Interspecific variability of δ13C among trees in rainforests of French Guiana: functional groups and canopy integration

The interspecific variability of sunlit leaf carbon isotope composition (δ¹³C), an indicator of leaf intrinsic water-use efficiency (WUE, CO₂ assimilation rate/leaf conductance for water vapour), was investigated in canopy trees of three lowland rainforest stands in French Guiana, differing in floristic composition and in soil drainage characteristics, but subjected to similar climatic conditions. We sampled leaves with a rifle from 406 trees in total, representing 102 species. Eighteen species were common to the three stands. Mean species δ¹³C varied over a 6.0‰ range within each stand, corresponding to WUE varying over about a threefold range. Species occurring in at least two stands displayed remarkably stable δ¹³C values, suggesting a close genetic control of species δ¹³C. Marked differences in species δ¹³C values were found with respect to: (1) the leaf phenology pattern (average δ¹³C=–29.7‰ and –31.0‰ in deciduous-leaved and evergreen-leaved species, respectively), and (2) different types of shade tolerance defined by features reflecting the plasticity of growth dynamics with respect to contrasting light conditions. Heliophilic species exhibited more negative δ¹³C values (average δ¹³C=–30.5‰) (i.e. lower WUE) than hemitolerant species (–29.3‰). However, tolerant species (–31.4‰) displayed even more negative δ¹³C values than heliophilic ones. We could not provide a straightforward ecophysiological interpretation of this result. The negative relationship found between species δ¹³C and midday leaf water potential (Ψ_wm) suggests that low δ¹³C is associated with high whole tree leaf specific hydraulic conductance. Canopy carbon isotope discrimination (Δ _A ) calculated from the basal area-weighed integral of the species δ¹³C values was similar in the three stands (average Δ _A =23.1‰), despite differences in stand species composition and soil drainage type, reflecting the similar proportions of the three different shade-tolerance types among stands. Received: 30 November 1999 / Accepted: 23 March 2000     

A first interspecific Oryza sativa×Oryza glaberrima microsatellite-based genetic linkage map

Oryza glaberrima is an endemic African cultivated rice species. To provide a tool for evaluation and utilisation of the potential of O. glaberrima in rice breeding, we developed an interspecific O. glaberrima×Oryza sativa genetic linkage map. It was based on PCR markers, essentially microsatellites and STSs. Segregation of markers was examined in a backcross (O. sativa/O. glaberrima//O. sativa) population. Several traits were measured on the BC₁ plants, and major genes and QTLs were mapped for these traits. Several of these genes correspond well to previously identified loci. The overall map length was comparable to those observed in indica×japonica crosses, indicating that recombination between the two species occurs without limitation. However, three chromosomes show discrepancies with the indica×japonica maps. The colinearity with intraspecific maps was very good, confirming previous cytological observations. A strong segregation-distortion hot spot was observed on chromosome 6 near the waxy gene, indicating the presence of s ₁₀ , a sporo-gametophytic sterility gene previously identified by Sano (1990). The main interests of such a PCR-based map for African rice breeding are discussed, including gene and QTL localisation, marker-assisted selection, and the development of interspecific introgression lines. Received: 1 June 1991 / Accepted: 22 June 1999     

Coexistence in the chemostat as a result of metabolic by-products

Classical chemostat models assume that competition is purely exploitative and mediated via a common, limiting and single resource. However, in laboratory experiments with pathogens related to the genetic disease Cystic Fibrosis, species specific properties of production, inhibition and consumption of a metabolic by-product, acetate, were found. These assumptions were implemented into a mathematical chemostat model which consists of four nonlinear ordinary differential equations describing two species competing for one limiting nutrient in an open system. We derive classical chemostat results and find that our basic model supports the competitive exclusion principle, the bistability of the system as well as stable coexistence. The analytical results are illustrated by numerical simulations performed with experimentally measured parameter values. As a variant of our basic model, mimicking testing of antibiotics for therapeutic treatments in mixed cultures instead of pure ones, we consider the introduction of a lethal inhibitor, which cannot be eliminated by one of the species and is selective for the stronger competitor. We discuss our theoretical results in relation to our experimental model system and find that simulations coincide with the qualitative behavior of the experimental result in the case where the metabolic by-product serves as a second carbon source for one of the species, but not the producer.     

