Tangled banks: A landscape genomic evaluation of Wallace's Riverine barrier hypothesis for three Amazon plant species

Wallace's Riverine Barrier hypothesis is one of the earliest biogeographic explanations for Amazon speciation, but it has rarely been tested in plants. In this study, we used three woody Amazonian plant species to evaluate Wallace's Hypothesis using tools of landscape genomics. We generated unlinked single‐nucleotide polymorphism (SNP) data from the nuclear genomes of 234 individuals (78 for each plant species) across 13 sampling sites along the Rio Branco, Brazil, for Amphirrhox longifolia (8,075 SNPs), Psychotria lupulina (9,501 SNPs) and Passiflora spinosa (14,536 SNPs). Although significantly different migration rates were estimated between species, the population structure data do not support the hypothesis that the Rio Branco—an allopatric barrier for primates and birds—is a significant genetic barrier for Amphirrhox longifolia, Passiflora spinosa or Psychotria lupulina. Overall, we demonstrated that medium‐sized rivers in the Amazon Basin, such as the Rio Branco, are permeable barriers to gene flow for animal‐dispersed and animal‐pollinated plant species.     

Distyly and incompatibility in Psychotria homalosperma (Rubiaceae), an endemic plant of the oceanic Bonin (Ogasawara) Islands

Distyly rarely occurs on oceanic islands. Indeed, this form of polymorphism is absent on the Hawaiian Islands and in New Zealand. However, Psychotria homalosperma (Rubiaceae), which is endemic to the oceanic Bonin Islands of Japan, was presumed to maintain a distylous breeding system and floral morphology. We investigated the floral and reproductive characteristics of this species and examined incompatibility in self- and intramorph pollination. Psychotria homalosperma is morphologically and functionally distylous, based on findings with the examined populations, but its stigma and anther heights are not exactly reciprocal between the two morphs. This is the second example of distyly among the flora from the Bonin Islands, the other being the endemic P. boninensis. Both of these distylous species contrast with the Hawaiian Psychotria species, which have already become dioecious. The flowers of the long (L)-styled (pin) morph of the Bonin Islands plants are completely self- and intramorph incompatible, while the flowers of the short (S)-styled (thrum) morphs are partially intramorph compatible. The S-styled morph was more abundant in the examined populations from three islands of the archipelago, probably due to the existence of partial S–S intramorph compatibility.     

广东中部两种常见灌木的生态学比较

 通过对广东中部的阳生性灌木桃金娘和阴生性灌木九节的形态学、解剖学、植物生态学以及植物生理学等方面的比较发现：处于强光照下的桃金娘通过大的根系、多的枝叶和小的叶片在水分和养分竞争中处于优势,并利用小的枝角和叶毛来避免强光的伤害,而九节则是通过其叶、枝的最经济数量和最佳位置排列来充分利用阴暗不足的光线;桃金娘通过叶片和栅栏组织厚度以及短的小脉间距在强光下能继续进行光合作用并尽快运出光合产物,而九节的叶片则可充分利用森林底层有限的光照;在南亚热带,30％左右的透光率是林下耐荫性树种九节入侵和阳生性灌木桃金娘消亡的辐射条件;九节的生态对策为K对策,而桃金娘遵循r对策;九节和桃金娘的平均光合速率分别为5.9±1.6μmol CO2·m-2·s-1和11.9±0.4μmol CO2·m-2·s-1,光补偿点分别为0.005和0.012mmol·m-2·s-1,光饱和点分别为0.04和0.39μmol CO2·m-2·s-1,气孔传导率分别为0.053±0.037μmolCO2·m-2·s-1和0.101±0.013 mol·m-2·s-l,暗呼吸速率分别为0.42±0.0lμmol CO2·m-2·s-1和0.16±0.15μmolCO2·m-2·s-1,这些生理学差异、形态解剖学差异等与其生境差异有密切的关系。     

Stomatal behavior and photosynthetic performance under dynamic light regimes in a seasonally dry tropical rain forest

