Response of Daphnia to substances released from crowded congeners and conspecifics

The effects of chemicals released from crowded congeners andconspecifics on life history parameters of the freshwater zooplanktersDaphnia cucullata and Daphnia pulex were examined. Length andage at maturity of D. pulex were affected by crowding chemicals.Reproduction was lower in crowded medium, and ephippia wereproduced. Newborn D. pulex in crowded medium were significantlylonger than the controls. The intrinsic rate of population increaseof D. pulex was 14 and 25% lower than the control when exposedto crowded medium from D. cucullata and D. pulex, respectively.Neither urea nor ammonia (at 1 mg l^-1) seemed to be responsiblefor these effects in D. pulex. In D. cucullata, no significanteffect of crowding infochemicals on length and age at maturitywas found. However, crowding chemicals reduced reproduction.No ephippia were produced in crowded medium, but up to 83% non-developingeggs were observed in D. cucullata. Newborns were similarlysized in crowded and standard medium. The intrinsic rate ofpopulation increase of D. cucullata was 44 and 96% lower thanthe control when exposed to crowded medium from D. cucullataand D. pulex, respectively. Clearance rates of D. pulex weresignificantly reduced in crowded media compared with standardmedium, which could partly explain why the animals exposed tocrowding chemicals reacted as if they were food limited.     

The molecular chaperone alpha-crystallin incorporated into red cell ghosts protects membrane Na/K-ATPase against glycation and oxidative stress.

Alpha-crystallin, a molecular chaperone and lens structural protein protects soluble enzymes against heat-induced aggregation and inactivation by a variety of molecules. In this study we investigated the chaperone function of alpha-crystallin in a more physiological system in which alpha-crystallin was incorporated into red cell 'ghosts'. Its ability to protect the intrinsic membrane protein Na/K-ATPase from external stresses was studied. Red cell ghosts were created by lysing the red cells and removing cytoplasmic contents by size-exclusion chromatography. The resulting ghost cells retain Na/K-ATPase activity. alpha-Crystallin was incorporated in the cells on resealing and the activity of Na/K-ATPase assessed by ouabain-sensitive 86Rb uptake. Incubation with fructose, hydrogen peroxide and methylglyoxal (compounds that have been implicated in diabetes and cataract formation) were used to test inactivation of the Na/K pump. Intracellular alpha-crystallin protected against the decrease in ouabain sensitive 86Rb uptake, and therefore against inactivation induced by all external modifiers, in a dose-dependent manner.     

THE TIME-COURSE OF PHOTOADAPTATION TO LOW-LIGHT IN PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE)1

The estuarine dinoflagellate, Prorocentrum mariaelebouriae (Parke & Ballantine 1957) Faust 1974 undergoes increases in pigmentation and photosynthetic efficiency within several days of downward light shifts. These changes can be described by first-order kinetics, as has been reported previously for Chlorophyll (Chl) a in several phytoplankton species. The studies described in this paper were conducted with isolates of populations of Prorocentrum from the Chesapeake Bay. We determined rates of adaptation to low-light for cultures grown at a range of photon flux densities (I₀= 2.65–26.2 E.m^?2, d^?1, shifted to 6.3–7.0% I₀) at three temperatures (10°, 15°, and 20° C), bracketing the conditions this species experiences in situ. In this paper, I report the time-course of changes in α, P_max Chl a, peridinin, and I_k and first-order rate constants, K₁ for changes in α, Chl a and peridinin. cell^?1. K₁ for changes in α cell^?1 averaged 1.58 × 10^?2 h^?1 for conditions encompassing five light treatments and three temperatures; the corresponding mean for Chl a was 1.59 × 10^?2 h^?1. Increases in peridinin measured for five light treatments at 15° C showed a mean K₁ of 1.22 × 10^?2 h^?1, Average percent changes in per cell α, Chl a, and peridinin ranged from 0.4–4.0% h^?1 (10–90% d^?1) following exposure to low-light. Photoadaptive changes are important to Prorocentrum because in nature it occupies turbid waters (K_t≥ 0.5 m^?1) where the mixing depth often exceeds the depth of the photic layer. Cells are entrained beneath a seasonally-stable density discontinuity and are exposed to very low-light (< I E.m^?2.d^?1) for days to weeks during subpycnocline transport. The ability of this species to undergo changes in pigmentation and photosynthetic physiology confers increased efficiency of light harvesting and contributes to this species’survival in the estuary where it is an important component of the dinoflagellate flora.     

PHOTOSYNTHETIC PHYSIOLOGY OF PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE) DURING ITS SUBPYCNOCLINE TRANSPORT IN CHESAPEAKE BAY1

This paper presents results of field studies on the estuarine dinoflagellate Prorocentrum mariae-lebouriae (Parke & Ballantine) Faust in Chesapeake Bay. We tested the hypothesis that the photosynthetic physiology of Prorocentrum shows adaptive responses to low-light during a lengthy subpycnocline transport in estuarine circulation. Prorocentrum underwent a seasonal, northward trnasport between February and June, 1984 and 1985. Low cell densities occurred in the seaward part of the estuary during winter and early-spring, subpycnocline populations progressed up-estuary in the ensuring 2–3 months, and dense surface populations developed in the mesohaline portion of the estuary thereafter. We sampled Prorocentrum from surface and subpycnocline waters and measured photosynthesis-light (P-I) relations with in situ incubations. The photophysiology of Prorocentrum collected below the pycnoline differed from that of cells in the surface mixed layer in that photosynthetic efficiency, α-cell^?1, was higher, photosynthetic capacity, P_max-cell^?1 was ·4 times greater for subpycnocline (≦ 10m) samples than for those from the surface mixed layer (≧ 6m). Comparison of in situ photosynthetic properties to those generated in laboratory studies showed that values of α·cell^?1 for both surface and subpycnocline samples were in the range found for cultures in low-light. Concentrations of Chls a, c and peridinin·cell^?1 and molar pigment ratios peridinin: Chl a and Chl a: Chl c were not significantly different for the surface and subpycnocline samples, nor were C · cell^?1 or C : Chl a. Chloroplast and starch volume fractions and the number of thylakoids were the same for samples collected at different depths, and there was no evidence of cytoplasmic vacuolization in any field samples. These morphometric data for cells from natural populations of Prorocentrum most closely resembled data for laboratory cultures grown at or near 2.6E·m-^?2·4d^?1. A lower growth irradiance of 0.3E·m^?2·d^?1 produced indications of stress in cultures, including starch depletion and vacuolization, that were never observed in natural populations. Based on the combination of these findings, we conclude that Prorocentrum is adapted to low-light both in the surface mixed layer and beneath the pycnocline, although certain photophysiological characteristics distinguish these two groups of samples.     

