Wind-dispersed Seeds Research Articles

Functional bio-inspired hybrid fliers with separated ring and leading edge vortices.

Recent advances in passive flying systems inspired by wind-dispersed seeds contribute to increasing interest in their use for remote sensing applications across large spatial domains in the Lagrangian frame of reference. These concepts create possibilities for developing and studying structures with performance characteristics and operating mechanisms that lie beyond those found in nature. Here, we demonstrate a hybrid flier system, fabricated through a process of controlled buckling, to yield unusual geometries optimized for flight. Specifically, these constructs simultaneously exploit distinct fluid phenomena, including separated vortex rings from features that resemble those of dandelion seeds and the leading-edge vortices derived from behaviors of maple seeds. Advanced experimental measurements and computational simulations of the aerodynamics and induced flow physics of these hybrid fliers establish a concise, scalable analytical framework for understanding their flight mechanisms. Demonstrations with functional payloads in various forms, including bioresorbable, colorimetric, gas-sensing, and light-emitting platforms, illustrate examples with diverse capabilities in sensing and tracking.

Predicting the spatio-temporal distribution of the invasive alien plant Andropogon virginicus, in the South Korean peninsula considering long-distance dispersal capacities.

The spread of invasive alien species is a major threat to biodiversity. Estimating the long-distance dispersal capacity of invasive alien plants is vital for understanding their population dynamics and community composition. We predicted the spatial-temporal distribution of the alien plant Andropogon virginicus, in the Korean peninsula under climate change scenario using Random Forest (RF) and Cellular Automaton (CA) methods. Land use, barriers to dispersal, long-distance dispersal frequency, and maximum long-distance dispersal range were considered in our analysis. Our results showed that, among the five selected environmental variables, annual mean temperature and Human Foot-Printing (HFP) were positively associated with the occurrence probability of A. virginicus. This suggests that A. virginicus is likely to spread to the disturbed northern part of the Korean Peninsula due to climate change and habitat preference. When comparing modeling results for dispersal to field survey data, the modeling raster sets drawn from the long-distance dispersal frequency of 0.05 and maximum long-distance dispersal distance of 30 km y-1 had the most similar spatial expansion among the six long-distance dispersal parameter sets. The dispersal directions were associated with the landscape. Specifically, seeds dispersed by wind (anemochorous seeds) could propagate into open landscapes more easily than in forests. Regarding A. virginicus management, this grass can quickly invade bare ground with their wind-dispersed seeds, therefore habitat destruction, such as excessive logging and weeding, should be restrained.

Naturalisation of the tree of love Aichryson laxum (Crassulaceae) and its implications for biosecurity surveillance in New Zealand

ABSTRACT Aichryson laxum is documented as newly naturalised in Aotearoa New Zealand. Although tree of love is its colloquial name, it is a small, succulent herb in the Crassulaceae, and is indigenous to the Canary Islands. It has been cultivated in New Zealand for at least several decades. The species has recently been collected wild at multiple sites around Wellington, with collections also from Napier and near Ōtaki Forks, and an additional report of wild plants from Christchurch. Despite its small size, A. laxum can grow densely, adding to the weeds smothering surfaces and displacing indigenous species from habitats such as open, rocky banks. Within Wellington, A. laxum was first noticed to be growing wild in 2019, but it has now been found to be established at multiple sites throughout the city. Either it is spreading aggressively via its tiny, wind-dispersed seeds, or it has lain undetected for some time, even though it is a distinctive species among Wellington’s flora. Both scenarios are concerning, and A. laxum provides another example of the shortcomings of the nation’s current surveillance – recently described by the Parliamentary Commissioner for the Environment as largely passive and serendipitous – for emerging weeds newly naturalising from the tens of thousands of exotic plant species cultivated in New Zealand.

Anemochorous and zoochorous seeds of trees from the Brazilian savannas differ in fatty acid content and composition.

