Life-history syndromes: integrating dispersal through space and time

Age and Density of Mated Females Affect Dispersal Strategies in Spider Mite Tetranychus ludeni Zacher

The dispersal strategies of a species can affect its invasion success. Investigations into the dispersal strategies of invasive species in relation to different factors help improve our understanding of invasion mechanisms and provide knowledge for population management and invasion evaluation. Tetranychus ludeni Zacher (Acari: Tetranychidae) is an invasive species which is native to Europe but is now cosmopolitan. Here, we examined the effects of age and density on dispersal in mated females. Our results show that older females that are capable of producing more eggs within 24 h were more likely to disperse and moved longer distances than younger ones with fewer eggs. Older females spread most of their eggs out of their natal habitats and over longer distances, which reduced competition and increased offspring fitness. Females exhibited significantly increased dispersal probability and distances with an increase in population density to avoid crowding. The synchronization of dispersal and reproduction, along with the positive density-dependent dispersal strategy, may facilitate the habitat colonization and invasion speed of T. ludeni.

Linking Seed Traits and Germination Responses in Caribbean Seasonally Dry Tropical Forest Species

Understanding the relationships between seed traits and germination responses is crucial for assessing natural regeneration, particularly in threatened ecosystems like the seasonally dry tropical forest (SDTF). This study explored links between seed traits (mass, volume, moisture content, and dispersal type), germination responses (germinability, germination speed (v¯), time to 50% of germination (T50), synchrony, and photoblastism), and physical dormancy (PY) in 65 SDTF species under experimental laboratory conditions. We found that species with smaller seeds (low mass and volume) had higher v¯ and reached T50 faster than species with larger seeds. For moisture content, species with lower moisture content had higher germinability and reached the T50 faster than seeds with high moisture content. Abiotic dispersed species germinated faster and reached the T50 in fewer days. Most of the SDTF species (60%) did not present PY, and the presence of PY was associated with seeds with lower moisture content. As for photoblastism (germination sensitivity to light), we classified the species into three ecological categories: generalists (42 species, non-photoblastic), heliophytes (18 species, positive photoblastic, germination inhibited by darkness), and sciadophytes (5 species, negative photoblastic, light inhibited germination). This study intends to be a baseline for the study of seed ecophysiology in the SDTF.

The Geography of Metacommunities: Landscape Characteristics Drive Geographic Variation in the Assembly Process through Selecting Species Pool Attributes

AbstractThe nonrandom association between landscape characteristics and the dominant life history strategies observed in species pools is a typical pattern in nature. Here, we argue that these associations determine predictable changes in the relative importance of assembly mechanisms along broadscale geographic gradients (i.e., the geographic context of metacommunity dynamics). To demonstrate that, we employed simulation models in which groups of species with the same initial distribution of niche breadths and dispersal abilities interacted across a wide range of landscapes with contrasting characteristics. By assessing the traits of dominant species in the species pool in each landscape type, we determined how different landscape characteristics select for different life history strategies at the metacommunity level. We analyzed the simulated data using the same analytical approaches used in the study of empirical metacommunities to derive predictions about the causal relationships between landscape characteristics and dominant life histories in species pools, as well as their reciprocal influence on empirical inferences regarding the assembly process. We provide empirical support for these predictions by contrasting the assembly of moth metacommunities in a tropical versus a temperate mountainous landscape. Together, our model framework and empirical analyses demonstrate how the geographic context of metacommunities influences our understanding of community assembly across broadscale ecological gradients.

Incorporating ecology into gene drive modelling

Gene drive technology, in which fast-spreading engineered drive alleles are introduced into wild populations, represents a promising new tool in the fight against vector-borne diseases, agricultural pests and invasive species. Due to the risks involved, gene drives have so far only been tested in laboratory settings while their population-level behaviour is mainly studied using mathematical and computational models. The spread of a gene drive is a rapid evolutionary process that occurs over timescales similar to many ecological processes. This can potentially generate strong eco-evolutionary feedback that could profoundly affect the dynamics and outcome of a gene drive release. We, therefore, argue for the importance of incorporating ecological features into gene drive models. We describe the key ecological features that could affect gene drive behaviour, such as population structure, life-history, environmental variation and mode of selection. We review previous gene drive modelling efforts and identify areas where further research is needed. As gene drive technology approaches the level of field experimentation, it is crucial to evaluate gene drive dynamics, potential outcomes, and risks realistically by including ecological processes.

Recruitment and migration patterns reveal a key role for seed banks in the meta-population dynamics of an aquatic plant

Progressive habitat fragmentation threatens plant species with narrow habitat requirements. While local environmental conditions define population growth rates and recruitment success at the patch level, dispersal is critical for population viability at the landscape scale. Identifying the dynamics of plant meta-populations is often confounded by the uncertainty about soil-stored population compartments. We combined a landscape-scale assessment of an amphibious plant's population structure with measurements of dispersal complexity in time to track dispersal and putative shifts in functional connectivity. Using 13 microsatellite markers, we analyzed the genetic structure of extant Oenanthe aquatica populations and their soil seed banks in a kettle hole system to uncover hidden connectivity among populations in time and space. Considerable spatial genetic structure and isolation-by-distance suggest limited gene flow between sites. Spatial isolation and patch size showed minor effects on genetic diversity. Genetic similarity found among extant populations and their seed banks suggests increased local recruitment, despite some evidence of migration and recent colonization. Results indicate stepping-stone dispersal across adjacent populations. Among permanent and ephemeral demes the resulting meta-population demography could be determined by source-sink dynamics. Overall, these spatiotemporal connectivity patterns support mainland-island dynamics in our system, highlighting the importance of persistent seed banks as enduring sources of genetic diversity.

