Spatial and Temporal Variation in the Antagonistic and Mutualistic Interactions among Seed Predator Arthropods, Seed-Dispersing Birds, and the Spanish Juniper.

Plants interact with both antagonistic and mutualistic animals during reproduction, with the outcomes of these interactions significantly influencing plant reproductive success, population dynamics, and the evolution of plant traits. Here, we investigated the spatial and temporal variations in the interactions between Juniperus thurifera, its seed-dispersing birds, and three specific arthropod species that attack the fleshy cones during the predispersal period. We assessed how plant traits affect levels of cone damage by arthropods and seed dispersal by birds, the occurrence of competition among arthropod species, and the impact of seed predators on the activity of frugivores. Plant traits, cone damage by arthropods, and seed dispersal by birds showed spatiotemporal variability. Fluctuation in cone abundance was the leading factor determining damage by arthropods and bird dispersal with a secondary role of cone traits. Large crops satiated predispersal seed predators, although the amount of frugivory did not increase significantly, suggesting a potential satiation of bird dispersers. Crop size and cone traits at individual trees determined preferences by seed predator species and the foraging activity of bird dispersers. Competition among arthropods increased during years of low cone production, and seed predators sometimes negatively affected bird frugivory. High supra-annual variations in cone production appear to be a key evolutionary mechanism enhancing J. thurifera reproductive success. This strategy reduces the impact of specialized seed predators during years of high seed production, despite the potential drawback of satiating seed dispersers.

Evolutionary trajectory of phenological escape in a flowering plant: Mechanistic insights from bidirectional avoidance of butterfly egg-laying pressure.

Phenological escape, whereby species alter the timing of life-history events to avoid seasonal antagonists, is usually analyzed either as a potential evolutionary outcome given current selection coefficients, or as a realized outcome in response to known enemies. We here gain mechanistic insights into the evolutionary trajectory of phenological escape in the brassicaceous herb Cardamine pratensis, by comparing the flowering schedules of two sympatric ecotypes in different stages of a disruptive response to egg-laying pressure imposed by the pierid butterfly Anthocharis cardamines, whose larvae are pre-dispersal seed predators (reducing realized fecundity by ~70%). When the focal point of highest intensity selection (peak egg-laying) occurs early in the flowering schedule, selection for late flowering dependent on reduced egg-laying combined with selection for early flowering dependent on reduced predator survival results in a symmetrical bimodal flowering curve; when the focal point occurs late, an asymmetrical flowering curve results with a large early flowering mode due to selection for reduced egg-laying augmented by selection for infested plants to outrun larval development and dehisce prior to seed-pod consumption. Unequal selection pressures on high and low fecundity ramets, due to asynchronous flowering and morphologically targeted (size-dependent) egg-laying, constrain phenological escape, with bimodal flowering evolving primarily in response to disruptive selection on high fecundity phenotypes. These results emphasize the importance of analyzing variation in selection coefficients among morphological phenotypes over the entire flowering schedule to predict how populations will evolve in response to altered phenologies resulting from climate change.

Costs and benefits of masting: economies of scale are not reduced by negative density-dependence in seedling survival in Sorbus aucuparia.

Masting is a widespread reproductive strategy in plants that helps to reduce seed predation and increase pollination. However, masting can involve costs, notably negative density-dependent (NDD) seedling survival caused by concentrating reproduction in intermittent events. Masting benefits have received widespread attention, but the costs are understudied, which precludes understanding why some plant species have evolved intense masting, while others reproduce regularly. We followed seed production, seed predation (both 13 yr), and seedling recruitment and survival (11 yr) in Sorbus aucuparia. We tested whether NDD in seedling survival after mast years can reduce the benefits of pulsed reproduction that come through predator satiation. Seed predation rates were extreme in our population (mean = 75%), but were reduced by masting. The commonly accepted, but untested, assertion that pulsed recruitment is associated with strong NDD was unsupported. Consequently, the proportion of seedlings that survived their first year increased with fruit production. This provides a rare test of economies of scale beyond the seed stage. Our results provide estimation of the costs of mast seeding, and indicate that these may be lower than expected. Low masting costs, if common, may help explain why masting is such a widespread reproductive strategy throughout the plant kingdom.

Inconsistent annual compensation for floral herbivory by an iterocarpic thistle.

