The role of visual cues in the facilitation of growth in a schooling fish

Synopsis This study tested the hypothesis that visual contact between fish may result in enhanced rates of growth in a schooling fish. Juvenile chum salmon, Oncorhynchus keta, were held singly and reared in isolation or in visual contact with conspecifics. Fish were fed at either a low (6% body weight d^–1) or high (20% body weight d^–1) ration for 42d. Specific rates of weight gain were 18% greater at low ration and 38% greater at high ration for fish in visual contract with conspecifics than for those held in isolation. The results demonstrate a selective advantage of visual cues associated with schooling behavior and suggest that the efficacy of growth models for schooling fishes may be enhanced by the consideration of social interactions which may facilitate growth.     

Phytochemical and morphological support for the existence of two species inMonoclea (Hepaticae)

Recognition of two different species in the liverwort genusMonoclea Hook. (monotypic orderMonocleales), viz.M. forsteri Hook. in New Zealand andM. gottschei Lindb. in the New World, is supported by characteristics of the sporophyte, antheridial receptacle and secondary metabolites.M. gottschei produces the greatest variety of flavonoids and the largest amount of bisbibenzyls ever encountered in a liverwort. In contrast,M. forsteri is poor in secondary metabolites. Two allopatric subspecies are recognized inM. gottschei, based on characteristics of the antheridial receptacle: subsp.gottschei in Chile (Valdivian region, Juan Fernandez Is.) and subsp.elongata Gradst. & Mues, subsp. nova, in tropical America. The exclusive occurrence inMonoclea of glucuronide and galacturonide flavone glycosides and the fact that capsule dehiscence may take place before full elongation of the seta are new arguments in support of the placement ofMonocleales in theMarchantiidae. Publication Nr. 43 of the Arbeitskreis Chemie und Biologie der Moose, Universität des Saarlandes, Saarbrücken. This paper is dedicated to DrElla O. Campbell, Massey University, Department of Botany and Zoology, New Zealand on the occasion of her 80th birthday.     

Gene variation and gene flow inOrchis morio (Orchidaceae) from Italy

Data are presented on genetic variation at 27 enzyme loci of the Green-Winged orchid,Orchis morio, in 18 population samples from Italy. The existence in Italy of two subspecies, i.e. subspp.morio andpicta, is not supported by allozyme data. No genetic heterogeneity was found betweenmorio-like andpicta-like samples and specimens. Moreover, morphological transition between the two forms was observed in different Italian populations. The parameters of genetic variability estimated forO. morio populations are consistent with those found among monocotyledon plants, and among those outcrossing, animal-pollinated and with wind-dispersed seeds. Genetic diversity of ItalianO. morio is mostly within populations. Correspondingly, low values of interpopulational genetic distance were found. This appears to be due to high levels of gene flow, which were estimated with different methods. The lack ofO. longicornu from Italian samples, as well as of any hybrid withO. morio (F₁, backcrossed or recombinant individuals) is demonstrated on the basis of genetic data. It is concluded that recurrent reports ofO. longicornu from Italy are due to confusion withO. morio or with otherOrchis species.     

Plant regeneration from haploid cell suspension-derived protoplasts of Mediterranean rice (Oryza sativa L. cv. Miara)

More than 750 plants were regenerated from protoplasts isolated from microspore callus-derived cell suspensions of the Mediterranean japonica rice Miara, using a nurse-feeder technique and N6-based culture medium. The mean plating efficiency and the mean regeneration ability of the protocalluses were 0.5% and 49% respectively. Flow cytometric evaluation of the DNA contents of 7 month old-cell and protoplast suspensions showed that they were still haploid. Contrastingly, the DNA contents of leaf cell nuclei of the regenerated protoclones ranged from 1C to 5C including 60% 2C plants. This was consistent with the morphological type and the fertility of the mature plants. These results and the absence of chimeric plants suggest that polyploidization occurred during the early phase of protoplast culture.Abbreviations BAP 6-benzylamino purine - 2,4-D 2,4-dichlorophenoxyacetic acid - FDA fluorescein diacetate - GA3 gibberellic acid - NAA -naphthaleneacetic acid - PAS periodic acid Schiff - PCM protoplast culture medium - PCV packed cell volume     

Modeling problems in conservation genetics using captive Drosophila populations: Consequences of equalizing founder representation