Isolation controls reestablishment mechanisms and post-drying community structure in an intermittent stream

Biota in disturbance-prone landscapes have evolved a variety of strategies to persist long term, either locally (resistance) or by regional recolonization (resilience). Habitat fragmentation and isolation can limit the availability of recolonization pathways, and thus the dynamics of post-disturbance community reestablishment. However, empirical studies on how isolation may control the mechanisms that enable community recovery remain scarce. Here, we studied a pristine intermittent stream (Chalone Creek, Pinnacles National Park, California) to understand how isolation (distance from a perennial pool) alters invertebrate community recolonization after drying. We monitored benthic invertebrate reestablishment during the rewetting phase along a ~2-km gradient of isolation, using mesh traps that selected for specific recolonization pathways (i.e., drift, flying, swimming/crawling, and vertical migration from the hyporheic). We collected daily emigration samples, surveyed the reestablished benthic community after 6 weeks, and compared assemblages across trap types and sites. We found that isolation mediated migration dynamics by delaying peak vertical migration from the hyporheic by ca. 1 day on average per 250 m of dry streambed. The relative importance of reestablishment mechanisms varied longitudinally-with more resistance strategists (up to 99.3% of encountered individuals) in the upstream reaches, and increased drift and aerial dispersers in the more fragmented habitats (up to 17.2% and 18%, respectively). Resistance strategists persisting in the hyporheic dominated overall (88.2% of individuals, ranging 52.9%-99.3% across sites), but notably most of these organisms subsequently outmigrated downstream (85.6% on average, ranging 52.1%-96% across sites). Thus, contrary to conventional wisdom, resistance strategists largely contributed to downstream resilience as well as to local community recovery. Finally, increased isolation was associated with a general decrease in benthic invertebrate diversity, and up to a 3-fold increase in the relative abundance of drought-resistant stoneflies. Our results advance the notion that understanding spatial context is key to predicting post-disturbance community dynamics. Considering the interaction between disturbance and fragmentation may help inform conservation in ecosystems that are subject to novel environmental regimes.

Co-evolution of dormancy and dispersal in spatially autocorrelated landscapes

The evolution of dispersal can be driven by spatial processes, such as landscape structure, and temporal processes, such as disturbance. Dormancy, or dispersal in time, is generally thought to evolve in response to temporal processes. In spite of broad empirical and theoretical evidence of trade-offs between dispersal and dormancy, we lack evidence that spatial structure can drive the evolution of dormancy. Here, we develop a simulation-based model of the joint evolution of dispersal and dormancy in spatially heterogeneous landscapes. We show that dormancy and dispersal are each favored under different landscape conditions, but not simultaneously under any of the conditions we tested. We further show that, when dispersal distances are short, dormancy can evolve directly in response to landscape structure. In this case, selection is primarily driven by benefits associated with avoiding kin competition. Our results are similar in both highly simplified and realistically complex landscapes.

Seed banks alter the molecular evolutionary dynamics of Bacillus subtilis

Fluctuations in the availability of resources constrain the growth and reproduction of individuals, which subsequently affects the evolution of their respective populations. Many organisms contend with such fluctuations by entering a reversible state of reduced metabolic activity, a phenomenon known as dormancy. This pool of dormant individuals (i.e. a seed bank) does not reproduce and is expected to act as an evolutionary buffer, though it is difficult to observe this effect directly over an extended evolutionary timescale. Through genetic manipulation, we analyze the molecular evolutionary dynamics of Bacillus subtilis populations in the presence and absence of a seed bank over 700 days. The ability of these bacteria to enter a dormant state increased the accumulation of genetic diversity over time and altered the trajectory of mutations, findings that were recapitulated using simulations based on a mathematical model of evolutionary dynamics. While the ability to form a seed bank did not alter the degree of negative selection, we found that it consistently altered the direction of molecular evolution across genes. Together, these results show that the ability to form a seed bank can affect the direction and rate of molecular evolution over an extended evolutionary timescale.

Ecological and Evolutionary Implications of Microbial Dispersal

Dispersal is simply defined as the movement of species across space and time. Despite this terse definition, dispersal is an essential process with direct ecological and evolutionary implications that modulate community assembly and turnover. Seminal ecological studies have shown that environmental context (e.g., local edaphic properties, resident community), dispersal timing and frequency, and species traits, collectively account for patterns of species distribution resulting in either their persistence or unsuccessful establishment within local communities. Despite the key importance of this process, relatively little is known about how dispersal operates in microbiomes across divergent systems and community types. Here, we discuss parallels of macro- and micro-organismal ecology with a focus on idiosyncrasies that may lead to novel mechanisms by which dispersal affects the structure and function of microbiomes. Within the context of ecological implications, we revise the importance of short- and long-distance microbial dispersal through active and passive mechanisms, species traits, and community coalescence, and how these align with recent advances in metacommunity theory. Conversely, we enumerate how microbial dispersal can affect diversification rates of species by promoting gene influxes within local communities and/or shifting genes and allele frequencies via migration or de novo changes (e.g., horizontal gene transfer). Finally, we synthesize how observed microbial assemblages are the dynamic outcome of both successful and unsuccessful dispersal events of taxa and discuss these concepts in line with the literature, thus enabling a richer appreciation of this process in microbiome research.

Early Development Drives Variation in Amphibian Vulnerability to Global Change

Understanding how natural selection determines species’ life histories can reveal their resilience or sensitivity to anthropogenic changes. For example, the safe harbor hypothesis posits that natural selection will favor life histories that maximize the time spent in the safest life stages; a second theoretical prediction suggests that species with complex life histories will maximize the growth potential of a life stage relative to its safety. Amphibians exhibit complex life histories, with a diversity of developmental strategies occurring across taxa. Many strategies involve the complete elimination of a particular life stage, and thus provide an excellent opportunity to evaluate the main tenets of the safe harbor hypothesis and understand the consequences of this developmental variation for conservation of threatened amphibians. We develop a general framework for understanding developmental life histories of amphibians – including the special cases of paedomorphism, direct development, and viviparity – based on the relative growth potential and safety offered by aquatic and terrestrial habitat, which we tested using a global trait database. We then compare the IUCN Red List status of species differing in developmental mode, revealing that most fully aquatic species and species with an aquatic larval stage are currently of Least Concern, despite the fact that freshwater habitats are being lost at a much faster rate compared with terrestrial ecosystems. The higher proportion of direct developing and viviparous species that are threatened can be attributed to their smaller ranges, the fact that they are more likely to be found in rainforest habitats, and their relatively slow life histories. We conclude that an amphibian’s developmental mode reflects the relative costs and benefits of different habitats, and that this could contribute to the resilience or vulnerability of amphibians to future anthropogenic change.

