Genome Size and Labellum Epidermal Cell Size Are Evolutionarily Correlated With Floral Longevity in Paphiopedilum Species

Genome size is known to influence phenotypic traits in leaves and seeds. Although genome size is closely related to cellular and developmental traits across biological kingdoms, floral longevity is a floral trait with important fitness consequence, but less is known about the link between floral longevity and sizes of genomes and cells. In this study, we examined evolutionary coordination between genome size, floral longevity, and epidermal cell size in flowers and leaves in 13 Paphiopedilum species. We found that, across all the study species, the genome size was positively correlated with floral longevity but negatively associated with labellum epidermal cell size, and a negative relationship was found between floral longevity and labellum epidermal cell size. This suggested that genome size is potentially correlated with floral longevity, and genome size has an important impact on life-history trait. In addition, genome size was positively correlated with leaf epidermal cell size, which was different from the relationship in flower due to different selective pressures they experienced or different functions they performed. Therefore, genome size constraints floral longevity, and it is a strong predictor of cell size. The impact of genome size on reproduction might have more implications for the evolution of flowering plants and pollination ecology.

A new brood-pollination mutualism between Stellera chamaejasme and flower thrips Frankliniella intonsa

Background Brood pollination mutualism is a special type of plant-pollinator interaction in which adult insects pollinate plants, and the plants provide breeding sites for the insects as a reward. To manifest such a mutualism between Stellera chamaejasme and flower thrips of Frankliniella intonsa, the study tested the mutualistic association of the thrips life cycle with the plant flowering phenology and determined the pollination effectiveness of adult thrips and their relative contribution to the host’s fitness by experimental pollinator manipulation. Results The adult thrips of F. intonsa, along with some long-tongue Lepidoptera, could serve as efficient pollinators of the host S. chamaejasme. The thrips preferentially foraged half-flowering inflorescences of the plants and oviposited in floral tubes. The floral longevity was 11.8 ± 0.55 (mean ± se) days, which might precisely accommodate the thrips life cycle from spawning to prepupation. The exclusion of adult thrips from foraging flowers led to a significant decrease in the fitness (i.e., seed set) of host plants, with a corresponding reduction in thrips fecundity (i.e., larva no.) in the flowers. Conclusions The thrips of F. intonsa and the host S. chamaejasme mutualistically interact to contribute to each other’s fitness such that the thrips pollinate host plants and, as a reward, the plants provide the insects with brooding sites and food, indicating the coevolution of the thrips life cycle and the reproductive traits (e.g., floral longevity and morphology) of S. chamaejasme.

Occurrence and Prevention of Delayed Autonomous Selfing in Salvia umbratica (Lamiaceae)

Delayed autonomous selfing (DAS) provides reproductive assurance under conditions of pollinator and/or pollen-limitation. Few plant species have been investigated to determine if DAS is terminated when a flower is sufficiently pollinated by a pollen vector, thereby saving plant resources for other purposes. We examined this possibility in bumblebee-pollinated Salvia umbratica. We first showed that DAS resulting in high fruit set (100%) and seed set (>80%) per flower occurred in the absence of insect pollinators by means of style recurvature and was completed in 94% of flowers 72 h after they opened. In contrast, in flowers pollinated immediately after opening, DAS was prevented by corollas dropping away before styles recurve toward the upper thecae. We next showed that hand-pollination of flowers immediately after they opened resulted in high fruit set (100%) and seed set (>80%) when 5–10 pollen grains or more were deposited on their stigmas, whereas fruit set and seed set were reduced to 45.00 and 22.50%, respectively, when pollen loads were reduced to 1–3 pollen grains. Finally, we showed that on average single pollinator visits deposited 26 pollen grains on stigmas of flowers that had just opened, which is more than enough to ensure high fruit and seed set. Our results indicate that flower longevity is highly correlated with the pollinator environment and female fitness of S. umbratica, with extended flower longevity allowing DAS to occur being advantageous when pollinators are absent, while reduced floral longevity and prevention of DAS being favored when flowers are pollinated by pollinators. Thus, flower longevity in S. umbratica varies so as to optimize reproductive output and resource efforts, and is dependent on the availability and effectiveness of pollinators to pollinate flowers.

