Karyotype evolution and phylogenetic analyses in the genus Cardiospermum L. (Paullinieae,Sapindaceae)

Cardiospermum L. belongs to the Paullinieae tribe (Sapindaceae) and comprises 16 species. Of these, 12 species are present in South America and all occur in Brazil. Cardiospermum shows the most variable chromosome number of the tribe. Phylogenetic relationships within the genus Cardiospermum, especially with other species of the tribe, are poorly understood. This research focuses on characterisation of the karyotypic features of Cardiospermum using conventional cytogenetic methods, CMA/DAPI chromosome banding and fluorescence in situ hybridisation (FISH). To elucidate the phylogeny of the genus, the nuclear markers ITS1 and ITS2 were sequenced and analysed using maximum parsimony and Bayesian inference. Cardiospermum shows important diversity in basic numbers, with x = 7, 9, 10, 11 and 12. All species studied have metacentric and submetacentric chromosomes, some species have subtelocentric chromosomes, while telocentric chromosomes are absent. The interphase nuclei differentiate the Cardiospermum species into two groups. The CMA₃/DAPI chromosome banding revealed the presence of an AT‐rich terminal region in C. corindum, C. grandiflorum and C. urvilleoides, whereas GC‐rich regions were found in C. grandiflorum, C. halicacabum var. halicacabum, C. halicacabum var. microcarpum, C. heringeri and C. integerrimum. FISH revealed syntenic and non‐syntenic distribution of the 18‐5.8‐26S and 5S rDNA. The syntenic distribution always occurred in the short arms of the same chromosome in all of the species. The phylogenetic relationships reveal, in part, the taxonomic arrangement of the genus Cardiospermum.     

Insects and light interact to mediate vine colonization of fast growing Microberlinia bisulcata tree seedlings in gaps of an African rain forest

Vines thrive in lowland tropical forests, yet the biotic factors underlying their colonization of host tree seedlings and saplings remain surprisingly understudied. Insect herbivores presumably could influence this process, especially where disturbance has opened the canopy (i.e., gaps)—temporary areas of higher primary productivity favoring the recruitment of vines and trees and invertebrates in forests—but their impact on vine colonization has never been experimentally tested. Using data from an insect herbivore exclusion (mesh-netting cages) experiment conducted in an African rain forest (Korup, Cameroon), I logistically modeled the probability of vines colonizing seedlings of three co-dominant species (Microberlinia bisulcata vs. Tetraberlinia bifoliolata and T. korupensis) in paired shaded understory and sunny gap locations (41 blocks across 80 ha, starting n = 664 seedlings) in a 1–2-yr period (2008–2009). Vine colonization occurred almost exclusively in gaps, occurring on 16% of seedlings there. Excluding herbivores in gaps doubled colonization of the light-demanding and faster growing M. bisulcata but had negligible effects on the two shade-tolerant, slower growing and less palatable Tetraberlinia species, which together were twice as susceptible to vines under natural forest gap conditions (controls). When protected from herbivores in gaps, more light to individual seedlings strongly increased vine colonization of M. bisulcata whereas its well-lit control individuals supported significantly fewer vines. These results suggest vines preferably colonize taller seedlings, and because light-demanding tree species grow faster in height with more light, they are more prone to being colonized in gaps; however, insect herbivores can mediate this process by stunting fast growing individuals so that colonization rates becomes more similar between co-occurring slow and fast growing tree species. Further influencing this process might be associational resistance or susceptibility to herbivores linked to host species’ leaf traits conferring shade-tolerant ability as seedlings or saplings. A richer understanding of how vines differentially influence forest regeneration and species composition may come from investigating vine–tree–herbivore interactions across light gradients, ideally via long-term studies and intercontinental comparisons. Abstract in French is available with online material.     

