Sexual polymorphism,growth, and reproductive effort in Egyptian Thymelaea hirsuta (Thymelaeaceae)

Gender phenotypes of Thymelaea hirsuta (L.) Endl. were surveyed in six major habitats in the western Mediterranean region of Egypt. Five gender phenotypes were observed at all sites: subandroecious (male), subgynoecious (female), protogynous, protandrous, and gender-labile individuals. Patterns of vegetative growth, reproductive effort, and sex-size relationships were also determined. Females and males were comparable in overall abundance (35.5% and 30.2%, respectively). However, the frequency of sex forms varied significantly among habitats. Plant size (canopy volume) was used as a measure of environmental quality for the species: the coastal dunes were by far the most favorable habitat, followed by the nonsaline depressions, inland plateau, and inland siliceous deposits. The smallest plants were associated with the inland ridges and saline depressions. Protandrous individuals, and female shrubs at the more favorable habitats (e.g., the coastal dunes and nonsaline depressions), had greater canopy volume than males. In contrast, males were larger than females at the less favorable habitats (e.g., the inland plateau and saline depressions). Advantageous growth conditions at the coastal dunes are demonstrated by the greater rate of increase in crown diameter and crown volume noted there, for each size class and sex form. The greatest rates of increase were present in smaller-sized individuals. Size differences between the sex forms were considered in terms of trade-offs between individual growth rate (GR) and reproductive effort (RE); evidence of a trade-off was mixed. Indeed, in a comparison of GR and RE at two extremes of habitat (coastal dune vs. inland plateau), females had greater GR and greater RE at the relatively benign coastal dunes, while at the more harsh, inland plateau site males showed greater GR and RE than females. Peak reproductive effort varied significantly with gender phenotype and habitat type.     

Sexual polymorphism and spatial segregation of Thymelaea hirsuta in Liguria (north-west Italy)

Abstract

Flowering phenology, sexual polymorphism and spatial segregation were studied over two consecutive years in a population of Thymelaea hirsuta (L.) Endl. (Thymelaeaceae) growing on coastal cliffs in north-western Italy. The study population was geographically segregated and, together with Croatian sites, it constituted the northernmost margin of the species' distribution range. Very frequent observations highlighted a sexual tendency towards dioecy already shown by T. hirsuta in other parts of the Mediterranean coast. The flowering period lasted 10?–?11 months, more or less. A high proportion of female flowers and a low number of hermaphrodite flowers were recorded, in contrast with the abundance borne by the species elsewhere; gender segregation into two different subgroups was noted, one consisting mainly of male and protogynous plants, the second consisting basically of female and protandrous specimens.     

Sex expression in EgyptianThymelaea hirsuta (Thymelaeaceae) populations

The sex expression inThymelaea hirsuta was assessed in five habitats in the western Mediterranean desert of Egypt. The survey over two main flowering periods indicated that the sexual expression of this plant is complex and labile. Beside the dioecious male and female states, five monoecious states were detected. The dioecious states are more abundant and less labile. There is a clear shift from monoecious towards dioecious states and in general favour of males from the first (late autumn) to the second (late winter) flowering period. These results are discussed in view of the adaptive theories and evolution.     

Breeding system and spatial variation in the pollination biology of the heterocarpic Thymelaea velutina (Thymelaeaceae)

Thymelaea velutina (Thymelaeaceae) is a unique dioecious and heterocarpic shrub, each female producing both dry and fleshy fruits. It is endemic to the Balearic Islands (western Mediterranean) and has suffered an important regression in recent decades, especially due to habitat loss. It lives in coastal areas, mainly in dunes, but a few populations occur up to 1300 m in the mountains of Mallorca. In the present study, we examined its breeding system and pollen vectors, determined whether seed production is pollen-limited, and quantified the relative importance of different insect visitors at coastal and mountain sites. Selective exclusions showed no differences between populations in the relative importance of insects and wind as pollen vectors. Pollen was limiting at both populations, though not consistently in time. Flowers of T. velutina were visited mostly by generalist insects, and species composition and abundance of flower visitors varied both in space and time. The flowering period is about a month later in the mountain than in the dune, and this results in a higher frequency of insect visits to plants in the mountain due to the higher insect abundance; insects were also more diverse in the mountain, although they visited a proportionally lower number of flowers than in the dune. Despite this spatio-temporal variation in the frequency of insect visits and in the importance of a particular insect group, the ambophilous system in this species (previously described as anemophilous) ensures a relatively high fruit set at the two different sites.     