Production of interspecific hybrids between Sesamum alatum Thonn and Sesamum indicum L. through ovule culture and screening for phyllody disease resistance

Sesame (Sesamum indicum L.) is an important oilseed crop grown in the tropical and subtropical regions of the world. Despite the nutritional value and cultural importance, the biotechnological research on sesame is very limited. In this study, we have optimized a simple and efficient protocol for producing an interspecific hybrid between Sesamum alatum and S. indicum through ovule culture. In the cross S. alatum × S. indicum, capsule retention without embryo abortion was extended up to 7 days after pollination by spraying the growth regulator mixture containing 289 µM gibberellic acid (GA₃), 80.6 µM α-naphthalene acetic acid (NAA) and 23.3 µM kinetin. Direct organogenesis was successfully achieved when the ovules, excised from 7-day-old capsules, were cultured on MS medium containing 8.8 µM benzylaminopurine (BAP), 2.8 µM indole acetic acid (IAA) and 1712.3 µM glutamine. The regenerants produced roots on half strength MS medium supplemented with 0.27 µM NAA. Phenotypically, the S. alatum × S. indicum hybrid plants were intermediate to those of parents for majority of the traits. Cytological studies revealed normal meiosis in the hybrid without any chromosomal abnormalities. Peroxidase and esterase isozymes were demonstrated to be useful in the identification of hybrid plants. Screening against phyllody disease under greenhouse conditions revealed that the hybrids were moderately resistant.     

小麦族下Hystrix longearistata和Hystrix duthiei的生物系统学研究

对Hystrix duthiei、H．longearistata和它们的人工种间杂种花粉母细胞减数分裂染色体配对行 为、繁育特征和形态特征进行了比较分析,结果表明：(1)这两个分类单位形态差异较小,H．longearista－ ta的外稃芒较长,叶片较宽,每小穗具2--3个小花;H．duthiei的外稃芒较短,叶片较窄,每小穗具1～2 个小花。(2)它们很容易杂交,杂种F_l染色体配对频率很高,为13～14个二价体。(3)亲本种花粉育 性和结实性正常,杂种F_l花粉育性较低,结实性较差。(4)H．longearistata和H．duthiei亲缘关系很 近,是同一物种。由于地理分布和生境的差异,使它们在形态上开始分异,并出现一定程度的生殖隔离。把H．longearistata处理为Hystrix duthiei的一亚种是合理的。     

Offspring performance in three cleistogamous Viola species

Seed germination and seedling/juvenile fitness in the cleistogamous perennials Viola hirta, V. mirabilis, and V. riviniana were investigated during three growing seasons, to compare the performance of chasmogamously (CH) and cleistogamously (CL) derived progeny. For V. hirta and V. mirabilis the effects of sibling competition were examined, for V. riviniana the effects of interspecific (grass) competition. Seed abortion and seed weight were also taken into account as fitness measures.In none of the species, seed abortion rate differed between CH and CL capsules. In V. mirabilis and V. riviniana, CL seeds had a lower germination rate than CH seeds. In V. hirta the two seed types did not differ in germinability. Mortality did not differ between the two seedling types in any of the species. In V. hirta and V. riviniana, CL progeny had shorter mean length of largest leaf than CH progeny. In V. mirabilis plant size did not differ between progeny types. Sibling competition had little effect on offspring performance, but grass competition increased mortality and reduced plant size of V. riviniana progeny. The two progeny types did not differ in their response to sibling and grass competition.The differences in performance between progeny types could be attributable to inbreeding depression in the CL phase, but the slightly lower fitness of CL offspring is probably balanced by their lower production costs. It is suggested that a dimorphic reproductive system is maintained in perennial Viola species to maximize total seed output in the face of environmental variation.     