PREMISE: Plants experiencing steep reproductive losses from herbivores should favor strategies promoting tolerance or resistance to that herbivory. However, the degree to which such strategies succeed in improving plant fitness under natural conditions needs further evaluation, especially for iterocarpic species. We tested whether reproductive effort by the iterocarpic Cirsium undulatum Spreng. (Wavyleaf thistle) provided within-season tolerance for floral herbivory through response to apical damage. METHODS: We imposed apical damage and manipulated floral herbivory on later-flowering, non-apical flowerheads for two seasons. We asked: (1) is there evidence of compensatory potential to tolerate apical flowerhead damage? If so, (2) does the amount of herbivore pressure on non-apical flowerheads influence the magnitude of any compensatory response; and (3) is the response to apical damage sufficient to increase plant seed production under ambient floral herbivory over the flowering season? RESULTS: Plants showed compensatory potential for apical head loss; apical damage increased seed contributions from later, lower positioned flowerheads. Further, the intensity of subsequent herbivore pressure influenced compensation outcomes. Equitable seed production under both levels of ambient herbivory occurred only in the year in which plants were larger and insect pressure was lower. Finally, the response to apical damage was sufficient to compensate for apical seed loss, but it did not consistently increase overall annual seed production under ambient floral herbivory. CONCLUSIONS: Although this iterocarpic species can compensate for apical damage, tolerance for floral herbivory varied between years.

Evaluation of the Impact of Eustenopus villosus on Centaurea solstitialis Seed Production in California.

The impact of the capitulum weevil Eustenopus villosus on Centaurea solstitialis seed production was examined at two field sites in central California. The study occurred in 1993-1995 during the early phases of the biological control program on C. solstitialis and before the current guild of capitulum insects had become widespread. Results showed that adult feeding on early flower buds resulted in 60-70% of buds failing to develop. Regrowth delayed capitulum production by 9 days and extended production by 4 weeks at season end. Between 69% and 92% of capitula were punctured from feeding or oviposition but the occurrence of larvae in capitula ranged from 27% to 49%. Seed production in C. solstitialis capitula increased linearly with size. The occurrence of larvae was proportionally higher in larger capitula (>8 mm) but the probability of attack for individual capitula did not vary with plant size. Total seed loss from larval feeding ranged from 34 to 47%. It is recommended that another survey be performed to determine if the level of infestation of E. villosus has increased since its initial introduction.

Acorn Crop, Seed Size and Chemical Defenses Determine the Performance of Specialized Insect Predators and Reproductive Output in a Mediterranean Oak.

Seed predation is an antagonistic interaction that negatively affects the performance of individual plants and can limit plant population dynamics. In animal-dispersed plants, crop size is an important determinant of plant reproductive success through its effect on seed dispersers and predators. Seed traits, such as size or chemical composition, can also increase the tolerance to seed predators or reduce their performance. We investigated the interaction between Quercus faginea and two specialized pre-dispersal insect seed predators (weevils and moths) during two years of contrasting crop size to determine the consequences of oak reproductive investment on seed production and insect performance. Crop size was 44% lower and acorns were 32% smaller in the second year, although acorn predation by insects was proportionally similar between both years at the population level. Individual trees producing larger crops showed a lower incidence of insect predators during the year of abundant acorn production, whereas trees producing bigger acorns experienced higher seed predation rates by insects, and acorns held more insect larvae in the low crop year. Competition between insects increased when acorn production was low, and higher tannin content in acorns further constrained the number of weevil larvae developing together in the same acorn. However, the abundance and size of insect larvae produced per tree were similar between the two crop years, and this was due to larvae often depleting acorn reserves when resources were low. Oak reproductive output increased nearly two-fold during the large crop year. Crop size variation, acorn production in a given year and acorn size and chemical composition seem to be important traits for reducing damage by insect predators in Quercus faginea and improve oak reproductive success.

Seed predation selects for reproductive variability and synchrony in perennial plants.

Annually variable and synchronous seed production by plant populations, or masting, is a widespread reproductive strategy in long-lived plants. Masting is thought to be selectively beneficial because interannual variability and synchrony increase the fitness of plants through economies of scale that decrease the cost of reproduction per surviving offspring. Predator satiation is believed to be a key economy of scale, but whether it can drive phenotypic evolution for masting in plants has been rarely explored. We used data from seven plant species (Quercus humilis, Quercus ilex, Quercus rubra, Quercus alba, Quercus montana, Sorbus aucuparia and Pinus pinea) to determine whether predispersal seed predation selects for plant phenotypes that mast. Predation selected for interannual variability in Mediterranean oaks (Q. humilis and Q. ilex), for synchrony in Q. rubra, and for both interannual variability and reproductive synchrony in S. aucuparia and P. pinea. Predation never selected for negative temporal autocorrelation of seed production. Predation by invertebrates appears to select for only some aspects of masting, most importantly high coefficient of variation, supporting individual-level benefits of the population-level phenomenon of mast seeding. Determining the selective benefits of masting is complex because of interactions with other seed predators, which may impose contradictory selective pressures.

