Flower size and longevity influence florivory in the large-flowered shrub Cistus ladanifer

Beneath the blooms: Unearthing the effect of rhizospheric bacteria on floral signals and pollinator preferences

The relationship between plants and pollinators is known to be influenced by ecological interactions with other community members. While most research has focused on aboveground communities affecting plant-pollinator interactions, it is increasingly recognized that soil-dwelling organisms can directly or indirectly impact these interactions. Although studies have examined the effects of arbuscular mycorrhizal fungi on floral traits, there is a gap in research regarding similar effects associated with plant growth-promoting rhizobacteria (PGPR), particularly concerning floral scent. Our study aimed to investigate the influence of the PGPR Bacillus amyloliquefaciens on the floral traits of wild (Solanum habrochaites, Solanum pimpinellifolium and Solanum peruvianum) and cultivated tomato (Solanum lycopersicum), as well as the impact of microbially-driven changes in floral scent on the foraging behaviour of the stingless bee Melipona quadrifasciata. Our findings revealed that inoculating tomatoes with PGPR led to an increased number of flowers and enhanced overall floral volatile emission. Additionally, we observed higher flower biomass and pollen levels in all species, except S. peruvianum. Importantly, these changes in volatile emissions influenced the foraging behaviour of M. quadrifasciata significantly. Our results highlight the impact of beneficial soil microbes on plant-pollinator interactions, shedding light on the multiple effects that plant-microbial interactions can have on aboveground organisms.

Effects of Florivory on Floral Visitors and Reproductive Success of Sagittaria lancifolia (Alismataceae) in a Mexican Wetland

Florivores consume floral structures with negative effects on plant fitness and pollinator attraction. Several studies have evaluated these consequences in hermaphroditic plants, but little is known about the effects on monoecious and dioecious species. We characterize the florivory and its effects on floral visitors and reproductive success in a monoecious population of Sagittaria lancifolia. Five categories of florivory were established according to the petal area consumed. Visits were recorded in male and female flowers within the different damage categories. Reproductive success was evaluated through fruit number and weight, as well as the number of seeds per fruit. Our results show that the weevil Tanysphyrus lemnae is the main florivore, and it mainly damages the female flowers. Hymenoptera were recorded as the most frequent visitors of both male and female flowers. Male and female flowers showed differences in visit frequency, which decreases as flower damage increases. Reproductive success was negatively related to the level of damage. We found that florivory is common in the population of S. lancifolia, which can exert a strong selective pressure by making the flowers less attractive and reducing the number of seeds per fruit. Future studies are needed to know how florivores affect plant male fitness.

Sex-driven neighborhood effects on herbivory in the dioecious Mediterranean palm Chamaerops humilis L

Although it is well recognized that the strength of plant-herbivore interactions can vary with the plant sex, the distance, and the density of conspecific neighbors, no study has yet assessed their combined influence. Here, we filled this knowledge gap by focusing on the dioecious palm Chamaerops humilis L., and its two main herbivores, the invasive moth Paysandisia archon Burmeister and the feral goat Capra hircus L. We evaluated levels and spatial patterns of herbivory, as well as those of plant size and number of inflorescences in two palm populations in Mallorca (Balearic Islands, Spain). Our spatial point pattern analyses revealed that palms not affected by moth herbivory or goat florivory were spatially aggregated, goats fed more strongly upon inflorescences in palms with more neighbors, but they consumed more leaves in isolated palms. Interestingly, we could reveal for the first time that plant sex is a key plant trait modulating neighborhood effects. For instance, whereas aggregated female palms experienced lower intensity of goat florivory than isolated ones, male palms showed the opposite pattern. Palm size and number of inflorescences also showed sex-related differences, suggesting that sexual dimorphism is a key driver of the observed neighborhood effects on herbivory. Our study highlights the importance of considering relevant plant traits such as sex when investigating plant neighborhood effects, calling for further research to fully understand the dynamics governing plant-herbivore interactions in dioecious systems.

Pollinators exert selection on floral traits in a pollen-limited, narrowly endemic spring ephemeral

PREMISE

Floral traits are frequently under pollinator-mediated selection, especially in taxa subject to strong pollen-limitation, such as those reliant on pollinators. However, antagonists can be agents of selection on floral traits as well. The causes of selection acting on spring ephemerals are understudied though these species can experience particularly strong pollen-limitation. I examined pollinator- and antagonist-mediated selection in a narrowly endemic spring ephemeral, Trillium discolor.