Floral Longevity of Paphiopedilum and Cypripedium Is Associated With Floral Morphology

Floral longevity (FL) is an important trait influencing plant reproductive success by affecting the chance of insect pollination. However, it is still unclear which factors affect FL, and whether FL is evolutionarily associated with structural traits. Since construction costs and water loss by transpiration play a role in leaf longevity, we speculated that floral structures may affect the maintenance and loss of water in flowers and, therefore, FL. Here, we investigated the slipper orchid Paphiopedilum and Cypripedium, which are closely related, but strongly differ in their FL. To understand the evolutionary association of floral anatomical traits with FL, we used a phylogenetic independent comparative method to examine the relationships between 30 floral anatomical traits and FL in 18 species of Paphiopedilum and Cypripedium. Compared with Paphiopedilum species, Cypripedium species have lower values for floral traits related to drought tolerance and water retention capacity. Long FL was basically accompanied by the thicker epidermal and endodermal tissues of the floral stem, the thicker adaxial and abaxial epidermis of the flower, and low floral vein and stomatal densities. Vein density of the dorsal sepals and synsepals was negatively correlated with stomatal density. Our results supported the hypothesis that there was a correlation between FL and floral anatomical traits in slipper orchids. The ability to retain water in the flowers was associated with FL. These findings provide a new insight into the evolutionary association of floral traits with transpirational water loss for orchids under natural selection.

Extreme Drought Affects Visitation and Seed Set in a Plant Species in the Central Chilean Andes Heavily Dependent on Hummingbird Pollination

Rising temperatures and increasing drought in Mediterranean-type climate areas are expected to affect plant–pollinator interactions, especially in plant species with specialised pollination. Central Chile experienced a mega drought between 2010 and 2020 which reached an extreme in the austral summer of 2019–2020. Based on intensive pollinator sampling and floral studies we show that the subalpine form of Mutisia subulata (Asteraceae) is a specialised hummingbird-pollinated species. In a two-year study which included the severest drought year, we quantified visitation frequency, flower-head density, flower-head visitation rates, two measures of floral longevity, nectar characteristics and seed set and monitored climatic variables to detect direct and indirect climate-related effects on pollinator visitation. Flower-head density, nectar standing crop and seed set were significantly reduced in the severest drought year while nectar concentration increased. The best model to explain visitation frequency included flower-head density, relative humidity, temperature, and nectar standing crop with highly significant effects of the first three variables. Results for flower-head density suggest hummingbirds were able to associate visual signals with reduced resource availability and/or were less abundant. The negative effect of lower relative humidity suggests the birds were able to perceive differences in nectar concentration. Reduced seed set per flower-head together with the availability of far fewer ovules in the 2019–2020 austral summer would have resulted in a major reduction in seed set. Longer and more intense droughts in this century could threaten local population persistence in M. subulata.

Conservation of Alstroemeria cut flowers stored under refrigeration

Alstroemeria flowers have shown great importance in the world trade of cut flowers due mainly to its beauty and wide variety of colors. However, the durability of its inflorescences is usually hampered by the rapid yellowing of the leaves, which impairs their decorative quality. Cut flowers require the use of technologies to improve postharvest quality and floral longevity. This research aimed to study the postharvest conservation of inflorescences of Alstroemeria cv. Ajax at different storage temperatures. Floral stems were placed in containers with distilled water and stored at four temperatures (4, 8, 12, and 22ºC) for 12 days. The following analyses were performed: fresh mass variation, respiratory activity, relative water content, soluble and reducing carbohydrate contents, polyphenol-oxidase and peroxidase enzymes, pigments (anthocyanin and carotenoids), and longevity. The experiment was conducted in a completely randomized design, the results were submitted to analysis of variance (ANOVA), and the effect of treatments submitted to F-test. Significant differences were compared using the least significant difference (LSD) at 95% confidence interval (p ≤ 0. 05). The temperatures of 8 and 12ºC were effective in maintaining the postharvest quality of inflorescences during storage period, as they remained turgid due to transpiration reduction caused by low temperatures, and longevity reaching 46 and 22 days, respectively.

