The global trend in plant twining direction

Aim  To examine, at a global scale, patterns in the direction in which climbing plants twine. We tested three hypotheses: (1) that twining direction is determined randomly; (2) that twining direction is determined by apices following the apparent movement of the sun across the sky; and (3) that twining direction is determined by the Coriolis effect.
Location  Seventeen sites spanning nine countries, both hemispheres and 65° of latitude.
Methods  Twining direction was recorded for the first c . 100 stems encountered along transects through natural vegetation at each site.
Results  Ninety-two per cent of the 1485 twining stems we recorded grew in right-handed helices, i.e. they twined in an anticlockwise direction. This is significantly ( P < 0.001) different from random. The proportion of stems twining right-handedly (anticlockwise) was independent of both latitude ( P = 0.33) and hemisphere ( P = 0.63). These data are inconsistent with the idea that twining direction is determined by either the relative passage of the sun through the celestial sphere or by the Coriolis effect. Thus, we reject all three of our hypotheses.
Main conclusions  The predominance of right-handed helical growth in climbing plants cannot be explained by hypotheses attempting to link plant growth behaviour and global location. One alternative hypothesis for our findings is that the widespread phenomenon of anticlockwise twining arises as a function of microtubule orientation operating at a subcellular level.     

Life History Traits of Lianas During Tropical Forest Succession

Tropical secondary forests form an important part of the landscape. Understanding functional traits of species that colonize at different points in succession can provide insight into community assembly. Although studies on functional traits during forest succession have focused on trees, lianas (woody vines) also contribute strongly to forest biomass, species richness, and dynamics. We examined life history traits of lianas in a forest chronosequence in Costa Rica to determine which traits vary consistently over succession. We conducted 0.1 ha vegetation inventories in 30 sites. To examine the establishment of young individuals, we only included small lianas (0.5–1.5 cm diameter at 1.3 m height). For each species, we identified seed size, dispersal mode, climbing mode, and whether or not the seedling is self‐supporting. We found a strong axis of variation determined by seed size and seedling growth habit, with early successional communities dominated by small‐seeded species with abiotic dispersal and climbing seedlings, while large‐seeded, animal‐dispersed species with free‐standing seedlings increased in abundance with stand age. Contrary to previous research and theory, we found a decrease in the abundance of stem twiners and no decrease in the abundance of tendril‐climbers during succession. Seed size appears to be a better indicator of liana successional stage than climbing mode. Liana life history traits change predictably over succession, particularly traits related to seedling establishment. Identifying whether these trait differences persist into the growth strategies of mature lianas is an important research goal, with potential ramifications for understanding the impact of lianas during tropical forest succession.     

Climbing to reach females: Romeo should be small

The race for reaching mates by the time they are receptive, or sexual selection by scramble competition, has received little attention. We argue that smaller males are favored in species in which the male must climb to reach females located in high habitat patches. This new explanation we term the "gravity hypothesis" of sexual size dimorphism (SSD). We show that a simple biomechanical model of animal movement predicts that: (1) selection should favor a comparatively smaller size in the searching sex when searching involves climbing; and (2) this effect should be stronger in larger species than in smaller species. In reaching high habitats, smaller, faster searchers will be favored either through sexual selection by scramble competition and/or by escaping predation easier by running faster on vertical surfaces. Different spider species are found at a wide range of heights. We compiled a dataset of spider taxa and arranged their habitats according to four height categories, ranked from soil surface to trees. We show that, after controlling for phylogeny, both predictions of the gravity hypothesis of SSD are met. Thus, it appears that the constraint imposed by gravity on climbing males is a selective factor in determining male dwarfism.     