Fatty acids (FAs) stored as triacylglycerols (TAGs) are an important source of carbon and energy for germination and seedling development, particularly for plants with small wind-dispersed seeds, allowing greater efficiency in storing both energy and carbon. These plants should be under strong selection to produce seeds rich in FAs and with large amounts of saturated FAs. Their closely packed single-chain configuration allows greater packing, more carbon and energy per unit mass, and are less costly to produce. Efficient carbon storage would be less crucial for zoochorous species, which can reach much larger seed sizes (mass). We analysed the transesterified FA profile from seeds of 22 anemochorous and zoochorous tree species from the Cerrado savannas of Central Brazil. We tested if seed FA content covaried with seed mass and if anemochorous and zoochorous seeds differed in FA contents and distribution. Fatty acids were an important seed source of carbon and energy for most species. Fifteen different FAs were identified. Oleic, linoleic and linolenic tended to be the predominant unsaturated FAs. Oleic acid corresponded to more than 60 % of the total transesterified FAs in seeds of Kielmeyera coriacea, Qualea dichotoma and Triplaris americana. Linoleic acid corresponded to more than 50 % of total FA in Dalbergia miscolobium, Parkia platycephala and Ferdinandusa elliptica while linolenic acid was the dominant component in Inga cylindrica. Across species, palmitic and stearic were the dominant saturated FAs. The only exception was lauric acid (68 % of total FA) in seeds of Qualea grandiflora. On a log10 scale, as the seed increased in mass, accumulation of FAs tends to proceed at a faster rate in anemochorous species than in zoochorous species. They also became increasingly richer in saturated FAs. Zoochorous species had seed TAGs with higher proportion of polyunsaturated FAs.

Spontaneous Rising of a Whirling-Swimmer Driven by a Bubble.

The wind-dispersed seeds can rotate and fall like small vehicles with the help of the wind to obtain a longer propagation distance. Inspired by this, we propose a novel bubble-driven three-bladed whirling-swimmer (WS) to travel in the fluid as a vehicle. Four types of WSs with blade folding angles (φ) ranging from 10 to 60° were designed, and their swimming performance was evaluated. Regardless of the WS shape, the velocity increases linearly with φ, while the angular frequency exhibits an asymptotic value. Further, both the St and rotational energy of the WS peak at 20° ≤ φ ≤ 30° for different WS shapes as well as the vertical force and the hydrodynamic torque were solved from a proposed mechanics model. This folding angle range is unexpectedly consistent with the coning angle during maple samaras' stable falling. The WS lift and drag forces greatly depend on the interaction between the leading-edge vortex and the hub vortex. The results showed that the WS-IV seems to have the highest performance. Our work may shed new light on developing unpowered wireless swimmers of high swimming performance to provide a new way for underwater information collection, information transmission, and enhanced mixing.

Modeling long-distance seed dispersal of the invasive tree Spathodea campanulata in the Society Islands.

Long-distance dispersal is a key factor explaining the success of invasive alien species, particularly across oceanic islands. However, it is often not feasible to reliably measure long-distance seed dispersal (LDD) over many kilometers in the field. Here, we used a three-dimensional kinematic trajectory model (Computing Atmospheric Trajectory tool [CAT]) initiated on the basis of regional wind field data to assess the potential for LDD of a wind-dispersed invasive tree, Spathodea campanulata (African tulip tree), across the Society Islands (French Polynesia, South Pacific Ocean) following its initial planting and spread on the island of Tahiti. The main objective of our study was to determine whether S. campanulata could be expected to spread naturally among islands. Atmospheric dynamics, seed terminal velocity, precipitation, and temperature of air masses were considered to assess the potential for LDD between oceanic islands, with the island of Tahiti serving as the island source for multiple, geographically distant invasions. Aerial trajectories of modeled S. campanulata seeds indicated that wind-dispersed seeds originating from trees on the island of Tahiti could reach most of the Society Islands and disperse as far as 1364 km. This result suggests that Spathodea can be expected to spread naturally among the Society Islands. When rainfall events were modeled as causal agents of seed settlement, fewer seeds reached distant islands, but more seeds settled on the closest island (20 km away). Including effects of island topography ("barrier effects") also resulted in more seeds settling on the closest island and fewer seeds reaching the most distant islands. Overall, our findings suggest that recent atmospheric models can provide valuable insights into LDD and invasion patterns of wind-dispersed invasive species.