Asymmetric interactions of seed-predation network contribute to rare-species advantage.

Although the asymmetry of species linkage within ecological networks is now well recognized, its effect on communities has scarcely been empirically investigated. Based on theory, we predicted that an asymmetric architecture of antagonistic plant-herbivore networks would emerge at the community level and that this asymmetry would negatively affect community-common plants more than rare ones. We tested this prediction by analyzing the architectural properties of an alpine plant and pre-dispersal seed-predator network and its effect on seed loss rate of plants in the Tibetan Plateau. This network showed an asymmetric architecture, where the common plant species (with a larger aboveground biomass per area) were infested by a higher number of predator species. Moreover, they asymmetrically interacted with specialized herbivores, presumably because of greater seed resource abundance. In turn, the asymmetric interactions led to a higher proportion of seed loss in the common plants at the species level. Our results suggest that asymmetric antagonistic networks may improve species coexistence by contributing to a mechanism of rare-species advantage.

The ecology of predispersal insect herbivory on tree reproductive structures in natural forest ecosystems.

Plant-insect interactions are key model systems to assess how some species affect the distribution, the abundance, and the evolution of others. Tree reproductive structures represent a critical resource for many insect species, which can be likely drivers of demography, spatial distribution, and trait diversification of plants. In this review, we present the ecological implications of predispersal herbivory on tree reproductive structures by insects (PIHR) in forest ecosystems. Both insect's and tree's perspectives are addressed with an emphasis on how spatiotemporal variation and unpredictability in seed availability can shape such particular plant-animal interactions. Reproductive structure insects show strong trophic specialization and guild diversification. Insects evolved host selection and spatiotemporal dispersal strategies in response to variable and unpredictable abundance of reproductive structures in both space and time. If PIHR patterns have been well documented in numerous systems, evidences of the subsequent demographic and evolutionary impacts on tree populations are still constrained by time-scale challenges of experimenting on such long-lived organisms, and modeling approaches of tree dynamics rarely consider PIHR when including biotic interactions in their processes. We suggest that spatially explicit and mechanistic approaches of the interactions between individual tree fecundity and insect dynamics will clarify predictions of the demogenetic implications of PIHR in tree populations. In a global change context, further experimental and theoretical contributions to the likelihood of life-cycle disruptions between plants and their specialized herbivores, and to how these changes may generate novel dynamic patterns in each partner of the interaction are increasingly critical.

Cumulative herbivory outpaces compensation for early floral damage on a monocarpic perennial thistle.

Floral herbivory represents a major threat to plant reproductive success, driving the importance of plant tolerance mechanisms that minimize fitness costs. However, the cumulative insect herbivory plants experience under natural conditions complicates predictions about tolerance contributions to net fitness. Apical damage can lead to compensatory seed production from late season flowering that ameliorates early season fitness losses. Yet, the compensation realized depends on successful development and herbivore escape by later season flowers. Using monocarpic perennial Cirsium canescens, we quantified seed-reproductive fitness of plants with vs. without experimental damage to the early-developing large apical flower head, with and without a 30-40% herbivory reduction on subsequent flower heads, for two flowering cohorts. Plants with reduced herbivory clearly demonstrated the release of apical dominance and compensation, not overcompensation, for apical damage via greater seed maturation by later flower heads. In contrast, plants that experienced ambient herbivory levels on subsequent heads undercompensated for early apical damage. Individuals had lower total seed set when the apical head was damaged. Compensation was, therefore, possible through a small increase in total flower heads, caused by a higher rate of floral bud survival, and a higher seed maturation rate by subsequent heads, leading to more viable seeds per matured flower head. With ambient cumulative floral herbivory, compensation for apical damage was not sufficient to improve fitness. Variation in the intensity of biological interactions played a role in the success of plant tolerance as a mechanism to maximize individual fitness.

You'd better walk alone: Changes in forest composition affect pollination efficiency and pre-dispersal cone damage in Iberian Juniperus thurifera forests.

