Propagule Release Research Articles

Bimodal spore release heights in the water column enhance local retention and population connectivity of bull kelp, Nereocystis luetkeana.

Dispersal of reproductive propagules determines recruitment patterns and connectivity among populations and can influence how populations respond to major disturbance events. Dispersal distributions can depend on propagule release strategies. For instance, the bull kelp, Nereocystis luetkeana, can release propagules (spores) from two heights in the water column ("bimodal release"): at the water surface, directly from the reproductive tissues (sori) on the kelp's blades, and near the seafloor after the sori abscise and sink through the water column. N. luetkeana is a foundation species that occurs from central California to Alaska and is experiencing unprecedented levels of population declines near its southern range limit. We know little of the kelp's dispersal distributions, which could influence population recovery and restoration. Here, we quantify how bimodal spore release heights affect dispersal outcomes based on a numerical model specifically designed for N. luetkeana. The model incorporates oceanographic conditions typical of the species' coastal range and kelp biological traits. With bimodal release heights, 34% of spores are predicted to settle within 10 m of the parental alga and 60% are predicted to disperse beyond 100 m. As an annual species, bimodal release heights can facilitate the local regeneration of adults within a source kelp forest while also supporting connectivity among multiple forests within broader bull kelp metapopulations. To leverage this pattern of bimodal spore dispersal in bull kelp restoration management, directing resources toward strategically located focal populations that can seed other ones could amplify the scale of recovery.

Carryover effects of salinity impact propagule release by a common marine biofouling species

Carryover effects of salinity impact propagule release by a common marine biofouling species

A simple mechanistic model of the invasive species Heracleum sosnowskyi propagule dispersal by wind.

BackgroundInvasive species are one of the key elements of human-mediated ecosystem degradation and ecosystem services impairment worldwide. Dispersal of propagules is the first stage of plant species spread and strongly influences the dynamics of biological invasion. Therefore, distance prediction for invasive species spread is critical for invasion management. Heracleum sosnowskyi is one of the most dangerous invasive species with wind-dispersed propagules (seeds) across Eastern Europe. This study developed a simple mechanistic model for H. sosnowskyi propagule dispersal and their distances with an accuracy comparable to that of empirical measurements.MethodsWe measured and compared the propagule traits (terminal velocity, mass, area, and wing loading) and release height for H. sosnowskyi populations from two geographically distant regions of European Russia. We tested two simple mechanistic models: a ballistic model and a wind gradient model using identical artificial propagules. The artificial propagules were made of colored paper with a mass, area, wing loading, and terminal velocity close to those of natural H. sosnowskyi mericarps.ResultsThe wind gradient model produced the best results. The first calculations of maximum possible propagule transfer distance by wind using the model and data from weather stations showed that the role of wind as a vector of long-distance dispersal for invasive Heracleum species was strongly underestimated. The published dataset with H. sosnowskyi propagule traits and release heights allows for modeling of the propagules’ dispersal distances by wind at any geographical point within their entire invasion range using data from the closest weather stations. The proposed simple model for the prediction of H. sosnowskyi propagule dispersal by wind may be included in planning processes for managing invasion of this species.

Stimulation and Isolation of Paraphysoderma sedebokerense (Blastocladiomycota) Propagules and Their Infection Capacity Toward Their Host Under Different Physiological and Environmental Conditions.

Paraphysoderma sedebokerense (P. sedebokerense) (Blastocladiomycota) is a facultative pathogenic chytrid that causes irreversible damage to some green microalgae. Specific attacks leading to culture collapse under different conditions have only been described in the lucrative microalga Haematococcus pluvialis (H. pluvialis), while generating biomass for ketocarotenoid astaxanthin production, both indoors and outdoors. In order to manage the infection, parasite propagules (zoospores/amoeboid swarmers), the initiators of the disease, must be studied. Until now, no report on isolated P. sedebokerense propagules has been published. Here, we report on a reproducible method for the stimulation of P. sedebokerense propagule release and their isolation from fungal cultures in synthetic media and infected H. pluvialis cultures, and we further studied their development under different conditions. The isolated propagules featured different spore morphotypes, with coatless spherical spores and amoeboid swarmers being the most dominant in the first pulse of propagule release in both cultures. Inoculating the pure propagules with the host, in both the presence and absence of nitrogen, resulted in epidemic development in both green and red cells; however, in red cells, the epidemic developed more quickly in the presence of nitrogen. Biologically non-active autoclaved host cells were used to distinguish the initial stages of recognition from more progressive stages of the epidemics; on these cells, propagules encysted but did not develop further. These results prove the existence of heat-stable recognition sites on the host and an obligatory signal transduction from the host to support fungal cyst development. The propagule isolation method described herein is a breakthrough that will enable researchers to study the influence of different substances on the propagules, specifically as the initiators of the infection, and thus assist in the management of chytrid diseases. Moreover, it will be useful in studying host-parasite recognition and, therefore, will increase our understanding of the multiple chytrid infections found in nature.