Antimicrobial Activity of the Asclepias syriaca L. Root Extract

Asclepias syriaca L. is an invasive plant in Serbia which threatens the biodiversity and ecosystem functionality with its high production of wind-dispersed seeds and the rapid proliferation by the lateral rhizomes. The mechanism that allows its competitiveness is allelopathy - the release of the chemical compounds identified in the roots and leaves which have negative effects on the other plants. These allelochemicals not only affect the development of the neighboring plants, but also are a potential source of the antioxidant and antimicrobial compounds, which increase the immunity of the plant itself, protecting it from the pests and the pathogens. The present study aimed to screen the antifungal activity of the A. syriaca water and methanol extracts. In vitro antimicrobial activity was analyzed by the radial growth assays against the three phytopathogenic fungi isolates: Alternaria alternata, Fusarium avenaceum and Discula platani. The results were processed by factorial ANOVA and the statistically significant differences were determined by Duncan’s multiple range test using the software STATISTICA 13.5. The obtained results suggest that the A. syriaca water extract has a significant fungistatic and potential fungicidal effect towards the tested phytopathogenic fungi and thus can be considered as a potential tool for their biological control.

Wake flow visualization of a dandelion pappus with posture change

A typical plant that is distributed by wind is the dandelion, which possesses a complex hairy pappus that aids in flying. A pappus or group of bristly filaments found in plumed seeds is believed to have a role in drag enhancement. The pappus prolongs the descent of the seed. For wind-dispersed seeds, maintaining stability while reducing falling speed in turbulent winds may be useful for long-distance dispersal. However, it is unclear why plumed seeds chose a bristly pappus over a membrane that resembles wings and is known to increase lift during passive flight. In the current study, we analyze the dandelion pappus flight mechanism by identifying the crucial structural elements that enable its stable flight. In addition, we investigate the flow behavior around the pappus by performing float testing on several dandelion pappi in a vertical airflow pipe. The flow fields in the wake of the pappus were also measured by 2-component particle image velocimetry. The falling speed of the pappus is reliant on the posture during free-fall motion, and the aerodynamic features of the pappus are substantially affected by the posture in flight. The pappus’s posture was changed to promote vortex growth in the wake, and this vortex behavior is related to the fluid forces acting on the pappus.

Superhydrophobic Strategy for Nature-Inspired Rotating Microfliers: Enhancing Spreading, Reducing Contact Time, and Weakening Impact Force of Raindrops

Wind-dispersal of seeds is a remarkable strategy in nature, enlightening the construction of microfliers for environmental monitoring. However, the flight of these microfliers is greatly affected by climatic conditions, especially in rainy days, they suffer serious raindrop impact. Here, a hierarchical superhydrophobic surface is fabricated and a novel strategy is demonstrated that the superhydrophobic coating can enhance spreading while reduce contact time and impact force of raindrops, all of which are beneficial for the rotating microfliers. When the surface rotating speed exceeds a critical value, the effect of centrifugal force becomes considerable so that the droplet spreading is enhanced. The rotating superhydrophobic surface can rotate an impacting droplet by the tangential drag force from the air boundary layer, and the rotation of the droplet generates a negative pressure zone inside it, reducing the contact time by more than 30%. The impact force by the droplet on the rotating superhydrophobic surface also has a remarkable reduction of 53% compared to that on unprocessed hydrophilic surfaces, which helps maintain the flight stability of the microfliers. This work pioneers in revealing the droplet impact effect on rotating microflier surfaces and demonstrates the effectiveness of protecting microfliers with superhydrophobic coatings, which shall guide the manufacture and flight of microfliers in rainy conditions.