Changes in land-use patterns are a major driver of global environmental change. Cessation of traditional land-use practices has led to forest expansion and shifts in forest composition. Consequently, former monospecific forests maintained by traditional management are progressing towards mixed forests. However, knowledge is scarce on how the presence of other tree species will affect reproduction of formerly dominant species. We explored this question in the wind-pollinated tree Juniperus thurifera. We hypothesised that the presence of heterospecific trees would have a negative effect on cone production and on the proportion of cones attacked by specialised predators. We assessed the relative importance of forest composition on cone production, seed development and pre-dispersal cone damage on nine paired pure and mixed J. thurifera forests in three regions across the Iberian Peninsula. The effects of forest composition on crop size, cone and seed characteristics, as well as damage by pre-dispersal arthropods were tested using mixed models. Cone production was lower and seed abortion higher in mixed forests, suggesting higher pollination failure. In contrast, cone damage by arthropods was higher in pure forests, supporting the hypothesis that presence of non-host plants reduces damage rates. However, the response of each arthropod to forest composition was species-specific and the relative rates of cone damage varied depending on individual tree crops. Larger crop sizes in pure forests compensated for the higher cone damage rates, leading to a higher net production of sound seeds compared to mixed forests. This study indicates that ongoing changes in forest composition after land abandonment may impact tree reproduction.

Difference on cone size preferences between two coniferous species by Great Spotted Woodpecker (Dendrocopos major).

The number of species that specialize in pre-dispersal seed predation is relatively small. Examples of specialized pre-dispersal seed predators adapted to feeding on closed cones include vertebrate species like Crossbills, Squirrels, Nutcrackers and Woodpeckers. Seed predation selects against certain phenotypic features of cones and favors another phenotypic features. In this study, we document preferences of the Great Spotted Woodpecker (Dendrocopos major) for specific traits in the cones of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). We found that the Great Spotted Woodpecker prefers to feed on medium sized Norway spruce cones. The results suggest a disruptive selection that favors the extreme cone lengths in Norway spruce. In Scots pine, the woodpeckers avoided cones with large apophyses. Further, the selectivity for the specific characteristics of the cones is probably related to the configuration of the anvil, a place at which woodpeckers extract seeds from the cones. We think that the Great Spotted Woodpecker preferences in relation to the morphological characteristics of cones are a key to the design of the anvil in order to maximize the use of it as a tool for processing cones of both the Norway spruce and the Scots pine.

Effects of season and population size on pollination and reproductive output in a Mediterranean shrub.

Pollinator guilds may change throughout extended flowering periods, affecting plant reproductive output, especially in seasonal climates. We hypothesised a seasonal shift in pollinator guild and an autumn reduction in pollinator abundance, especially in small and sparse populations. We recorded pollinator identity, abundance and behaviour in relation to flower density from plant to population throughout the extended flowering of Ononis tridentata. We evaluated female reproductive output by recording pollination success and pre-dispersal seed predation in eight populations of contrasting size and density. Offspring quality was also characterised through seed weight and germination. A diverse guild of insects visited O. tridentata in spring, while only Apis mellifera was observed in autumn. Visitation frequency did not vary seasonally, but the number of flowers per foraging bout was lower, and seeds were heavier and had a higher germination rate in autumn. Plant and neighbourhood flowering display were not related to pollinator visitation frequency or behaviour. However, the rate of fertilised ovules, seed set and autumn flowering display size were positively related to population density. The maintenance of pollination in autumn enhances the reproductive performance of O. tridentata due to higher quality of autumn seed, and to a large reduction in seed predator pressure. We also suggest that observed changes in pollinator behaviour could be one of the processes behind seasonal variation in seed performance, since geitonogamous crosses were less likely to occur in autumn.

Caterpillar seed predators mediate shifts in selection on flowering phenology in their host plant.

Variation in selection among populations and years has important implications for evolutionary trajectories of populations. Yet, the agents of selection causing this variation have rarely been identified. Selection on the time of reproduction within a season in plants might differ both among populations and among years, and selection can be mediated by both mutualists and antagonists. We investigated if differences in the direction of phenotypic selection on flowering phenology among 20 populations of Gentiana pneumonanthe during 2 yr were related to the presence of the butterfly seed predator Phengaris alcon, and if butterfly incidence was associated with the abundance of the butterfly's second host, Myrmica ants. In plant populations without the butterfly, phenotypic selection favored earlier flowering. In populations where the butterfly was present, caterpillars preferentially attacked early-flowering individuals, shifting the direction of selection to favoring later flowering. Butterfly incidence in plant populations increased with ant abundance. Our results demonstrate that antagonistic interactions can shift the direction of selection on flowering phenology, and suggest that such shifts might be associated with differences in the community context.