陆地棉与斯特提棉的种间杂种及其色素腺体性状的遗传研究

用陆地棉（G．hirsutumL,AD染色体组;2n＝52）的不同色素腺体基因型与澳洲野生二倍体斯特提棉（G．sturtianumWillis;C染色体组,2n＝26）进行种间杂交,得到4个带不同色素腺体基因的（陆地棉×斯特提棉）F1种间杂种。种间杂种植株总体性状介于两个棉种之间,全株光滑无毛,表皮上有一层较薄的蜡质层,花大,深红色。不同色素腺体基因对种间杂种种子和F1植株色素腺体性状有较大的影响,其中gl2gl2gl3gl3和Gl2Gl2gl3gl3与斯特提棉杂交产生的种间杂种具有种子无色素腺体而植株有色素腺体的特性,只是用gl2gl2gl3gl3配制的种间杂种F1植株的色素腺体较一般有色素腺体陆地棉显著稀少。用gl2gl2Gl3Gl3和Gl2Gl2Gl3Gl3配制的种间杂种种子和F1植株均有色素腺体。研究结果初步表明,控制斯特提棉的子叶色素腺体延缓形成性状的基因对陆地棉无色素腺体基因（gl2gl2gl3gl3）和有色素腺体基因之一（Gl2Gl2）为显性上位,对陆地棉另一有色素腺体基因（Gl3Gl3）为隐性上位。     

Competition for spawning sites between two gobiid fishes, Bathygobius fuscus and Eviota abax, derived by alteration of mating tactics of the former

Interspecific competition for spawning sites between two gobiid fishes, Bathygobius fuscus and Eviota abax, was studied on a rocky shore. Large males (LM: 55–80mm in standard length: SL) and small males (SM: 34–52mm SL) of B. fuscus acted as nest holders and sneakers, respectively, in the early spawning season (July). The sympatric male E. abax (22–33mm SL) was smaller than SM B. fuscus, and synchronically used rocky holes much smaller than those of LM B. fuscus. In this season, aggressions between the two species were rarely observed. In late season (August), as the number of the LM decreased, the SM converted their tactics to nest holding, occupying nests of a sizes similar to those of E. abax. Eviota abax males were dispossessed by SM and shifted their nest sites to cavities between cobbles and sandy bottom, which might be poorer nest sites than rocky holes.     

Analysis of interspecific competition in perennial plants using Life Table Response Experiments

The impact of interspecific competition is usually measured by its effect upon plant growth, neglecting impacts upon other stages of the life cycle such as fecundity which have a direct influence upon individual fitness and the asymptotic population growth rate of a population (λ). We used parameterized matrix models for three perennial plant species grown with and without interspecific competition to illustrate how the methodology of Life Table Response Experiments (LTRE) can be used to link any change in population dynamics to changes in any part of the life cycle. Plants were herbaceous grassland species grown for two years in a field experiment at Rothamsted Experimental Station, England. Interspecific competition reduced λ by over 90% in all species. Survival and growth were slightly affected by competition whereas plant fecundity was greatly reduced. Nearly all of the observed difference in λ between the competition treatments was explained by the fecundity terms, and more precisely by a large difference in the number of seeds, and a high sensitivity of λ to the germination rate. Whereas most competition studies focus on the measurement of change in individual fitness, our study illustrates how informative it is to take account not only of the effect of competition upon vital rates but also of how different vital rates affect population growth rate.     

An aphid-ant interaction: effects on different trophic levels

The interaction between the aphid Aphis coreopsidis (Thomas) (Hemiptera, Aphididae) and the ant Camponotus sp.1 (Hymenoptera, Formicidae) on the plant Bidens pilosa L. (Asteraceae) was studied. We manipulated the presence of ants and other insects to understand the effects of this aphid-ant interaction on: (a) the growth of A. coreopsidis population, (b) the seed production of B. pilosa, (c) the density of predator spiders. The growth of the A. coreopsidis population was positively affected by attending ants, showing greater increase on ant-present control plants than on ant-excluded plants. The density of aphids on control plants was positively correlated with the density of attending ants, while the density of aphids on ant-excluded plants was positively correlated with the density of spiders. Plants with ants had a significantly lower quantity of viable seeds than those without ants. These results show that: (a) the presence of Camponotus ants reduces the number of predator spiders on B. pilosa, (b) the population of A. coreopsidis increases when attended by the ants, (c) this increase in aphid density as a result of ant attendance reduces the number of viable seeds of B. pilosa, and thus (d) an interspecific interaction between two species can have an indirect negative fitness effect on other partners.