Wind-dispersed seeds blur phylogeographic breaks: The complex evolutionary history of Populus lasiocarpa around the Sichuan Basin

The strength of phylogeographic breaks can vary among species in the same area despite being subject to the same geological and climate history due to differences in biological traits. Several important phylogeographic breaks exist around the Sichuan Basin in Southwest China but few studies have focused on wind-dispersed plants. Here, we investigated the phylogeographic patterns and the evolutionary history of Populus lasiocarpa, a wind-pollinated and wind-dispersed tree species with a circum-Sichuan Basin distribution in southwest China. We sequenced and analyzed three plastid DNA fragments (ptDNA) and eight nuclear microsatellites (nSSRs) of 265 individuals of P. lasiocarpa from 21 populations spanning the entire distribution range. Distribution patterns based on nSSR data revealed that there are three genetic groups in P. lasiocarpa. This is consistent with the three phylogeographic breaks (Sichuan Basin, the Kaiyong Line and the 105°E line), where the Sichuan basin acts as the main barrier to gene flow between western and eastern groups. However, the distribution pattern based on ptDNA haplotypes poorly matched the phylogeographic breaks, and wind-dispersed seeds may be one of the main contributing factors. Species distribution modelling suggested a larger potential distribution in the last glacial maximum with a severe bottleneck during the last interglacial. A DIYABC model also suggested a population contraction and expansion for both western and eastern lineages. These results indicate that biological traits are likely to affect the evolutionary history of plants, and that nuclear molecular markers, which experience higher levels of gene flow, might be better indicators of phylogeographic breaks.

Genetic diversity and population structure of the antimalarial plant Cryptolepis sanguinolenta in Ghana

Cryptolepis sanguinolenta is an important medicinal plant used in the treatment of malaria in Ghana. Overharvesting, destruction of entire plant populations and poor seed viability have resulted in a substantial decrease in wild populations thereby threatening its long-term potential and survivability. In this study, fifteen polymorphic microsatellite loci were used to evaluate the genetic diversity and population structure of 179 C. sanguinolenta individuals among eight subpopulations in Ghana. The subpopulations were separated by a distance of 8.3 – 233.3 km. Our results indicated relatively high levels of genetic diversity (Ho= 0.41; He=0.61) and high gene flow (Nm=7.06), an indication of greater stability and adaptability within the ecosystem, limited genetic differentiation (mean FST=0.05; highest FST=0.1), which suggested insignificant differentiation among the subpopulations. The high levels of gene flow resulting from the wind-dispersed seeds might have contributed to the limited genetic differentiation among the subpopulations. The Bayesian cluster analysis revealed the presence of a population structure (K=2). A lack of isolation by distance (r=0.012; P=0.34) indicated an increase in the genetic similarity among the subpopulations as the geographic distance between them decreased. This study described the genetic diversity and population structure in the current C. sanguinolenta accessions and laid a foundation for future breeding efforts.

Improving measurements of the falling trajectory and terminal velocity of wind-dispersed seeds.

Seed dispersal by wind is one of the most important dispersal mechanisms in plants. The key seed trait affecting seed dispersal by wind is the effective terminal velocity (hereafter “terminal velocity”, V t ), the maximum falling speed of a seed in still air. Accurate estimates of V t are crucial for predicting intra‐ and interspecific variation in seed dispersal ability. However, existing methods produce biased estimates of V t for slow‐ or fast‐falling seeds, fragile seeds, and seeds with complex falling trajectories. We present a new video‐based method that estimates the falling trajectory and V t of wind‐dispersed seeds. The design involves a mirror that enables a camera to simultaneously record a falling seed from two perspectives. Automated image analysis then determines three‐dimensional seed trajectories at high temporal resolution. To these trajectories, we fit a physical model of free fall with air resistance to estimate V t . We validated this method by comparing the estimated V t of spheres of different diameters and materials to theoretical expectations and by comparing the estimated V t of seeds to measurements in a vertical wind tunnel. V t estimates closely match theoretical expectations for spheres and vertical wind tunnel measurements for seeds. However, our V t estimates for fast‐falling seeds are markedly higher than those in an existing trait database. This discrepancy seems to arise because previous estimates inadequately accounted for seed acceleration. The presented method yields accurate, efficient, and affordable estimates of the three‐dimensional falling trajectory and terminal velocity for a wide range of seed types. The method should thus advance the understanding and prediction of wind‐driven seed dispersal.

