The phylogeny and systematics of European predacious Syrphidae (Diptera) based on larval and puparial stages

The external larval morphology of predacious Syrphidae is examined and compared with that of other groups of syrphids. Predacious larvae form a distinctive, monophyletic group. Relationships among 29 of the 34 European genera and subgenera are analysed using cladistic methods based on larval and puparial characters. Interpretation of the cladogram suggests that, within Syrphinae, a system of five tribes can be recognized and that a major trend has been a shift from ground layer to arboreal larval habitats, with an increasing degree of obligate dependence on soft-bodied Homoptera as prey. Generic diagnoses with biological and taxonomic notes are given and a key to genera based on larvae and puparia is provided.     

An Electron Microscopic Study of Double Fertilization in Allohexaploid Wheat Triticum aestivum L.

Double fertilization has been examined by electron microscopyin allohexaploid wheat, Triticum aestivum L. cv. Mardler. Serialsections through fertilized ovules revealed that following dischargeof the pollen tube contents into the degenerate synergid thelatter extended to form a continuum between the egg and centralcells. The two naked sperm nuclei were seen at the far end ofthis extended synergid. These observations suggest that thedegenerate synergid may play a role in transporting the spermnuclei to the site where they can be accepted by the egg andcentral cell. In comparison with double fertilization in Plumbagozeylanica L., we also suggest that the degenerate synergid preventsmale cytoplasms from being transmitted to the egg and centralcell. The present study also confirms that in the fertilizedcentral cell the maternal and paternal genomes remain physicallyseparate at least until the first nuclear division of the coenocyticphase of endosperm development. Double fertilization, degenerate synergid, Triticum aestivum     

The Cardiac Lethal Mutant of Ambystoma mexicanum: A Re-examination

SYNOPSIS. Hearts of embryonic axolotls (Ambystoma mexicanum)homozygous for gene c do not beat in situ. Under appropriateculture conditions they rapidly commence beating, albeit lessvigorously than similarly explanted hearts of comparably stagednormal siblings. As part of this symposium, we have shown acine record demonstrating heartbeat in mutant hearts and comparingit to normal heartbeat. Myocardia of normal embryos exhibita characteristic pattern of birefringent, striated myofibrils.Mutants of the same stage contain hearts with birefringent fibrilsorganized in a pattern similar to that found in normal myocardia.A striking difference is that obvious striations are lackingin fibrils of the mutant. Electrophoresis of normal and mutanthearts in SDS-polyacrylamide gels shows that the major myofibrillarproteins are present. We conclude that induction of c/c heartshas been relatively normal and suggest that, due to the rapidityof recovery, the observed phenomena are perhaps due to somethingas simple as a defect in ionic conditions.     

Population Size,Clones and Morphogenesis in Naegleria gruberi*

SYNOPSIS. The size of the population of Naegleria gruberi at the time the amoebae are offered the opportunity to become flagellated is not a critical factor in the morphogenesis of this organism. Small populations (1-15 cells) readily become flagellated. Small populations (1-5 cells) washed several times also become flagellated. Clonal populations (25) have been established. All clones yield flagellates under the usual conditions. It is suggested that the physiological state of the amoebae is a factor in determining the number of cells that will undergo morphogenesis at any given time.     

Inhibition of Leukaemia Virus Replication by Polyadenylic Acid

A PREVIOUS communication from this laboratory demonstrated that the DNA polymerase of the Rauscher leukaemia virus is strongly inhibited in vitro by unprimed, single stranded polyribonucleotides¹ as a result of competition between the polymers and the active template for the same enzyme binding site. This inhibition was apparently specific, since partially purified preparations of DNA polymerase from Escherichia coli and BALB/c mouse embryos were not inhibited in the same conditions. We attempted to determine therefore whether single stranded polyribonucleotides would have any effect on the activities of oncogenic RNA viruses in cultured cells.     

Models of floral pattern in detached flowers of Silene coeli-rosa (L) Godr. (Caryophyllaceae)

Organ number per whorl was analysed in aberrant flowers of the long-day (LD) plant , Silene coeli-rosa , to test a hypothesis that organ number in a whorl takes its cue from an adjacent outer whorl and that perturbed organ number per whorl is not random but defaults to that of closely related taxa or genera of the Caryophyllaceae. When plants were grown under short-days (SD), transferred to LD and the shoot meristem excised and cultured in vitro under SD, the normal pattern of flower development was often disrupted. For example, we observed flowers which comprised floral whorls with an aberrant number of floral organs. In part, this was an effect of tissue culture; however, the over-and-above effect was the establishment of an alternative pattern of development. Our data indicate that two distinct and recurrent patterns occurred in the aberrant flowers we observed in five separate experiments. First, pairs of floral whorls were linked so that aberration in one whorl resulted in the next whorl being more aberrant than normal. Second, the number of organs in aberrant whorls was not random, but defaulted to an organ number which mimicked the flowers of closely related species of Silene or related genera in the Caryophyllaceae.  © 2002 The Linnean Society of London , Botanical Journal of the Linnean Society , 2002, 140 , 229−235.     

Warm-Bodied Fish

SYNOPSIS. Two groups of fishes, the tuna and the lamnid sharks,have evolved ounter-currentheat-exchange mechanisms for conservingmetabolic heat and raising their body temperatures. Warm musclecan produce more power, and considering the other adaptationsfor fast swimming in these fish, it seems likely that the selectiveadvantages of greater speed made possible by the warm musclewere important in the evolution of this system. Some tunas suchas the yellowfin and skip jack are at a fixed temperature differenceabove the water, but bluefin tuna can thermoregulate. Telemetryexperiments show that the bluefin tuna can maintain a constantdeep body temperature during marked changes in the temperatureof its environment.