Propagule Morphology Research Articles

Dispersal of aquatic and terrestrial organisms by waterbirds: A review of current knowledge and future priorities

Abstract We review progress in our understanding of the importance of waterbirds as dispersal vectors of other organisms, and identify priorities for further research. Waterbirds are excellent for long‐distance dispersal (LDD), whereas other vectors such as fish and mammals disperse similar propagules, but over shorter distances. Empirical studies of internal and external transport by waterbirds have shown that the former mechanism generally is more important. Internal transport is widely recognised for aquatic plants and aquatic invertebrates with resting eggs, but also is important for other organisms (e.g., terrestrial flowering plants not dispersed by frugivores, bryophytes, tardigrades, fish eggs). Waterbird vectors also are important in terrestrial habitats, and provide connectivity across terrestrial–aquatic boundaries. There are important differences in the roles of different waterbird species, especially those using different habitats along the aquatic–terrestrial gradient. Early attempts to predict zoochory based on propagule morphology have been found wanting, and more research is needed into how the traits of vectors and vectored organisms (including life history, dormancy and growth traits) explain dispersal interactions. Experimental studies have focused on the potential of propagules to survive internal or external transport, and research into factors determining the establishment success of propagules after dispersal is lacking. Recent spatially explicit models of seed dispersal by waterbirds should be expanded to include invertebrate dispersal, and to compare multiple bird species in the same landscape. Network approaches have been applied to plant–waterbird dispersal interactions, and these are needed for invertebrates. Genetic studies support effective LDD of plants and invertebrates along waterbird flyways, but there remains a lack of examples at a local scale. Next Generation Sequencing and genomics should be applied to waterbird‐mediated dispersal across the landscape. More studies of biogeography, community ecology, or population genetics should integrate waterbird movements at the design stage. Zoochory research has paid little attention to the dispersal of non‐pathogenic microbes (both eukaryotic and prokaryotic). Nevertheless, there is evidence that dispersal via avian guts can be central to the connectivity of aquatic microbial metacommunities. More work on microbial dispersal by waterbirds should explore its implications for biogeochemistry, and the interchange with gut flora of other aquatic organisms. In the Anthropocene, the role of migratory waterbirds in LDD of plants and other organisms is particularly important, for example in compensating for loss of large migratory mammals and fish, allowing native species to adjust their distributions under global warming, and spreading alien species along flyways after their initial introductions by human vectors. Recent technological advances have opened exciting opportunities that should be fully exploited to further our understanding of dispersal by waterbirds.

Wind variability limits the potential influence of propagule morphology and descent rate on dispersal in the winged fruits of Carpinus (Betulaceae)

The dispersal of propagules is an important aspect of land plant life history that has the potential to impact diverse evolutionary and ecological processes. Identifying the relationship between form and function of extant propagules provides the opportunity to infer past dispersal processes using morphological information from fossils, especially for abiotic dispersal of winged propagules. Many studies under laboratory conditions have identified wing loading (propagule mass divided by wing area) as the character most important for descent rates of winged propagules, but its influence on dispersal distances in natural environments over entire dispersal seasons remains unclear. To clarify this relationship, morphological measurements and experimental drops were performed on dispersed propagules from two species of Carpinus collected along highly resolved transects radiating from individual source trees. A significant relationship was found between wing loading and descent rate in still air, but the relationship between wing loading and actual dispersal distance in the field was random in all directions. Results indicate that variable wind conditions over a dispersal season can erase any signal of form and descent rate on dispersal patterns. Consequently, this randomization should impact evolutionary patterns by hampering selective potential for details of form that might further slow descent rates once enough of a wing evolves for propagules to exhibit a consistent specialized aerodynamic behavior.