METHODS

I measured pollen limitation in T. discolor across two years and evaluated its breeding system. I compared selection on floral traits (display height, petal size, petal color, flowering time) between open-pollinated, and pollen-supplemented plants to measure the strength and mode of pollinator-mediated selection. I assessed whether natural levels of antagonism impacted selection on floral traits.

RESULTS

Trillium discolor was self-incompatible and experienced pollen limitation in both years of the study. Pollinators exerted negative disruptive selection on display height and petals size. In one year, pollinator-mediated selection favored lighter petals but in the second year pollinators favored darker petals. Antagonist damage did not alter selection on floral traits.

CONCLUSIONS

Results demonstrate that pollinators mediate the strength and mode of selection on floral traits in T. discolor. Interannual variation in the strength, mode, and direction of pollinator-mediated selection on floral traits could be important for maintaining of floral diversity in this system. Observed levels of antagonism were weak agents of selection on floral traits.

Mutualist- and antagonist-mediated selection contribute to trait diversification of flowers

Flowers are generally short-lived, and they all face a multidimensional challenge because they have to attract mutualists, compel them to vector pollen with minimal investment in rewards, and repel floral enemies during this short time window. Their displays are under complex selection, either consistent or conflicting, to maximize reproductive fitness under heterogeneous environments. The phenological or morphological mismatches between flowers and visitors will influence interspecific competition, resource access, mating success and, ultimately, population and community dynamics. To better understand the effects of the plant visitors on floral traits, it is necessary to determine the functional significance of specific floral traits for the visitors; how plants respond to both mutualists and antagonists through adaptive changes; and to evaluate the net fitness effects of biological mutualisms and antagonism on plants. In this review, we bring together insights from fields as diverse as floral biology, insect behavioral responses, and evolutionary biology to explain the processes and patterns of floral diversity evolution. Then, we discuss the ecological significance of plant responses to mutualists and antagonists from a community perspective, and propose a set of research questions that can guide the research field to integrate studies of plant defense and reproduction.

Revisiting florivory: an integrative review and global patterns of a neglected interaction

Florivory is an ancient interaction which has rarely been quantified due to a lack of standardized protocols, thus impairing biogeographical and phylogenetic comparisons. We created a global, continuously updated, open-access database comprising 180 species and 64 families to compare floral damage between tropical and temperate plants, to examine the effects of plant traits on floral damage, and to explore the eco-evolutionary dynamics of flower-florivore interactions. Flower damage is widespread across angiosperms, but was two-fold higher in tropical vs temperate species, suggesting stronger fitness impacts in the tropics. Flowers were mostly damaged by chewers, but neither flower color nor symmetry explained differences in florivory. Herbivory and florivory levels were positively correlated within species, even though the richness of the florivore community does not affect florivory levels. We show that florivory impacts plant fitness via multiple pathways and that ignoring this interaction makes it more difficult to obtain a broad understanding of the ecology and evolution of angiosperms. Finally, we propose a standardized protocol for florivory measurements, and identify key research avenues that will help fill persistent knowledge gaps. Florivory is expected to be a central research topic in an epoch characterized by widespread decreases in insect populations that comprise both pollinators and florivores.

Floral traits influence the opportunity for selection among male gametophytes: independent and combined effects of style length and petal area

PREMISE

Strong correlations between traits can obscure their independent effects on components of reproduction. Style length (SL) and petal area (PA) vary within species, for example, but their independent effects on the opportunity for selection among pollen genotypes are poorly understood. Previous work in Clarkia detected a positive effect of SL on pollen receipt, potentially intensifying selection. However, this apparent effect of SL may be influenced by a correlated trait, such as PA. Here, we examine the independent effects of these two traits on pollen receipt and performance.

METHODS

We collected petals and styles from wild populations of two insect-pollinated Clarkia taxa and estimated the independent and combined effects of SL and PA on pollen receipt and performance.

RESULTS

In both taxa, SL and PA are positively correlated. In C. unguiculata, both traits positively and independently affect pollen receipt, but in C. xantiana ssp. xantiana, the two traits act only in combination to affect pollen receipt. In both taxa, pollen receipt positively affects the numbers of pollen tubes entering and penetrating the style, as well as pollen tube attrition.

CONCLUSIONS

The effects of SL and PA on pollen receipt and performance are taxon specific. In C. unguiculata, both traits may be independent targets of selection due to their effects on pollen receipt. In C. xantiana ssp. xantiana, by contrast, the combined (but not independent) effects of SL and PA influence pollen receipt. Ecological differences between these taxa require exploration to understand the mechanisms by which these traits affect pollinator behavior.