Equalizing founder representation is a recommended practice for maintaining captive populations. However, this procedure has not been subject to controlled experimental evaluation. The effects on inbreeding, genetic variation, and reproductive fitness of maintaining small captive populations by equalizing founder representation (EFR) versus randomly choosing parents (RC) were compared. Ten replicate lines were created with unequal founder representations, split into EFR and RC lines, and maintained for a further eight generations. Founder representations computed from pedigrees were closer to equality in the EFR lines than in the RC lines or the base population, most of the changes being evident after one generation. Significant benefits of EFR were found in lowered inbreeding (mean inbreeding coefficients of 0.35 and 0.41, respectively, for EFR and RC lines) and average heterozygosity (0.141 for EFR, 0.084 for RC, compared with 0.216 in the base population). However, EFR was not significantly better than RC in moving allele frequencies towards equalized founder representation. No significant difference was found in reproductive fitness between EFR and RC (relative fitnesses compared to the base population were 0.179 for EFR and 0.182 for RC). The use of equalization of founder representation for a few generations can be recommended in the genetic management of captive populations derived from a small number of founders that contribute unequally. © 1992 Wiley-Liss, Inc.     

Leaf photosynthetic rate is correlated with biomass and grain production in grain sorghum lines

Significant genetic variation in leaf photosynthetic rate has been reported in grain sorghum [Sorghum biocolor (L.) Moench]. The relationships between leaf photosynthetic rates and total biomass production and grain yield remain to be established and formed the purpose of this experiment. Twenty two grain sorghum parent lines were tested in the field during the 1988 growing season under well-watered and water-limited conditions. Net carbon assimilation rates were measured at mid-day during the 30 day period from panicle initiation to head exertion on upper-most fully expanded leaves using a portable photosynthesis system (LI-6200). Total biomass and grain production were determined at physiological maturity. The lines exhibited significant genetic variation in leaf photosynthetic rate, total biomass production and grain yield. Significant positive correlations existed between leaf photosynthesis and total biomass and grain production under both well-watered and water-limited conditions. The results suggest that leaf photosynthetic rate measured prior to flowering is a good indicator of productivity in grain sorghum.     

Carbon isotope composition of CH4 from rice paddies in Japan

Carbon isotope ratios (¹³C) for bubble CH₄ in a submerged paddy soil were studied in Yokohama, Japan, throughout a growing period, and its variation was found. Bubble CH₄ collected from other 33 paddy fields in Japan was also measured for its ¹³C and the results agreed with Yokohama. Furthermore, the variation occurred irrespective of the amount and the type of supplied organic substances to the fields (whole rice straw, rice stubble, or compost). The ¹³C value (average value of -55.9 ± 4.24) from these paddy fields was higher than those of the CH₄ emitted from African and North American paddies. The higher value was little affected by their difference in the supplied organic substances. CH₄ oxidation likely occurs for bubble CH₄ in the shallow paddy fields. A rough estimate of the total CH₄ production, using isotope mass balance, showed that 17 to 22% of organic carbon supplied to Japanese paddies transforms to CH₄.     

Disulfide bridges in tomato pectinesterase: variations from pectinesterases of other species; conservation of possible active site segments.

Analysis of tomato pectinesterase by carboxymethylation, with and without reduction, shows that the enzyme has two intrachain disulfide bridges. Analysis of fragments obtained from the native enzyme after digestion with pepsin identified bridges connecting Cys-98 with Cys-125, and Cys-166 with Cys-200. The locations of disulfide bridges in tomato pectinesterase are not identical to those in three distantly related pectinesterases (18-33% residue identities) from microorganisms. However, one half-Cys (i.e., Cys-166) position is conserved in all four enzymes. Sequence comparisons of the overall structures suggest a special importance for three short segments of the entire protein. One segment is at the N-terminal part of the tomato pectinesterase, another in the C-terminal portion near the distal end of the second disulfide loop, and the third segment is located in the central part between the two disulfide bridges. The latter segment, encompassing only 40 residues of the entire protein, appears to high-light a functional site in a midchain segment.     

Genetic variation in relation to demography of peripheral pool frog populations (Rana lessonae)

Summary Genetic variation in an isolated northern metapopulation of the pool frog (Rana lessonae) in Sweden was compared to that of Central European populations using enzyme electrophoresis and literature data. Of the 31 loci scored, two (EST-2 andIDH-2) were polymorphic while no variation occurred in seven of the eight loci which are polymorphic in Central European populations.The heterozygosity level of the Swedish pool frogs is very low compared to that of other anuran populations, but their mean proportion of fertilized eggs within egg masses (97.5%) was not lower than in more heterozygous species, and their body size-specific fecundity did not differ from that of Polish conspecifics. The low genetic variability of the Swedish pool frogs is discussed in relation to features of the local populations such as size (N), calculated effective size (N _e ) reproductive success and probable history. It is concluded that long-term strong fluctuations in population size caused by reporductive failure in cold years have contributed more to the low genetic variability than could a single founder event due to a recent introduction by man.