Changes in functional traits and stoichiometry of Aegiceras corniculatum propagule in three shrimp aquaculture effluent regions

Shrimp aquaculture has caused broadscale shifts in mangrove ecosystems worldwide, including changes in habitats and functional traits of mangroves, to the point of widespread destruction in some countries. The propagule is an important stage in mangrove life history, reflecting the resource investment of parents and the ability of offspring to build a population. However, the impacts of shrimp aquaculture effluent on propagule functional traits and stoichiometry are poorly understood. Here, we comparatively investigated the functional traits and stoichiometry of Aegiceras corniculatum propagules in different shrimp aquaculture effluent-affected habitats on the coast of the South China Sea, including a control plot with no effluent discharge, a direct discharge area, and a landfill restoration area. We found that shrimp aquaculture effluent was associated with substantial impacts on the functional traits and stoichiometry of A. corniculatum propagules. In functional traits, both propagule morphology and biomass traits decreased in habitats affected by shrimp aquaculture effluent; in stoichiometry, the discharge of shrimp aquaculture effluent increased N and P contents, and after stopping the discharge, N and P in propagules remained at high concentration; propagule C/N and C/P ratios in all habitats were consistent with those of soils in that both were reduced and exhibited consistent N limits. Our findings highlight the effects of shrimp aquaculture effluent on functional traits and stoichiometric characteristics of A. corniculatum propagules, which may help improve our understanding of the underlying mechanisms of mangrove propagule adaptability. It also provides a scientific basis for assessing its impact on mangrove reproduction potential and population renewal and applies to mangrove management and restoration.

Dispersal potential in two restricted and five wide-ranging Senecio (Asteraceae) taxa from central eastern New South Wales, Australia

Knowledge on how life history traits affect distribution in range-restricted and endemic plants is paramount for conservation and management, particularly for threatened species. Traits relating to dispersal ability are important in the ongoing persistence of range restricted species and may present a pathway to extinction or invasion. This is evident in the highly diverse and cosmopolitan genus Senecio (Asteraceae), where both threatened and invasive species occur within Australia. In this study, propagule geometry, settling velocity and dispersal potential for two range-restricted and threatened native taxa (S. linearifolious var. dangarensis Belcher ex I.Thomps., S. spathulatus var. attenuatus I.Thomps.) are contrasted with four native taxa that occupy wider ranges (S. amygdalifolius F.Muell., S. l. var. arachnoideus I.Thomps., S. l. var. macrodontus (DC.) I.Thomps., S. pinnatifolius A.Rich. var. pinnatifolius) and one introduced, wide-ranging species (S. madagascariensis Poir.). Differences were found in settling velocity and propagule morphology across all taxa. Based on propagule morphology, S. amygdalifolius has the greatest dispersal potential, S. spathulatus var. attenuatus the smallest, whereas all other taxa were similar. Although useful, dispersal potential alone does not fully explain distributional differences between all range-restricted and widespread taxa, and close assessment of habitat attributes may be required to further elucidate dispersal limitations in some taxa.

Propagules are not all equal: traits of vegetative fragments and disturbance regulate invasion success.

Invasion success is regulated by multiple factors. While the roles of disturbance and propagule pressure in regulating the establishment of non-native species are widely acknowledged, that of propagule morphology (a proxy for quality) is poorly known. By means of a multi-factorial field experiment, we tested how the number (5 vs. 10) and quality (intact, without fronds or without rhizoids) of fragments of the clonal invasive seaweed, Caulerpa cylindracea, influenced its ability to establish in patches of the native seagrass, Posidonia oceanica, exposed to different intensities of disturbance (0, 50, or 100% reduction in canopy cover). We hypothesized that the ability of fragments to establish would be greater for intact fragments (high quality) and reduced more by frond removal (low quality) than rhizoid removal (intermediate quality). At low propagule pressure or quality, fragment establishment was predicted to increase with increasing disturbance, whereas, at high propagule pressure or quality, it was predicted to be high regardless of disturbance intensity. Disturbance intensity, fragment number and quality had independent effects on C.cylindracea establishment success. Disturbance always facilitated fragment establishment. However, fragments retaining fronds, either intact or deprived of rhizoids, had higher establishment success than fragments deprived of fronds. Increasing propagule number had weak effects on the cover of C.cylindracea. Our results demonstrate that propagule traits enabling the acquisition of resources made available by disturbance can be more important than propagule number in determining the establishment and spread of clonal non-native plants. More generally, our study suggests that propagule quality is a key, yet underexplored, determinant of invasion success.

