Two Stages in the Redifferentiation of Amyloplasts in the Microspores of Lilium

The first stage in the redifferentiation of plastids in themeiocytes of Lilium occurs late in meiotic prophase and involvesthe formation of an association between particles and membranouscisterna. The distribution of carbohydrate within this associationhas been examined cytochemically, and the particles are demonstratedto contain a high proportion of carbohydrate. The osmiophilicglobules of the stroma also react with the cytochemical probefor carbohydrate, indicating that they must, at least in part,be composed of glycolipid. Structure within the organelles remainsunchanging until the break-up of the tetrad, when elements ofthe membrane—particle association expand to fill the stroma.Electron microscopic evidence suggests that the particles formthe nuclei of the starch grains which then swiftly develop.It is proposed that the association represents the limit ofdifferentiation possible in the tetrad of microspores, and thatthe callosic special wall restricts the availability of materialsfrom the thecal fluid required for full development of the amyloplast.The association should thus be more correctly termed the proamyloidbody. Amyloplasts, Lilium, pollen development, proplastids     

Rabbits and the failure of regeneration in Australian arid zone Acacia

Three experiments are reported concerning the effect of rabbit grazing (Oryctolagus cuniculus L.) upon the recruitment of Acacia seedlings to populations in the South Australian arid zone. In western myall woodland (Acacia papyrocaqsa Benth.) under prevailing rabbit and sheep densities, seedlings exposed to grazing by these two herbivores or to rabbits alone were severely pruned, whereas totally protected seedlings grew unchecked. Seedlings of four Acacia species; A. papyrocarpa, A. oswaldii (F. Muell.), A. kempeana (F. Muell.) and A. burkittii (F. Muell. ex Benth.) were transplanted into four 50 m × 50 m rabbit-proof enclosures. Six rabbits were introduced into each enclosure and within 24 h half of the total seedling population had been grazed. This was at a seedling dry weight ratio of 1|150 000 of the total fodder on offer. In one of the enclosures no seedlings were eaten and there is evidence to suggest that a dense patch of grass had a buffering effect, reducing grazing pressure. Small shoots cut from old Acacia and transferred to the ground throughout 1000 ha of western myall woodland were grazed rapidly near rabbit warrens and progressively less rapidly with increased distance from warrens. The experiments demonstrated that even with the lowered post-myxomatosis population densities, rabbit grazing pressure would significantly affect recruitment in arid zone Acacia populations in the absence of stock.     

Xylem Hydraulic Characteristics, Water Relations and Wood Anatomy of the Resurrection PlantMyrothamnus flabellifoliusWelw.

Myrothamnus flabellifoliusWelw. is a desiccation-tolerant (‘resurrection’)plant with a woody stem. Xylem vessels are narrow (14 µmmean diameter) and perforation plates are reticulate. This leadsto specific and leaf specific hydraulic conductivities thatare amongst the lowest recorded for angiosperms (k_s0.87 kg m^-1MPa^-1s^-1;k_l3.28x10^-5kg m^-1MPa^-1s^-1, stem diameter 3 mm). Hydraulic conductivitiesdecrease with increasing pressure gradient. Transpiration ratesin well watered plants were moderate to low, generating xylemwater potentials of -1 to -2 MPa. Acoustic emissions indicatedextensive cavitation events that were initiated at xylem waterpotentials of -2 to -3 MPa. The desiccation-tolerant natureof the tissue permits this species to survive this interruptionof the water supply. On rewatering the roots pressures thatwere developed were low (2.4 kPa). However capillary forceswere demonstrated to be adequate to account for the refillingof xylem vessels and re-establishment of hydraulic continuityeven when water was under a tension of -8 kPa. During dehydrationand rehydration cycles stems showed considerable shrinking andswelling. Unusual knob-like structures of unknown chemical compositionwere observed on the outer surface of xylem vessels. These maybe related to the ability of the stem to withstand the mechanicalstresses associated with this shrinkage and swelling.Copyright1998 Annals of Botany Company cavitation, desiccation, hydraulic conductivity, refilling, resurrection plant, root pressure, xylem anatomy,Myrothamnus flabellifolius     