Philomatry in plants: why do so many species have limited seed dispersal?

Many have noted limited seed dispersal of plants in diverse environments and attempted evolutionary explanations for it. Although philopatric ("love of fatherland") is used by zoologists to describe organisms that remain near their place of origin, philomatric ("love of motherland") is proposed as more appropriate for plants because seeds develop on the maternal parent, fecundity and dispersal are maternally influenced characteristics, and the term dovetails with the mother-site hypothesis (MSH) for the evolution of restricted dispersal. Proximate reasons for philomatry include intrinsic drivers such as morphological features of diaspores and where on the maternal parent they are produced. Extrinsic drivers include local environmental conditions, surrounding vegetation, and ineffective dispersal agents. The MSH proposes that selection should favor philomatry in a population adapted to a particular habitat because offspring will likewise be adapted to that same habitat. Several studies show philomatry can mitigate distance-dependent costs of dispersing into surrounding inhospitable areas. Undispersed diaspores can eliminate energetic costs of accessory structures or biochemicals needed by dispersible diaspores, but it is unclear whether these costs are significant to the evolution of philomatry. Disadvantages of limited dispersal are inability to escape deteriorating habitat conditions, inability to colonize new habitats, and inbreeding among offspring. Heterocarpic species offset these disadvantages by producing dispersed plus undispersed diaspores. A conceptual framework is presented relating dispersal distance to the probability of seedling establishment. Future research should recognize dispersal as a covarying syndrome of multiple life history traits and focus on ecological selection agents that favor philomatry.

Seed banks alter metacommunity diversity: The interactive effects of competition, dispersal and dormancy

Dispersal and dormancy are two common strategies allowing for species persistence and the maintenance of biodiversity in variable environments. However, theory and empirical tests of spatial diversity patterns tend to examine either mechanism in isolation. Here, we developed a stochastic, spatially explicit metacommunity model incorporating seed banks with varying germination and survival rates. We found that dormancy and dispersal had interactive, nonlinear effects on the maintenance and distribution of metacommunity diversity. Seed banks promoted local diversity when seed survival was high and maintained regional diversity through interactions with dispersal. The benefits of seed banks for regional diversity were largest when dispersal was high or intermediate, depending on whether local competition was equal or stabilising. Our study shows that classic predictions for how dispersal affects metacommunity diversity can be strongly influenced by dormancy. Together, these results emphasise the need to consider both temporal and spatial processes when predicting multi-scale patterns of diversity.

Trait variation, trade-offs, and attributes may contribute to colonization and range expansion of a globally distributed weed

PREMISE

Trait variation, trade-offs, and attributes can facilitate colonization and range expansion. We explored how those trait features compare between ancestral and nonnative populations of the globally distributed weed Centaurea solstitialis.

METHODS

We measured traits related to survival, size, reproduction, and dispersal in field sampling following major environmental gradients; that of elevation in Anatolia (ancestral range) and that of precipitation in Argentina (nonnative range). We also estimated abundance.

RESULTS

We found that overall variation in traits in ancestral populations was similar to that in nonnative populations. Only one trait-seed mass-displayed greater variation in ancestral than nonnative populations; coincidentally, seed mass has been shown to track global range expansion of C. solstitialis. Traits displayed several associations, among which seed mass and number were positively related in both ranges. Many traits varied with elevation in the ancestral range, whereas none varied with precipitation in the nonnative one. Interestingly, most traits varying with elevation within the ancestral range also displayed differences in attributes between ancestral and nonnative ranges. Unexpectedly, ancestral plants were more fecund than nonnative plants, but density was greater in the nonnative than ancestral range, indicating that C. solstitialis survives at larger proportions in the nonnative than ancestral range.

CONCLUSIONS

Our results suggest that maintaining levels of trait variation in nonnative populations comparable to those in ancestral populations, avoiding trait trade-offs, and developing differences in trait attributes between ranges can play a major role in the success of many weeds in novel environments.

Drought effects on invertebrate metapopulation dynamics and quasi-extinction risk in an intermittent river network

Ecological communities can remain stable in the face of disturbance if their constituent species have different resistance and resilience strategies. In turn, local stability scales up regionally if heterogeneous landscapes maintain spatial asynchrony across discrete populations-but not if large-scale stressors synchronize environmental conditions and biological responses. Here, we hypothesized that droughts could drastically decrease the stability of invertebrate metapopulations both by filtering out poorly adapted species locally, and by synchronizing their dynamics across a river network. We tested this hypothesis via multivariate autoregressive state-space (MARSS) models on spatially replicated, long-term data describing aquatic invertebrate communities and hydrological conditions in a set of temperate, lowland streams subject to seasonal and supraseasonal drying events. This quantitative approach allowed us to assess the influence of local (flow magnitude) and network-scale (hydrological connectivity) drivers on invertebrate long-term trajectories, and to simulate near-future responses to a range of drought scenarios. We found that fluctuations in species abundances were heterogeneous across communities and driven by a combination of hydrological and stochastic drivers. Among metapopulations, increasing extent of dry reaches reduced the abundance of functional groups with low resistance or resilience capacities (i.e. low ability to persist in situ or recolonize from elsewhere, respectively). Our simulations revealed that metapopulation quasi-extinction risk for taxa vulnerable to drought increased exponentially as flowing habitats contracted within the river network, whereas the risk for taxa with resistance and resilience traits remained stable. Our results suggest that drought can be a synchronizing agent in riverscapes, potentially leading to regional quasi-extinction of species with lower resistance and resilience abilities. Better recognition of drought-driven synchronization may increase realism in species extinction forecasts as hydroclimatic extremes continue to intensify worldwide.