Exploring the Influence of Temperature on Aspects of the Reproductive Phenology of Temperate Seaweeds

As plants on land, seaweeds are likely to be susceptible to temperature-mediated changes in phenology such as shifts in their reproductive timing. With this review, we aimed to investigate the importance of temperature on reproductive phenophase transitions (i.e. maturation and release of propagules) of temperate seaweeds while discussing how global warming might affect their reproductive phenology. A systematic literature search returned a total of 81 relevant papers, which were reviewed for evidence of environmental, factors (including temperature) driving reproductive phenology. Only a few of studies reported effects of temperature on propagule release (spores and gametes). In contrast, reproductive maturation (both sporogenesis and gametogenesis) was found predominantly to be controlled by temperature. Our findings highlight the potential for phenological shifts in seaweeds in response to ocean warming. In contrast to the consistent advancement of spring events observed for terrestrial plants, there was evidence that warming can both advance and delay the timing of reproductive events for temperate seaweeds, especially the maturation of propagules. Because temperature was often found to act in combination with either day length or spectral composition, ocean warming might result in a mismatch between light and temperature requirements that could lead to reduced reproductive performance.

Use of Lagrangian simulations to hindcast the geographical position of propagule release zones in a Mediterranean coastal fish

The study of organism dispersal is fundamental for elucidating patterns of connectivity between populations, thus crucial for the design of effective protection and management strategies. This is especially challenging in the case of coastal fish, for which information on egg release zones (i.e. spawning grounds) is often lacking. Here we assessed the putative location of egg release zones of the saddled sea bream (Oblada melanura) along the south-eastern coast of Spain in 2013. To this aim, we hindcasted propagule (egg and larva) dispersal using Lagrangian simulations, fed with species-specific information on early life history traits (ELTs), with two approaches: 1) back-tracking and 2) comparing settler distribution obtained from simulations to the analogous distribution resulting from otolith chemical analysis. Simulations were also used to assess which factors contributed the most to dispersal distances. Back-tracking simulations indicated that both the northern sector of the Murcia region and some traits of the North-African coast were hydrodynamically suitable to generate and drive the supply of larvae recorded along the coast of Murcia in 2013. With the second approach, based on the correlation between simulation outputs and field results (otolith chemical analysis), we found that the oceanographic characteristics of the study area could have determined the pattern of settler distribution recorded with otolith analysis in 2013 and inferred the geographical position of main O. melanura spawning grounds along the coast. Dispersal distance was found to be significantly affected by the geographical position of propagule release zones. The combination of methods used was the first attempt to assess the geographical position of propagule release zones in the Mediterranean Sea for O. melanura, and can represent a valuable approach for elucidating dispersal and connectivity patterns in other coastal species.

Interannual variation in bryophyte dispersal: linking bryophyte phenophases and weather conditions

In the context of global changes that modify the distribution range of species, there is an urgent need to identify climate variables affecting species dispersal. We investigated patterns of aerial propagule release (sexual and asexual) of boreal bryophytes in response to weather. We present the first community-level study that examines the impact of weather on the phenology of bryophytes, and we divided it into phases. Bryophyte propagule rain was trapped in 2013 (summer and fall) and 2014 (spring and fall), and climatic variables were collated from the years 2012 to 2014. The phases of the phenology and the weather variables one season to two years preceding propagule release, which may influence the dispersal of propagules, were identified. Propagule release varies with weather conditions at the time of dispersal (direct effects), but is also associated with weather during the winter and summer one year preceding dispersal (indirect effects), which presumably influences survival, growth, and fertilization of the mother plant as well as propagule and sporophyte development. We suggest that propagule release is related to weather conditions occurring from one to several previous seasons, particularly humidity, temperature, and length (duration) of winter. Dividing the phenology into phases, we present an innovative method that should provide new insights into bryophyte dispersal dynamics in response to climate.