Seed-predator satiation and Janzen-Connell effects vary with spatial scales for seed-feeding insects.

BACKGROUND AND AIMS: The Janzen-Connell model predicts that common species suffer high seed predation from specialized natural enemies as a function of distance from parent trees, and consequently as a function of conspecific density, whereas the predator satiation hypothesis predicts that seed attack is reduced due to predator satiation at high seed densities. Pre-dispersal predation by insects was studied while seeds are still on parent trees, which represents a frequently overlooked stage in which seed predation occurs. METHODS: Reproductive tree density and seed production were investigated from ten Quercus serrata populations located in south-west China, quantifying density-dependent pre-dispersal seed predation over two years by three insect groups. KEY RESULTS: Acorn infestation was nearly twice as high in the low-seed year as that in the high-seed year, with considerable spatio-temporal variation in the direction and magnitude of density-dependent pre-dispersal seed predation evident. Across whole populations of trees, a high density of reproductive trees caused predator satiation and reduced insect attack in the high-seed year. Within individual trees, and consistent with the Janzen-Connell model, overall insect seed predation was positively correlated with seed production in the low-seed year. In addition, there was variation among insect taxa, with positive density-dependent seed predation by Curculio weevils in the high-seed year and moths in the low-seed year, but apparent density independence by Cyllorhynchites weevils in both years. CONCLUSIONS: The overall trend of negative density-dependent, pre-dispersal seed predation suggests that predator satiation limited the occurrence of Janzen-Connell effects across Q. serrata populations. Such effects may have large impacts on plant population dynamics and tree diversity, depending on the extent to which they are reduced by counteracting positive density-dependent predation for seeds on individual trees and other factors affecting successful recruitment.

Contrasting effects of ploidy level on seed production in a diploid tetraploid system.

Previous studies demonstrated the effects of polyploidy on various aspects of plant life. It is, however, difficult to determine which plant characteristics are responsible for fitness differences between cytotypes. We assessed the relationship between polyploidy and seed production. To separate the effects of flowering phenology, flower head size and herbivores from other possible causes, we collected data on these characteristics in single flower heads of diploid and tetraploid Centaurea phrygia in an experimental garden. We used structural equation modelling to identify the main pathways determining seed production. The results showed that the relationship between polyploidy and seed production is mediated by most of the studied factors. The different factors acted in opposing directions. Wider flower heads displayed higher above the ground suggested higher seed production in diploids. In contrast, earlier flowering and a lower abundance of herbivores suggested higher seed production in tetraploids. However, because phenology was the strongest driver of seed production in this system, the sum of all the pathways suggested greater seed production in tetraploids than in diploids. The pathway linking ploidy level directly to seed production, representing unstudied factors, was not significant. This suggests that the factors studied likely are drivers of the between-cytotype differences. Overall, this study demonstrated that tetraploids possess overall higher fitness estimated as seed production. Regardless of the patterns observed here, strong between year fluctuations in the composition and diversity of insect communities have been observed. The direction of the selection may thus vary between years. Consequently, understanding the structure of the interactions is more important for understanding the system than the overall effects of cytotype on a fitness trait in a specific year. Such knowledge can be used to model the evolution of species traits and plant-herbivore and plant-pollinator interactions in diploid-polyploid systems.

Geographic consistency and variation in conflicting selection generated by pollinators and seed predators.

BACKGROUNDS AND AIMS: Floral traits that attract pollinators may also attract seed predators, which, in turn, may generate conflicting natural selection on such traits. Although such selection trade-offs are expected to vary geographically, few studies have investigated selection mediated by pollinators and seed predators across a geographic mosaic of environments and floral variation. METHODS: Floral traits were investigated in 14 populations of the bumble-bee-pollinated herb, Pedicularis rex, in which tubular flowers are subtended by cupular bracts holding rain water. To study potentially conflicting selection on floral traits generated by pollinators and florivores, stigmatic pollen loads, initial seed set, pre-dispersal seed predation and final viable seed production were measured in 12-14 populations in the field. KEY RESULTS: Generalized Linear Model (GLM) analyses indicated that the pollen load on stigmas was positively related to the exsertion of the corolla beyond the cupular bracts and size of the lower corolla lip, but so too was the rate of seed predation, creating conflicting selection on both floral traits. A geographic mosaic of selection mediated by seed predators, but not pollinators, was indicated by significant variation in levels of seed predation and the inclusion of two-, three- and four-way interaction terms between population and seed predation in the best model [lowest corrected Akaike Information Criterion (AICc)] explaining final seed production. CONCLUSIONS: These results indicate opposing selection in operation: pollinators generated selection for greater floral exsertion beyond the bracts, but seed predators generated selection for reduced exsertion above the protective pools of water, although the strength of the latter varied across populations.