Models of Plant Resistance Deployment

Owing to their evolutionary potential, plant pathogens are able to rapidly adapt to genetically controlled plant resistance, often resulting in resistance breakdown and major epidemics in agricultural crops. Various deployment strategies have been proposed to improve resistance management. Globally, these rely on careful selection of resistance sources and their combination at various spatiotemporal scales (e.g., via gene pyramiding, crop rotations and mixtures, landscape mosaics). However, testing and optimizing these strategies using controlled experiments at large spatiotemporal scales are logistically challenging. Mathematical models provide an alternative investigative tool, and many have been developed to explore resistance deployment strategies under various contexts. This review analyzes 69 modeling studies in light of specific model structures (e.g., demographic or demogenetic, spatial or not), underlying assumptions (e.g., whether preadapted pathogens are present before resistance deployment), and evaluation criteria (e.g., resistance durability, disease control, cost-effectiveness). It highlights major research findings and discusses challenges for future modeling efforts.

DAF-16/FoxO and DAF-12/VDR control cellular plasticity both cell-autonomously and via interorgan signaling

Many cell types display the remarkable ability to alter their cellular phenotype in response to specific external or internal signals. Such phenotypic plasticity is apparent in the nematode Caenorhabditis elegans when adverse environmental conditions trigger entry into the dauer diapause stage. This entry is accompanied by structural, molecular, and functional remodeling of a number of distinct tissue types of the animal, including its nervous system. The transcription factor (TF) effectors of 3 different hormonal signaling systems, the insulin-responsive DAF-16/FoxO TF, the TGFβ-responsive DAF-3/SMAD TF, and the steroid nuclear hormone receptor, DAF-12/VDR, a homolog of the vitamin D receptor (VDR), were previously shown to be required for entering the dauer arrest stage, but their cellular and temporal focus of action for the underlying cellular remodeling processes remained incompletely understood. Through the generation of conditional alleles that allowed us to spatially and temporally control gene activity, we show here that all 3 TFs are not only required to initiate tissue remodeling upon entry into the dauer stage, as shown before, but are also continuously required to maintain the remodeled state. We show that DAF-3/SMAD is required in sensory neurons to promote and then maintain animal-wide tissue remodeling events. In contrast, DAF-16/FoxO or DAF-12/VDR act cell-autonomously to control anatomical, molecular, and behavioral remodeling events in specific cell types. Intriguingly, we also uncover non-cell autonomous function of DAF-16/FoxO and DAF-12/VDR in nervous system remodeling, indicating the presence of several insulin-dependent interorgan signaling axes. Our findings provide novel perspectives into how hormonal systems control tissue remodeling.

Range expansion, habitat use, and choosiness in a butterfly under climate change: Marginality and tolerance of oviposition site selection

Poleward range shifts under climate change involve the colonization of new sites and hence the foundation of new populations at the expanding edge. We studied oviposition site selection in a butterfly under range expansion (Lycaena dispar), a key process for the establishment of new populations. We described and compared the microhabitats used by the species for egg laying with those available across the study sites both in edge and in core populations. We carried out an ecological niche factor analysis (ENFA) to estimate (1) the variety of microhabitats used by the butterfly for egg laying (tolerance) and (2) the extent to which these selected microhabitats deviated from those available (marginality). Microhabitat availability was similar in edge and core populations. Ambient temperature recorded at the site level above the vegetation was on average lower at core populations. In contrast with what is often assumed, edge populations did not have narrower microhabitat use compared to core populations. Females in edge populations even showed a higher degree of generalism: They laid eggs under a wider range of microhabitats. We suggest that this pattern could be related to an overrepresentation of fast deciding personalities in edge populations. We also showed that the thermal time window for active female behavior was reduced in edge populations, which could significantly decrease the time budget for oviposition and decrease the threshold of acceptance during microhabitat selection for oviposition in recently established populations.

Ecological, (epi)genetic and physiological aspects of bet-hedging in angiosperms

KEY MESSAGE

Bet-hedging is a complex evolutionary strategy involving morphological, eco-physiological, (epi)genetic and population dynamics aspects. We review these aspects in flowering plants and propose further research needed for this topic. Bet-hedging is an evolutionary strategy that reduces the temporal variance in fitness at the expense of a lowered arithmetic mean fitness. It has evolved in organisms subjected to variable cues from the external environment, be they abiotic or biotic stresses such as irregular rainfall or predation. In flowering plants, bet-hedging is exhibited by hundreds of species and is mainly exerted by reproductive organs, in particular seeds but also embryos and fruits. The main example of bet-hedging in angiosperms is diaspore heteromorphism in which the same individual produces different seed/fruit morphs in terms of morphology, dormancy, eco-physiology and/or tolerance to biotic and abiotic stresses in order to 'hedge its bets' in unpredictable environments. The objective of this review is to provide a comprehensive overview of the ecological, genetic, epigenetic and physiological aspects involved in shaping bet-hedging strategies, and how these can affect population dynamics. We identify several open research questions about bet-hedging strategies in plants: 1) understanding ecological trade-offs among different traits; 2) producing more comprehensive phylogenetic analyses to understand the diffusion and evolutionary implications of this strategy; 3) clarifying epigenetic mechanisms related to bet-hedging and plant responses to environmental cues; and 4) applying multi-omics approaches to study bet-hedging at different levels of detail. Clarifying those aspects of bet-hedging will deepen our understanding of this fascinating evolutionary strategy.

Selection against immigrants in wild seabird populations

Immigration is a major demographic parameter shaping population dynamics and is an important driver of eco-evolutionary patterns, but the fitness consequences for individuals following their settlement to a new population (immigrants) remain poorly tested in wild animal populations, particularly among long-lived species. Here we show that immigrants have a lower fitness than residents in three wild seabird populations (wandering albatross Diomedea exulans, southern fulmar Fulmarus glacialoides, snow petrel Pagodroma nivea). Across all species and during a 32-year period, immigrants made on average -9 to 29% fewer breeding attempts, had 5-31% fewer fledglings, had 2-16% lower breeding success and produced 6-46% fewer recruits. Female immigration and male residency were also favored through differences in breeding performance. We provide evidence for selection against immigrants in wild populations of long-lived species and our results are consistent with female-biased dispersal in birds being driven by asymmetric limiting resources and the competitive ability of dispersers vs. non-dispersers.