Submerged seed, turion and oospore rain: A trap quantifying propagule deposition under aquatic vegetation

Submerged, free-floating and floating-leaved macrophytes produce a broad variety of specialized propagules to ensure population continuity and enhance dispersal. We quantified macrophyte propagule deposition in shallow ponds using a trap positioned near the sediment, designed to monitor diaspore rain in lentic aquatic environments. Propagule traps were tested under different set-ups, firstly within enclosed mesocosm experiments and secondly in vegetation communities growing in the open field. Mesocosms were installed in ponds containing monospecific stands of Chara globularis and Potamogeton pusillus under two contrasting conditions, with and without duckweed (Lemna minor), to evaluate cover impact on propagule release from the submerged macrophytes. During the studied interval, deposition of C. globularis oospores was not affected by Lemna cover. In P. pusillus, lemnid cover coincided with strong phenotypic alterations, including high turion investment. Traps openly installed in ponds containing Parvopotamion- and Magnopotamion/Hydrocharition-type associations showed that propagule rain was intensive underneath some macrophyte species and generally mirrored vegetation composition. Certain species were either over- or underrepresented. Generally, macrophyte abundance did not influence propagule deposition. Propagule traps are useful in studies assessing reproductive dynamics and resource allocation, potentially bypassing or complementing sediment propagule bank research, and aiding identification of recruitment bottlenecks.

Seasonal release of propagules in mangroves – Assessment of current data

Phenology is often neglected in dispersal research, in spite of its potential effects on the patterns of propagule deposition. Based on peer-reviewed literature, we collated data on propagule release timing for mangroves and aimed at understanding the relation between mangrove propagule release timing and monthly average rainfall and temperature. There were data on 47 species of 25 genera, accounting for 67% of mangrove species, but most (35%) of the available data are related to Avicennia marina, Avicennia germinans and Rhizophora mangle. We found significant correlations (r>0.8, P<0.001) between mangrove propagule release and rainfall, with 72% of data reporting propagule release during the wet season, except in the southernmost latitudes. In the equatorial zone (10°N–10°S), propagules fall from parent trees throughout most of the year with no pronounced production peaks. At latitudes higher than the equatorial zone, propagule release was also significantly correlated with temperature (r>0.6, P<0.05). Our results show phenological complementarity between the northern and southern hemisphere, with a peak in propagule release corresponding to the boreal and austral summer, respectively. We encourage mangrove researchers to report data on propagule release and availability to render an increasingly accurate and precise interpretation of geographic patterns as the current dataset increases, both in terms of geographic and species coverage.

Amplified recruitment pressure of biofouling organisms in commercial salmon farms: potential causes and implications for farm management

The development of biofouling on finfish aquaculture farms presents challenges for the industry, but the factors underlying nuisance growths are still not well understood. Artificial settlement surfaces were used to examine two possible explanations for high rates of biofouling in Norwegian salmon farms: (1) increased propagule release during net cleaning operations, resulting in elevated recruitment rates; and (2) potential reservoir effects of farm surfaces. The presence of salmon farms was associated with consistently and substantially (up to 49-fold) elevated recruitment rates. Temporal patterns of recruitment were not driven by net cleaning. Resident populations of biofouling organisms were encountered on all submerged farm surfaces. Calculations indicate that a resident population of the hydroid Ectopleura larynx, a major biofouling species, could release between 0.3 × 109 and 4.7 × 109 larvae per farm annually. Such resident populations could form propagule reservoirs and be one explanation for the elevated recruitment pressure at salmon farms.