Rates of photosynthetic induction upon exposure to high light and rates of induction loss after darkening the leaf were measured in the field for four species of tropical shrubs in the family Rubiaceae. During wet season mornings, stomatal conductance (g _s) in the shade prior to induction was generally high enough so that the time course of induction was determined primarily by rates of activation of biochemical processes. During wet season afternoons, however, g _s values in the shade tended to be considerably lower and photosynthetic induction following a light increase exhibited a slower time course. In the afternoon, the time course of induction was determined by a combination of stomatal opening time and the rates of activation of light regulated enzymes. Stomatal behavior was also correlated with patterns of induction loss following a transfer from high light to darkness. In the afternoon, maximum g _s was lower for all species, and for a given time in the darkness, leaves showed a greater loss of induction in the afternoon than in the morning. During the dry season, maximum g _s and average values for g _s in the shade were reduced in all species. Along with these shifts in stomatal behavior, reduced rates of photosynthetic induction were observed. In the high-light species, the lower maximum g _s values observed during the dry season were also correlated with increased induction loss for a given time in the darkness. For all species, stomatal behavior was affected by season and time of day and, with the exception of wet season mornings, stomata appeared to exert significant control over rates of induction and patterns of induction loss. The results of simulation modeling suggest that the observed seasonal and diurnal changes in rates of induction and induction loss can have significant consequences on sunfleck carbon gain under a dynamic light regime. Received: 17 March 1999 / Accepted: 26 October 1999     

全光和遮阴下两种亚热带木本植物的光合作用对光的响应

以气体交换和调制叶绿素荧光测定技术测定了2年生亚热带乔木黧蒴,林下灌木九节在全自然光和17％自然光下叶片同部位的光合作用和与之相关的荧光参数的日变化。和全光照比较,遮阴下植物叶片净光合速率Pn,气孔导度gs,胞间CO2浓度与大气CO2浓度之比Ci/Ca,类胡萝卜素与叶绿素含量之比Car/Chl,光系统Ⅱ原初光[化学效率Fv/Fm 的变化幅度相对较小,种间差异较不明显,全光照黧蒴和九节Pn的口变化图式与gs,Ci/Ca类似,与Φpsll,qp的下降吻合。全光下黧蒴叶片qN和Car/Chl的口进程表现为增加,九节则下降,低的Car/Chl可能是导致强光下九节未能提高其qN的原因,正午前后,黧蒴qN和Car/Chl增大,而qp和Φpsll降低,Fv/Fm则保持相对稳定,反映其开放的PSII反应中心数目在此期间虽有所减少,但仍然维持了较高的光化学效率,提高的Car/Chl和qN则说明其肯有较强的对过剩激发能的耗散能力,此条件下九节的gs,Fv/Fm和qN下降且明显低于黧蒴,Φpsll和qp保持相对稳定但高于黧蒴的水平,表明九节的PSII反应中心活性较稳定,但强光下气孔部分关闭,较低的Fv/Fm和qN限制了CO2供应和对光能的有效利用,且未能诱导热能耗散机制的积极运行及对光合器起到保护作用。总体上说,九节对高光强反应比黎蒴敏感。     

Breeding system and floral morphometry of distylous Psychotria L. species in the Atlantic rain forest, SE Brazil

General patterns of floral morphology and incompatibility mechanisms have been described for many distylous plants. The absence of these patterns in typically distylous groups, as observed especially in tropical environments, is interpreted as atypical distyly, or as a new reproductive strategy derived from it. Data are presented here on the morphological and compatibility relations between floral morphs of four Psychotria dimorphic species in the Atlantic rain forest in SE Brazil: Psychotria jasminoides, P. birotula, P. mapourioides, and P. pubigera. When significant differences were found, floral parts were larger in thrum flowers. Results of controlled crosses showed that most incompatible pollen tubes were arrested in the stigma, and only in a low proportion in the upper parts of the style. We conclude that, at the study site, the majority and most important morphological and mating features of typical distyly seem to be conserved in P. jasminoides and P. mapourioides, which presented reciprocal herkogamy, self and intramorph incompatibility, and a balanced morph ratio in the population. Typical distyly in P. birotula is supported by floral morphology, pollen tube data and morph ratio and, in P. pubigera, only by floral morphology and pollen tube data.     