Adaptive phenotypic plasticity of Avicennia officinalis L. across the salinity gradient in the Sundarbans of Bangladesh

Adaptive phenotypic plasticity of Avicennia officinalis across the salinity gradient in the Sundarbans of Bangladesh was studied. Propagule morphology was compared through use of a completely randomized design. Propagule growth initiation traits across the salinity gradient (from 0 to 35 ppt at 5 ppt interval) were studied by means of a randomized block design. Propagules showed variability in length, width, and weight across the salinity gradient in the Sundarbans. Propagule growth initiation time, mean growth initiation time, growth initiation index, and propagule growth initiation percentage of A. officinalis varied significantly with the increasing salinity and among low, medium, and high saline zones. However, propagules originating from the high and medium saline zones started their growth initiation more rapidly and vigorously at high salinities compared to those from the low saline zone. Therefore, A. officinalis exhibited adaptive phenotypic plasticity in terms of variability in propagule size and weight as well as physiologically adaptive plastic responses during propagule growth initiation across the salinity gradient in the Sundarbans. A. officinalis in high and medium saline zones of Sundarbans is the most salt-adapted phenotype, and a good knowledge about this will be widely useful for successful regeneration, coastal afforestation, and conservation of this species in increasing saline environments in the future.

Comparison growth of Kappaphycus alvarezii (Rhodophyta, Solieriaceae) cultivation in floating cage and longline in Indonesia

Currently, cultivation using cages for Kappaphycus alvarezii was limited reported before. This study aims to reveal growth of K. alvarezii cultivated in floating cages and longline. The study was conducted in one of cultivation areas in Southeast Sulawesi, Indonesia. Total gross weight, propagule growth rate and specific growth rate were performing in this study. During our field experiment, total gross weight of K. alvarezii after 40 days, from 5 kg was growth to 22.5 ± 1.40 kg and 38.8 ± 1.6 kg on longline and floating cages, respectively. Propagule growth rate after 40 days, from 50 g was 107.8 ± 7.0 g and 152.5 ± 7.9 g during April, and 132.0 ± 8.0 g and 218.8 ± 8.6 g during August, on longline and floating cage, respectively. Specific growth rate of K. alvarezii was high during August, 2.43% day−1 and 3.69% day−1 cultivated in longline and floating cage, respectively. Propagule morphology was white and damage in 40% cultivated by longline and no damage by using floating cage particular in August and September while high dense of herbivorous fish surrounding the experimental sites.

Propagule size and shape may promote local wind dispersal in freshwater zooplankton-a wind tunnel experiment

Current evidence supports that dormant eggs of many zooplankton species from inland waters can be transported by wind. However, little is known about variation in wind dispersal propensity among different species and propagule types. Here, we experimentally investigate the wind speed required to pick-up propagules of a wide range of freshwater zooplankton species on different substrates. Counter-intuitively, larger propagules were consistently picked-up at lower wind speeds than smaller propagules. Grain size of the substrate affected adhesion because propagules were more easily picked-up from fine grained than from coarse grained or smooth surfaces. Overall, these results suggest that propagule morphology affects wind dispersal propensity and propagule bank erosion, providing a possible explanation for the large interspecific and intraspecific variation in propagule size and shape observed in nature. Ultimately, a better understanding of the link between propagule morphology, habitat structure, and dispersal propensity will be useful to understand diversity patterns and temporal dynamics in lentic aquatic habitats. It could also help to predict range expansion of freshwater zooplankton species, many of which are invasive outside of their natural ranges.