Release thresholds for moss spores: the importance of turbulence and sporophyte length

Summary Adequately describing the dispersal mechanisms of a species is important for understanding and predicting its distribution dynamics in space and time. For wind‐dispersed species, the transportation of airborne propagules is comparatively well studied, while the mechanisms triggering propagule release are poorly understood, especially for cryptogams. We investigated the effect of wind speed and turbulence on spore release in the moss Atrichum undulatum in a wind tunnel. Specifically, we measured the amount of spores released from sporophytes when exposed to different wind speeds, in high and low turbulence, using a particle counter. We also related spore release to variation in vibrations of the sporophyte and investigated how the vibrations were affected by wind speed, turbulence and sporophyte length (here including capsule, seta and the top part of the shoot). We show that in high turbulence, the amount of spores released increased with increasing wind speed, while in low turbulence, it did not, within the wind speed range 0.8–4.3 m s−1. However, there was a threshold in wind speed (˜2.5–3 m s−1) before large amounts of spores started to be released in turbulent flow, which coincided with incipient vibrations of the sporophyte. Thresholds in wind variation, rather than average wind speed, seemed to initiate sporophyte vibrations. The vibration threshold increased with decreasing sporophyte length. The deposition of spores near the source decreased with increasing wind variation during the time of their release, based on simulated spore deposition from another study of moss dispersal. Synthesis. We suggest that vibration of moss sporophytes is an important mechanism to regulate spore release and that turbulence and sporophyte length regulate the onset of sporophyte vibration. Spore release thresholds affect dispersal distances and have implications for our understanding and predictions of species distribution patterns, population dynamics and persistence. The mechanisms of this phase of the dispersal process are also important to explore for other species, as there may be a substantial variation depending on the species' different traits.

Retention-favorable timing of propagule release in barnacles and periwinkles

Recent studies on the ecology of marine larvae suggest that retention near coastal areas and self-recruitment are probably much more common than previously thought. In light of this, the advective potential of pelagic stages can be partially determined by the timing of propagule release. We sampled the upper-shore levels of a subtropical coastline in southeastern Brazil to examine the temporal patterns of propagule release for the common barnacle Chthamalus bisinuatus and the peri- winkle Nodilittorina lineolata. The release timing in both species was very consistent between sites a few kilometers apart. Barnacles released nauplii in a rhythmic pattern, mostly coinciding with neap tides, when the speed of tidal currents was lowest. There was no variation in propagule release in relation to diel or flood-ebb tidal cycles. Periwinkles released propagules in a very irregular pattern, which remarkably matched a time series of wave heights. Egg capsules were released during periods of rough seas, when onshore surface currents were expected to prevail. Eggs were released mostly during ebb tides, and there was no diel variation. Propagule release rhythms are usually viewed as a means to ensure fast offshore advection, thus avoiding presumed hazardous conditions for larvae. However, propagule release strategies in these upper-shore species would more likely contribute to the retention of offspring close to parental stocks.

The role of hydrochory in structuring riparian and wetland vegetation

Hydrochory, or the passive dispersal of organisms by water, is an important means of propagule transport, especially for plants. During recent years, knowledge about hydrochory and its ecological consequences has increased considerably and a substantial body of literature has been produced. Here, we review this literature and define the state of the art of the discipline. A substantial proportion of species growing in or near water have propagules (fruits, seeds or vegetative units) able to disperse by water, either floating, submerged in flowing water, or with the help of floating vessels. Hydrochory can enable plants to colonize sites out of reach with other dispersal vectors, but the timing of dispersal and mechanisms of establishment are important for successful establishment. At the population level, hydrochory may increase the effective size and longevity of populations, and control their spatial configuration. Hydrochory is also an important source of species colonizing recruitment-limited riparian and wetland communities, contributing to maintenance of community species richness. Dispersal by water may even influence community composition in different landscape elements, resulting in landscape-level patterns. Genetically, hydrochory may reduce spatial aggregation of genetically related individuals, lead to high gene flow among populations, and increase genetic diversity in populations receiving many propagules. Humans have impacted hydrochory in many ways. For example, dams affect hydrochory by reducing peak flows and hence dispersal capacity, altering the timing of dispersal, and by presenting physical barriers to dispersal, with consequences for riverine plant communities. Hydrochory has been inferred to be an important vector for the spread of many invasive species, but there is also the potential for enhancing ecosystem restoration by improving or restoring water dispersal pathways. Climate change may alter the role of hydrochory by modifying the hydrology of water-bodies as well as conditions for propagule release and plant colonization.