Classifying Streamflow Duration: The Scientific Basis and an Operational Framework for Method Development

Streamflow duration is used to differentiate reaches into discrete classes (e.g., perennial, intermittent, and ephemeral) for water resource management. Because the depiction of the extent and flow duration of streams via existing maps, remote sensing, and gauging is constrained, field-based tools are needed for use by practitioners and to validate hydrography and modeling advances. Streamflow Duration Assessment Methods (SDAMs) are rapid, reach-scale indices or models that use physical and biological indicators to predict flow duration class. We review the scientific basis for indicators and present conceptual and operational frameworks for SDAM development. Indicators can be responses to or controls of flow duration. Aquatic and terrestrial responses can be integrated into SDAMs, reflecting concurrent increases and decreases along the flow duration gradient. The conceptual framework for data-driven SDAM development shows interrelationships among the key components: study reaches, hydrologic data, and indicators. We present a generalized operational framework for SDAM development that integrates the data-driven components through five process steps: preparation, data collection, data analysis, evaluation, and implementation. We highlight priorities for the advancement of SDAMs, including expansion of gauging of nonperennial reaches, use of citizen science data, adjusting for stressor gradients, and statistical and monitoring advances to improve indicator effectiveness.

Trade-off between seed dispersal in space and time

Seed movement and delayed germination have long been thought to represent alternative risk-spreading strategies, but current evidence covers limited scales and yields mixed results. Here we present the first global-scale test of a negative correlation between dispersal and dormancy. The result demonstrates a strong and consistent pattern that species with dormant seeds have reduced spatial dispersal, also in the context of life-history traits such as seed mass and plant lifespan. Long-lived species are more likely to have large, non-dormant seeds that are dispersed far. Our findings provide robust support for the theoretical prediction of a dispersal trade-off between space and time, implying that a joint consideration of risk-spreading strategies is imperative in studying plant life-history evolution. The bet-hedging patterns in the dispersal-dormancy correlation and the associated reproductive traits have implications for biodiversity conservation, via prediction of which plant groups would be most impacted in the changing era.

A Metacommunity Approach to Improve Biological Assessments in Highly Dynamic Freshwater Ecosystems

Rapid shifts in biotic communities due to environmental variability challenge the detection of anthropogenic impacts by current biomonitoring programs. Metacommunity ecology has the potential to inform such programs, because it combines dispersal processes with niche-based approaches and recognizes variability in community composition. Using intermittent rivers-prevalent and highly dynamic ecosystems that sometimes dry-we develop a conceptual model to illustrate how dispersal limitation and flow intermittence influence the performance of biological indices. We produce a methodological framework integrating physical- and organismal-based dispersal measurements into predictive modeling, to inform development of dynamic ecological quality assessments. Such metacommunity-based approaches could be extended to other ecosystems and are required to underpin our capacity to monitor and protect ecosystems threatened under future environmental changes.

Variation in morphological traits affects dispersal and seedling emergence in dispersive diaspores of Geropogon hybridus

PREMISE

Intraspecific variation in diaspore characteristics could affect various aspects of plant performance at the population, individual plant, and seed levels. We quantified variation in dispersal traits in a wind-dispersed annual, Geropogon hybridus (Asteraceae), focusing on continuous morphological traits of dispersive diaspores and their relationships to dispersal ability and seedling emergence.

METHODS

We measured the morphological traits, terminal velocity, and seedling emergence of 1140 seeds from 10 populations in two successive years. We assessed the variation in traits among three hierarchical levels of organization and between years, and quantified their effects on diaspore terminal velocity and seedling emergence.

RESULTS

Diaspore morphological traits varied substantially at the population, plant, and diaspore levels. Variables of pappus geometry, especially pappus width and pappus opening angle, were consistent between years and were found to be the best predictors of diaspore terminal velocity and seedling emergence. There was a significant negative relationship between diaspore terminal velocity and seedling emergence.

CONCLUSIONS

The intraspecific variation in diaspore traits is sufficiently large to substantially allow a dispersal-dormancy trade-off of individual diaspores. Our results support the hypothesis that traits of dispersive diaspores evolve in concert to select for increased dispersal potential, and provide an avenue to predict plant offspring performance through simply measured traits.

Optimal germination timing in unpredictable environments: the importance of dormancy for both among- and within-season variation

For organisms living in unpredictable environments, timing important life‐history events is challenging. One way to deal with uncertainty is to spread the emergence of offspring across multiple years via dormancy. However, timing of emergence is not only important among years, but also within each growing season. Here, we study the evolutionary interactions between germination strategies that deal with among‐ and within‐season uncertainty. We use a modelling approach that considers among‐season dormancy and within‐season germination phenology of annual plants as potentially independent traits and study their separate and joint evolution in a variable environment. We find that higher among‐season dormancy selects for earlier germination within the growing season. Furthermore, our results indicate that more unpredictable natural environments can counter‐intuitively select for less risk‐spreading within the season. Furthermore, strong priority effects select for earlier within‐season germination phenology which in turn increases the need for bet hedging through among‐season dormancy.

The role of seed appendage in improving the adaptation of a species in definite seasons: a case study of Atriplex centralasiatica

BACKGROUND

As a common accompanying dispersal structure, specialized seed appendages play a critical role in the successful germination and dispersal of many plants, and are regarded as an adaptation character for plants survival in diverse environments. However, little is known about how the appendages modulate the linkage between germination and environmental factors. Here, we tested the responses of germination to seasonal environmental signals (temperature and humidity) via seed appendages using Atriplex centralasiatica, which is widely distributed in salt marshlands with dry-cold winter in northern China. Three types of heteromorphic diaspores that differ in morphology of persistent bracteole and dormancy levels are produced in an individual plant of A. centralasiatica.

RESULTS

Except for the nondormant diaspore (type A, with a brown seed enclosed in a persistent bracteole), bracteoles regulated inner seed dormancy of the other two dormant diaspore types, i.e., type B (flat diaspore with a black inner seed) and type C (globular diaspore with a black inner seed). For types B and C, germination of bracteole-free seeds was higher than that of intact diaspores, and was limited severely when incubated in the bracteole-soaking solution. Dormancy was released at a low temperature (< 10 °C) and suitable humidity (5-15%) condition. Oppositely, high temperature and unfit humidity induced secondary dormancy via inhibitors released by bracteoles. Type C with deeper dormancy needed more stringent conditions for dormancy release and was easier for dormancy inducement than type B. The germination windows were broadened and the time needed for dormancy release decreased after the bracteole flushing for the two dormant types in the field condition.

