Structural and Functional Properties of Trichomes of Xeromorphic Leaves

Trichomes of xeromorphic leaves of 12 different species (Banksiaspeciosa, Corokia buddleioides, Correa backhousiana, Lavandulaofficinalis, Leucospermum grandiflorum, Metrosideros excelsa,Olea europaea, Olearia rotundifolia, Pittosporum crassifolium,Pittosporum sp., Rosmarinus officinalis, Senecio cineraria)and trichomes of mesomorphic leaves of five species (Achimenesgrandiflora, Geum urbanum, Gynura aurantiaca, Populus alba,and Styrax officinalis) were stained with Sudan IV and Sudanblack. In the trichomes of all xeromorphic leaves the wallsof the basal or stalk cells stained with these reagents. However,none of the cell walls of the trichomes of the mesomorphic leaveswere stained by the Sudan reagents. Portions of leaves of three of the xeromorphic species (Corokia,Correa, Olea) and leaves of three of the mesomorphic species(Achimenes, Geum, Gynura) were floated on 0.1 per cent Calcofluorwhite solution. Examination of cross-sections of these leafportions in the fluorescence microscope indicated that evenafter 4 days of floating the Calcofluor, which is an apoplastictracer, did not enter the trichome walls of the xeromorphicleaves. However, the Calcofluor brightener could already bedetected in the trichome walls of the mesomorphic leaves afterone day. The adapted properties of the trichomes of the xeromorphic leavesare discussed. Endodermal cell, mesomorphic leaves, trichomes, xeromorphic leaves, water diffusion boundary layer     

Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance

VON TEICHMAN, I. & VAN WYK, A. E., 1991. Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance. The possible evolutionary status of the endothelium, hypostase, pachychalaza and the recalcitrant viability behaviour of seeds is considered in relation to bitegmy/unitegmy, crassinucellate/tenuinucellate ovules, nuclear/cellular endosperm development, large/small seed size, woody/herbaceous habit and tropical/temperate habitat. The presence of the endothelium, hypostase, pachychalaza and recalcitrance in dicotyledonous families is plotted against Dahlgren's system of classification. Results are compared with Sporne's advancement index for the various families. An endothelium is considered derived since it occurs more often in highly evolved superorders and is significantly associated with derived ovule and endosperm character states as well as with smaller seed size. A hypostase appears to be relatively ancestral and is significantly associated with pachychalazy and recalcitrance. The endothelium and hypostase have developed independently in many taxa and could be interpreted as being structurally and functionally analogous. Pachychalazy and recalcitrance are significantly associated with ancestral ovule character states and, at the species level, with large seed size (overgrown seed), woody habit and tropical habitat. The presence of pachychalazy, recalcitrance and associated large seed size are therefore regarded as ancestral character states of the dicotyledons. Consideration of currently accepted dicta on seed character state polarity, suggests a reversal in the evolutionary status of pachychalazy and large seed size.     

Using Digital Photographs to Evaluate the Effectiveness of Plover Egg Crypsis

Abstract: The focus of digital photography has moved from documentation to quantitative analysis. To illustrate the potential application of this diagnostic tool to quantify color and shape, we photographed both artificial and natural semipalmated plover (Charadrius semipalmatus) nests to determine what benefits, if any, were derived from egg crypsis (i.e., eggshell color and egg marking shape). This simple and cost-effective method provides precise and repeatable quantification of color and shape that discriminated subtle differences in egg crypsis of artificial and natural nests that were not visible to us. The advantages of digital photography and image-editing software outweigh any shortcomings, as long as standard protocols are followed for capturing and analyzing images. Used with due care, digital photography is useful in studies that need to quickly assign biological traits, such as age and sex, to individuals, and to document temporal change that may occur as a response to management or disturbance.     

Expression of H-Y Antigen in the Guppy (Lebistes reticulatus)

Expression of a mammalian cross-reactive H-Y antigen on the surface of cells derived from the male guppy ( Lebistes reticulatus ) is demonstrated. This finding further establishes the evolutionary conservation of H-Y antigen among lower vertebrates and provides a basis for speculation on the possible evolutionary association between H-Y antigen and sex determination.     

Taxonomic significance of leaf surface morphology in Aloe section Pictae (Xanthorrhoeaceae)

Leaf surface morphology was analysed in 32 species representing the maculate species complex (the poorly resolved section Pictae) in the genus Aloe (Xanthorrhoeaceae). Few comparative morphological data are available for the complex. Leaf surface and stomatal characters observed by scanning electron microscopy show taxonomically significant interspecific variation. Most species are characterized by irregularly outlined, four‐ to six‐sided epidermal cells, the periclinal walls of which are flat and embellished with micropapillae and the anticlinal walls of which are indicated by channels on the leaf surface. The outer stomatal pore is typically sunken or plane and surrounded by four lobes on the leaf surface that may overarch the epistomatal chamber. The guard cells have distinct outer and inner stomatal ledges. Two geographical groups, comprising southern and east African species, are distinguishable by their leaf surface morphology. These characters are diagnostic in A. ellenbeckii, A. prinslooi and A. suffulta and support changes in the delimitation of A. greatheadii, A. macrocarpa and A. swynnertonii. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 418–428.     

Intra‐specific body size variation in Polistes paper wasps as a response to social parasite pressure

1. Like avian brood parasites, obligate insect social parasites exploit the parental care of a host species to rear their brood, causing an evident loss of host reproductive success. This fitness cost imposes selective pressure on the host to reduce the parasite effect. A possible outcome of an evolutionary arms race is the selection of host morphological counter‐adaptations to resist parasite attacks. 2. We studied host–parasite pairs of Polistes wasps in which the fighting equipment of the parasite's body allows it to enter the host colony. 3. We searched for host morphological traits related to fighting ability that could be considered counter‐adaptations. As a host–parasite co‐evolutionary arms race can only occur where the two lineages co‐exist, we compared morphological traits of hosts belonging to populations with or without parasite pressure. We report that host foundresses belonging to populations under strong parasite pressure have a larger body size than those belonging to populations without parasite pressure. 4. Behavioural experiments carried out to test if an increase in host body size is useful to oppose parasite usurpation show that large body size foundresses exhibit a greater ability of nest defence.