Inherent allocation patterns and potential growth rates of herbaceous climbing plants

We tested the hypothesis that herbaceous climbing plants, unlike non-climbing herbs, maximize height growth and leaf area, with minimal expenditure in support structures. The enhanced investment in leaf area was expected to result in high relative growth rates in terms of biomass increment. Four leguminous herbaceous climbers from nutrient-poor sites and four non-leguminous herbaceous climbers from nutrient-rich sites, were compared with non-climbing, self-supporting leguminous and non-leguminous herbaceous species from similar habitats. Plants were grown in hydroponic cultures in controlled environment chambers. All climbers had inherently taller shoots than self-supporting plants when compared at an equal amount of total plant dry weight, due to longer stems per unit of support biomass. In contrast to the hypothesis, the relative growth rates of all climbers were relatively low compared to the range found for self-supporting species. The biomass allocation patterns of the non-leguminous climbers were similar to those of the self-supporting species. Leguminous climbers allocated more biomass to support tissue and less biomass to leaves than non-climbers. As a result, height growth was even more emphasized in leguminous climbers than in non-leguminous climbers. Climbing legumes had high rates of net carbon gain, which partly compensated the lower relative leaf weight. We conclude that leguminous herbaceous climbers maximize height growth by a large investment in support biomass, enabling them to keep a large proportion of their leaves in the better illuminated environment at the top of the vegetation canopy.     

Terrestrial locomotion in the climbing perch, Anabas testudineus (Bloch) (Anabantidea, Pisces)

Climbing perches use the tail for forward propulsion when on land. The spiny gill covers are used to obtain purchase on the substratum. Unusually amongst teleosts, the opercular and subopercular bone are not bound strongly together into a single operculum. Instead they are joined only by a thin, flexible membrane, so that the fish has two sections of the gill cover hinged separately; the opercular on the suspensorium and the subopercular on the rearmost part of the lower jaw. The gill covers open very widely and the subopercular rotates ventrally as well as laterally. Two modes of locomotion are employed. Usually Anabus adopts a near-upright posture and alternately drives the left and right spiny suboperculars into the substratum, using the tail to vault over the subopercular (which acts in the manner of a short vaulting pole). During vigorous movement the fish may leave the substratum altogether during the vault. Fatigued fish, or fish which have fallen during climbing, move on their sides, using the tail for propulsion and a single spiny opercular which is repeatedly driven into the substratum. Maximum speeds observed on land corresponded to 1.8 body lengths S^?1. No evidence of involvement of the pelvic fins in locomotion was obtained; the pectorals seemed only to help in tilting the head from side to side and did not contribute significantly to forward propulsion. On mud and tree bark the fish were laterally unstable, often resting on their sides. Grassy substrata provided support and permitted a more upright posture. Slope climbing ability was restricted to 25° when climbing tree bark and 30° when climbing grass. Coupled with lateral instability these observations disqualify the species from any tree-climbing capacity. Anabas can climb vertical obstacles of at least half body length in height by pushing the head against the obstacle, using the spiny gill covers for purchase until one or other subopercular hooks over the top of the barrier. The subopercular is then used as a fulcrum for an upwards vault to clear the obstacle.     

Number of Lianas per Tree and Number of Trees Climbed by Lianas at Los Tuxtlas,Mexico1

In the tropical rainforest of Los Tuxtlas, Mexico, lianas (woody‐climbing plants) had a clumped distribution on trees, and 63.3 percent of trees ≥10 cm in diameter carried at least one liana. Trees with larger diameters supported more lianas and a higher total basal area of lianas than trees with smaller diameters. There was no relationship between liana diameter and the number of trees a liana climbed, but tendril climbers climbed on more trees than stem‐twiners.     

Ontogenetic change in novel functions: waterfall climbing in adult Hawaiian gobiid fishes