Impact of landscape structure on propagule dispersal in mangrove forests

Although many riparian and semi-aquatic plant species disperse via water currents, little is known about how this process interacts with the landscape matrix. In mangroves, the dense aerial root network could act as a strong dispersal barrier for the morphologically diverse propagules found in these trees. In this study, we combined field and laboratory experiments to test the effect of root density, propagule morphology and hydrodynamic variables on retention rates and trajectories of the propagules of 4 common species. Overall, flume experiments showed that larger propagules were more frequently retained than smaller ones. For the larger propagules, retention rates increased with increasing obstacle density in the landscape matrix. In elongated propagules, intraspecific variation was linked to floating orientation. Experimental wave action and increased water flow velocity reduced retention. Dispersal in the field was constrained by major tidal currents and experiments confirmed less retention of smaller propagules, which moved farther than larger ones. Overall, our results reveal that the pronounced morphological variation in mangrove propagules interacts with the landscape matrix, contributing to strong differences in dispersal capacity among species and morphotypes. These results may help to explain observed mangrove distribution patterns, including zonation at local, regional and global scales. Additionally, given that many mangrove biotopes are currently strongly threatened by human pressure and fragmentation, this information is important as an input variable for dispersal models that aim to predict dispersal patterns at multiple scales and species responses to environmental change.

Hydration history and attachment morphology regulate seed release in Chorizanthe rigida (Polygonaceae), a serotinous desert annual.

• Premise of the study: Most seed dispersal studies focus on the spatial aspects of propagule dissemination, i.e., the movement of seeds away from the mother plant. However, the timing of seed release can also be a critical variable influencing the probability of seedling survival. We used a biomechanical approach to analyze seed release in Chorizanthe rigida, a serotinous desert annual, to understand the adaptive significance of seed retention in this species.• Methods: We performed pull-to-break tests on individual propagules (i.e., involucres and achene) from newly developed and older plants, under dry and wet conditions, and recorded the breaking force. We measured the involucral base area using digital images and image processing software.• Key results: There is a positive correlation between the force required to detach an involucre and the size of its base area. The force required to detach involucres from soaked and older plants was lower than that for dry and new plants. This pattern provides a mechanism for the plant to regulate the number of involucres released in different rain events.• Conclusions: Seed release in C. rigida is mediated by propagule morphology, rainfall conditions, and age of the dry plant. These factors allow this species to cope with desert environmental variability by influencing the timing and number of seeds released.

Propagule morphology and river characteristics shape secondary water dispersal in tree species

Plant migration is a multi-stage process often driven by multiple dispersal vector systems. Water-mediated dispersal (hydrochory) is known to move propagules of nonaquatic species over long distances, but whether propagule morphology affects floating processes is an open question. We used a multi-species approach to assess the role of propagule morphology in the dispersal of primarily wind-dispersed tree species in different urban rivers; the impact of hydraulic structures (locks, spillways) on floating was also considered. We released tagged propagules of eight tree species (Acer platanoides, Acer negundo, Acer saccharinum,Ailanthus altissima, Fraxinus excelsior, Robinia pseudoacacia, Tilia platyphyllos, Ulmus glabra) in the main lowland Spree River and in the small tributary Panke River (Berlin, Germany) and directly observed the fate of the floating propagules over river sections of 1,200 m. Our results demonstrate the following: (1) Water is an effective dispersal agent for wind-dispersed tree species, extending typical wind-related transport distances by several times. (2) Interspecific differences in transport distances reflect propagule characteristics (dry weight, maximum wing width) and river system. (3) Propagule morphology also affects deposition patterns as it was generally the large propagules that were trapped along semi-natural embankments in slow flow areas. (4) Hydraulic structures hampered but did not entirely stop water-mediated dispersal and diminished the effects of propagule morphology on floating processes. These results provide novel insights into the functioning of hydrochory as an important dispersal vector of tree species in river systems and as a driver of plant invasions.

