Propagule Size Research Articles

Propagule size and seed development duration: high photosynthate allocation and growth allometry.

The divergences in propagule mass have been more consistently associated with divergences in seed development duration or fruit pedicel cross-sectional area than with divergences in any other biotic factors. Allometry and Corner's rule became an important theme in evolutionary biology of plant trait structure and function. Being one of the most widely noticed plant traits, propagule (seed and fruit) mass variation mechanism across species is still controversial. Here we examined correlations between propagule mass and seed development duration as well as other traits, such as cross-sectional area of fruit pedicel, life form, fruit type and leaf area over four census years, to test an important life history strategy for propagule biomass allocation. We investigated 491 species, belonging to 91 families and 320 genera, representing 95% of native wild species in Beijing Botanical Garden. The scaling correlations between propagule mass and seed development duration and the other traits were determined using phylogenetic generalized linear models. Results show a significant positive relationship among propagule mass and seed development duration, leaf area and pedicel cross-sectional area for all species and for each life form (except vines) regardless of phylogeny. The variation in seed mass has been more consistently associated with variation in seed development duration than with divergences in any other variable, such as growth form, fruit type, pedicel cross-sectional area and leaf area, whereas variation in fruit weight was found to be more associated with variation in pedicel cross-sectional area than the other. Biotic factors, such as seed development duration, pedicel cross-sectional area, growth form and leaf area, mediate propagule size variation, of which seed development duration or pedicel cross-sectional area is the most important. The results further supported a hypothesis that large-seeded species evolved owing to high photosynthate availability and growth allometry in plant body. A mechanistic mathematical model involving seed development duration was provided to expound propagule mass variations across species.

Propagule size and sex ratio influence colonisation dynamics after introduction of a non-native lizard.

The composition of founding populations plays an important role in colonisation dynamics and can influence population growth during early stages of biological invasion. Specifically, founding populations with small propagules (i.e. low number of founders) are vulnerable to the Allee effect and have reduced likelihood of establishment compared to those with large propagules. The founding sex ratio can also impact establishment via its influence on mating success and offspring production. Our goal was to test the effects of propagule size and sex ratio on offspring production and annual population growth following introductions of a non-native lizard species (Anolis sagrei). We manipulated propagule composition on nine small islands, then examined offspring production, population growth and survival rate of founders and their descendants encompassing three generations. By the third reproductive season, per capita offspring production was higher on islands seeded with a relatively large propagule size, but population growth was not associated with propagule size. Propagule sex ratio did not affect offspring production, but populations with a female-biased propagule had positive growth, whereas those with a male-biased propagule had negative growth in the first year. Populations were not affected by propagule sex ratio in subsequent years, possibly due to rapid shifts towards balanced (or slightly female biased) population sex ratios. Overall, we show that different components of population fitness have different responses to propagule size and sex ratio in ways that could affect early stages of biological invasion. Despite these effects, the short life span and high fecundity of A. sagrei likely helped small populations to overcome Allee effects and enabled all populations to successfully establish. Our rare experimental manipulation of propagule size and sex ratio can inform predictions of colonisation dynamics in response to different compositions of founding populations, which is critical in the context of population ecology and invasion dynamics.

Assessing Tolerance to the Hydrodynamic Exposure of Posidonia oceanica Seedlings Anchored to Rocky Substrates