Timing of propagule release significantly alters the deposition area of resulting aerial dispersal

AbstractAim The aim of this study is to determine whether changes to the seasonal and circadian timing of propagule release can a have a significant effect on the area covered by resulting aerial dispersal.Location Western Australia.Methods Using the atmospheric pollution model (TAPM), an existing meso‐scale dispersal model, a range of release patterns was simulated and the resulting deposition compared. Comparisons were based on observations of deposition patterns and the calculated area of deposition.Results Small changes to the timing of propagule release were shown to significantly impact on the area experiencing deposition from the resulting aerial dispersal.Main conclusions Simulations performed in this study show that, for small propagules, changes to the timing of release can lead to alternate, clearly differentiable dispersal events. Small changes in both the seasonal and circadian patterns of release can have significant effects on the area that experiences deposition during the resulting dispersal event. This effect is particularly important at the landscape scale and when there is a need to quantify individual dispersal events. Predictive modelling of aerial dispersal needs to be undertaken with an understanding of the manner in which biological and environmental factors that affect the timing of propagule release can influence results. Results presented highlight the need to characterize the epidemiology of pathogenic organisms of importance to biosecurity as much as possible before they arrive.

Biological invasions and the neutral theory

AbstractAim The invasion of natural communities by alien species represents a serious threat, but creates opportunities to learn about community functions. Neutral theory proposes that the niche concept may not be needed to explain the assemblage and diversity of natural communities, challenging the classical view of community ecology and generating a lasting debate. Biological invasions, when considered as natural experiments, can be used to contrast some of the predictions of neutral and classic niche theories.Location Global.Methods We use data from biological invasions as natural experiments to contrast some of the fundamental predictions of neutral theory.Results Some emerging patterns did not differ from neutral model expectations (e.g. the relationship between native and exotic species richness, invasibility of resource‐rich habitats, and the relationship between propagule release and invasion success). Nevertheless, other patterns (e.g. experimental evidence of the relationship between diversity and susceptibility to invasion, the invasion of communities with a low resource availability, invasiveness related to species traits) contrasted with the predictions that can be inferred from neutral theory.Main conclusions Neutral theory correctly highlights the need to include randomness in models of community structure. Biological invasion patterns show that neutral forces are important in structuring natural communities, but the patterns differ from those inferred from a complete neutral model. For biodiversity‐conservation purposes, the implications of accepting or not accepting neutral theory as a process‐based theory are very important.

A sampling device to quantify offspring release of sessile marine invertebrates

Summary Quantifying the rate of propagule release is of most importance to estimate reproductive output of natural populations, but simple methods to obtain such data are seldom reported. We designed and tested an inexpensive apparatus capable of reliably measure the release of gametes, eggs or larvae of sessile marine invertebrates in vertical walls. A population of the acorn barnacle Chthamalus bisinuatus was sampled with this trap over 68d to obtain a time series of naupliar release. An apparent semilunar trend is shown, indicating the effectiveness of this sampling method.

Phenology of the red mangrove, Rhizophora mangle L., in the Caeté Estuary, Pará, equatorial Brazil

The current study presents phenology data for Rhizophora mangle from two equatorial mangrove stands with different salinity regimes in Brazil. Observations based on litter fall and individual shoot development were compared and related to environmental factors. Patterns observed in litter fall were consistent with results of direct monitoring. While both reproductive organs and leaves were produced throughout the year, rates of formation followed seasonal trends. Distinct differences in propagule production between low and high salinity sites and between years of observation were detected; main propagule release was, however, restricted to the wet season which offers enhanced conditions for propagule establishment. Emergence of flowers was linked to leaf production. While there was no obvious single peak in leaf production, it was reduced towards the end of the dry season at both high and low salinity sites. Time series analysis revealed an independent pattern of leaf development superimposed on this annual seasonal trend, indicating slower development of leaf primordia during periods of low light availability in the wet season. No significant difference in age structure was detected between sun and shade leaves; maximum leaf life-time was approximately 1 year.