Yucca brevifolia fruit production, predispersal seed predation, and fruit removal by rodents during two years of contrasting reproduction.

PREMISE OF THE STUDY: The distribution of Yucca brevifolia, a keystone species of the Mojave Desert, may contract with climate change, yet reproduction and dispersal are poorly understood. We tracked reproduction, seed predation, and fruit dispersal for two years and discuss whether Y. brevifolia is a masting species. METHODS: Fruit maturation, seed predation (larval yucca moths), and fruit dispersal (rodents) were monitored on a random sample of panicles during 2013 and 2014, which were years of high and low reproduction, respectively. Fates of fruits placed on the ground and in canopies were also tracked. Rodents were live-trapped to assess abundance and species composition. KEY RESULTS: In 2013, 66% of inflorescences produced fruit of which 53% escaped larval predation; 19.5% of seeds were destroyed in infested fruits. Total seed production was estimated to be >100 times greater in 2013 than 2014. One-third of the fruit crop fell to the ground and was removed by rodents over the course of 120 d. After ground fruits became scarce, rodents exploited canopy fruits. Rodent numbers were low in 2013, so fruits remained in canopies for 370 d. In 2014, fruit production was approximately 20% lower. Larvae infested the majority of fruits, and almost twice the number of seeds were damaged. Fruits were exploited by rodents within 65 d. CONCLUSIONS: High fertilization, prolific seed production, and low predispersal predation in 2013 suggests that pollinator attraction and satiation of seed predators influence masting in Y. brevifolia. Abundant, prolonged fruit availability to seed-dispersing rodents likely extends recruitment opportunities during mast years.

Efficiency of pollination and satiation of predators determine reproductive output in Iberian Juniperus thurifera woodlands.

Fruit production in animal-dispersed plants has a strong influence on fitness because large crops increase the number of seeds dispersed by frugivores. Large crops are costly, and environmental control of plant resources is likely play a role in shaping temporal and spatial variations in seed production, particularly in fluctuating environments such as the Mediterranean. The number of fruits that start to develop and the proportion of viable seeds produced are also linked to the number of flowers formed and the efficiency of pollination in wind-pollinated plants. Finally, large fruit displays also attract seed predators, having a negative effect on seed output. We assessed the relative impact of environmental conditions on fruit production, and their combined effect on seed production, abortion and seed loss through three predispersal predators in Juniperus thurifera L., sampling 14 populations across the Iberian Peninsula. Wetter than average conditions during flowering and early fruit development led to larger crop sizes; this effect was amplified at tree level, with the most productive trees during more favourable years yielding fruits with more viable seeds and less empty and aborted seeds. In addition, large crops satiated the less mobile seed predator. The other two predispersal predators responded to plant traits, the presence of other seed predators and environmental conditions, but did not show a satiation response to the current-year crop. Our large-scale study on a dioecious, wind-pollinated Mediterranean juniper indicates that pollination efficiency and satiation of seed predators, mediated by environmental conditions, are important determinants of reproductive output in this juniper species.

Separation in flowering time contributes to the maintenance of sympatric cryptic plant lineages.

Sympatric cryptic lineages are a challenge for the understanding of species coexistence and lineage diversification as well as for management, conservation, and utilization of plant genetic resources. In higher plants studies providing insights into the mechanisms creating and maintaining sympatric cryptic lineages are rare. Here, using microsatellites and chloroplast sequence data, morphometric analyses, and phenological observations, we ask whether sympatrically coexisting lineages in the common wetland plant Juncus effusus are ecologically differentiated and reproductively isolated. Our results show two genetically highly differentiated, homoploid lineages within J. effusus that are morphologically cryptic and have similar preference for soil moisture content. However, flowering time differed significantly between the lineages contributing to reproductive isolation and the maintenance of these lineages. Furthermore, the later flowering lineage suffered less from predispersal seed predation by a Coleophora moth species. Still, we detected viable and reproducing hybrids between both lineages and the earlier flowering lineage and J. conglomeratus, a coexisting close relative. Flowering time differentiation between the lineages can be explained by neutral divergence alone and together with a lack of postzygotic isolation mechanisms; the sympatric coexistence of these lineages is most likely the result of an allopatric origin with secondary contact.