Morphable three-dimensional electronic mesofliers capable of on-demand unfolding

Development of miniaturized three-dimensional (3D) fliers with integrated functional components has important implications to a diverse range of engineering areas. Among the various active and passive miniaturized 3D fliers reported previously, a class of 3D electronic fliers inspired by wind-dispersed seeds show promising potentials, owing to the lightweight and noiseless features, aside from the stable rotational fall associated with a low falling velocity. While on-demand shape-morphing capabilities are essential for those 3D electronic fliers, the realization of such miniaturized systems remains very challenging, due to the lack of fast-response 3D actuators that can be seamlessly integrated with 3D electronic fliers. Here we develop a type of morphable 3D mesofliers with shape memory polymer (SMP)-based electrothermal actuators, capable of large degree of actuation deformations, with a fast response (e.g., ∼1 s). Integration of functional components, including sensors, controllers, and chip batteries, enables development of intelligent 3D mesoflier systems that can achieve the on-demand unfolding, triggered by the processing of real-time sensed information (e.g., acceleration and humidity data). Such intelligent electronic mesofliers are capable of both the low-air-drag rising and the low-velocity falling, and thereby, can be used to measure the humidity fields in a wide 3D space by simple hand throwing, according to our demonstrations. The developed electronic mesofliers can also be integrated with other types of physical/chemical sensors for uses in different application scenarios.

\u201cPhoenix in Flight\u201d: an unique fruit morphology ensures wind dispersal of seeds of the phoenix tree (Firmiana simplex (L.) W. Wight)

BackgroundMany seed plants produce winged diaspores that use wind to disperse their seeds. The morphology of these diaspores is directly related to the seed dispersal potential. The majority of winged diaspores have flat wings and only seeds; however, some angiosperms, such as Firmiana produce winged fruit with a different morphology, whose seed dispersal mechanisms are not yet fully understood. In this study, we observed the fruit development of F. simplex and determined the morphological characteristics of mature fruit and their effects on the flight performance of the fruit.ResultsWe found that the pericarp of F. simplex dehisced early and continued to unfold and expand during fruit development until ripening, finally formed a spoon-shaped wing with multiple alternate seeds on each edge. The wing caused mature fruit to spin stably during descent to provide a low terminal velocity, which was correlated with the wing loading and the distribution of seeds on the pericarp. When the curvature distribution of the pericarp surface substantially changed, the aerodynamic characteristics of fruit during descent altered, resulting in the inability of the fruit to spin.ConclusionsOur results suggest that the curved shape and alternate seed distribution are necessary for the winged diaspore of F. simplex to stabilize spinning during wind dispersal. These unique morphological characteristics are related to the early cracking of fruits during development, which may be an adaptation for the wind dispersal of seeds.

Incomplete recovery of seeds from scatterhoards by granivorous rodents: Implications for plant establishment.