And the beak shall inherit – evolution in response to invasion

The increased demographic performance of biological invaders may often depend on their escape from specifically adapted enemies. Here we report that native taxa in colonized regions may swiftly evolve to exploit such emancipated exotic species because of selection caused by invaders. A native Australian true bug has expanded it host range to include a vine imported from tropical America that has become a serious environmental weed. Based on field comparisons and historical museum specimens, we show that over the past 30–40 years, seed feeding soapberry bugs have evolved 5–10% longer mouthparts, better suited to attack the forest‐invading balloon vines, which have large fruits. Laboratory experiments show that these differences are genetically based, and result in a near‐doubling of the rate at which seeds are attacked. Thus a native biota that initially permits invasion may rapidly respond in ways that ultimately facilitate control.     

Effects of below- and aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on the growth of the tree host Liquidambar styraciflua

Detrimental effects of vines on tree growth in successional environments have been frequently reported. Little is known, however, about the relative importance of below and aboveground competition from vines on tree growth. The objective of this study was to quantify and compare the growth responses of Liquidambar styraciflua saplings to below and/or aboveground competition with the exotic evergreen vine, Lonicera japonica (Japanese honeysuckle), and the native deciduous vine, Parthenocissus quinquefolia (Virginia creeper). Soil trenching and/or vine-trellising were used to control the type of vine competition experienced by trees. Comparisons among untrenched treatments tested for effects of belowground competition. Comparisons among trenched treatments tested for effects of aboveground competition. After two growing seasons, Lonicera japonica had a greater effect on the growth of L. styraciflua than did P. quinquefolia. This effect was largely due to root competition, as canopy competition only had a negative effect on tree growth when it occurred in combination with root competition. Leaf expansion was consistently and similarly affected by all treatments which involved belowground competition.     

Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host

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Feeding behavior of Heliconius erato phyllis (Fabricius) (Lepidoptera: Nymphalidae) larvae on passion vines

Of the 15 species of passion vines recorded for the Rio Grande do Sul State, Brazil, nine are used by Heliconius erato phyllis (Fabricius, 1775). The larvae of this species feed preferentially on Passiflora misera H.B.K., which confers greater performance despite presenting smaller amounts of nutrients than other host plants. Thus, the performance associated with the consumption of a passion vine is possibly related not only to its nutritional content but also to the morphological and behavioral mechanisms involved in the feeding. In this study, the difficulties in accessing food imposed by the hosts (P. misera, Passiflora suberosa L., Passiflora caerulea L., Passiflora edulis Sims, and Passiflora alata Dryand.) were evaluated. Focal observations were performed every 2 min during 6-h sessions (sequential sampling), and the relative time spent for different behaviors (resting, feeding, walking, tasting, and vein cutting) was quantified on both young and old leaves. Larvae devoted more time feeding on P. misera in most cases. Larvae observed on P. alata devoted more to time resting and less time feeding, performing one or two meals of small duration, every 6 h. First instar caterpillars on old leaves of P. suberosa and P. caerulea spent more time walking, searching for a favorable feeding site. The hardness of leaves may be a limiting factor for the initial instars in this heliconian.     

The influence of vines on an oligohaline marsh community: results of a removal and fertilization study

The effects of competitive suppression by vines on the non-vine plant community have received little attention in temperate habitats. This study investigated the impact vines have on their herbaceous hosts in a wetland community at two soil fertility levels. Plots in an oligohaline marsh were treated in a 2 × 2 factorial design with vine removal and fertilization over two growing seasons. There was no significant interaction between removal and fertilization treatments on any of the measured variables. Vine removal initially caused an increase in light penetration through the canopy, but by the end of the study, plots with vines removed had less light due to a 25% increase in biomass by the plants released from competition with vines. For plots with vines removed, species richness was higher during a brief period in the spring of the second year, but by the end of the study, richness in removal plots decreased relative to controls. Fertilization caused a 40% increase in biomass overall, although only two species, Sagittaria lancifolia L. and Polygonum punctatum Ell., showed dramatic increases. Despite fertilization causing a 40% decrease in light penetration to the ground, no change in species richness was observed. Overall, these results show that vine cover in this wetland suppresses non-vine species and reduces community biomass. Removal of vines increased biomass of non-vine dominants but resulted in only an ephemeral change in species richness. Fertilization did not increase the effects of vines on the non-vine community. Received: 14 November 1996 / Accepted: 10 June 1997     