Among a suite of abiotic and biotic factors, the hydrodynamic regime strongly influences the success of seagrass recruitment through sexual propagules. Uprooting of propagules by drag forces exerted by currents and waves is one of the main causes for the failed establishment and the consequent recruitment. Substrate type and stability play a key role in determining the success of colonization through sexual propagules, as seedling establishment probabilities proved to be significantly higher on rocky bottoms than on unstable unconsolidated substrates. In this research, the current and wave flow intensity thatPosidonia oceanicaseedlings anchored to rocky substrates can withstand before uprooting were evaluated and the influence of substrate complexity on seedling anchorage success and anchorage strength was investigated.P. oceanicaseedlings withstood the current velocity of 70 cm s–1and increased orbital flow velocities up to 25 cm s–1. Seedling adhesion strength ranged from 3.92 to 29.42 N. Results of the present study corroborate the hypothesis that substrate complexity at scales relevant to the size of propagules is a crucial feature forP. oceanicaseedling establishment. The intensity of unidirectional and oscillatory flow that seedlings can withstand without being dislodged assessed in this study support the hypothesis thatP. oceanicasexual propagules, once adhered to a consolidated substrate, are able to tolerate high hydrodynamic stress. The results of the present study contribute to re-evaluation of the habitat requirements ofP. oceanica, assessing the range of hydrodynamic conditions that this species can tolerate during the early stages of its life history.

RESGATE VEGETATIVO DE Azadirachta indica POR ESTAQUIA

ABSTRACT Finding forest species adapted to different soil and climatic conditions and, that provide favorable attributes to commercial use is a challenge. Azadirachta indica is a potential species to attend to this goal. Thus, this paper aims to carry out the vegetative rescue of different Azadirachta indica Juss adult trees by cuttings. For that, Azadirachta indica individuals were randomly selected in a plantation of species set ten years ago and the cut was carried out at 30 cm in height. In sequence, verification was carried out on: (a) the stem cut ability to regrowth (collections and measurements of the shoot length on the 15th, 30th, 45th, and 60th days); (b) the need to use exogenous auxin for rooting induction [testing 0 (control), 2000, 4000, and 6000 mg.l-1 of Indole-3-butyric acid (IBA)]; (c) the ideal of the propagule size (with 8 cm and 13 cm in height); and (c) the rooting dynamics (every seven days for thirty-five days; the propagules were evaluated for callus formation, oxidation, and rooting). The species showed high regrowth ability, as well as easy rooting with or without the use of IBA; it was found that the ideal size for the propagule is 13 cm and that the process of rooting and root elongation is completed after thirty-five days of staking. The conclusion is: (a) using cuttings for the species vegetative rescue is interesting; (b) 13 cm is considered appropriate for the propagule size, and; (c) the aid of IBA at a dose of 2,000 mg L-1 is ideal to standardize rooting.

Decay of similarity across tropical forest communities: integrating spatial distance with soil nutrients.

Understanding the mechanisms that drive the change of biotic assemblages over space and time is the main quest of community ecology. Assessing the relative importance of dispersal and environmental species selection in a range of organismic sizes and motilities has been a fruitful strategy. A consensus for whether spatial and environmental distances operate similarly across spatial scales and taxa, however, has yet to emerge. We used censuses of four major groups of organisms (soil bacteria, fungi, ground insects, and trees) at two observationscales (1-m2 sampling point vs. 2,500-m2 plots) in a topographically standardized sampling design replicated in two tropical rainforests with contrasting relationships between spatial distance and nutrient availability. We modeled the decay of assemblage similarity for each taxon set and site to assess the relative contributions of spatial distance and nutrient availability distance. Then, we evaluated the potentially structuring effect of tree composition over all other taxa. The similarity of nutrient content in the litter and topsoil had a stronger and more consistent selective effect than did dispersal limitation, particularly for bacteria, fungi, and trees at the plot level. Ground insects, the only group assessed with the capacity of active dispersal, had the highest species turnover and the flattest nonsignificant distance-decay relationship, suggesting that neither dispersal limitation nor nutrient availability were fundamental drivers of their community assembly at this scale of analysis. Only the fungal communities at one of our study sites were clearly coordinated with tree composition. The spatial distance at the smallest scale was more important than nutrient selection for the bacteria, fungi, and insects. The lower initial similarity and the moderate variation in composition identified by these distance-decay models, however, suggested that the effects of stochastic sampling were important at this smaller spatial scale. Our results highlight the importance of nutrients as one of the main environmental drivers of rainforest communities irrespective of organismic or propagule size and how the overriding effect of the analytical scale influences the interpretation, leading to the perception of greater importance of dispersal limitation and ecological drift over selection associated with environmental niches at decreasing observation scales.

