Food and feeding habits of four species of juvenile mullet (Mugilidae) in a tidal lagoon in Ghana

Juvenile mugilid fishes, Liza falcipinnis, L. dumerilii, Mugil bananensis and M. curema , which enter the Elmina Lagoon in the Cape Coast District of Ghana, have a similar diet comprising mainly bacteria, diatoms, blue-green/green algae, protozoans, detritus and particulate organic matter. No seasonal changes in the diet and feeding activity were observed. The relative gut length (intestine to standard length ratio) and diet showed no significant changes with size of fish in all the species. All four species were diurnal feeders, but their peak feeding times differed. Interspecific competition for food was possibly limited by species preferences for substrate particles of particular size range and differences in feeding chronology.     

Sexual reproduction of the high mountain plant Saxifraga moschata Wulfen at varying lengths of the growing season

Flowering phenology, dynamics of seed development and reproductive success of Saxifraga moschata Wulfen, occurring from the alpine to the nival zone, was investigated in three climatically varying years on early- and late-thawing sites at 2340 m a.s.l. in the Austrian Alps. The growing season was particularly short in 2001, about normal in 2002 and exceptionally long and warm in 2003. S. moschata is a mid-season flowering species, which started to bloom about 1 month after snowmelt. From onset of anthesis until seed maturity an individual flower required 6–7 weeks, and all individuals of a site 9–11 weeks. In 2001, late flowering individuals lost about 40% of the seed crop because of too early snowfalls in autumn. No clear relationship could be found between thermal time and the length of different reproductive phases, which indicates that temperature was not a limiting factor for reproductive development in the growing seasons 2001–2003.

Plants from the earliest-thawing site produced about double the reproductive structures (reproductive shoots per individual, number of flowers per inflorescence, number of ovules per ovary), and had a significantly higher reproductive output (number of fruits and mature seeds per inflorescence) compared with individuals from the late-thawing site. Reproductive success was additionally affected by the seasonal climate and was lowest in the warm and dry summer of 2003. Fruit/flower ratio ranged between 0.6 and 0.8, seed/ovule ratio between 0.4 and 0.5 and relative reproductive success (RRS) between 0.3 and 0.4, depending on the site and year.

Different from our expectations, it took S. moschata relatively long to undergo reproductive development; however, its phenological plasticity and ability to continue seed maturation even under snow are most advantageous for a life at higher altitudes.     

Location of cell cycle changes in relation to morphological changes in the shoot apex ofSilene coeli-rosa immediately before sepal initiation

Summary Changes in morphology, the mitotic index and the proportions of cells in G₁ and G₂ were measured in shoot meristems ofSilene coeli-rosa immediately before floral morphogenesis in order to determine whether the known changes to the cell cycle at this time are restricted to a particular region of the apex. Twenty-eight day-old plants were given either 7 long days (LD) plus 2 short days (SD) (day 8 of the LD treatment) or 9 SD [day 8 of the SD control (SDC) treatment]. Plants were sampled on day 8 every 2 h for 12 h and the various cell cycle measurements were performed on sections of the apical meristem. In the inductive LD treatment there was a peak in the mitotic index at 13.00 h and, possibly, the start of another at 19.00 h. At 21.00 h all meristems in this treatment initiated sepals. The mitotic activity at 13.00 and 19.00 h in the LD treatment was a result of significant increases in the mitotic index in the axial, lateral and central sub-axial areas of the apex compared with the corresponding zones in the SDC treatment. At 13.00 h of day 8, 80% of cells were in G₂ phase in the axial region in the LD treatment whilst 85% of cells were in G₁ in the axial zone in the SDC treatment. In the other zones significantly more cells were in G₂ in the LD compared with the SDC treatment as was the case at 19.00 h although not to the same extent as the axial zone at 13.00 h. Thus these data emphasize, for the first time, the mitotic activation and predominance of the G₂ population of cells particularly in the axial zone of shoot meristems in the LD treatment. These data are discussed in relation to the synchronisation of cell division which could occur in the prefloral shoot meristem at this time, affecting each shoot apical zone.Abbreviations LD long day - SD short day - SDC short day control     

A comparative analysis of developmental profiles for DNA methylation in 5-azacytidine-induced early-flowering flax lines and their control

Earlier experiments demonstrated that DNA from young plants of 5-azacytidine-induced flax (Linum usitatissimum) lines that flower earlier-than-normal is hypomethylated relative to DNA from their control lines and detected differences in methylation level between plants sampled at different ages, which suggested that the methylation level in flax changes during development. To investigate this possibility, and its potential impact on the difference in methylation level between early-flowering and control lines, developmental profiles were established for the cytosine methylation levels in DNA from post-germination seedlings and from the shoot tips of main stems and the cotyledons sampled throughout vegetative phase. The methylation profiles for two early-flowering lines and their control lines were compared. The methylation profiles were then compared to profiles for DNA content, tissue weight and chlorophyll content (green tissues); these additional parameters provided information on tissue status in terms of cell division, tissue expansion and/or photosynthetic maturity. With one exception, methylation levels were either static or increased with plant age and/or tissue maturity; the highest methylation levels were seen in senescent cotyledons. Although DNA from immature plants or tissues of the early-flowering lines was usually hypomethylated, the hypomethylation was not always apparent in tissues from older plants.     