One for all and all for one: retention of colour-unchanged old flowers increases pollinator attraction in a hermaphroditic plant

Long-lived flowers increase pollen transfer rates, but these entail high water and carbon maintenance costs. The retention of pollinated and reward-free old flowers enhances pollinator visitation to young receptive flowers by increasing floral display size. This mechanism is associated with acropetal inflorescences or changes in flower colour and openness, but the retention of unchanging solitary flowers remains overlooked. We examined pollination-dependent variation in floral longevity and determined stigmatic receptivity, pollen viability and pollen removal rates among flower ages in Kielmeyera regalis, a Neotropical savanna shrub. We also evaluated the effects of floral display size on pollinator visitation rates. Lastly, we determined whether old flowers are unvisited and exclusively increase pollinator attraction to young flowers through flower removal experiments. Regardless of pollination treatment, flowers lasted fully open with no detectable physical changes for 3 days. Over time, stigmas remained receptive but >95% of pollen was removed. Pollinator visitation significantly increased with floral display size and intermediate percentages (15-30%) of newly opened flowers. Accordingly, the retention of reward-free and unvisited old flowers increased young flower-pollinator interaction. Our results reveal the importance of a prolonged floral longevity in increasing pollinator attraction toward newly opened receptive flowers without changes in flower colour and form. We conclude that the retention of pollinated, reward-free and unvisited colour-unchanged old flowers in K. regalis is a strategy that counteracts the water use costs associated with the maintenance of large flowers with increased mate opportunities in a pollen-limited scenario.

Asterid Ray Floret Traits Predict the Likelihood of Florivory by the Polyphagous Katydid, Phaneroptera brevis (Orthoptera: Phaneropterinae)

Insect-flower visitation is crucial for many angiosperms because insects can facilitate pollination. Floral traits can attract pollinators so studying how they correlate with insect-flower visitation can elucidate how insects and plants interact and coevolve. However, there are few studies on how floral traits correlate with florivory. Not all floral traits that predict attractiveness of flowers to pollinators are applicable for florivory because they may not necessarily reflect the palatability of the flower parts. Leaf functional traits have been studied extensively to predict herbivory, but we are not aware of studies that adopt such leaf traits in florivory. We addressed these limitations by investigating the research questions: 1) How do floral traits differ among different species? 2) How do the floral traits predict the likelihood of florivory? We measured 10 floral traits, including adopting common leaf traits associated with herbivory (e.g., specific leaf area and leaf dry matter content), among three Asteraceae species: Bidens pilosa L., Sphagneticola trilobata (L.) Pruski, and Tridax procumbens L. We then performed the cafeteria assay using a polyphagous floriphilic katydid, Phaneroptera brevis (Serville 1838). We found that ray floret dry matter content correlates negatively with the likelihood of florivory of the asterid ray floret, whereas the total biomass of the ray floret correlates positively with the likelihood of florivory of the entire capitulum. The specific ray floret area also correlates nonlinearly with the likelihood of florivory of the asterid ray florets. We believe that these florivory traits can be applied to the flowers of other species.

Florivory indirectly decreases the plant reproductive output through changes in pollinator attraction

Species often interact indirectly with each other via their traits. There is increasing appreciation of trait-mediated indirect effects linking multiple interactions. Flowers interact with both pollinators and floral herbivores, and the flower-pollinator interaction may be modified by indirect effects of floral herbivores (i.e., florivores) on flower traits such as flower size attracting pollinators. To explore whether flower size affects the flower-pollinator interaction, we used Eurya japonica flowers. We examined whether artificial florivory decreased fruit and seed production, and also whether flower size affected florivory and the number of floral visitors. The petal removal treatment (i.e., artificial florivory) showed approximately 50% reduction in both fruit and seed set in natural pollination but not in artificial pollination. Furthermore, flower size increased the number of floral visitors, although it did not affect the frequency of florivory. Our results demonstrate that petal removal indirectly decreased 75% of female reproductive output via decreased flower visits by pollinators and that flower size mediated indirect interactions between florivory and floral visitors.