Seed fate, seedling establishment and the role of propagule size in forest regeneration under climate change conditions

Climate change can affect tree recruitment altering post-dispersal seed fates and impairing seedling development, and these effects will be stronger at man-disturbed areas than beneath forest canopies. Seed biomass, however, positively influences tree recruitment processes and its relevance increases with environmental harshness. Therefore, this seed trait may become critical for forest regeneration under climate change scenarios. We experimentally tested these hypotheses with two Mexican oaks that dominate forests at sites where temperature will increase and rainfall will decrease in the next 20 years. At both experimental sites, we sowed acorns of varying biomass at forest understories and deforested areas under the current climate and simulated climate change conditions. We measured microclimate, incidence of seed parasitism by insects and fungi, germination, shoot emergence, and seedling survival and growth over a year. Temperature in climate change simulations was increased 2 °C and rainfall was reduced 17–18%, and this concurred with the near-term changes expected for both variables at the experimental sites. Climate change conditions intensified insect parasitism and decreased fungal infestation on seeds, but these effects were only found within forests and they did not relate with propagule size. Increased warming and drought reduced germination, shoot emergence, and seedling survival and growth at forests and deforested areas, but all these processes were positively related with seed biomass. Indeed, in an oak species, these relationships displaced towards bigger-sized seeds under climate change conditions. Our findings suggest that climate change can alter the intensity of seed-parasite interactions and impair tree establishment processes, also suggesting that this phenomenon will favor large-sized over small-sized seeds during recruitment of some tree species.

Multilevel selection favors fragmentation modes that maintain cooperative interactions in multispecies communities.

Reproduction is one of the requirements for evolution and a defining feature of life. Yet, across the tree of life, organisms reproduce in many different ways. Groups of cells (e.g., multicellular organisms, colonial microbes, or multispecies biofilms) divide by releasing propagules that can be single-celled or multicellular. What conditions determine the number and size of reproductive propagules? In multicellular organisms, existing theory suggests that single-cell propagules prevent the accumulation of deleterious mutations (e.g., cheaters). However, groups of cells, such as biofilms, sometimes contain multiple metabolically interdependent species. This creates a reproductive dilemma: small daughter groups, which prevent the accumulation of cheaters, are also unlikely to contain the species diversity that is required for ecological success. Here, we developed an individual-based, multilevel selection model to investigate how such multi-species groups can resolve this dilemma. By tracking the dynamics of groups of cells that reproduce by fragmenting into smaller groups, we identified fragmentation modes that can maintain cooperative interactions. We systematically varied the fragmentation mode and calculated the maximum mutation rate that communities can withstand before being driven to extinction by the accumulation of cheaters. We find that for groups consisting of a single species, the optimal fragmentation mode consists of releasing single-cell propagules. For multi-species groups we find various optimal strategies. With migration between groups, single-cell propagules are favored. Without migration, larger propagules sizes are optimal; in this case, group-size dependent fissioning rates can prevent the accumulation of cheaters. Our work shows that multi-species groups can evolve reproductive strategies that allow them to maintain cooperative interactions.

'Accidents waiting to happen'-Insights from a simple model on the emergence of infectious agents in new hosts.