EFFECTS OF VINE COMPETITION ON AVAILABILITY OF LIGHT,WATER, AND NITROGEN TO A TREE HOST (LIQUIDAMBAR STYRACIFLUA)

Competitive effects of vines on their tree hosts are well documented, but the mechanisms involved in these interactions are poorly understood. The objectives of this study were to measure the effects of below- and/or aboveground competition from the vines Lonicera japonica and Parthenocissus quinquefolia on availability of light, water, and nitrogen to the host tree Liquidambar styraciflua, and to examine the relationship between resource availability and tree growth. Light penetration through tree canopies, pre-dawn leaf water potential, and leaf nitrogen concentration were used as predictors of light, water, and nitrogen availability to the tree, respectively. Vine presence significantly reduced light penetration through the tree canopies, but this reduction was not clearly related to the growth responses of trees. Vines did not reduce the pre-dawn leaf water potential of competing trees, which was consistently above -0.5 MPa for the duration of the study. Leaf nitrogen concentration of trees, on the other hand, was significantly reduced by belowground competition with L. japonica. The positive correlation between the annual average leaf nitrogen concentration and tree diameter growth suggested that competition for nitrogen mediated the effects of belowground competition of vines on tree growth.     

Seasonal variation in larval host plants and consequences for Heliconius erato (Lepidoptera: Nymphalidae) adult body size

Abstract Adult body size, a key life history component, varies strongly within and between Heliconius erato phyllis (Lepidoptera: Nymphalidae) populations. In the present study, we determined whether seasonal variation in adult body size is temperature related and/or determined by seasonal changes of host plants (Passifloraceae) used by the larval stage. A population of H. erato phyllis located in a Eucalyptus plantation (Barba Negra Forest, Barra do Ribeiro County, Rio Grande do Sul State, Brazil) was sampled every 45 days from March 1997 to October 1998 to quantify seasonal variation in adult body size and use of larval host plants. In the laboratory, the effects of the following factors on adult body size were quantified: (i) host plant species (Passiflora misera or Passiflora suberosa); (ii) food quantity consumed by larvae (experimentally manipulated for each passion vine species); (iii) winter and summer temperatures (15 and 25°C, respectively); and (iv) the interaction between host plant species and temperature. Adults emerging during summer were larger than those emerging in other seasons. Female butterflies oviposited selectively on P. misera even when the dominant passion vine was P. suberosa. They only switched from using P. misera to P. suberosa during later autumn and winter, when P. misera vines were completely defoliated. The laboratory feeding trials with both passion vines showed a strong positive association between food quantity consumed by larvae and adult size. They also confirmed that adults are larger when their larvae are reared on P. misera than on P. suberosa. Temperature during larval development had no effect on H. erato phyllis adult size. Thus, seasonal variation of H. erato phyllis adult size in a given place is primarily determined by the availability and quality of host plant species used by the larval stage.     

A test of adaptive divergence in a newly discovered host association of the soapberry bug Jadera haematoloma on Mexican buckeye,Ungnadia speciosa