Propagule release and recruitment in Porphyra perforata (Rhodophyta) from Baja California, Mexico

This study determined the effect of irradiance, temperature and photoperiod on the release of zygotospores and spermatia in Porphyra perforata from the Pacific coast of Baja California, Mexico. Reproductive blades were placed under controlled conditions of irradiance (5, 75, 150 and 300 μmol photons m−2 s−1), photoperiod [8:16; 12:12 and 16:8 light:dark (L:D)] and temperature (15, 18, 21 and 25°C). Peak zygotospore release occurred at 15–18°C and photoperiod of 16:8 L:D. Reproductive tissue released between 60% and 90% of zygotospores and spermatia during the first 10 days of incubation at 50 μmol photons m−2 s−1, 18°C and photoperiod of 16:8 L:D. Maximum zygotospore and spermatium release occurred in tissue collected between June and November. The number of zygotospores released was approximately 40% greater than that of spermatia (2.7×106 vs. 1.6×106 g FW−1 d−1). The reproductive foliar phase was observed throughout the year, but only thalli collected from April to January released zygotospores and spermatia. Collectively, the results suggest that low temperature, as observed in upwelling events, may induce high zygotospore and spermatium release during summer months.

Effects of water motion on propagule release from algae with complex life histories

Reproductive marine algae with complex life histories may respond differently to water motion depending upon whether the spore-producing or gamete-producing phase is considered. Two such species, the kelp Alaria esculenta (L.) Greville (Phaeophyceae) and Ulva lactuca L. (Chlorophyta), were examined experimentally in the laboratory. The kelp was collected in April–June 2000 and U. lactuca was collected in July–August 2000, from four intertidal habitats at Schoodic Point, Maine, USA. Orbital shakers were used to generate water motion. Sporophylls of A. esculenta released more zoospores under shaken versus calm conditions, whereas fewer antheridia on the microscopic male gametophytes released sperm under shaken versus calm conditions when male and female gametophytes were placed together. However, antheridial sperm release was equivalent when male gametophytes were exposed to undiluted media from dense cultures of mature female gametophytes under shaken versus calm conditions. These data suggest that water motion inhibited sperm release by diluting the sperm-releasing pheromone produced by ripe eggs below a threshold required to cause sperm release. Water motion stimulated both gamete and zoospore release from U. lactuca. This is the first report in an alga of stimulation of gamete release by increased water motion, but it is notable that parthenogenesis occurs in Ulva spp.; thus, gametes may develop into gametophytes (1 N) or parthenosporophytes (2 N). This study demonstrates that water motion has strong effects upon algal reproduction, but that the effects may vary between species, possibly due to their different life histories.

Effects of iron-ore particles on propagule release, growth and photosynthetic performance of Sargassum vulgare C. Agardh (Phaeophyta, Fucales)

Os efeitos das particulas de minerio de ferro na liberacao e desenvolvimento de propagulos de Sargasssum vulgare C. Agardh foram testados em diferentes concentracoes de minerio de ferro: 0,1, 1,0, 10,0 g.L-1 e na solucao de 10,0 g.L-1 de filtrado de minerio. Agua do mar filtrada foi utilizada como controle. Curvas de fotossintese vs. irradiância (P-I) foram calculadas para S. vulgare na presenca de minerio de ferro e em agua do mar. Nao houve diferenca significativa no numero de propagulos liberados e nem na percentagem de zigotos formados entre os tratamentos. Os propagulos liberados atuam como centro de agregacao para as particulas, onde as mais densamente recobertas por ferro (10,0 g.L-1) apresentaram a mais alta velocidade de decantacao (32,6 ± 9,8 mm.s-1). Nenhuma diferenca na percentagem de sobrevivencia de embrioes foi observada durante a primeira semana de cultivo. Apos quatro semanas de experimento, os embrioes cresceram em todos os tratamentos. O desenvolvimento maximo das frondes (5,3 ± 0,8 mm) ocorreu no tratamento com agua do mar enriquecida com o meio de Provasoli (PES). Em tres tratamentos sem PES e com minerio de ferro, o inicial dos filoides nao se desenvolveram (0,1, 1,0 e 10,0 g.L-1). Os valores de Pmax, alpha e respiracao nao apresentaram diferenca significativa entre as curvas de P-I. Os valores calculados para IK foram 106,26 µmol.m-2s-1 para curva controle e 981,49 µmol.m2.s-1 para a curva com minerio de ferro. Os resultados indicam que as particulas de minerio de ferro em alta concentracao reduzem o crescimento de S. vulgare uma vez que elas recobrem os embrioes, juvenis e plantas jovens. Ja a presenca das particulas nao afetou a liberacao de gametas, a percentagem de formacao de zigotos ou a sobrevivencia de embrioes.