Metabolic Adaption in Mature Roots of Salt-stressed Zea mays

Respiratory gas exchange and incorporation of ¹⁴C-leucine intoprotein were studied in proximal root segments from 25-day-oldmaize plants grown for the last ten days in 50 mM Na₂SO₄. ¹⁴C-leucineincorporation, and oxygen uptake in the presence of glucose,were as large in Na₂SO₄-grown tissues tested under saline conditionsas in tissues exposed to non-saline solutions throughout Thisadaptation was attributed to an increased metabolic capacityof Na₂SO₄-treated tissues, because these tissues, when returnedto non-saline solutions, evolved oxygen and incorporated ¹⁴C-leucinefaster than tissues exposed continuously to non-saline solutions. These changes are interpreted as a ‘compensation’for the inhibitory effects found when non-adapted tissues wereexposed to 50 mM Na₂SO₄. Moreover, we have related them to ultrastructuralchanges observed previously in xylem parenchyma cells of thesetissues, and to the possible involvement of these xylem parenchymacells in the re-absorption of sodium from the ascending xylemfluid Zea mays L., maize, salt-stress, respiration, protein synthesis     

Mixed-species bird flocks in dipterocarp forest of north-central Burma (Myanmar)

We studied the bird community in deciduous, dipterocarp forest of north-central Burma (Myanmar) during December 1994, March 1996, and January 1997 and 1999. Most members of this community participated in mixed-species flocks. Seventy-three flocks were encountered during our study, containing 52 species. Of these, 25 species occurred in more than 10% of flocks, and were included in our analyses. There were 26 significant correlations among species pairs, 25 of which were positive. Cluster analysis indicated that there were three principal types of flocks: one consisting mostly of small passerines and picids, commonly including Common Wood-Shrike, Small Minivet and White-browed Fantail, among others; a second type consisting mainly of sylviids, e.g. Arctic, Dusky and Radde's Warblers; and a third type which generally centred around Greater and Lesser Necklaced Laughingthrushes. Bird-eating hawks were numerous at these sites, and we witnessed several attacks on flocks during the study. Thus we infer that enhanced protection from predation is an important benefit conferred by flock membership. In contrast, there was little overlap in foraging behaviour among species, suggesting that foraging facilitation is a relatively minor benefit enjoyed by flock members, although we did observe White-browed Fantails and Greater Racket-tailed Drongos kleptoparasitizing other species on occasion.     

THE COURTSHIP, PSEUDO-COPULATION BEHAVIOUR AND SPERMATOPHORE OF TURRITELLA COMMUNIS RISSO 1826 (PROSOBRANCHIA: TURRITELLIDAE)

Underwater field observations of reproductive behaviour in Turritellacommunis Risso were made in Killary Harbour on the west coastof Ireland during May and June in both 1986 and 1987. Thesesightings are documented and complemented by temperature, salinityand oxygen measurements, population structure, sex-ratio REMOTS®sediment profile imagery data and additional laboratory experimentationand observations. The population had a density of 639.5 individuals/m²at the study site with males comprising between 62.3 to 65.6%of the sexed population. Females were larger than males, thepopulation frequency distribution was negatively skewed andcharacterised by slow-growing, mainly adult individuals. Pseudo-copulationgroupings of 3 to 11 male specimens in star-shaped arrangementsappeared on the sediment surface in May and June as early summerbottom water temperatures increased above 10.0°C to 11.5°C.At its highpoint, c. 6 groups/m² were observed, with a meanof 5.9 males/grouping. Surface trails left by fertile malesindicated that they probably responded to a pheromone releasedby a passive fertile female lying within a radius of at least0.5 m. Smaller males were proportionately more active than largermales in sperm transfer. It was estimated that c. 15% of malesand 3% of females were synchronously fertile at the maximumobserved level of pseudocopulation activity. Laboratory observationsidentified the production of a complex doublewalled cylindricalspermatophore containing paired and unpaired euspermatozoa,and multiflagellate paraspermatozoa. Paired euspermatozoa weremost dominant and were arranged spirally at a 45° angleto the spermatophore axis. These were also frequently foundin morulae. An additional, spirallybound membranous tube exhibitingbulbous diverticula within the spermatophore contained paraspermatozoaonly. The observations confirm that sperm transfer is not apassive process as previously thought, and that the specieshas a far greater capacity for movement than was believed. Gregariousness,a noted feature among populations of turritellid species appearsto be a critically essential life strategy among these aphallic,internally-fertilising gastropods. Present address: Dr. J.J. Kennedy, Kantstrasse 38, 22089 Hamburg,Germany (Received 7 November 1994; accepted 15 March 1995)     

House flies delay fungal infection by fevering: at a cost

1. Many ectothermic species have evolved the ability to invoke a ‘behavioural fever’ when infected with a pathogen. The relative costs and benefits of this response, however, have rarely been quantified. 2. The aim of this study was investigate the nature and consequences of behavioural fever in the house fly, Musca domestica L., in response to infection with a possible biocontrol agent, the fungal entomopathogen, Beauveria bassiana (Balsamo) Vuillemin. 3. It was found that infected flies preferred higher temperatures and allocated more effort to thermoregulation than uninfected flies. Flies could not overcome infection but the altered thermal behaviour allowed infected flies to extend their survival and to lay more eggs relative to infected flies maintained under constant conditions. However, flies allowed to fever had lower egg viability suggesting a possible cost. 4. Under the present experimental conditions, the putative costs and benefits fever balanced one another resulting in no net change in fitness. Fever did not, therefore, limit the control potential of the fungus. We discuss whether the costs and benefits of behavioural fever might differ in other ecological contexts.     

Complete Elimination of Mitosis and DNA Synthesis in the Lens of the Hypophysectomized Frog: Effects on Cell Migration and Fiber Growth

Three weeks after hypophysectomy mitosis and DNA synthesis are absent in the lens of the leopard frog ( Rana pipiens ). By labeling germinative zone cells in their last DNA synthetic period we were able to follow them in the absence of further proliferation. By this means it has been demonstrated that migration of epithelial cells to the equator of the lens is stopped. Based on indirect measurements it seems that lens fiber formation also ceases. A correlation coefficient of 0.86 was computed between average labeling index and average distance migrated. In hypophysectomized animals the correlation coefficient between time and migration was 0.02 while in intact animals it is 0.87.