CONCLUSIONS

Bracteoles determine the germination adaptation by bridging seeds and environmental signals and promising seedlings establishment only in proper seasons, which may also restrict species geographical distribution and shift species distributing ranges under the global climate change scenarios.

Facing Adversity: Dormant Embryos in Rotifers

An in-depth look at the basic aspects of dormancy in cyclic parthenogenetic organisms is now possible thanks to research efforts conducted over the past two decades with rotifer dormant embryos. In this review, we assemble and compose the current knowledge on four central themes: (1) distribution of dormancy in animals, with an overview on the phylogenetic distribution of embryo dormancy in metazoans, and (2) physiological and cellular processes involved in dormancy, with a strong emphasis on the dormant embryos of cyclically parthenogenetic monogonont rotifers; and discussions of (3) the selective pressures and (4) the evolutionary and population implications of dormancy in these animals. Dormancy in metazoans is a widespread phenomenon with taxon-specific features, and rotifers are among the animals in which dormancy is an intrinsic feature of their life cycle. Our review shows that embryo dormancy in rotifers shares common functional pathways with other taxa at the molecular and cellular level, despite the independent evolution of dormancy across phyla. These pathways include the arrest of similar metabolic routes and the usage of common metabolites for the stabilization of cellular structures and to confer stress resistance. We conclude that specific features of recurrent harsh environmental conditions are a powerful selective pressure for the fine-tuning of dormancy patterns in rotifers. We hypothesize that similar mechanisms at the organism level will lead to similar adaptive consequences at the population level across taxa, among which the formation of egg banks, the coexistence of species, and the possibility of differentiation among populations and local adaptation stand out. Our review shows how studies of rotifers have contributed to improved knowledge of all of these aspects.

Long-term clipping causes carbohydrate accumulation and induced transition of Alhagi sparsifolia from herbs to shrubs

A field experiment was conducted on Alhagi sparsifolia Shap. with a long-term clipping history (5-8 years) to investigate the adaptation strategy of A. sparsifolia to long-term clipping. The present study found that long-term clipping can reduce self-shading and increase the photosynthesis rate (Pn) in May. During the whole growth season, clipped plants can maintain a high Pn with less variation, which we denote as a 'stable photosynthesis strategy'. Although Pn in unclipped plants was higher than in the long-term clipping treatment in August, clipped plants accumulated more carbohydrates in shoots. The enhanced amount of carbohydrates could be correlated with the greater amount of lignin synthesis in stems. Therefore, long-term clipping induced the transition of A. sparsifolia from herbs to shrubs. After long-term clipping, plants allocated more resources to plant defence against stress, whereas the ratio of resources allocated to leaf growth decreased. Consequently, photosynthesis in long-term clipped plants decreased in August. In PSII, the energy used for both photochemical quenching and non-photochemical quenching decreased in the clipped plants during the early stage of the growth season. In addition, due to the lower stomatal conductance (gs), clipped plants retained more water in their leaves and suffered less water stress. Thus, clipped plants produced less reactive oxygen species (ROS), which in turn, delayed leaf senescence. Plants also exhibited over-compensatory growth after long-term clipping, but this phenomenon was not caused by the increase in specific leaf area (SLA). The stable photosynthesis strategy helped to extend the lifespan of plants in the growth season and improve their adaptation to light, temperature, and water stress.

Abandoning the ship using sex, dispersal or dormancy: multiple escape routes from challenging conditions

Natural populations often experience environments that vary across space and over time, leading to spatio-temporal variation of the fitness of a genotype. If local conditions are poor, organisms can disperse in space (physical movement) or time (dormancy, diapause). Facultatively sexual organisms can switch between asexual and sexual reproduction, and thus have a third option available to deal with maladaptedness: they can engage in sexual reproduction in unfavourable conditions (an 'abandon-ship' response). Sexual reproduction in facultatively sexual organisms is often coupled with dispersal and/or dormancy, while bet-hedging theory at first sight predicts sex, dispersal and dormancy to covary negatively, as they represent different escape mechanisms that could substitute for each other. Here we briefly review the observed links between sex, dormancy and dispersal, and model the expected covariation patterns of dispersal, dormancy and the reproductive mode in the context of local adaptation to spatio-temporally fluctuating environments. The correlations between sex, dormancy and dispersal evolve differently within species versus across species. Various risk-spreading strategies are not completely interchangeable, as each has dynamic consequences that can feed back into the profitability of others. Our results shed light on the discrepancy between previous theoretical predictions on covarying risk-spreading traits and help explain why sex often associates with other means of escaping unfavourable situations.This article is part of the theme issue 'Linking local adaptation with the evolution of sex differences'.

Dispersal biophysics and adaptive significance of dimorphic diaspores in the annual Aethionema arabicum (Brassicaceae)

Heteromorphic diaspores (fruits and seeds) are an adaptive bet-hedging strategy to cope with spatiotemporally variable environments, particularly fluctuations in favourable temperatures and unpredictable precipitation regimes in arid climates. We conducted comparative analyses of the biophysical and ecophysiological properties of the two distinct diaspores (mucilaginous seed (M⁺ ) vs indehiscent (IND) fruit) in the dimorphic annual Aethionema arabicum (Brassicaceae), linking fruit biomechanics, dispersal aerodynamics, pericarp-imposed dormancy, diaspore abscisic acid (ABA) concentration, and phenotypic plasticity of dimorphic diaspore production to its natural habitat and climate. Two very contrasting dispersal mechanisms of the A. arabicum dimorphic diaspores were revealed. Dehiscence of large fruits leads to the release of M⁺ seed diaspores, which adhere to substrata via seed coat mucilage, thereby preventing dispersal (antitelechory). IND fruit diaspores (containing nonmucilaginous seeds) disperse by wind or water currents, promoting dispersal (telechory) over a longer range. The pericarp properties confer enhanced dispersal ability and degree of dormancy on the IND fruit morph to support telechory, while the M⁺ seed morph supports antitelechory. Combined with the phenotypic plasticity to produce more IND fruit diaspores in colder temperatures, this constitutes a bet-hedging survival strategy to magnify the prevalence in response to selection pressures acting over hilly terrain.

