Reproductive biology of the andromonoecious shrub Trevoa quinquenervia (Rhamnaceae)

Various aspects of the reproductive biology of the andromonoecious shrub Trevoa quinquenervia Gill. & Hook, were studied in a population located in central Chile. Flowering extends from mid August to the end of December. The small, white, entomophilous flowers are incompletely protandrous and last c. 5 days. A weak, pleasant odour along with nectar and pollen attracts 17 diurnal insect species, seven of which are probable pollinators: these include Diptera (Syrphidae and Bombyliidae), Hymenoptera (Apidae and Colletidae) and Coleoptera (Melyridae). Besides perfect flowers T. quinquenervia individuals possess c. 10% staminate flowers, which are lighter, seem to be shorter-lived, and show a smaller gynoecium with abnormal ovules. Reproduction is exclusively sexual and apparently xenogamous, with pollen transfer depending on insect vectors. Although flower morphology and individual flower phenology do not fully prevent self-pollination (and geitonogamy can easily take place) the level of autogamy is low. Therefore, some self-incompatibility mechanism seems operative in this species. Fruit set of open-pollinated flowers is 6.6%, and ripe fruits contain on average 0.66 viable seeds. Predispersal (maternal) reproductive success (percent ovules becoming viable seeds) is 1.45%. For medium to full-sized individuals this corresponds to c. 2600 to 8600 potential offspring per year. Beyond the production of male flowers, four other aspects of the species' reproductive biology seem directed to enhance pollen export, partly implying increased male allocation: (a) a high pollen:ovule ratio, (b) protection of anthers against pollen-robbing by means of the cucullate petals, (c) secondary pollen presentation in a hairy barrier located above the nectary, and (d) a reduction in female allocation achieved by the regular abortion of two out of the three ovules in each ovary, thus producing a mostly one-seeded fruit provided with a thin, energy-poor pericarp. It is proposed that the advantages of enhanced pollen flow for a self-incompatible organism, which is moreover structured in isolated populations, might explain the increased male effort, including the joint evolution of andromonoecy and one-seededness.     

Epigenetic control of plant immunity

In eukaryotic genomes, gene expression and DNA recombination are affected by structural chromatin traits. Chromatin structure is shaped by the activity of enzymes that either introduce covalent modifications in DNA and histone proteins or use energy from ATP to disrupt histone–DNA interactions. The genomic ‘marks’ that are generated by covalent modifications of histones and DNA, or by the deposition of histone variants, are susceptible to being altered in response to stress. Recent evidence has suggested that proteins generating these epigenetic marks play crucial roles in the defence against pathogens. Histone deacetylases are involved in the activation of jasmonic acid‐ and ethylene‐sensitive defence mechanisms. ATP‐dependent chromatin remodellers mediate the constitutive repression of the salicylic acid‐dependent pathway, whereas histone methylation at the WRKY70 gene promoter affects the activation of this pathway. Interestingly, bacterial‐infected tissues show a net reduction in DNA methylation, which may affect the disease resistance genes responsible for the surveillance against pathogens. As some epigenetic marks can be erased or maintained and transmitted to offspring, epigenetic mechanisms may provide plasticity for the dynamic control of emerging pathogens without the generation of genomic lesions.     

The Mechanism of Melanocyte Dendrite Formation: The Impact of Differentiating Keratinocytes

In human epidermis one dendritic melanocyte interacts with about 36 keratinocytes and supplies them with melanin. In contrast to the vivo situation melanocytes in culture are far less dendritic. In the present study different culture systems were tested in order to observe the mechanism of melanocyte dendrite formation. In particular, we focused on the role of keratinocytes in this process. Time lapse studies revealed that only differentiated keratinocytes enhance melanocyte dendricity. Differentiated keratinocytes form connected cell sheets, which attach to part of the melanocyte plasma membrane. By contraction and retraction of keratinocyte units, new dendrites were drawn out from the melanocytes. Melanocytes remain passive during this process, which is indicated by the observation that sometimes extended dendrites could not withstand the tension and shear.     

Colleters in Turnera and Piriqueta (Turneraceae)

The anatomy of colleters was examined by light and scanning electron microscopy in 25 species of Turnera and nine species of Piriqueta. Based on morphology, four categories of colleters were recognized: standard, sessile, lachrymiform and trochleariform, all of which differ in shape and length/width ratio. They all have a similar anatomy: they consist of an axis of parenchymatous cells, sheathed by a palisade epidermis. The standard type is the most widespread in the studied taxa; the lachrymiform example was found in those species of Piriqueta with setiform glandular hairs; only one trochleariform example appeared in T: diffusa. The sessile type is considered to be a morphological transitional form between extrafloral nectaries and colleters. This is the first record of sessile, lachrymiform and trochleariform colleters. The anatomy of colleters is compared with other secretory structures such as glandular trichomes and extrafloral nectaries.     