Granivorous rodents are important components of ecosystems not only because they consume seeds but also because some aid in seed dispersal through seed‐caching behaviors. Some rodents bury seeds in shallow pits throughout territories, called scatterhoards, that individuals recover, pilfer, or transfer to other caches. We suspect some single‐seed caches in environments represent missed seeds from reclaiming or pilfering caches. We documented the sloppiness of seed removal from scatterhoards of soapweed yucca (Yucca glauca) seeds by Ord's kangaroo rats (Dipodomys ordii). We quantified the frequency and location of seeds remaining. In an experiment with artificial caches of three sizes, kangaroo rats harvested 51% of caches after one night, and 53% had incomplete recovery with at least one seed remaining. The greater the number of seeds in caches, the greater frequency of incomplete recovery. In another experiment with natural and artificial caches, 75% of caches were excavated after 8 days, with at least 70% having at least one seed remaining. Regardless of original cache size, a single seed represented the mode for seeds remaining. Incomplete recovery of seeds likely benefits plant establishment, potentially significantly in some systems. Remaining seeds, especially those buried at bottoms of caches, likely will stay undetected in landscapes, yielding propagules for subsequent plant generations. Soapweed yucca has large but light, flat wind‐dispersed seeds, and removal of caches with smaller seeds might have greater frequency of missed seeds during recovery and pilfering by rodents. Our results suggest that scatter‐hoarding granivores also contribute to plant establishment by leaving limited numbers of seeds behind when removing caches, at least in some systems.

Native seed dispersal by rodents is negatively influenced by an invasive shrub

Refuge–mediated apparent competition is the mechanism by which invasive plants increase pressure on native plants by providing refuge for generalist consumers. In the UK, the invasive Rhododendron ponticum does not provide food for generalist seed consumers like rodents, but evergreen canopy provides refuge from rodent predators, and predation and pilferage risk are key factors affecting rodent foraging and caching behaviour. Here we used a seed removal/ seed fate experiment to understand how invasion by an evergreen shrub can alter seed dispersal, seed fate and early recruitment of native trees. We used seeds of four species, small and wind–dispersed (sycamore maple Acer pseudoplatanus and European ash Fraxinus excelsior) and large and animal–dispersed (pedunculate oak Quercus robur and common hazel Corylus avellana), and monitored seed predation and caching in open woodland, edge habitats, and under Rhododendron. In the open woodland, wind–dispersed seeds had a higher probability of being eaten in situ than cached seeds, while the opposite occurred with animal–dispersed seeds. The latter were removed from the open woodland and edge habitats and cached under Rhododendron. This pattern was expected if predation risk was the main factor influencing the decision to eat or to cach a seed. Enhanced dispersal towards Rhododendron cover did not increase the prospects for seed survival, as density of hazel and oak saplings under its cover was close to zero as compared to open woodland, possibly due to increased cache pilferage or low seedling survival under dense shade, or both. Enhanced seed predation of ash and sycamore seeds close to Rhododendron cover also decreased recruitment of these trees. Rhododendron patches biased rodent foraging behaviour towards the negative (net predation) side of the conditional rodent / tree interaction. This effect will potentially impact native woodland regeneration and further facilitate Rhododendron spread due to refuge–mediated apparent competition.

Three-dimensional electronic microfliers inspired by wind-dispersed seeds.

Large, distributed collections of miniaturized, wireless electronic devices1,2 may form the basis of future systems for environmental monitoring3, population surveillance4, disease management5 and other applications that demand coverage over expansive spatial scales. Aerial schemes to distribute the components for such networks are required, and-inspired by wind-dispersed seeds6-we examined passive structures designed forcontrolled, unpowered flight across natural environments or city settings. Techniques in mechanically guided assembly of three-dimensional (3D) mesostructures7-9 provide access to miniature, 3D fliers optimized for such purposes, in processes that align with the most sophisticated production techniques for electronic, optoelectronic, microfluidic and microelectromechanical technologies. Here we demonstrate a range of 3D macro-, meso- and microscale fliers produced in this manner, including those that incorporate active electronic and colorimetric payloads. Analytical, computational and experimental studies of the aerodynamics of high-performance structures of this type establish a set of fundamental considerations in bio-inspired design, with a focus on 3D fliers that exhibit controlled rotational kinematics and low terminal velocities. An approach that represents these complex 3D structures as discrete numbers of blades captures the essential physics in simple, analytical scaling forms, validated by computational and experimental results. Battery-free, wireless devicesand colorimetric sensors for environmental measurements provide simple examples of a wide spectrum of applications of these unusual concepts.