Novel interactions of non-pollinating ants with pollinators and fruit consumers in a tropical forest

The tropical ants Ectatomma ruidum and E. tuberculatum (Formicidae) regularly patrol leaves, flowers, and fruits of the understory shrub, Psychotria limonensis (Rubiaceae), on Barro Colorado Island, Panama. Ant and pollinator exclusion experiments elucidated both positive and negative effects of ant attendance on plant reproductive success, including pollination, fruit set, fruit loss, and fruit removal. Ants did not pollinate flowers but did contribute to higher pollination success, probably by increasing the relocation frequency of winged pollinators and thus the rate of flower visitation. Ants also prevented fruit loss to herbivorous insects which were common during the early stages of fruit development. Thus, ant attendance strongly improved both pollination and fruit set whereby plants with ants set more fruit per flower and also lost fewer fruits during fruit maturation. In contrast, ants had a negative effect on the removal of ripe fruits by avian frugivores. Thus, ant attendance has a non-trivial influence on plant reproduction, this interaction being beneficial at some stages of the plant reproductive cycle and carrying costs at another stage. A tight ecological or co-evolved relationship between these Ectatomma spp. and P. limonensis is unlikely given that ant attendance of plants is detrimental to fruit removal. Received: 18 May 1998 / Accepted: 1 March 1999     

Distyly and sequential pollinators of Psychotria nuda (Rubiaceae) in the Atlantic rain forest, Brazil

Reciprocal herkogamy is known to promote intermorph-pollination in distylous species, which are generally self- and intramorph-incompatible. Legitimate crossing rates are also influenced by pollinator foraging strategy, which determines most of the pollen flow in natural populations. This study reports on the floral morphology, compatibility relations and pollination biology of Psychotria nuda (Cham. and Schltdl.) Wawra in the Atlantic rain forest, southeastern Brazil, based on floral measurements, hand-pollination experiments and focal observation of floral visitors. It was found that P. nuda does not present an exactly reciprocal herkogamy, however, this morphological trait in P. nuda is as good as in most of Rubiaceae. Reproductive experiments showed compatibility relations similar to those frequently observed in distylous species. The hummingbirds Ramphodon naevius and females of Thalurania glaucopis were the main pollinators of P. nuda, presenting the traplining foraging strategy, which seems to maximize intermorph crosses in P. nuda flowers. These hummingbirds pollinated P. nuda flowers sequentially throughout the flowering period.     

Dioecy derived from distyly and pollination in Psychotria rubra (Rubiaceae) occurring in the Ryukyu Islands,Japan

Floral morphology and breeding system were examined in natural populations of Psychotria rubra (Rubiaceae) occurring in the Ryukyu Islands in southwest Japan. This species is morphologically dimorphic with long‐ and short‐styled morphs; however, these morphs are functionally dioecious. All long‐styled morphs set fruits, but their short anthers completely lack pollen grains; thus, they function as pistillate flowers. Alternately, short‐styled morphs usually have fertile pollen and never set fruit, whether after open or obligate pollinations; thus, they function as staminate flowers. However, some short‐styled morphs in Mounts Katsuu‐dake and Oppa‐dake populations have no fertile pollens. No fruit was obtained from bagging experiments, indicating that P. rubra requires pollinators for its reproduction. In our pollinator observations, flies and short‐tongued wasps were the main visitors of the flowers of P. rubra. Thus, these insects are probably effective pollinators for P. rubra in the Ryukyu Islands. Considering the morphological features, the dioecy found in P. rubra is probably derived from distyly; however, no sufficient evidence is available showing that dioecy has evolved “directly” from distyly.     

Integrated analysis of tropical trees growth: a multivariate approach

BACKGROUND AND AIMS: One of the problems analysing cause-effect relationships of growth and environmental factors is that a single factor could be correlated with other ones directly influencing growth. One attempt to understand tropical trees' growth cause-effect relationships is integrating research about anatomical, physiological and environmental factors that influence growth in order to develop mathematical models. The relevance is to understand the nature of the process of growth and to model this as a function of the environment. METHODS: The relationships of Aphananthe monoica, Pleuranthodendron lindenii and Psychotria costivenia radial growth and phenology with environmental factors (local climate, vertical strata microclimate and physical and chemical soil variables) were evaluated from April 2000 to September 2001. The association among these groups of variables was determined by generalized canonical correlation analysis (GCCA), which considers the probable associations of three or more data groups and the selection of the most important variables for each data group. KEY RESULTS: The GCCA allowed determination of a general model of relationships among tree phenology and radial growth with climate, microclimate and soil factors. A strong influence of climate in phenology and radial growth existed. Leaf initiation and cambial activity periods were associated with maximum temperature and day length, and vascular tissue differentiation with soil moisture and rainfall. The analyses of individual species detected different relationships for the three species. CONCLUSIONS: The analyses of the individual species suggest that each one takes advantage in a different way of the environment in which they are growing, allowing them to coexist.