Goldfish cones secrete a two-repeat interphotoreceptor retinoid-binding protein

Vitamin A and fatty acids are critical to photoreceptor structure, function, and development. The transport of these nutrients between the pigment epithelium and neural retina is mediated by interphotoreceptor retinoid-binding protein (IRBP). IRBP, a 133-kDa (human) glycolipoprotein, is the major protein component of the extracellular matrix separating these two cell layers. In amphibians and mammals, IRBP consists of four homologous repeats of about 300 amino acids which form two retinol and four fatty acid-binding sites. Here we show that IRBP in teleosts is a simpler protein composed of only two repeats. Western blot analysis shows that goldfish IRBP is half the size (70 kDa) of IRBP in higher vertebrates. Metabolic labeling studies employing Brefeldin A taken together with in situ hybridization studies and the presence of a signal peptide show that goldfish IRBP is secreted by the cone photoreceptors. The translated amino acid sequence has a calculated molecular weight of 66.7 kDa. The primary structure consists of only two homologous repeats with a similarity score of 52.5%. The last repeats of human and goldfish IRBPs are 69.1% similar with hydrophobic regions being the most similar. These data suggest that two repeats were lost during the evolution of the ray-finned fish (Actinopterygii), or that the IRBP gene duplicated between the emergence of bony fish (Osteichthyes) and amphibians. Acquisition of a multirepeat structure may reflect evolutionary pressure to efficiently transport higher levels of hydrophobic molecules within a finite space. Quadruplication of an ancestral IRBP gene may have been an important event in the evolution of photoreceptors in higher vertebrates. Correspondence to: F. Gonzalez-Fernandez     

High diversity of alpha-globin haplotypes in a Senegalese population, including many previously unreported variants.

RFLP haplotypes at the alpha-globin gene complex have been examined in 190 individuals from the Niokolo Mandenka population of Senegal: haplotypes were assigned unambiguously for 210 chromosomes. The Mandenka share with other African populations a sample size-independent haplotype diversity that is much greater than that in any non-African population: the number of haplotypes observed in the Mandenka is typically twice that seen in the non-African populations sampled to date. Of these haplotypes, 17.3% had not been observed in any previous surveys, and a further 19.1% have previously been reported only in African populations. The haplotype distribution shows clear differences between African and non-African peoples, but this is on the basis of population-specific haplotypes combined with haplotypes common to all. The relationship of the newly reported haplotypes to those previously recorded suggests that several mutation processes, particularly recombination as homologous exchange or gene conversion, have been involved in their production. A computer program based on the expectation-maximization (EM) algorithm was used to obtain maximum-likelihood estimates of haplotype frequencies for the entire data set: good concordance between the unambiguous and EM-derived sets was seen for the overall haplotype frequencies. Some of the low-frequency haplotypes reported by the estimation algorithm differ greatly, in structure, from those haplotypes known to be present in human populations, and they may not represent haplotypes actually present in the sample.     

Determinants of postnatal weight in infant rhesus monkeys: Implications for the study of interindividual differences in neonatal growth

This paper provides an analysis of infant body weights obtained from a sample of 38 rhesus monkey infants (Macaco mulatta) aged 29–165 days, i.e., animals still nutritionally dependent on their mothers. We examine the data on neonatal weights in relation to a number of factors, most notably, the sex of the infants, and the age and adiposity of their mothers. The infant body weights represent cross-sectional rather than longitudinal data; because they were mostly free-ranging animals, the infants were weighed just once each. Nevertheless, the results of our analysis strongly suggest that early postnatal growth in free-ranging rhesus is dependent on both maternal fatness and age. They also suggest that, although male infants are generally heavier than like-aged female infants, they do not grow any faster during the early postnatal period. Here, we speculate that the associations between infant size and both maternal age and adiposity are the result of between-mother differences in lactational output. © 1995 Wiley-Liss, Inc.     

Myocardial uptake kinetics of tocainide enantiomers in the isolated perfused rabbit heart

The extent of myocardial accumulation of tocainide, administered as single enantiomers and as well as racemate, was determined in the isolated, spontaneous beating rabbit heart. The heart was retrogradely perfused at a constant rate and fractions of the perfusate were collected during and after infusion. Kinetic parameters for myocardial accumulation and disposition of tocainide were indirectly determined from drug concentration/time course in the outflow perfusate. No stereoselectivity in myocardial accumulation was observed. A two compartment model with mean half-lives for distribution and elimination of 0.60 and 3.78 min, respectively, was fitted to the accumulation and disposition data. At steady-state, tocainide enantiomers were accumulated about three times in the myocardium relative to the perfusion liquid. © 1995 Wiley-Liss, Inc.