Spatial Analysis as a Tool for Plant Population Conservation: A Case Study of Tamarix chinensis in the Yellow River Delta, China

Saltcedar (Tamarix chinensis) is undergoing population declination and fragmentation due to climate change and human disturbance. The existing restoration strategies usually focus on improving the environmental conditions based on the environment–saltcedar relationship, while they ignore the role of spatial autocorrelation resulting from biological interaction and ecological processes. This oversight limits the efficiency and sustainability of the restoration. Here, we explored the spatial pattern of the saltcedar population in the Yellow River Delta, China, and its relationship with environmental factors, incorporating spatial autocorrelation. The plant and soil parameters were extracted by an airborne LiDAR system integrated with fixed soil environment measurements. The environment–saltcedar relationship incorporating spatial autocorrelation was evaluated with different regression models. Results showed that saltcedars aggregated at small scales (2–6 m), resulting from intraspecific facilitation and wind dispersal of seeds, while intraspecific competition was responsible for the random distribution at large scales (>10 m). The long-distance dispersal of seeds through water explained the significant positive spatial autocorrelation of saltcedars at distances up to 125 m. Consequently, resulting from intraspecific facilitation and seed dispersal, aggregation distribution and positive spatial autocorrelation within the saltcedar population improved the adaptability of saltcedar to environmental stress and thereby reduced the impact of environmental factors on the abundance of saltcedar.

Contrasting genetic signal of recolonization after rainforest fragmentation in African trees with different dispersal abilities

Although today the forest cover is continuous in Central Africa, this may have not always been the case, as the scarce fossil record in this region suggests that arid conditions might have significantly reduced tree density during the ice ages. Our aim was to investigate whether the dry ice age periods left a genetic signature on tree species that can be used to infer the date of the past fragmentation of the rainforest. We sequenced reduced representation libraries of 182 samples representing five widespread legume trees and seven outgroups. Phylogenetic analyses identified an early divergent lineage for all species in West Africa (Upper Guinea) and two clades in Central Africa: Lower Guinea-North and Lower Guinea-South. As the structure separating the Northern and Southern clades-congruent across species-cannot be explained by geographic barriers, we tested other hypotheses with demographic model testing using δαδι. The best estimates indicate that the two clades split between the Upper Pliocene and the Pleistocene, a date compatible with forest fragmentation driven by ice age climatic oscillations. Furthermore, we found remarkably older split dates for the shade-tolerant tree species with nonassisted seed dispersal than for light-demanding species with long-distance wind-dispersed seeds. Different recolonization abilities after recurrent cycles of forest fragmentation seem to explain why species with long-distance dispersal show more recent genetic admixture between the two clades than species with limited seed dispersal. Despite their old history, our results depict the African rainforests as a dynamic biome where tree species have expanded relatively recently after the last glaciation.

A complex genetic structure ofTetraclinis articulata(Cupressaceae) in the western Mediterranean

AbstractSome tree species have distributions on both sides of the Strait of Gibraltar and the Strait of Sicily. It is a challenge to determine whether such distributions result from the Tertiary or Pleistocene or from more recent dispersal related to human activities. Tetraclinis articulata (Cupressaceae) is a gymnosperm that offers an ideal model to deal with this problem because it has a limited area of distribution and has been used only moderately by humans. Three hundred and twenty-three individuals from 30 populations covering the entire distribution of the species were analysed. A multiple approach was developed: (1) by assessing the genetic structure through two molecular techniques, AFLP and nSSR markers, which were used to evaluate the genetic diversity of these populations and the relationships among them and (2) by estimating past distributions. Four lineages of populations that are geographically intermixed to a certain extent are documented here. Results obtained are discussed in the context of palaeontological records and climatic models. There is evidence of an ancient widespread distribution, including Europe, and the subsequent appearance of four isolated lineages that, nowadays, are partially intermixed. Nevertheless, the origin of the current populations could not be fully ascertained through this work, although logical deductions are discussed that consider human activities or, much less probably, wind dispersal of seeds out of refugia in northern Africa-southern Europe during the Quaternary, including shore connections.