and phosphatases. © 1995 Wiley-Liss, Inc.     

Distribution of male yellow dungflies around ovipasition sites: the effect of body size

Abstract.

• 1 Spatial and temporal variation in body size of yellow dungflies, Scatophaga stercoraria, gathering on and around cow droppings was studied in an Icelandic population in order to elucidate the effect of male and female size on male mating tactics.
• 2 Males copulating on droppings were on average larger than males copulating in the grass, but of similar size to males guarding ovipositing females. Males searching on droppings were smaller than males copulating or guarding females on droppings but larger than males copulating in the grass. No such differences were found in female size.
• 3 Resource-holding power of males (RHP, i.e. male: female size ratio) differed between the three mating groups and was highest for males on the droppings. Size and RHP clearly affect the tactics of copulating males. Males with low RHP tend to copulate in the grass in spite of the cost of longer copulation duration. We argue that this is caused by risk of takeovers from large searching males.
• 4 There was no change in male size with the age of individual droppings. Contrary to what might be expected, large searching males are not predominantly found at fresh droppings when the probability of catching unpaired females is highest. We suggest instead that good prospects in taking females over from other males must make the strategy to search for females on older droppings profitable.
• 5 RHP did not change with age of dropping in the three mating groups. The size of ovipositing females increased with age of dropping, probably reflecting longer copulation and egg-laying times of large females.
• 6 We found an overall positive relationship between sizes of male and female partners. This correlation was highly significant for copulating pairs in the grass. This is probably a consequence of males with low RHP copulating in the grass and fights in which larger males take over females from smaller males. A weaker, but significant, correlation was found amongst ovipositing pairs. This must be due to take-over effects. No size correlation was found for pairs copulating on droppings.