Promotion of flowering in the Pinaceae by gibberellins

Significant female flowering of 6- to 11-year-old seedlings and grafted ramets of sexually mature scions of lodgepole pine (Pinus contorta Dougl.) was promoted by both topical and spray applications of a gibberellin (GA) A_4/7 mixture (1.6 to c. 5 mg per plant in total) during that period (June to September) when sexual differentiation of lateral primordia would be expected to take place. Girdling was used in most experiments to enhance the GA_4/7 effect, as was the auxin, naphthaleneacetic acid (NAA). Average frequency of flowering branches on treated plants over all experiments ranged from 27 to 59% (control ranged from 0 to 36%) and average number of female strobili was increased from 2- to 6-fold by growth regulator treatment, relative to controls. Within an experiment, clonal or family frequency of flowering for treated plants ranged from 11 to 67% (controls were 0 to 28%), and number of female strobili was increased from 2- to 14-fold by growth regulator treatment, relative to controls. Movement of the flowering stimulus from the point of application was apparent in several experiments, the response in adjacent branches being correlated positively with increasing dosage of GA_4/7. Significant male flowering occurred only in one experiment, girdling and GA_4/7 treatment being promotive factors. The use of spray applications of GA_4/7+ NAA is warranted to induce early and enhanced flowering in lodgepole pine seedlings and vegetative propagules for genetic improvement programs.     

First approximation to a phenology of the honeybees (Apis mellifera) and flora of Africa

Peak flowering by the total flora of Africa coincides with or immediately follows peak rainfall. Flowering intensity of the total flora decreases with distance from the equator, but that of the honeybee plant resource base (±2% of total flora) does not. Flowering in the latter is highly synchronous (months 1–5 north of and 9–11 south of the equator). Both total and honeybee flora are completely incongruent with either the biomes or phytochoria of Africa. There is no significant correspondence between honeybee phenology and the total flora but significant correspondence occurs between honeybees and flowering in honeybee plant genera. A logistic regression model reveals that honeybee plant flowering predicts major honeybee colony events with a probability of 0.81 south of the equator and 0.71 for the whole continent. It is postulated that promiscuity in the bee plant genera and honeybees of Africa have contributed to their continental ubiquity.     

Fruit set and cytokinin-like activity in the xylem sap of sweet cherry (Prunus avium) as affected by rootstock

Using a trace-enrichment procedure involving solvent partitioning and high pressure liquid chromatography, followed by bioassay, two cytokinin-like substances believed to be zeatin and zeation riboside were detected in the xylem sap of sweet cherry ( Prunus avium L.). The levels of cytokinin varied between rootstocks with the higher yielding and fruit setting rootstocks producing the highest cytokinin levels. Most of the cytokinin activity occurred in the spring during bloom and early fruit set. A relationship between cytokinin level in the xylem sap and fruit set is proposed.     

Habitat preference,food habits and growth of juveniles ofLates angustifrons andLates mariae (Pisces: Centropomidae) in Lake Tanganyika

Habitat preference of juveniles ofLates angustifrons andLates mariae, endemic fish species in Lake Tanganyika, was investigated in the field and in the laboratory. Both species settle on the grass bed after the post-larval pelagic phase.L. angustifrons preferred the short grass bed composed ofVallismeria sp., whileL. mariae preferred the tall grass bed composed ofPotamogeton schweinfurthii. L. angustifrons always rested near the root, keeping a position parallel to the bottom; dark cross bands on the body may be advantageous as camouflage in the short grass bed. On the other hand,L. mariae always stayed in mid-water, keeping a head-down position parallel to a leaf or stem of grass; such posture and longitudinal stripes on the body may be advantageous as camouflage in the tall grass bed. Both species were more active at night, and fed mainly on atyid shrimps.Lates angustifrons shifted its main food from shrimps to fish with growth, as was suggested inL. mariae. Difference in the habitat preference may play an important role in their coexistence.     

QTL analysis of flowering time inArabidopsis thaliana

Quantitative trait loci (QTL) analyses based on restriction fragment length polymorphism maps have been used to resolve the genetic control of flowering time in a cross between twoArabidopsis thaliana ecotypes H51 and Landsbergerecta, differing widely in flowering time. Five quantitative trait loci affecting flowering time were identified in this cross (RLN1-5), four of which are located in regions containing mutations or loci previously identified as conferring a late-flowering phenotype. One of these loci is coincident with theFRI locus identified as the major determinant for late flowering and vernalization responsiveness in theArabidopsis ecotype Stockholm.RLN5, which maps to the lower half of chromosome five (between markers mi69 and m233), only affected flowering time significantly under short day conditions following a vernalization period. The late-flowering phenotype of H51 compared to Landsbergerecta was due to alleles conferring late flowering at only two of the five loci. At the three other loci, H51 possessed alleles conferring early flowering in comparison to those of Landsbergerecta. Combinations of alleles conferring early and late flowering from both parents accounted for the transgressive segregation of flowering time observed within the F₂ population. Three QTL,RLN1,RLN2 andRLN3 displayed significant genotype-by-environment interactions for flowering time. A significant interaction between alleles atRLN3 andRLN4 was detected.