Juveniles from three species of Hawaiian gobiid fishes climb waterfalls as part of an amphidromous life cycle, allowing them to re-penetrate adult upstream habitats after being swept out to the ocean upon hatching. The importance of climbing for juvenile stream gobies is well established, but adult fish in upstream island habitats also face potential downstream displacement by periodic disturbances. Thus, retention of climbing ability could be advantageous for adult stream gobies. Climbing performance might be expected to decline among adults, however, due to the tendency for mass-specific muscular power production to decrease with body size, and a lack of positively allometric growth among structures like the pelvic sucker that support body weight against gravity. To evaluate changes in waterfall-climbing ability with body size in Hawaiian stream gobies, we compared climbing performance and kinematics between adults and juveniles from three species: Awaous guamensis , Sicyopterus stimpsoni and Lentipes concolor . For species in which juveniles climbed using 'powerbursts' of axial undulation, adult performance and kinematics showed marked changes: adult A. guamensis failed to climb, and adult L. concolor used multiple pectoral fin adductions to crutch up surfaces at slow speeds, rather than rapid powerbursts. Adult S. stimpsoni , like juveniles, still used oral and pelvic suckers to 'inch' up surfaces and climbed at speeds comparable to those of juveniles. However, unlike juveniles, adult S. stimpsoni also add pectoral fin crutching to every climbing cycle. Thus, although powerburst species appear to be particularly susceptible to size-related declines in waterfall-climbing performance, the addition of compensatory mechanisms prevents the loss of this novel function in some species.     

Effects of human disturbance on liana community diversity and structure in a tropical rainforest,Malaysia: implication for conservation

Aim Due to the important role of lianas in the functioning of forest ecosystem, knowledge of the factors that affect them are important in the management of forests. Currently, there are conflicting reports on the response of liana communities to disturbance, calling for more research in the area. The present study was carried out to investigate the response of liana diversity and structure to human disturbance within two major forests in the Penang National Park, Malaysia. The study also looked at the implication of the findings for conservation.Methods A total of 15 40 × 40-m 2 (or 40-m × 40-m) plots each were randomly located across a range of habitats in a primary forest and disturbed secondary forest. Trees with diameter at breast height ≥10 cm were examined for lianas with diameter ≥2 cm. Both lianas and trees were enumerated and compared between the two forests. Diversity and structural variables of lianas were compared between the two forests using the t -test analysis. Tree abundance was also compared between the two forests with t -test, while linear regression analysis was run to determine the effects of tree abundance on liana abundance.Important findings A total of 46 liana species belonging to 27 genera and 15 families were identified in the study. Human disturbance significantly reduced liana species richness and species diversity in the secondary forest. Liana abundance remained the same in both forests whereas liana basal area was significantly higher in the primary forest. Twiners and hook climbers were significantly more abundant in the primary and secondary forest, respectively. Large diameter lianas were more abundant in the primary forest compared with the secondary forest. The diameter distribution of most families in the primary forest followed the inverted J-shaped curve whereas only a few of the families in the secondary forest did so. Tree abundance was significantly higher in the primary forest. The abundance of lianas significantly depended on tree abundance in all the forests. The study has provided evidence of negative effects of human disturbance on liana diversity and structure that does not auger well for biodiversity in the forest. In view of the critical role of lianas in maintaining biodiversity in the forest ecosystem, lianas in the national park should be protected from further exploitation.     

Evolutionary trade‐offs in locomotor capacities in lacertid lizards: are splendid sprinters clumsy climbers?

We tested the hypothesis that an evolutionary trade‐off exists between the capacity to run on level terrain and the ability to climb inclined structures in lacertid lizards. Biomechanical and physiological models of lizard locomotor performance suggest that the morphological design requirements of a ground‐dwelling vs. scansorial life style are difficult to reconcile. This conflict is thought to preclude simultaneous evolution of maximal locomotor performance on level and inclined terrain. This notion has been corroborated by comparative studies on lizard species from other groups (Anolis, Chamaeleo, Sceloporus), but is not supported by our data on 13 species from the family Lacertidae. We found no indication of a negative association between maximal sprint speed of lizards over a level racetrack (indicative of ground‐dwelling locomotor performance), on an inclined stony surface (indicative of climbing performance over rock faces) and inclined mesh surface (indicative of clambering performance among vegetation). Moreover, morphological characteristics associated with fast sprinting capacities (e.g. long hind limbs) apparently enhance, rather than hinder climbing and clambering performance. We conclude that in our sample of lacertid lizards, the evolution of fast sprinting capacity on level terrain has not inflicted major restrictions on climbing and clambering performance.