Shade avoidance and Zahavi's handicap principle in dense plant populations

I propose that tall plants 'show off' and that the shade avoidance syndrome is a case of spectral communication among plants in dense populations, enabling the operation of Zahavi's handicap principle in plants. The costly signal triggering shade avoidance is composed of: (1) the far-red (FR) irradiation that plants emit as a by-product of photosynthesis, and (2) the phytochromes and the down-stream factors that respond to phytochrome signalling that evolved to analyse the FR emission and respond. This is a special case of a complex system serving as a signal. Because various types and levels of shade avoidance are common in most, if not all, dense plant populations, it seems that the operation of Zahavi's handicap principle in plants is a common phenomenon. Although plants do not see, they can use light for interplant communication about their relative strength. Unlike the many types of species-specific operations of Zahavi's handicap principle in animals, the handicap signal in plants is not species-specific, like prey–predator interactions. This difference probably stems from the fact that plants are sessile, have no animal-like vision, and compete with individuals of many other species.   © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 313–319.     

El Niño and tree growth near Jerusalem over the last 20 years

A strong correlation is observed between an El Niño index (anomalies in tropical Pacific sea surface temperature) and rainfall in the Judean foothills near Jerusalem over the past 20 years. These relationships clearly influenced the growth of local pine trees, as reflected in the width of their annual tree rings. The ability to predict El Niño events about a year in advance lend a special significance to relationships reported here for ecology, agriculture and water management in this climatic transition zone. To help explain the observed, long-range teleconnection we propose a possible mechanism based on a newly identified direct cloud connection between equatorial Africa (more directly affected by El Niño) and the Southeastern Mediterranean shoreland. The penetration and contribution of the moisture current from equatorial Africa to this region may depend on a shift in the usual rain generating moisture currents to southwesterly trajectories (passing over north Africa). The occurrence of such shifts is supported by the observed decrease in the mean ¹⁸O content of the local precipitation during El Nino winters.     

The spiny,thorny and prickly plants in the flora of Israel

To examine whether spininess evolved at random or differently in various life forms and plant organs, we characterized spiny, thorny and prickly organs in the entire wild flora of Israel (294 such species). Of the species, 63.3% defended their reproductive organs (the most‐defended organ) and 67.0% defended various non‐reproductive organs. Ninety‐three species defended both their reproductive organs and at least one other part; 48.3% defended their leaves and 36.4% their stems and branches. Spiny wings defended stems and branches only in herbaceous (annual or perennial) species. There were clear differences between the life forms. Annuals and perennial herbs defended mostly their reproductive organs (95.7 and 83.0%, respectively), dwarf shrubs defended mostly their leaves (54.2%) and shrubs and trees mostly their branches (89.7 and 76.2%, respectively). Trees do not defend their reproductive organs by associated sharp appendages. The differences in defence on various organs among different life forms may influence the results of meta‐analysis studies of the optimal defence allocation if such differences are not taken into account. We noted spine, thorn and prickle colours for 167 species with yellow, red, orange and white being the dominant, supporting hypotheses about spines being visually aposematic. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 344–352.     

When may green plants be aposematic?

During the long, dry summers, the deserts of the Middle East are almost devoid of green plants. In the summer, most annuals, geophytes and hemicryptophytes either are dormant in the soil or have already been eaten by the grazing flocks. Many shrubs are summer deciduous or enter summer dormancy with minimal green canopy. However, there are several common plants that, contrary to the general phenology, are conspicuously green during summer, when all the surroundings are yellow. In such conditions, green is conspicuous and contrasts with the background, as do yellow, red and black in 'greener' ecosystems. The summer-green plants are also characterized by being poisonous or thorny as protection against herbivory. During winter and spring, when there are plenty of other green, more palatable annual plants, herbivory pressure is much lower and they need less protection. We propose that during summer in the dry desert, when most other plants are dry or indistinctive, a vivid green colour can be aposematic.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 413–416.     

Experimental Induction of Dilatation Meristems in Melia azedarach L.

Dilatation meristems were induced experimentally in the barkof Melia azedarach L. by mechanical bark blocking, wounding,and by application of 1.0% of either naphthaleneacetic acid(NAA) or of ethrel. The treatments induced the formation ofdilatation meristems in the rays, in the axial phloem parenchyma,and in the primary cortex. Dilatation was the result of bothcell divisions and cell enlargement. The dilatation meristemswere sometimes several cells wide, and were formed in all possibleorientations; some were even branched. In many cases, whirlswere formed as the result of dilatation activity in many directionsover a small bark area. The possible hormonal regulation ofdilatation activity is discussed. Auxin, bark, cortex, dilatation, ethylene     

Defensive ant,aphid and caterpillar mimicry in plants?

Here we describe three apparently novel types of visual insect mimicry in plants. In the first type, plants of Xanthium trumarium L. have dark spots and flecks that resemble ants (Formicidae) in size and shape in the epidermis of stems, branches and petioles, and plants of Arisarum vulgare Targ.-Tozz. have them on petioles and inflorescence stems. In the second type, the dark anthers of Paspalum paspaloides (Michaux) Scribner (= P. distichum ) are the size, shape and colour of aphids (Homoptera; Aphidoidea) and they sway in the wind like swivelling aphids. Similarly, the stems of Alcea setosa (Boiss.) Alef. are covered with dark flecks that look like aphids. Finally, immature pods of three wild annual legumes ( Lathyrus ochrus (L.) DC.; Pisum fulvum Sm.; Vicia peregrina L.) have conspicuous reddish spots, arranged along the pods, that appears to mimic lepidopteran caterpillars. In one of the species ( V . peregrina ) two different mimicking morphs were found. We propose that these morphological traits may serve as herbivore repellent cues and are part of the defence system of the plants.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 393–398.     

A developmental variant of indentation in the scales of female cones of Cupressus sempervirens L.

A developmental variant, in which the contact zone between female cone scales is ectopically expressed in many female cones of Cupressus sempervirens , is common in trees growing in Israel. There are two phenotypes: type A with grooves emerging from the contact zone between two scales, and type B with a blind groove in the inner area of a scale. Some scales show a combination of both. These structures are formed constantly, but in different proportions in individual cones, trees and populations. Within the cone, more ectopic indentations are found in the basal scales. The female cones of other members of the Cupressaceae examined, namely Cupressus macrocarpa, C. arizonica and Thuja orientalis , did not have ectopic indentations.