Evidence for dispersal syndromes in freshwater fishes

Dispersal is a fundamental process defining the distribution of organisms and has long been a topic of inquiry in ecology and evolution. Emerging research points to an interdependency of dispersal with a diverse suite of traits in terrestrial organisms, however the extent to which such dispersal syndromes exist in freshwater species remains uncertain. Here, we test whether dispersal in freshwater fishes (1) is a fixed property of species, and (2) correlates with life-history, morphological, ecological and behavioural traits, using a global dataset of dispersal distances collected from the literature encompassing 116 riverine species and 196 locations. Our meta-analysis revealed a high degree of repeatability and heritability in the dispersal estimates and strong associations with traits related to life-history strategies, energy allocation to reproduction, ecological specialization and swimming skills. Together, these results demonstrate that similar to terrestrial organisms, the multi-dimensional nature of dispersal syndromes in freshwater species offer opportunities for the development of a unifying paradigm of movement ecology that transcend taxonomic and biogeographical realms. The high explanatory power of the models also suggests that trait-based and phylogenetic approaches hold considerable promises to inform conservation efforts in a rapidly changing world.

Mosaics, mixtures, rotations or pyramiding: What is the optimal strategy to deploy major gene resistance?

Once deployed uniformly in the field, genetically controlled plant resistance is often quickly overcome by pathogens, resulting in dramatic losses. Several strategies have been proposed to constrain the evolutionary potential of pathogens and thus increase resistance durability. These strategies can be classified into four categories, depending on whether resistance sources are varied across time (rotations) or combined in space in the same cultivar (pyramiding), in different cultivars within a field (cultivar mixtures) or among fields (mosaics). Despite their potential to differentially affect both pathogen epidemiology and evolution, to date the four categories of deployment strategies have never been directly compared together within a single theoretical or experimental framework, with regard to efficiency (ability to reduce disease impact) and durability (ability to limit pathogen evolution and delay resistance breakdown). Here, we used a spatially explicit stochastic demogenetic model, implemented in the R package landsepi, to assess the epidemiological and evolutionary outcomes of these deployment strategies when two major resistance genes are present. We varied parameters related to pathogen evolutionary potential (mutation probability and associated fitness costs) and landscape organization (mostly the relative proportion of each cultivar in the landscape and levels of spatial or temporal aggregation). Our results, broadly focused on qualitative resistance to rust fungi of cereal crops, show that evolutionary and epidemiological control are not necessarily correlated and that no deployment strategy is universally optimal. Pyramiding two major genes offered the highest durability, but at high mutation probabilities, mosaics, mixtures and rotations can perform better in delaying the establishment of a universally infective superpathogen. All strategies offered the same short-term epidemiological control, whereas rotations provided the best long-term option, after all sources of resistance had broken down. This study also highlights the significant impact of landscape organization and pathogen evolutionary ability in considering the optimal design of a deployment strategy.

Host-parasite coevolution can promote the evolution of seed banking as a bet-hedging strategy

Seed (egg) banking is a common bet-hedging strategy maximizing the fitness of organisms facing environmental unpredictability by the delayed emergence of offspring. Yet, this condition often requires fast and drastic stochastic shifts between good and bad years. We hypothesize that the host seed banking strategy can evolve in response to coevolution with parasites because the coevolutionary cycles promote a gradually changing environment over longer times than seed persistence. We study the evolution of host germination fraction as a quantitative trait using both pairwise competition and multiple mutant competition methods, while the germination locus can be genetically linked or unlinked with the host locus under coevolution. In a gene-for-gene model of coevolution, hosts evolve a seed bank strategy under unstable coevolutionary cycles promoted by moderate to high costs of resistance or strong disease severity. Moreover, when assuming genetic linkage between coevolving and germination loci, the resistant genotype always evolves seed banking in contrast to susceptible hosts. Under a matching-allele interaction, both hosts' genotypes exhibit the same seed banking strategy irrespective of the genetic linkage between loci. We suggest host-parasite coevolution as an additional hypothesis for the evolution of seed banking as a temporal bet-hedging strategy.

Environmental Adaptations, Ecological Filtering, and Dispersal Central to Insect Invasions

Insect invasions, the establishment and spread of nonnative insects in new regions, can have extensive economic and environmental consequences. Increased global connectivity accelerates rates of introductions, while climate change may decrease the barriers to invader species' spread. We follow an individual-level insect- and arachnid-centered perspective to assess how the process of invasion is influenced by phenotypic heterogeneity associated with dispersal and stress resistance, and their coupling, across the multiple steps of the invasion process. We also provide an overview and synthesis on the importance of environmental filters during the entire invasion process for the facilitation or inhibition of invasive insect population spread. Finally, we highlight important research gaps and the relevance and applicability of ongoing natural range expansions in the context of climate change to gain essential mechanistic insights into insect invasions.

Evolution with a seed bank: The population genetic consequences of microbial dormancy

Dormancy is a bet‐hedging strategy that allows organisms to persist through conditions that are suboptimal for growth and reproduction by entering a reversible state of reduced metabolic activity. Dormancy allows a population to maintain a reservoir of genetic and phenotypic diversity (i.e., a seed bank) that can contribute to the long‐term survival of a population. This strategy can be potentially adaptive and has long been of interest to ecologists and evolutionary biologists. However, comparatively little is known about how dormancy influences the fundamental evolutionary forces of genetic drift, mutation, selection, recombination, and gene flow. Here, we investigate how seed banks affect the processes underpinning evolution by reviewing existing theory, implementing novel simulations, and determining how and when dormancy can influence evolution as a population genetic process. We extend our analysis to examine how seed banks can alter macroevolutionary processes, including rates of speciation and extinction. Through the lens of population genetic theory, we can understand the extent that seed banks influence the evolutionary dynamics of microorganisms as well as other taxa.