Host races represent an important step in the speciation process of phytophagous insects as they reflect the maintenance of genetically divergent host-associated populations in the face of appreciable gene flow. The red-shouldered soapberry bug, Jadera haematoloma (Herrich-Schäffer) (Hemiptera: Rhopalidae), is an oligophagous seed predator with a history of host race evolution on plant associations in the (soapberry) family Sapindaceae. Soapberry bugs are a model group for understanding rapid ecological adaptation to their hosts, and hence good candidates for investigating evolutionary divergence in host associations over short timescales. Here, we describe the recent discovery of Mexican buckeye, Ungnadia speciosa Endl., as a host of J. haematoloma in a region of the Chihuahuan desert including west Texas and southeastern New Mexico, USA. This host differs from J. haematoloma’s previously recorded hosts in the Sapindaceae in seed chemistry, ecology, and phylogeny. The tendency toward rapid, host-associated adaptations by populations of J. haematoloma and the unique biology of the newly discovered Ungnadia host create the opportunity for potential host race formation, as it overlaps geographically with two previously recorded host plants in this region – the native western soapberry tree, Sapindus saponaria var. drummondii (Hook & Arn.), and the non-native goldenrain tree, Koelreuteria paniculata Laxm. We explore the possibility of host race formation on Ungnadia-associated insects by testing for host-associated differentiation in morphology and feeding behaviors. We find evidence of differentiation in the length of the mouth parts, which is an ecologically relevant feeding trait between host plant species with larger or smaller seed capsules. This divergence is maintained in the face of potential gene flow by reproductive isolation in the form of habitat isolation, which we detect in host preference trials. Together, our results demonstrate that soapberry bugs associated with this newly discovered host exhibit morphological and behavioral traits consistent with host race formation, but additional work is required to confirm its state along the speciation continuum.     

Do vine species in neotropical forests see the forest or the trees?

Questions: Is the occurrence of vine species in neotropical rain forests primarily determined by properties of the forest (environmental factors), by properties of the trees (tree species or tree size) or are vines randomly distributed? Location: Maya Biosphere Reserve, Guatemala. Methods: In five 1‐ha plots that span variation from unlogged forest to forest impacted by recurrent human disturbance we recorded the presence of all climbing vine species on every tree. The presence of all free standing vine species and 11 environmental variables were recorded in 100‐m² subplots. The relationship of host tree diameter and host tree identity on single tree vine species richness was investigated by GLM modelling. Partial redundancy analyses were used to partition the variation in vine species composition on two sources: environmental factors and tree species identity. Results: Single tree vine richness increased with increasing host tree DBH and differed significantly among host species. For climbing vines, the ratio of variation in subplot presence explained by tree species and by environmental variables was ca. 4:1 (in the most disturbed logged plots slightly lower), for free standing vines this ratio varied from 1:2 in the most disturbed logged plots to 9:1 in reserve plots, while a ratio of ca. 1:1 was found for all plots analysed together. Conclusion: Different tree species have different probabilities of being infested by vines. Vines see both the forest and the trees; the environment is more important in earlier developmental stages, properties of individual trees become more important from the time vines start to climb.     

Roles of non‐native species in large‐scale regeneration of moist tropical forests on anthropogenic grassland

This paper presents a new synthesis of the role of native and non‐native species in diverse pathways and processes that influence forest regeneration on anthropogenic grassland in the moist tropics. Because of altered species composition, abiotic conditions and landscape habitat mosaics, together with human interventions, these successional pathways differ from those seen in pre‐clearing forests. However, representation of different functional life forms of plant (tree, vine, grass, herb and fern) and animal (frugivorous seed disperser, granivorous seed predator, seedling herbivore and carnivore) shows consistent global variation among areas of pasture, intact forest, and post‐grassland regrowth. Biotic webs of interaction involve complex indirect influences and feedbacks, which can account for wide observed variation in regeneration trajectories over time. Important processes include: limitation of tree establishment by dense grasses; recruitment and growth of pioneer pasture trees (shading grasses and facilitating bird‐assisted seed dispersal); and smothering of trees by vines. In these interactions, species’ functional roles are more important than their biogeographic origins. Case studies in eastern Australia show native rain forest plant species diversity in all life forms increasing over time when pioneer trees are non‐native (e.g., Cinnamomum camphora, Solanum mauritianum), concurrent with decreased grass and fern cover and increased abundance of trees and vine tangles. The global literature shows both native and non‐native species facilitating and inhibiting regeneration. However conservation goals are often targeted at removing non‐native species. Achieving large‐scale tropical forest restoration will require increased recognition of their multiple roles, and compromises about allocating resources to their removal.     