Florivory and nectar-robbing perforations in flowers of pointleaf manzanita Arctostaphylos pungens (Ericaceae) and their effects on plant reproductive success

Damage to petals may have varying effects on the reproductive success of the plant. The variation may depend on the kind of damage to the corolla. Whether the damage is limited to the corolla, as is usually the case with nectar-robbing perforations, or extending to the reproductive parts of the flower, as in the case of florivory holes, might determine the extent of the effect on the plant's reproduction. We examined the various perforations in the flowers of Arctostaphylos pungens and correlated their presence with fruiting success. We found that though florivory holes were highly associated with damage to reproductive parts, fruiting success did not differ significantly between flowers with the two kinds of damage. Although nectar-robbing perforations were not associated with reduced number of fruit produced, they were significantly correlated with reduced number of fruit that contained seemingly viable seeds. The implications of our findings are discussed in the context of pollination and antagonism.

Evolution of the Selfing Syndrome in Arabis alpina (Brassicaceae)

Introduction

The transition from cross-fertilisation (outcrossing) to self-fertilisation (selfing) frequently coincides with changes towards a floral morphology that optimises self-pollination, the selfing syndrome. Population genetic studies have reported the existence of both outcrossing and selfing populations in Arabis alpina (Brassicaceae), which is an emerging model species for studying the molecular basis of perenniality and local adaptation. It is unknown whether its selfing populations have evolved a selfing syndrome.

Methods

Using macro-photography, microscopy and automated cell counting, we compared floral syndromes (size, herkogamy, pollen and ovule numbers) between three outcrossing populations from the Apuan Alps and three selfing populations from the Western and Central Alps (Maritime Alps and Dolomites). In addition, we genotyped the plants for 12 microsatellite loci to confirm previous measures of diversity and inbreeding coefficients based on allozymes, and performed Bayesian clustering.

Results and Discussion

Plants from the three selfing populations had markedly smaller flowers, less herkogamy and lower pollen production than plants from the three outcrossing populations, whereas pistil length and ovule number have remained constant. Compared to allozymes, microsatellite variation was higher, but revealed similar patterns of low diversity and high Fis in selfing populations. Bayesian clustering revealed two clusters. The first cluster contained the three outcrossing populations from the Apuan Alps, the second contained the three selfing populations from the Maritime Alps and Dolomites.

Conclusion

We conclude that in comparison to three outcrossing populations, three populations with high selfing rates are characterised by a flower morphology that is closer to the selfing syndrome. The presence of outcrossing and selfing floral syndromes within a single species will facilitate unravelling the genetic basis of the selfing syndrome, and addressing which selective forces drive its evolution.

Relation between flower head traits and florivory in Asteraceae: a phylogenetically controlled approach

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PREMISE OF THE STUDY

While much research has examined the relation between leaf traits and herbivory, very little is known about the interaction between floral traits, particularly biochemical traits, and florivory. We investigated patterns between floral traits and florivory across multiple species using phylogenetic comparative approaches to enhance our understanding of the evolution of plant-florivore interactions.•

METHODS

The relation between the intensity of florivory and five biochemical traits (concentrations of carbon, nitrogen, phosphorus, water, and total phenolics) and two morphological traits (diameter and number of flower heads) were investigated in wild individuals of 18 native species of Asteraceae. The phylogenetic signals in the morphological traits and intensity of florivory were also tested.•

KEY RESULTS

We found that species with higher nitrogen, water, and total phenolics and lower phosphorus concentrations in the flower heads and species with a large number and diameter of flower heads tended to be attacked by florivores. In addition, we found significant phylogenetic signals in florivory and morphological traits.•

CONCLUSIONS

Our results clearly show that biochemical traits also play important roles in plant-florivore interactions, as previously shown in plant-leaf herbivore interactions. The positive relationship between florivory and total phenolics implies that phenolic compounds in flower heads may not act as a defense in the species. In addition, the observed pattern of signals in florivory might not be solely explained by the signals of the measured traits and other plant traits may also play significant roles in plant-florivore interaction in these species.

Variation in pollen limitation and floral parasitism across a mating system transition in a Pacific coastal dune plant: evolutionary causes or ecological consequences?

BACKGROUND AND AIMS

Evolutionary transitions from outcrossing to self-fertilization are thought to occur because selfing provides reproductive assurance when pollinators or mates are scarce, but they could also occur via selection to reduce floral vulnerability to herbivores. This study investigated geographic covariation between floral morphology, fruit set, pollen limitation and florivory across the geographic range of Camissoniopsis cheiranthifolia, a Pacific coastal dune endemic that varies strikingly in flower size and mating system.

