Water Flow Through Vessel Perforation Plates--A Fluid Mechanical Approach

The effect of scalariform perforation plates on the flow ofwater through plant vessels remains poorly understood. In thisstudy, a new computational tool based on finite element methodsolutions to the Navier-Stokes equation was applied to modellingfluid flow through these structures in plant vessels. Modelsdeveloped for Liriodendron tulipifera vessel elements were solvedfor cells with and without the perforation plate to study effectsof the plate on the pressure drop along the cell. Results indicatethat the pressure gradient was 5-fold greater through the platethan for regions before and after the plate. However, the perforationplate in this species accounts for only about 8% of the resistanceto flow through typical vessels because the plate influencesflow for only a short distance along the cell relative to itslength. Details of the flow characteristics through pores ofthe perforation plate are also described. Key words: Conductance, finite element method, perforation plate, vessel, water flow     

Physiological Adaptations in the Gastrointestinal Tract of Crayfish

SYNOPSIS. Crayfish are the dominant macrocrustacean in manyaquatic ecosystems and are the largest crustacean aquaculturalindustry in the United States, yet we know relatively littleabout their preferred and nutritionally important foods, aswell as their ability to utilize those foods. This review focuseson the ability of crayfish to detect foods, reduce food particlesize, digest macronutrients and the control of those functions.Of particular interest are the enzymatic capabilities of crayfish,especially trypsin, an alkaline protease, cellulase, muramidase,and possibly chitinase and chitobiase. The coordinated neuralcontrol of crayfish food location, ingestion and movement hasbeen well documented, while hormonal control mechanisms havenot. The conclusion we must draw from our current state of knowledgeis that crayfish have ample abilities to taste and locate potentialfoods and enzymatic adaptations developed in crayfish that allowuse of many of the foods they encounter in a benthic aquaticenvironment; other adaptations are lacking or have not beenelucidated.     

Genic microsatellite markers derived from EST sequences of switchgrass (Panicum virgatum L.)

Switchgrass is a large, North American, perennial grass that is being evaluated as a potential energy crop. There is a need to assess genetic diversity in stored accessions and in remaining native stands to assist breeding and conservation efforts. Marker development will also be necessary for genetic linkage mapping. Toward this end, 32 switchgrass genic di‐, tri‐ and tetranucleotide repeat microsatellites were identified from expressed sequence tags (ESTs). These microsatellites were used to screen individuals from two different named cultivars. The markers displayed a high level of polymorphism consistent with the tetraploid, allogamous behaviour of the cultivars tested.     

Seasonal changes in the distribution and composition of common seal (Phoca vitulina) haul-out groups

Seasonal changes in the distribution and composition of common seal haul–out groups were followed in a study area in Orkney, Scotland. A marking programme was also undertaken, using both conventional and radio–tags, to study individual movements between sites and seasonal changes in site–use. Certain haul–out sites were used only in the breeding season, while others were used during the winter. Seals were seen at one site all year round and at another during only the pre–pupping and moult period. On one island where two sites were used during the summer, there were significant differences in the sex ratio of groups at the two sites: at one site males predominated and few pups were seen; on another, nearby, mothers and pups were regularly seen, although the site was also used by males. There was also evidence for segregation of the sexes outside the breeding season. Repeated observations of marked seals showed that seals used several different haul–out sites throughout the year, and that the seasonal changes in abundance at different sites resulted from individual changes in site–use. These changes in site–use are discussed in relation to feeding movements, breeding requirements and the physical characteristics of different sites.     

Contractile Proteins of a Benthic Fish. III. Subunit Composition of Myosin

SYNOPSIS. Ultracentrifugal and electrophoretic experiments arereported on the subunit composition of myosin from skeletalmuscle of a benthic fish, Coryphaenoides species. Coryphaenoidesmyosin undergoes extensive association in concentrated KGI solutionsat neutral pH, but sedimentation equilibrium experiments indicatethe presence of a small fraction (3%) of monomeric myosin withmolecular weight approximately 440,000. At pH 11, some of theaggregated myosin is dissociated, and monomeric myosin is itselfdissociated into a heavy component (410,000 mol wt) and a lightcomponent (14,000 mol wt) that comprises 5–7% of the protein.The lialkali component of Coryphaenoides myosin yields a singlepredominant band on cellulose acetate electrophoresis and SDS-ureaelectrophoresis in 9% acrylamide gel. The stoichiometric evidenceindicates that Coryphaenoides myosin contains two heavy chains(205,000 mol wt) and two light chains (14,000 mol wt) that areequivalent with respect to net electrostatic charge and molecularweight. Preparations of myosin obtained by direct extractionfrom muscle mince and by dissociation of actomyosin extractedfrom muscle mince also contain 5% of a 47,000 mol wt componentpresumably actin), traces of 34–36,000 mol wt component,and about 5.7% of low molecular weight material (10,000–15,000)that probably represents contaminant protein, although the possibilityof denatured nivosin subunits cannot be excluded.     

The Ontogeny of Kin Recognition in Two Species of Ground Squirrels1

SYNOPSIS. We report results of a three year comparative laboratorystudy of kin recognition abilities in Arctic ground squirrels(Spermophilus parryii) and Belding's ground squirrels (S. beldingi),and a field investigation of kin recognition in S. beldingi.Our laboratory work shows that in both species, preweaned pupsreared together, whether they are biological siblings or cross-fostered(unrelated) nestmates, are equally aggressive in subsequentpaired arena tests. Thus, pups that share a natal nest are treatedlike siblings. Among pups reared apart, sister-sister pairsare less aggressive in arena tests than are pairs of nonkinfemales, whereas relatedness does not affect male-male or male-femaleaggression. Thus both relatedness and rearing environment mediaterecognition among female S. parryii and S. beldingi. In free-livingBelding's ground squirrels at Tioga Pass, California, dam-offspringand sister-sister recognition apparently first occur at weaning,coincident with aboveground emergence of juveniles. Most intriguing(electrophoretically identified) littermate full-sisters andmaternal half-sisters, which result from multiple mating byfemales, seem to treat each other differently despite havingshared a natal nest. The full-sisters are less agonistic andmore cooperative than the half-sisters. In interpreting theselaboratory and field results, we explore four proximal mechanismsby which kin might be identified, including one in which recognitionis based on (learned) phenotypic similarity to an individual'snestmates or itself (phenotype matching). Our data and thoseof several recent investigators of recognition in other taxaimplicate both association with relatives and phenotype matchingin the ontogeny of kin recognition.