Morphology and Morphogenesis of Two Species of the Genus Lembadion (Ciliophora, Oligohymenophora): Lembadion lucens and Lembadion bullinum

ABSTRACT. The morphology and morphogenesis of two species of the genus Lembadion, L. lucens and L. bullinum , are described. In both species, left and right ventral kineties converge behind the mouth forming a postoral suture. Buccal infraciliature is formed by one polykinety and two very close paroral kineties (inner and outer). During stomatogenesis, the new oral structures originate from the paroral kineties. The inner paroral kinety forms the new adoral polykinety and regenerates the outer paroral kinety of the proter, while the paroral kineties of the opisthe originate from the outer paroral kinety of the parental cell. Somatic proliferation starts before the stomatogenesis at the equatorial level of the cell, and extends towards the poles forming an equatorial band. Two large invariant zones, anterior and posterior, remain in the dividing cell. Moreover, the kinetodesmal fibers disappear in the proliferation band during the bipartition (fission) process.     

Warthin''s tumour: unusual vs. common morphological findings in fine needle aspiration biopsies

Fine needle aspiration biopsies (FNA) of 47 Warthin's tumours confirmed by histology were re-evaluated for cytomorphological findings. The majority of aspirates (37/47) contained a typical background with proteinaceous substance and cell debris, along with cellular elements represented by oncocytic, lymphoid, and mast cells with degranulated cytoplasm. Uncommon cellular findings were true squamous cells (1/47), atypical cells with vacuoles (1/47), osteoclastic giant cells (1/47), epithelioid cells (1/47), mast cells with preserved granules in cytoplasm (3/47), and siderophages (4/47). Uncommon findings in the background were corpora amylacea-like structures and homogeneous bright red droplets. Squamous cells and atypical cells with vacuoles caused diagnostic difficulties in distinguishing a Warthin's tumour from a squamous cell or mucoepidermoid carcinoma. However, other unusual cellular and background findings were not worrying; therefore, they are merely regarded as a curiosity in the cytomorphological appearance of the tumour.     

Hybridization between Ischnura graellsii (Vander Linder) and 2. elegans (Rambur) (Odonata: Coenagrionidae): are they different species?

Two closely related damselflies, Ischnura graellsii and I. elegans , were analysed for morphological differences and reproductive isolation in the north coast of Galicia (NW Spain). We compared animals from sympatric and allopatric localities, including I. elegans from Belgium and I. graellsii from southern Spain as pure allopatric populations. A set of morphometric characters were studied by means of multivariate discriminant analysis to determine if these two species can be unambiguously distinguished. Discriminant analysis revealed that I. graellsii and I. elegans are well differentiated on the first two axis (86% and 11%, respectively). I. graellsii individuals are distinguished from I. elegans by their smaller size and, specifically, by their narrower and shorter wings and shorter tibiae. In addition, I. elegans has a narrower space between the branches of each cercus, and greater distance between the branches of each paraproct. Sympatric individuals are morphologically intermediate, suggesting hybridization. When the species were put together in the laboratory, they showed partial temporal separation in mating behaviour, but males of I. elegans readily mated with females of I. graellsii , and hybrid individuals were obtained. The opposite heterospecific cross was almost impossible, apparently because of mechanical problems with the tandem linkage. Laboratory-reared hybrids (from male I. elegans × female I. graellsii ) are morphologically intermediate, mainly resembling the maternal phenotype. Although hybridization between both taxa is common, we suggest maintaining the specific status for both phenotypes because they show incipient reproductive isolation, as it is reported in the literature. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 225–235.     

Summer distribution of Red-legged Partridges Alectoris rufa in relation to water availability on Mediterranean farmland

The suggestion that the summer distribution of Red-legged Partridges Alectoris rufa in the Mediterranean region is determined by the availability of surface water was examined on the agricultural farm, Alto Alentejo, southern Portugal. Partridge coveys were surveyed between 15 July and 15 August in 1993 and 1994. Using a vector-based Geographic Information System, we assessed, for each covey location and for the locations of a double number of random points, the distance to the nearest water point, distance to field boundaries, distance to water lines and land use classes. Univariate comparisons were made between the two groups of locations, and three multivariate logistic models were fitted through forward stepwise selection to the 1993, 1994 and pooled data sets to estimate the probability of sighting partridge coveys in the study area. Distance to water was significantly lower for partridge locations than for random points in both years and was the only variable selected for all logistic models. Apart from water availability, Red-legged Partridge locations were also affected by land use and distance to field boundaries.     

Contribution to the taxonomy and ecology of the Azorean benthic marine algae

Algal zonation patterns were studied in two sites (Caloura, south coast and Ribeirinha, north coast) of the island of Sao Miguel, Azores. At each site two stations were studied and the transects revealed the occurrence of two distinct and well established algal zones. In the first zone, daily immersed and emersed by the tide, the algae were growing in a dense and short tangle forming a mat, referred to as algal turf. In the second zone, which was wet most of the time, the algae were larger and frondose. A list of the species of benthic marine algae occurring on the algal turf of each station is given. Of the total of 47 species found, eight are new for the Azores and another 13 species are recorded for the first time for Sao Miguel. Gigartina acicularis (Roth) Lamouroux and articulate coralline algae (Corallina oficinalis Linnaeus and Jania spp.) were the more common species. Seasonal variation of the algal turf was studied and related to mean monthly values of air and sea water temperatures, insolation and hours of light. The zonation patterns and composition of algal species were compared with those from other open rocky shores.