This study evaluates through modelling the possible individual and combined effect of three populational parameters of pathogens (reproduction rate; rate of novelty emergence; and propagule size) on the colonization of new host species-putatively the most fundamental process leading to the emergence of new infectious diseases. The results are analysed under the theoretical framework of the Stockholm Paradigm using IBM simulations to better understand the evolutionary dynamics of the pathogen population and the possible role of Ecological Fitting. The simulations suggest that all three parameters positively influence the success of colonization of new hosts by a novel parasite population, but contrary to the prevailing belief, the rate of novelty emergence (e.g. mutations) is the least important factor. Maximization of all parameters results in a synergetic facilitation of the colonization and emulates the expected scenario for pathogenic microorganisms. The simulations also provide theoretical support for the retention of the capacity of fast-evolving lineages to retro-colonize their previous host species/lineage by ecological fitting. Capacity is, thus, much larger than we can anticipate. Hence, the results support the empirical observations that opportunity of encounter (i.e. the breakdown in mechanisms for ecological isolation) is a fundamental determinant to the emergence of new associations-especially Emergent Infectious Diseases-and the dynamics of host exploration, as observed in SARS-CoV-2. Insights on the dynamics of Emergent Infectious Diseases derived from the simulations and from the Stockholm Paradigm are discussed.

A biome-wide experiment to assess the effects of propagule size and treatment on the survival of Portulacaria afra (spekboom) truncheons planted to restore degraded subtropical thicket of South Africa.

Insights from biome-wide experiments can improve efficacy of landscape-scale ecological restoration projects. Such insights enable implementers to set temporal and geographical benchmarks and to identify key drivers of success during the often decades-long restoration trajectory. Here we report on a biome-wide experiment aimed at informing the ecological restoration of thousands of hectares of degraded subtropical thicket dominated by the succulent shrub, Portulacaria afra (spekboom). Restoration using spekboom truncheons has the potential to sequester, for a semi-arid region, large amounts of ecosystem carbon, while regenerating a host of associated ecosystem services. This study evaluates, after about three years post-propagation, the effects of spekboom truncheon size and treatment on survivorship in 40 fence-enclosed (0.25 ha) plots located in target habitat across the entire spekboom thicket biome. In each plot, locally harvested spekboom truncheons, comprising eight size/treatment combinations, were planted in replicated rows of between 24 and 49 individuals, depending on treatment. The experiment assessed the role of truncheon size, spacing, application of rooting hormone and watering at planting on survivorship percentage as an indicator of restoration success. All eight combinations recorded extreme minimum survivorship values of zero, while the range of extreme maximum values was 70-100%. Larger truncheons (>22.5 mm diameter) had almost double the survivorship (ca. 45%) than smaller truncheons (< 15 mm) (ca. 25%). Planting large, untreated truncheons at 1 m intervals-as opposed to 2 m intervals recommended in the current restoration protocol-resulted in no significant change in survivorship. The application of rooting hormone and water at planting had no significant effect on restoration success for both large and small truncheons. While our results do not provide an evidence base for changing the current spekboom planting protocol, we recommend research on the financial and economic costs and benefits of different propagation strategies in real-world contexts.

A quantitative assessment of site-level factors in influencing Chukar (Alectoris chukar) introduction outcomes.

Chukar partridges (Alectoris chukar) are popular game birds that have been introduced throughout the world. Propagules of varying magnitudes have been used to try and establish populations into novel locations, though the relationship between propagule size and species establishment remains speculative. Previous qualitative studies argue that site-level factors are of importance when determining where to release Chukar. We utilized machine learning ensembles to evaluate bioclimatic and topographic data from native and naturalized regions to produce predictive species distribution models (SDMs) and evaluate the relationship between establishment and site-level factors for the conterminous United States. Predictions were then compared to a distribution map based on recorded occurrences to determine model prediction performance. SDM predictions scored an average of 88% accuracy and suitability favored states where Chukars were successfully introduced and are present. Our study shows that the use of quantitative models in evaluating environmental variables and that site-level factors are strong indicators of habitat suitability and species establishment.

Managing propagule pressure to prevent invasive species establishments: propagule size, number, and risk-release curve.