METHODS

Fruit set was quantified in 75 populations, and in 41 of these floral herbivory by larvae of a specialized moth (Mompha sp.) that consumes anthers in developing buds was also quantified. Experimental pollen supplementation was performed to quantify pollen limitation in three large-flowered, outcrossing and two small-flowered, selfing populations. These parameters were also compared between large- and small-flowered phenotypes within three mixed populations.

KEY RESULTS

Fruit set was much lower in large-flowered populations, and also much lower among large- than small-flowered plants within populations. Pollen supplementation increased per flower seed production in large-flowered but not small-flowered populations, but fruit set was not pollen limited. Hence inadequate pollination cannot account for the low fruit set of large-flowered plants. Floral herbivory was much more frequent in large-flowered populations and correlated negatively with fruit set. However, florivores did not preferentially attack large-flowered plants in three large-flowered populations or in two of three mixed populations.

CONCLUSIONS

Selfing alleviated pollen limitation of seeds per fruit, but florivory better explains the marked variation in fruit set. Although florivory was more frequent in large-flowered populations, large-flowered individuals were not generally more vulnerable within populations. Rather than a causative selective factor, reduced florivory in small-flowered, selfing populations is probably an ecological consequence of mating system differentiation, with potentially significant effects on population demography and biotic interactions.

Herbivore pressure by weevils associated with flower color polymorphism in Geranium thunbergii (Geraniaceae)

Although floral herbivory has recently received increased attention as an important factor influencing plant reproduction, relatively little is known about how its frequency and intensity vary depending on traits of host plants. Here we report that herbivore pressure by a weevil, Zacladus geranii, is associated with a flower color polymorphism of Geranium thunbergii (Geraniaceae). Pink and white flower color morphs have been reported in G. thunbergii, and we found in a three-year field survey in multiple populations that, generally, adult weevils more preferentially visited white flowers than pink flowers. Consistently, we found more severe damage by weevil larvae in white flowers. Overall herbivore pressure for G. thunbergii varied strongly between populations, and the difference seems to be partly explained by the co-occurrence of a related plant species, Geranium yezoense, in a population, as weevils preferred it to both color morphs of G. thunbergii, thereby relaxing overall herbivore pressure for G. thunbergii. Nonetheless, despite such high variability, the preference of weevils for white morphs over pink morphs of G. thunbergii was found across multiple populations. We discuss possible mechanisms causing the association between flower color and herbivore preference as well as its evolutionary consequences.

Florivore impacts on plant reproductive success and pollinator mortality in an obligate pollination mutualism

Florivores are present in many pollination systems and can have direct and indirect effects on both plants and pollinators. Although the impact of florivores are commonly examined in facultative pollination mutualisms, their effects on obligate mutualism remain relatively unstudied. Here, we used experimental manipulations and surveys of naturally occurring plants to assess the effect of florivory on the obligate pollination mutualism between yuccas and yucca moths. Yucca filamentosa (Agavaceae) is pollinated by the moth Tegeticula cassandra (Lepidoptera: Prodoxidae), and the mutualism also attracts two florivores: a generalist, the leaf-footed bug Leptoglossus phyllopus (Hemiptera: Coreidae), and a specialist, the beetle Hymenorus densus (Coleoptera: Tenebrionidae). Experimental manipulations of leaf-footed bug densities on side branches of Y. filamentosa inflorescences demonstrated that feeding causes floral abscission but does not reduce pollen or seed production in the remaining flowers. Similar to the leaf-footed bugs, experimental manipulations of beetle densities within individual flowers demonstrated that beetle feeding also causes floral abscission, but, in addition, the beetles also cause a significant reduction in pollen availability. Path analyses of phenotypic selection based on surveys of naturally occurring plants revealed temporal variation in the plant traits important to plant fitness and the effects of the florivores on fitness. Leaf-footed bugs negatively impacted fitness when fewer plants were flowering and leaf-footed bug density was high, whereas beetles had a positive effect on fitness when there were many plants flowering and their densities were low. This positive effect was likely due to adult beetles consuming yucca moth eggs while having a negligible effect on floral abscission. Together, the actions of both florivores either augmented the relationship of plant traits and fitness or slightly weakened the relationship. Overall, the results suggest that, although florivores are always present during flowering, the impact of florivores on phenotypic selection in yuccas is strongly mitigated by changes in their densities on plants from year to year. In contrast, both florivores consistently influenced pollinator larval mortality through floral abscission, and H. densus beetles additionally via the consumption of pollinator eggs.