Phylogenetic Separation in Limb Use in Captive Gibbons (Hylobatidae): A Comparison Across the Primate Order

Although there have been few studies of self‐scratching in primates, some have reported distinct differences in whether hands or feet are used, and these variations seem to reflect the evolutionary history of the Order. Monkeys and prosimians use both hands and feet to self‐scratch while African great apes use hands almost exclusively. Gibbons represent an evolutionary divergence between monkeys and great apes and incidental observations at the Gibbon Conservation Center pointed to a difference in self‐scratching among the four extant gibbon genera (Hoolock, Nomascus, Symphalangus, and Hylobates). To validate and further explore these preliminary observations, we collected systematic data on self‐scratching from 32 gibbons, including nine species and all four genera. To supplement gibbon data, we also collected self‐scratching information from 18 great apes (four species), five prosimians (two species), 26 New World Monkeys (nine species) and 20 Old World Monkeys (seven species). All monkeys and some prosimians used both hands and feet to self‐scratch, whereas one prosimian species used only feet. All African great apes used hands exclusively (orangutans were an exception displaying occasional foot‐use). This appears to represent a fundamental difference between monkeys and great apes in limb use. Interestingly, there was a clear difference in self‐scratching between the four gibbon genera. Hylobates and Symphalangus self‐scratched only with hands (like all African great apes), while Hoolock and Nomascus self‐scratched with both hands and feet (like monkeys and prosimians). This difference in gibbon behavior may reflect the evolutionary history of gibbons as Hoolock and Nomascus are thought to have evolved before both Hylobates and Symphalangus. What evolutionary pressures led to this divergent pattern is currently opaque; however, this shift in limb preference may result from niche separation across the order facilitating differences in the behavioral repertoire associated with hind and forelimbs. Am. J. Primatol. 74:1035‐1043, 2012. © 2012 Wiley Periodicals, Inc.     

A preliminary molecular phylogenetic assessment of the lichen moths (Lepidoptera: Erebidae: Arctiinae: Lithosiini) with comments on palatability and chemical sequestration

The lichen moth tribe Lithosiini is best known for its hypothesized larval feeding behaviour, lichenivory. The larvae of some species have been found to be capable of sequestering polyphenolics, and the adults of some species are unpalatable to vertebrate predators. However, the chemical basis for the defence is unknown. Here we reconstruct a phylogenetic hypothesis using likelihood methods (maximum likelihood, Bayesian inference) for 65 species of Lithosiini representing 37 genera and seven outgroup species using 2806 bp of sequence data obtained from two mitochondrial gene fragments (COI barcoding region, CytB), and two nuclear gene fragments (RpS5 and ribosomal gene region 28S). Lithosiine species representing four of the seven subtribes and unplaced taxa are included in the analysis. The deeper relationships within the tribe are not strongly supported, and the monophyly of three of the four subtribes is not supported. The placement of the fourth subtribe, Acsalina, is weakly supported. We also conduct a survey of the secondary metabolites present within adults of five species. The species are examined for the presence of lichen polyphenolics and plant secondary metabolites sequestered by arctiines. Seven lichen polyphenolics are identified in the taxa examined, but no plant secondary metabolites are found using either analytical method. The results of this study and prior reports in the literature of chemical sequestration and unpalatability are plotted onto the resulting Bayesian inference phylogeny to examine the evolution of chemical defence within Lithosiini. Species that sequester lichen polyphenolics and unpalatable species occur in each of the major clades recovered in the analysis.     

The condition and age of Thomson's gazelles killed by cheetahs and wild dogs

The condition and age of Thomson's gazelles ( Gazella thomsoni ) killed by two species of predators were compared. The wild dog, a coursing predator, was predicted to take a greater proportion of young, old and sick animals than the cheetah, a stalker. As measured by the marrow fat content of limb bones, wild dogs captured more Thomson's gazelles in poor condition than cheetahs. This appeared to be a consequence of their preference for male gazelles, which were in worse condition than females. Cheetahs did not capture fewer young and old gazelles than wild dogs.