Hybridization of cultivated Vitis vinifera with wild V. californica and V. girdiana in California

Hybridization of introduced domesticates and closely related natives is well documented in annual crops. The widespread introduction of the domesticated grapevine, Vitis vinifera, into California where it overlaps with two native congenerics, with which it is interfertile, provides opportunity to investigate hybridization between woody perennials. Although geographically widespread, the introduction over the past two centuries has been limited to a few elite clonal cultivars, providing a unique opportunity to study the effects of hybridization on the native species. The amount of hybridization with V. vinifera and the genetic diversity of wild‐growing Vitis californica and Vitis girdiana were examined using nineteen microsatellite markers. STRUCTURE analysis was used to define hybrid and introgressed individuals and to analyze genetic structure of the native species. FAMOZ software was used to identify which V. vinifera cultivars served as parents of F₁ hybrids. The three species were clearly distinguished by STRUCTURE analysis. Thirty percent of 119 V. californica vines were hybrids. The domesticated parent was identified for 16 F₁ hybrid vines; the original California cultivar, ‘Mission’, was the parent of eight. Backcrosses were also found, showing introgression into subsequent generations. Similar results were obtained for a small sample of V. girdiana. Removing hybrids greatly reduced the genetic variation of the presumed pure species, among which there was essentially no genetic structure. Limited genetic variability indicates the California natives may be threatened by genetic erosion. The discovery of F₁ hybrids of ‘Mission’, a cultivar not grown in the areas for ~100 years, suggests long generation times for wild vines that, often, grow into expansive liana and propagate by layering, all factors that limit recruitment in populations already disjunct by habitat lose. Hermaphroditic flowers and fruit that is more attractive to birds may favor the production of backcross seed and establishment of introgressed individuals.     

Influence of genetic architecture on contemporary local evolution in the soapberry bug,Jadera haematoloma: artificial selection on beak length

Little is known about the influence of genetic architecture on local adaptation. We investigated the genetic architecture of the rapid contemporary evolution of mouthparts, the flight polymorphism and life history traits in the soapberry bug Jadera haematoloma (Hemiptera) using laboratory selection. The mouthparts of these seed‐feeding bugs have adapted in 40–50 years by decreasing in length following novel natural selection induced by a host switch to the seeds of an introduced tree with smaller fruits than those of the native host vine. Laboratory selection on beak length in both an ancestral population feeding on the native host and a derived population feeding on the introduced host reveals genetic variance allowing a rapid response (heritabilities of 0.51–0.87) to selection for either longer or shorter beaks. This selection resulted in reverse evolution by restoring long beaks in the derived population and forward evolution by re‐creating short beaks in the ancestral bugs. There were strong genetic correlations (0.68–0.84) in both populations between beak lengths and the frequency of flight morphs, with short beaks associated with short wings. The results reveal a genetically interrelated set of adaptive multivariate traits including both beak length and flight morph. This suite of traits reflects host plant patchiness and seeding phenology. Weaker evidence suggests that egg mass and early egg production may be elements of the same suite. Reversible or forward evolution thus may occur in a broad set of genetically correlated multivariate traits undergoing rapid contemporary adaptation to altered local environments.     

Ecology and economic impact of two plant bugs (Hemiptera: Miridae) in commercial vineyards