There is considerable evidence that keeping propagule pressure low can drastically reduce establishment probability of potential invasive species. Yet, most management plans and research efforts fail to explicitly acknowledge all three of the components of propagule pressure: size, number, and the risk-release relationship. It is unclear how failing to specify one or more of these components can influence the efficacy of management plans in preventing invasive species establishment. Furthermore, even if all components are acknowledged and quantified, there currently is no mathematical tool available to calculate the levels of propagule pressure that ensure attainment of a predetermined, and system-specific, target establishment probability. Here, we quantify the resulting uncertainty in establishment probability when one or more components of propagule pressure is unknown by using parameter uncertainty analysis on realistic values of propagule pressure. In addition, to aid in the development of management plans that explicitly set propagule pressure limits, we develop a propagule-pressure sensitivity analysis that we use to determine the required reduction in levels for propagule size and number (representative of management actions) to maintain a target establishment probability. We show that the precision of establishment estimates is highly dependent on knowledge of all three propagule pressure components, where the possible range of values for establishment probability can vary by over 50% without full specification. In addition, our sensitivity analysis showed that propagule size and number can be altered independently or in conjunction to lower establishment probability below a target level. Importantly, our sensitivity analysis was able to specifically quantify how much reduction in a propagule pressure component(s) is needed to reach a given target establishment probability. Our findings suggest that quantifying the three components of propagule pressure should be a priority for invasive species prevention moving forward. Furthermore, our sensitivity analysis tool can serve to guide the development of new invasive species management plans in a transparent and quantitative manner. Together with information on the costs associated with approaches to reducing propagule pressure, our tool can be used to identify the most cost-effective approach to prevent invasive species establishments.

Genome Size Covaries More Positively with Propagule Size than Adult Size: New Insights into an Old Problem.

Simple SummaryThe amount of hereditary information (DNA) contained in the cell nuclei of larger or more complex organisms is often no greater than that of smaller or simpler organisms. Why this is so is an evolutionary mystery. Here, I show that the amount of DNA per cell nucleus (‘genome size’) relates more positively to egg size than body size in crustaceans (including shrimp, lobsters and crabs). Genome size also seems to relate more to the size of eggs or other gametes and reproductive propagules (e.g., sperm, spores, pollen and seeds) than to adult size in other animals and plants. I explain these patterns as being the result of genome size relating more to cell size (including that of single-celled eggs) than the number of cells in a body. Since most organisms begin life as single cells or propagules with relatively few cells, propagule size may importantly affect or be affected by genome size regardless of body size. Relationships between genome size and body size should thus become weaker as body size (and the amount of cell multiplication required during development) increases, as observed in crustaceans and other kinds of organisms.The body size and (or) complexity of organisms is not uniformly related to the amount of genetic material (DNA) contained in each of their cell nuclei (‘genome size’). This surprising mismatch between the physical structure of organisms and their underlying genetic information appears to relate to variable accumulation of repetitive DNA sequences, but why this variation has evolved is little understood. Here, I show that genome size correlates more positively with egg size than adult size in crustaceans. I explain this and comparable patterns observed in other kinds of animals and plants as resulting from genome size relating strongly to cell size in most organisms, which should also apply to single-celled eggs and other reproductive propagules with relatively few cells that are pivotal first steps in their lives. However, since body size results from growth in cell size or number or both, it relates to genome size in diverse ways. Relationships between genome size and body size should be especially weak in large organisms whose size relates more to cell multiplication than to cell enlargement, as is generally observed. The ubiquitous single-cell ‘bottleneck’ of life cycles may affect both genome size and composition, and via both informational (genotypic) and non-informational (nucleotypic) effects, many other properties of multicellular organisms (e.g., rates of growth and metabolism) that have both theoretical and practical significance.

A clue to invasion success: genetic diversity quickly rebounds after introduction bottlenecks