Origin and diversification of Thymelaea (Thymelaeaceae): inferences from a phylogenetic study based on ITS (rDNA) sequences

Thymelaea is a Mediterranean genus belonging to a primarily tropical and subtropical family. This genus is here presented as a particular case on which the hypothesis of an in situ evolution of the Mediterranean flora from a Tertiary subtropical stock can be phylogenetically tested. To better understand the evolutionary history of Thymelaea, molecular phylogenies based on ITS (rDNA) sequences are estimated. Phylogenetic analyses strongly support the monophyly of Thymelaea and the sister position of Daphne. Unexpected relationships between sequences of T. granatensis, T. pubescens and T. sanamunda are found and explained as a case of cryptic nuclear introgression. Phylogenetic analyses also reveal the polyphyletic character of Diarthron, sensu Tan, suggesting that Dendrostellera and Stelleropsis should be reinstated as independent genera. Based on the resulting phylogenetic hypothesis and using statistical tests it is suggested that Thymelaea experienced an initial rapid diversification. Time estimates for the origin and radiation of Thymelaea based on independent sources of evidence—paleontological, paleoclimatic and paleogeographic data, on one hand, and ITS substitution rates reported for other angiosperm groups, on the other—give strikingly similar results. The early radiation of Thymelaea is inferred to have occurred in the Upper Miocene, after this lineage diverged from that of Daphne in the Lower or Middle Miocene. Both evolutionary events are related to the overall climatic deterioration (declining temperature and increasing dryness) registered throughout the Miocene in Eurasia. The rapid and extensive diversification of Thymelaea is placed in the Iberian Peninsula or here and in the neighbouring North African territory.     

Reproductive ecology of Thymelaea velutina (Thymelaeaceae)- Factors contributing to the maintenance of heterocarpy

Thymelaea velutina (Thymelaeaceae) is a dioecious shrub that presents a unique type of heterocarpy which consists of the simultaneous production of dry and fleshy fruits. It is endemic to the Balearic Islands (Western Mediterranean) and is found both in dunes and mountain areas. The goal of this study was to identify which factors influence the production of both fruit types, examining the variation of their effects at a spatio-temporal scale (comparing two localities in different years). Specifically, we investigated (1) whether pollen limitation influences the type of fruit produced, and (2) the possible differences in seed size, mass, dispersal capacity, seed predation, germination patterns and seedling survival between fruit types. We also examined if the production of fleshy fruits was modified with the application of gibberellins to reproductive branches. Although fleshy fruits were consistently more abundant than dry ones at both populations, their proportion was significantly higher at the site with greater precipitation. The addition of either pollen or gibberellins did not affect the proportion of each fruit type. Seeds in fleshy fruits are consistently larger, heavier and more likely to be dispersed than seeds in dry fruits, but germinability, germination rate and seedling survival was similar among fruit types. Heterocarpy in this species is currently maintained as there is no apparent factor that exerts any strong selective pressure on either fruit type. The two fruit types might even have different `functions', one serving especially for dispersal and population expansion and the other for producing a seed bank that ensures an eventual germination.     

Sexual size dimorphism and sex ratios in dragonflies (Odonata)

Sexual size dimorphism and biased sex ratios are common in animals. Rensch's rule states that sexual size dimorphism (SSD) would increase with body size in taxa where males are larger than females and decrease with body size in taxa where females are larger. We tested this trend in dragonflies (Odonata) by analysing body size of 21 species and found support for Rensch's rule. The increase in SSD with increasing size among species can be explained by sexual selection favouring large males. We also estimated the slope of the relationship between sex ratio and size ratio in populations of the 21 species. A negative slope would suggest that the larger sex suffers from high mortality in the larval stage, consistent with riskier foraging. The slope of this relationship was negative, but after correcting for phylogentic non-independence with independent contrasts the relationship was no longer statistically significant, perhaps because of phylogenic inertia or low sample size.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 507–513.     