The current study investigated the seasonal phenology, spatial distribution, feeding damage and economic impact of two plant bugs, Lygocoris inconspicuous Knight and Taedia scrupeus Say, in commercial vineyards. For both plant bugs, densities of nymphs were higher on vines located near the edge of woodlots rather than in the interior of vineyards, which may be attributed to the presence of wild vines and other alternate host-plants in wooded areas. Nymphs of both species fed on apical leaves and developing fruit clusters of vine shoots, initiating development after swelling of buds in the spring and reaching the adult stage when vines were in bloom. Confining high densities of L. inconspicuous (10 nymphs) on individual shoots early in the season resulted in significant reduction of the number of fruit clusters per shoot, even when feeding was restricted to short (7 d) duration; the average weight of fruit clusters, in contrast, was not affected to a large extent by feeding activity of nymphs. An experiment evaluating the impact of low density of L. inconspicuous (0-0.3 nymphs per shoot) indicated a marginally significant negative relationship between density of nymphs and average weight of fruit clusters. Control measures may be economically justified when population density exceeds a combined threshold of one nymph of either L. inconspicuous or T. scrupeus per 10 shoots of vines.     

Patterns in the diversity and distribution of epiphytes and vines in a New Zealand forest

Abstract Plants that rely on other plants for support (i.e. epiphytes and vines) are common in many forest ecosystems. However, they are poorly understood relative to terrestrial plants, especially in the Southern Hemisphere. To help bridge this gap, we evaluated the diversity and distribution of vascular epiphytes and vines on seven common tree species in a conifer‐broadleaf forest on New Zealand's North Island. Ground‐based surveys of 274 host trees were used to test whether epiphyte and vine diversity increased with tree diameter, and whether diversity‐diameter relationships differed among host tree species. Occurrence patterns of individual epiphyte and vine species were also assessed. We first evaluated the accuracy of ground‐based inventories by comparing surveys of trees made from the ground to those made from a canopy walkway. On average, 1 in 10 species of epiphytes and vines were unseen from the ground. However, sampling accuracy did not differ among the three host tree species growing along the walkway, suggesting unbiased comparisons could be made between hosts. Results from ground‐based surveys showed that species diversity of epiphytes and vines increased with host tree diameter. However, epiphytes showed stronger diversity‐diameter relationships than vines. Epiphyte diversity increased markedly in four host species and less strongly in the remaining three host species. Conversely, vines showed weak diversity‐diameter relationships in all host species. Occurrence patterns of individual species helped to explain diversity‐diameter relationships. All common epiphyte species occurred more frequently on large trees, regardless of host species, but occurrence patterns in most vine species were unrelated to tree size. Rather, the vines often showed strong host ‘preferences’. Overall results illustrate a rich diversity of distributional patterns in New Zealand's epiphytes and vines, and suggest that a similarly diverse set of ecological and evolutionary processes are responsible for them.     

Impact of the invasive shrub <Emphasis Type="Italic">Lonicera maackii</Emphasis> on stand transpiration and ecosystem hydrology in a wetland forest

Invasive shrubs can increase ecosystem transpiration and potentially affect hydrology in forested ecosystems. We examined two adjacent sites in a wetland forest in northern Kentucky, USA. One site contained little Lonicera maackii (Amur honeysuckle), while the other contained considerably more. Using Granier (thermal dissipation) and heat balance probes, transpiration was determined for trees, vines and shrubs at the two sites. Tree and vine transpiration in 2009 was usually 1–2 mm day⁻¹, typical of that seen in humid temperate forests. Additional transpiration from L. maackii was roughly proportional to its basal area, and it totaled 1.0% of tree and vine transpiration from the site with less L. maackii cover and 6.0% from the site with considerable cover. This additional transpiration amounts to roughly 10% of stream flow draining the study area. As L. maackii basal areas at these sites are at the lower end of that seen in other invaded forests in the region, regional impacts on transpiration and hydrology may be larger than those reported here. We expect L. maackii to shorten the lives of ephemeral ponds and streams in wetlands and cause adverse impacts on the organisms, such as amphibians, that require these aquatic environments to complete their life cycle.     