One of the fundamental questions in invasion biology is to understand the genetic mechanisms behind success or failure during the establishment of a species. However, major limitations to understanding are usually a lack of spatiotemporal population data and information on the populations’ colonisation history. In a large-scale, detailed study on the bush-cricket Metrioptera roeselii 70 groups of founders were introduced in areas outside the species’ distribution range. We examined how (1) the number of founders (2–32 individuals), (2) the time since establishment (7 or 15 years after introduction) and (3) possible gene flow affected establishment success and temporal genetic changes of the introduced populations. We found higher establishment success in introductions with larger propagule sizes but genetic diversity indices were only partly correlated to propagule size. As expected, introduced populations were more similar to their founder population the larger the propagule size was. However, even if apparent at first, most of the differentiation in the small propagule introductions disappeared over time. Surprisingly, genetic variability was regained to a level comparable to the large and outbreeding founder population only 15 generations after severe demographic bottlenecks. We suggest that the establishment of these populations could be a result of several mechanisms acting in synergy. Here, rapid increase in genetic diversity of few introductions could potentially be attributed to limited gene flow from adjacent populations, behavioural adaptations and/or even increased mutation rate. We present unique insights into genetic processes that point towards traits that are important for understanding species’ invasiveness.

Compositional variation in understorey fern and palm communities along a soil fertility and rainfall gradient in a lower montane tropical forest

AbstractQuestionsFerns and palms are key components of tropical wet forest understories. The distributions of these groups are influenced by variation in rainfall and soil properties, although the degree to which their resource requirements overlap remains unclear. Palms and ferns also represent extremes in a spectrum of reproductive traits, which may impact habitat requirements and compositional turnover. We asked whether: (a) environmental variables influence fern and palm distributions in a similar manner across a gradient in soil nutrient availability; and (b) larger propagule size and lower reproductive output in palms result in greater spatial aggregation of populations and, consequently, greater distance–decay rates in community similarity in palms than ferns.LocationOld‐growth premontane forest, Fortuna, western Panama.MethodsAll ferns and palms were sampled in fifteen 5 m × 5 m subplots in each of 12 one‐hectare plots. The plots span a strong gradient in soil nutrient availability related to parent material. Light, precipitation and soil variables were measured in each subplot. Species associations were analyzed using ordination and regression, as well as Procrustes and Mantel tests.ResultsParent material significantly impacted compositional similarity of both ferns and palms, with fern compositional variation related to total soil N:P ratio and red:far red (R:FR), and palms with bulk density (p &lt; 0.05). Palm and fern abundances were not correlated; however, tree fern abundances showed an opposing abundance relationship with total soil N:P and R:FR compared to herbaceous ferns and palms. Distance–decay rates in compositional similarity were slightly higher for palms than ferns.ConclusionsFerns and palms show similar patterns of compositional variation in response to resource availability but were related to distinct environmental factors. Soil fertility and light availability emerged as key factors in predicting the abundance of plant groups, with clear partitioning of environmental gradients only apparent when tree ferns were compared with other groups.

EFFECTS OF THE PROPAGULE SIZE ON THE TUBEROUS RHIZOME PRODUCTION AND PHYSICOCHEMICAL CHARACTERISTICS OF JERUSALEM ARTICHOKE

As a crop that is rich in oligosaccharides, Jerusalem artichoke is considered one of the most promising plants for production because of its ability to survive in marginal lands, strong resistance to biotic and abiotic stresses, ease of conversion into biofuels, and use for food consumption. In the present study, the effects of propagule size on tuberous rhizome production and the physicochemical characteristics of Jerusalem artichoke were evaluated. Five propagule sizes of tuberous rhizome, 10 g (T1), 30 g (T2), 50 g (T3), 70 g (T4), and 90 g (T5), were used in a completely randomized experiment with 5 replicates and 11 plants per replicate. Harvesting was carried out 164 days after planting. The results showed that T1 resulted in the lowest emergence rate, number of tuberous rhizomes and aboveground fresh weight per plant of all the treatments. However, there was no significant difference among treatments in the tuberous rhizome dry weight, pH, titratable acidity, Brix, or reducing sugar. Propagule with tuberous rhizome of 30-50 g is recommended to achieve a high emergence rate and yield.