中国瑞香科植物——柳叶荛花的确认及补充描述

确认了中国瑞香科Thymelaeaceae存疑植物柳叶荛花Wikstroemia salicina（Levl．）Levl．＆Blin为中国植物记录,同时补充描写了一些其重要的分类学特征。     

A comparison of genetic information from open-pollinated and control-pollinated progeny tests in two eucalypt species

Genetic-parameter estimates and parental breeding-value predictions were compared from open-pollinated and control-pollinated progeny populations of Eucalyptus globulus and two populations of E. nitens. For E. globulus there were two types of open-pollinated populations (native stand open-pollinated and seed orchard open-pollinated) and two types of control-pollinated populations (intra-provenance and interprovenance full-sib families). For E. nitens there were two populations, a seed orchard open-pollinated population and intra-provenance full-sib families. Progeny tests were established across multiple sites and 2-year height and diameter were measured and volume calculated. Genetic parameters from native stand open-pollinated E. globulus were unlike the parameters from the other three E. globulus populations; heritability estimates were severely inflated, presumably due to high levels, and possibly differential levels, of inbreeding depression relative to the other populations. Estimates of dominance variance in the E. globulus full-sib populations were high, but were zero in the E. nitens population. Correlations among parental breeding values, predicted using data from the different populations, were generally low and non-significant, with two exceptions: predictions from the two E. globulus full-sib populations were significantly correlated (r=0.54, P = 0.001), as were predictions from the E. nitens seed orchard OP and full-sib population (r = 0.61, P = 0.08). There was some indication that superior parents of E. globulus native stand open-pollinated families also tended to have above-average breeding values based on the performance of intra-provenance full-sib offspring. The consequences of these results for exploitation of base-population collections from native stands are discussed.     

Male morph determination in Rhizoglyphus echinopus (Acaridae)

In Rhizoglyphus echinopus (Fumouze and Robin) two male morphs occur: heteromorphs, with a thickened and sharply terminated third pair of legs that serve as a weapon in intrasexual conflicts, and homeomorphs, with unmodified legs. This study investigated the system of male morph determination. No significant heritability of male morph was found, but cues emanating from a dense colony were found to suppress the production of heteromorphs. Developmental plasticity was retained throughout the protonymphal stage. Diet did not influence morph expression, but lowered temperature decreased the proportion of heteromorphs emerging.     

Sexual morph determination in the aphid, Acyrthosiphon pisum

The effects of two temperatures and a series of photoperiods on sexual morph determination in an aphid are examined. Photoperiodic response curves are presented and analysed. Female morph determination and male production were influenced by both these environmental factors. Sexuals were produced only at shorter photoperiods and the critical photoperiods for sexual production were shorter at the higher temperature. The critical photoperiod for male production differed from that for female morph determination and was more sensitive to temperature. These results are discussed in relation to the ‘maternal switching mechanism’ and sex determination. The significance of the temperature effect and also the variation in photoperiodic response are discussed.     

Structure of mucilaginous epidermal cell walls in Passerina (Thymelaeaceae)

Leaves of Passerina are inversely ericoid. Adaxial epidermal cells are relatively small; abaxial ones are large and tanniniferous. Mucilaginous epidermal cells are usually present in many Thymelaeaceae, including Passerina , mainly in the abaxial epidermis. They are unequally divided by a periclinal wall-like septum into two separate compartments: (1) the outer, adjacent to the cuticle, containing mostly tanniniferous substances and (2) the inner, containing mucilage. This type of epidermis has often been incorrecdy described as uni-, bi- or multiseriate. Transmission electron microscopy revealed mucilage, characterized by microfibrils, embedded between die innermost wall-like septum and outermost layers of the inner periclinal cell wall. As accumulation of mucilage increases, the innermost (adjacent to the cell contents) layer of the original periclinal cell wall is pressed against the cytoplasm, thus forming a clearly demarcated cellulose periclinal wall which divides the epidermis cell into two compartments, the inner wiuh mucilage and the outer comprising the cell lumen. Existing controversy is critically discussed. Our observations confirm the authenticity of mucilagination in epidermal cell walls.     

New species of Schoenobiblus (Thymelaeaceae) from Venezuela

Schoenobiblus suffruticosa andSchoenobiblus crassisepala, from the Parque Nacional “Henri Pittier” and adjacent montane forests, are described and illustrated.     

A new species of Lasiadenia (Thymelaeaceae) from Venezuela

Lasiadenia ottohuberi from Venezuela is described and illustrated. Differences between the South American genusLasiadenia and the related Cuban genusLinodendron are discussed.