Taxonomic Reappraisal of Sphacelaria rigidula and S. fusca (Sphacelariales, Phaeophyceae) Based on Morphology and Molecular Data with Special Reference to S. didichotoma

The taxonomic status of three closely related species of the genus Sphacelaria, S. rigidula Kutzing, S. fusca (Hudson) C.F Gray and S. didichotoma Saunders was reassessed on the basis of morphological observations from herbarium specimens and phylogenetic analysis of RUBISCO spacer sequences. Sphacelaria rigidula was characterized by having only 2-armed propagules and somewhat slender filaments. Culture experiments revealed that its propagules commonly formed secondary arms, even though they were rarely produced in the field. It is concluded that S. divaricata Montagne characterized by dichotomously branched arms in propagules shoud be synonymized with S. rigidula, based on propagule morphology and measurements. Sphacelaria fusca clearly be separated from S. rigidula by having 2-4 armed propagules. These morphological differences were highly supported by the differences in the RUBISCO spacer sequences. S. didichotoma resembles S. rigidula in having propagules with two dichotomously branched arms. However, it commonly produces the secondary arms in the field. Additionally, this species has shorter primary arms than S. rigidula. Phylogenetic analyses supported the distinction of S. didichotoma from S. rigidula. The northwestern Pacific plants, previously recorded as S. divaricata, were recognized as S. didichotoma.

Analysis of weed dispersal to predict chances of re-colonisation

Abstract The protection of rare arable weeds and the restoration of biodiversity in agroecosystems have become an important issue in most European countries. Traditional analyses of weed dispersal focussing on the prediction and control of infestations have to be adapted to the new aim of restoration ecology by quantifying chances of re-colonisation within fields and across field borders. This study analyses within-field spread of weeds under usual arable cultivation whereas between-field colonisation usually not aided by machinery was simulated in undisturbed controls. The experiments were conducted on an arable farm in the central German lowlands 6 years after conversion to organic management. The test species, Lithospermum arvense and Silene noctiflora, have declined in recent decades but belong to the characteristic weed community. Dispersal was analysed by recording seedling emergence around patches of introduced mother plants where the species were absent. Negative exponential models provided a good fit of the dispersal curves from the mode outward. In the “arable” treatment, the percentage seedlings - distance regression line fell below 0.5% at 5 m, in the control this level was reached at a distance of about 2 m indicating that long-distance dispersal is a rare event. Cultivation increased the peak distance of the dispersal curves significantly whereas the slope of the curves from the mode outward was hardly affected. Despite different fruit and propagule morphology, seed shadows of both species were very similar. Spatial distribution of the seedlings in the arable treatment occurred along the axis of management and against the prevailing wind direction. The results may help to improve targeting subsidies in agri-environment schemes and assessing the need for re-introduction by sowing.

Water mold infections of freshwater fish: Recent advances

Various investigations have identified morphological and physiological differences among water mold isolates. There is some evidence that isolates taken from fish lesions are more infective for live fish and are more resistant to host defenses, compared to environmental isolates. Many other characteristics, including propagule retention on fish, propagule morphology, propagule response to nutrients, fungal isozyme patterns, and antigenic relatedness of fungal isolates, have been examined. However, the significance of these characteristics to pathogenicity is uncertain, either because the putative pathogenic marker does not consistently differentiate pathogenic from saprophytic isolates, or the adaptive significance of the marker is unclear. Water molds grow rapidly in dead tissue, yet do not easily cause disease in healthy, unstressed hosts. They are usually relegated to the skin and superficial muscle. The fact that they are common secondary invaders of wounds implies that in these instances there is a significant compromise of host defenses. Trauma, nutritional deficiencies, endocrine changes, and stressful water quality have been implicated. There may be major differences in how different fish species respond to such stresses. Both humoral and cellular defensive responses to invading water molds have been observed. The type of response may modulate the gross clinical signs of the resulting infection.