Gut microbial pulse provides nutrition for parental provisioning in incipient termite colonies

Success in aerial dispersal involves a trade-off between propagule size and dispersal ability, such that reducing weight may increase dispersal capability. Therefore, dispersing propagules such as plant seeds, fungal spores, and insect alates need to settle in new habitats with very limited resources. In termites, the time from alate dispersal to colony foundation is the most critical period in their life cycle, because a male and female pair establishes a new colony without help from others. In addition, termites depend largely on gut microbes for their nutrition. However, little is known about how termite founding pairs with limited resources establish new colonies and raise their first brood in association with their gut symbionts. Here, we provide an integrated analysis of the reproduction schedule, gut microbial fluctuations, and resource allocation of founding pairs in incipient colonies of the subterranean termite Reticulitermes speratus. There was a steep increase followed by a rapid decrease in the numbers of intestinal protozoa (hereafter, gut microbial pulse) at the time of larval hatching. Besides the monogamous pairs, same-sex (male-male and female-female) pairs also form tentative colonies in this species. Comparisons of changes in the amounts of protein and lipids in the different pair types revealed that the gut microbial pulse played an essential role in the parental feeding of the first-brood larvae. It was also observed that founders utilized stored protein and lipids for brood production. Our study highlights a significant role for intestinal symbionts during the early stage of the termite life cycle. Propagules of most animals and plants encounter resource limitations after dispersal. This is especially true for termite alates; monogamous pairs found new colonies without help from workers. How do they manage the limited resources, including their nutritional reserves and gut microbes, during colony foundation? To gain a better understanding, we analyzed time-series data of reproduction schedules, gut microbial fluctuations, and resource allocation patterns in the founders of incipient termite colonies. We identified a “gut microbial pulse”, i.e., a steep increase followed by a rapid decrease in the number of intestinal protozoa, that occurred at the time of larval hatching. Our data imply that resources derived from the pulse play an essential role in parental provisioning to larvae. This study highlights a novel strategy of termites to overcome resource-limited situations and successfully establish a new colony.

Effect of mini-cutting size on adventitious rooting and morphophysiological quality of Ilex paraguariensis plantlets

As the energizing and therapeutic effects of infusions of mate (Ilex paraguariensis A.St.-Hil) leaves are increasingly recognized, rising global consumption is also increasing the demand for plantlets with high genetic and morphological qualities. Mini-cuttings are an alternative for clonal plantlets; however, more details are needed on factors that affect the success of this technique. Here, toward maximizing production, we evaluated adventitious rooting competence of mini-cuttings of different sizes and the morphophysiological quality of the resultant plantlets. Small (one bud; length up to 2.5 cm), medium (multiple buds; length 2.6–5.0 cm), and large (multiple buds; length 5.1–10.0 cm) mini-cuttings were planted in a mixture of commercial substrate, vermiculite, and coarse sand (1:1:1 v:v:v), grown in a humidity chamber, then evaluated after 45, 60, 75, and 90 days for survival, percentage of callus and shoot formation, number and length of shoots, percentage of rooted cuttings, and number and length of roots. Any rooted mini-cuttings were then cultivated in commercial substrate and subsurface soil (2:1 v:v) and evaluated after 30, 60, 90 and 120 days of cultivation for morphophysiology of the plantlets, percentage of survival, number of leaves, shoot height, stem diameter, and ratio of shoot height to stem diameter. After 120 days, the plantlets were evaluated for the ratio of shoot and root dry mass, total length, surface area, total volume, and mean diameter of roots and Dickson quality index. Adventitious rooting of the mini-cuttings and the morphophysiological quality of the plantlets were not influenced by the size of the vegetative propagule. Therefore, single-bud mini-cuttings have similar adventitious rooting competence, and result in plantlets with adequate morphophysiological quality, based upon leaf development, shoot height, stem diameter and length, and surface area, volume and diameter of roots. Single-bud mini-cuttings up to 2.5 cm long can thus be used to maximize production of mate plantlets by mini-cuttings.