The Coevolution of Life and Environment on Mars: An Ecosystem Perspective on the Robotic Exploration of Biosignatures

Earth's biological and environmental evolution are intertwined and inseparable. This coevolution has become a fundamental concept in astrobiology and is key to the search for life beyond our planet. In the case of Mars, whether a coevolution took place is unknown, but analyzing the factors at play shows the uniqueness of each planetary experiment regardless of similarities. Early Earth and early Mars shared traits. However, biological processes on Mars, if any, would have had to proceed within the distinctive context of an irreversible atmospheric collapse, greater climate variability, and specific planetary characteristics. In that, Mars is an important test bed for comparing the effects of a unique set of spatiotemporal changes on an Earth-like, yet different, planet. Many questions remain unanswered about Mars' early environment. Nevertheless, existing data sets provide a foundation for an intellectual framework where notional coevolution models can be explored. In this framework, the focus is shifted from planetary-scale habitability to the prospect of habitats, microbial ecotones, pathways to biological dispersal, biomass repositories, and their meaning for exploration. Critically, as we search for biosignatures, this focus demonstrates the importance of starting to think of early Mars as a biosphere and vigorously integrating an ecosystem approach to landing site selection and exploration. Key Words: Astrobiology-Biosignatures-Coevolution of Earth and life-Mars. Astrobiology 18, 1-27.

Life-history strategy, resource dispersion and phylogenetic associations shape dispersal of a fig wasp community

BACKGROUND

The combined influence of life-history strategy and resource dispersion on dispersal evolution of a biological community, and by extension, on community assemblage, has received sparse attention. Highly specialized fig wasp communities are ideal for addressing this question since the life-history strategies that affect their pace of life and the dispersion of their oviposition resources vary. We compared dispersal capacities of the wasp community of a widespread tropical fig, Ficus racemosa, by measuring flight durations, somatic lipid content and resting metabolic rates.

RESULTS

Wasp species exhibiting greater flight durations had higher energy reserves and resting metabolic rates. "Fast"-paced species showed higher dispersal capacities reflecting requirements for rapid resource location within short adult lifespans. Longer-lived "slow"-paced species exhibited lower dispersal capacities. Most dispersal traits were negatively related with resource dispersion while their variances were positively related with this variable, suggesting that resource dispersion selects for dispersal capacity. Dispersal traits exhibited a phylogenetic signal.

CONCLUSIONS

Using a combination of phylogeny, trait functionality and community features, we explain how dispersal traits may have co-evolved with life-history strategies in fig wasps and influenced a predisposition for dispersal. We speculate how processes influencing dispersal trait expression of community members may affect resource occupancy and community assemblage.

Between semelparity and iteroparity: Empirical evidence for a continuum of modes of parity

The number of times an organism reproduces (i.e., its mode of parity) is a fundamental life-history character, and evolutionary and ecological models that compare the relative fitnesses of different modes of parity are common in life-history theory and theoretical biology. Despite the success of mathematical models designed to compare intrinsic rates of increase (i.e., density-independent growth rates) between annual-semelparous and perennial-iteroparous reproductive schedules, there is widespread evidence that variation in reproductive allocation among semelparous and iteroparous organisms alike is continuous. This study reviews the ecological and molecular evidence for the continuity and plasticity of modes of parity-that is, the idea that annual-semelparous and perennial-iteroparous life histories are better understood as endpoints along a continuum of possible strategies. I conclude that parity should be understood as a continuum of different modes of parity, which differ by the degree to which they disperse or concentrate reproductive effort in time. I further argue that there are three main implications of this conclusion: (1) that seasonality should not be conflated with parity; (2) that mathematical models purporting to explain the general evolution of semelparous life histories from iteroparous ones (or vice versa) should not assume that organisms can only display either an annual-semelparous life history or a perennial-iteroparous one; and (3) that evolutionary ecologists should base explanations of how different life-history strategies evolve on the physiological or molecular basis of traits underlying different modes of parity.

Comparative Analyses of Phenotypic Trait Covariation within and among Populations

Many morphological, behavioral, physiological, and life-history traits covary across the biological scales of individuals, populations, and species. However, the processes that cause traits to covary also change over these scales, challenging our ability to use patterns of trait covariance to infer process. Trait relationships are also widely assumed to have generic functional relationships with similar evolutionary potentials, and even though many different trait relationships are now identified, there is little appreciation that these may influence trait covariation and evolution in unique ways. We use a trait-performance-fitness framework to classify and organize trait relationships into three general classes, address which ones more likely generate trait covariation among individuals in a population, and review how selection shapes phenotypic covariation. We generate predictions about how trait covariance changes within and among populations as a result of trait relationships and in response to selection and consider how these can be tested with comparative data. Careful comparisons of covariation patterns can narrow the set of hypothesized processes that cause trait covariation when the form of the trait relationship and how it responds to selection yield clear predictions about patterns of trait covariation. We discuss the opportunities and limitations of comparative approaches to evaluate hypotheses about the evolutionary causes and consequences of trait covariation and highlight the importance of evaluating patterns within populations replicated in the same and in different selective environments. Explicit hypotheses about trait relationships are key to generating effective predictions about phenotype and its evolution using covariance data.

Impact of temperature shifts on the joint evolution of seed dormancy and size

Seed dormancy and size are two important life-history traits that interplay as adaptation to varying environmental settings. As evolution of both traits involves correlated selective pressures, it is of interest to comparatively investigate the evolution of the two traits jointly as well as independently. We explore evolutionary trajectories of seed dormancy and size using adaptive dynamics in scenarios of deterministic or stochastic temperature variations. Ecological dynamics usually result in unbalanced population structures, and temperature shifts or fluctuations of high magnitude give rise to more balanced ecological structures. When only seed dormancy evolves, it is counter-selected and temperature shifts hasten this evolution. Evolution of seed size results in the fixation of a given strategy and evolved seed size decreases when seed dormancy is lowered. When coevolution is allowed, evolutionary variations are reduced while the speed of evolution becomes faster given temperature shifts. Such coevolution scenarios systematically result in reduced seed dormancy and size and similar unbalanced population structures. We discuss how this may be linked to the system stability. Dormancy is counter-selected because population dynamics lead to stable equilibrium, while small seeds are selected as the outcome of size-number trade-offs. Our results suggest that unlike random temperature variation between generations, temperature shifts with high magnitude can considerably alter population structures and accelerate life-history evolution. This study increases our understanding of plant evolution and persistence in the context of climate changes.