Effect of Plant Age on Endophytic Bacterial Diversity of Balloon Flower (Platycodon grandiflorum) Root and Their Antimicrobial Activities

Balloon flower (Platycodon grandiflorum) is widely cultivated vegetable and used as a remedy for asthma in East Asia. Experiments were conducted to isolate endophytic bacteria from 1-, 3-, and 6-year-old balloon flower roots and to analyze the enzymatic, antifungal, and anti-human pathogenic activities of the potential endophytic biocontrol agents obtained. Total 120 bacterial colonies were isolated from the interior of all balloon flower roots samples. Phylogenetic analysis based on 16S rRNA gene sequences showed that the population of ‘low G + C gram-positive bacteria’ (LGCGPB) gradually increased 60.0–80.0% from 1 to 6 years balloon flower sample. On the other hand, maximum hydrolytic enzyme activity showing endophytic bacteria was under LGCGPB, among the bacterial strains, Bacillus sp. (BF1-1 and BF3-8), Bacillus sp. (BF1-2 and BF3-5), and Bacillus sp. (BF1-3, BF3-6, and BF6-4) showed maximum enzyme activities. Besides, Bacillus licheniformis (BF3-5 and BF6-6) and Bacillus pumilus (BF6-1) showed maximum antifungal activity against Phytophthora capsici, Fusarium oxysporum, Rhizoctonia solani, and Pythium ultimum. Moreover, Bacillus licheniformis was found in 3 and 6 years balloon flower roots, but Bacillus pumilus was found only in 6 years sample. It is presumed that older balloon flower plants invite more potential antifungal endophytes for there protection from plant diseases. In addition, Bacillus sp. (BF1-2 and BF3-5) showed maximum anti-human pathogenic activity. So, plant age is presumed to influence diversity of balloon flower endophytic bacteria.     

Microenvironmental Heterogeneity and Space Utilization by Desert Vines within their Host Trees

The three-dimensional biomass distribution and the microenvironmentsexperienced by several desert vine species growing within thecanopy of host trees were studied at the Centro Ecológicode Sonora in México. The light environment within thecrown of the host tree Cercidium microphyllum showed a horizontaland vertical gradient from the base of the trunk to the edgesof the canopy. Within this gradient total daily photosyntheticallyactive radiation (PAR) varied from 47.8 mol m^-2outside the crownto 4.6 mol m^-2at the centre of the crown and close to the ground.Maximum air temperature was 3 °C lower beneath the crownthan outside. Within the canopy, most vines experienced lessthan 50% of the daily available PAR outside the canopy. Formost of the day, leaves of vines received 15% or less of themaximum available PAR. Our study shows that vines do not growtowards full sunlight but rather they exploit different habitatpossibilities within their host tree crown. Leaves along thestems of vines experienced a wide range of light environments,showing coefficients of variation (CV) in total daily PAR from36.4 to 94.6%. Daily courses of PAR also showed that leaveswithin the canopy experienced short-term temporal variationin the light environment. Differences in CV of daily PAR valuesand preferences in heterogeneous light microenvironments amongspecies suggested that different vine species might be spatiallyseparated in the canopy. We suggest that in desert habitats,conditions within the crown of host trees result in an importantmicrohabitat that vines can exploit, allowing them to avoidthe high light, temperature and water deficits found in thesurrounding environment. Copyright 1999 Annals of Botany Company Sonoran Desert, vines, host trees, canopy light environment.     

Why vines have narrow stems: Histological trends in Bauhinia (Fabaceae)

Summary Xylem (wood) tissue in plants functions both for mechanical support and water transport. Since vines are mechanical parasites, they allocate less biomass for xylem tissue than do free-standing trees or shrubs. With-in the genus Bauhinia, stems of vine species were found to have not only less xylem per distal leaf area, but also less phloem and cortical tissue when compared to tree and shrub species. The phloem and cortical reductions are interpreted as an indirect effect of the developmental/geometric constraints imposed by the evolution of a reduced mechanical system. Apparently vines overcame these constraints with the evolution of wider vessels and wider sieve tubes and with many types of variant (anomalous) secondary growth. The long and wide vessels of vines, which compensate hydraulically for the reduced xylem areas, may help limit the distribution of vine species in nature.