Propagule composition regulates the success of an invasive seaweed across a heterogeneous seascape

Abstract Propagule pressure is acknowledged as a key determinant of invasion success. Nonetheless, the role of morphological or physiological attributes of propagules (i.e. their quality) in regulating invader establishment has been little explored. In particular, no study has investigated how the presence of propagules differing in quality within an inoculum influences establishment across heterogeneous landscapes. We experimentally tested the hypothesis that the quality (+Fronds+Rhizoids; +Fronds−Rhizoids; −Fronds+Rhizoids) and the diversity (1, 2 and 3 fragment types) of vegetative fragments of the seaweed Caulerpa taxifolia determine their establishment success across seascapes consisting of bare sediments and patches of the seagrass Zostera muelleri exposed to different disturbance intensities (control, seagrass canopy clipping and total removal). After 6 weeks, seaweed biomass, stolon and frond length, frond and rhizoid number were generally greater in unvegetated habitats (bare sediments and total seagrass removal) than full or reduced seagrass canopies. The type and the diversity of types of fragments inoculated had significant effects on the final biomass and morphological features of C. taxifolia only in vegetated habitats. In control plots, inocula of fragments retaining both fronds and rhizoids achieved higher biomass, developed longer stolons and more fronds. In canopy clipping plots, mixed inocula of +Fronds+Rhizoids and −Fronds+Rhizoids fragments had the greatest biomass and stolon length. Synthesis. Assessing how propagules differing in quality perform in different habitats might be not sufficient to draw a comprehensive picture of invasion risk, as their establishment can be modulated by both negative and positive interactions among them. Propagule composition should be, therefore, considered as a further dimension of propagule pressure. Our results also suggest that the relevance of specific propagule traits for invader establishment decreases from intact to degraded habitats. Considering propagule size in terms of amount of competent propagules, rather than an absolute measure, would refine our ability of predicting invasion risk across habitats differing in biotic or abiotic conditions.

Propagule pressure does not consistently predict the outcomes of exotic bird introductions.

Some have argued that the role of propagule pressure in explaining the outcomes of bird introductions is well-supported by the historical record. Here, we show that the data from a large published database (including 832 records with propagule information) do not support the conclusion that propagule pressure is the primary determinant of introduction success in birds. A few compendia of historical reports have been widely used to evaluate introduction success, typically by combining data from numerous species and introduction locations. Very few taxa, other than birds, have usable spatially explicit records of introductions over time. This availability of data inflates the perceived importance of bird analyses for addressing factors related to invasion success. The available data allow limited testing of taxonomic and site-level factors of introduction outcomes. We did find significant differences in effort and success probabilities among avian orders and across highly aggregated spatial regions. As a test of a standard and logical expectation of the propagule pressure hypothesis, we concentrated on introductions with the smallest propagules, because it is for these the hypothesis is most likely to be correct. We analyzed the effect of numbers released in small propagules (two through 10) for 227 releases. Weighted linear regression indicated no significant effect of propagule size for this range of release size. In fact, the mean success rate of 28% for propagules of 2–10 isn’t significantly different than that of 34% for propagules of 11–100. Following the example of previous analyses, we expanded the statistical test of propagule pressure to include the full range of release numbers. No significant support for the propagule pressure hypothesis was found using logistic regression with either logit or complementary log-log link functions.

The determinants of genetic diversity in butterflies

Under the neutral theory, genetic diversity is expected to increase with population size. While comparative analyses have consistently failed to find strong relationships between census population size and genetic diversity, a recent study across animals identified a strong correlation between propagule size and genetic diversity, suggesting that r-strategists that produce many small offspring, have greater long-term population sizes. Here we compare genome-wide genetic diversity across 38 species of European butterflies (Papilionoidea), a group that shows little variation in reproductive strategy. We show that genetic diversity across butterflies varies over an order of magnitude and that this variation cannot be explained by differences in current abundance, propagule size, host or geographic range. Instead, neutral genetic diversity is negatively correlated with body size and positively with the length of the genetic map. This suggests that genetic diversity is determined both by differences in long-term population size and the effect of selection on linked sites.