Dracula’s mistress: removal of blood-red floral nectar results in secretion of more nectar

Background and aims – Flowers of Jaltomata quipuscoae (Solanaceae) secrete blood-red nectar that serves as an energy reward and possible attractant to pollinators. The purposes of this study were to determine whether simulated pollinator visits (manual removal of nectar) stimulates replenishment of nectar, and report the pattern of nectar presentation during the lifespan of the flower. Methods – For the nectar replenishment experiments flowers were paired: each pair of flowers was selected to be on the same plant and at the same developmental stage. From all 62 flowers nectar was removed and discarded (not measured) at time zero. Then, over a period of eight hours, the nectar of one flower was measured four times, i.e., every two hours, while nectar of the paired control flower was measured only at the end of the eight-hour period. In the nectar dynamics experiment five sets of flowers received different treatments: flowers were unmanipulated for zero, one, two, three or four days and then nectar was removed once every day. The volume of nectar produced and concentration of sugar in the nectar were recorded at each extraction for both studies.Key results – In the nectar replenishment study significantly higher nectar volume and consequently significantly higher total sugar content was present in the experimental nectar-extracted flowers. In the nectar dynamics study, nectar was produced starting on day one or two, continuously through the life of the open flowers until one or two days before the corolla senesced. Delay of nectar removal from different flower sets for zero, one, two, three or four days resulted in a linear increase in nectar volume and total nectar sugar production, and had little or no effect on the cumulative (life of the flower) nectar production. Floral longevity, seven to ten days, was not affected by a single removal of nectar each day.Conclusions – The floral nectary of J. quipuscoae responded to nectar removal by secreting more nectar, and thus more total sugar (not a higher concentration of sugar) than was secreted by control flowers. In flowers from which nectar was not removed, nectar volume and thus total sugar secreted continued to accumulate linearly, suggesting that reabsorption of nectar either does not occur or is slow relative to the rate of secretion. The more we (or pollinators) take, the more the flowers make: the volume of nectar and sugar production increase if nectar is removed frequently but not if nectar is removed infrequently.

How does timing of flowering affect competition for pollinators, flower visitation and seed set in an early spring grassland plant?

Knowledge on how the timing of flowering is related to plant fitness and species interactions is crucial to understand consequences of phenological shifts as they occur under climate change. Early flowering plants may face advantages of low competition for pollinators and disadvantages of low pollinator abundances and unfavourable weather conditions. However, it is unknown how this trade-off changes over the season and how the timing affects reproductive success. On eight grasslands we recorded intra-seasonal changes in pollinators, co-flowering plants, weather conditions, flower visitation rates, floral longevity and seed set of Pulsatilla vulgaris. Although bee abundances and the number of pollinator-suitable hours were low at the beginning of the season, early flowers of P. vulgaris received higher flower visitation rates and estimated total number of bee visits than later flowers, which was positively related to seed set. Flower visitation rates decreased over time and with increasing number of co-flowering plants, which competed with P. vulgaris for pollinators. Low interspecific competition for pollinators seems to be a major driver for early flowering dates. Thus, non-synchronous temporal shifts of co-flowering plants as they may occur under climate warming can be expected to strongly affect plant-pollinator interactions and the fitness of the involved plants.

Floral Longevity and Attraction of Arctic Lupine, Lupinus arcticus: Implications for Pollination Efficiency

Pollination by insects is a mutualistic relationship in which flowers receive pollen for reproduction while pollinators are rewarded with pollen or nectar. Floral longevity (the period an individual flower blooms) and floral attraction (the period during which pollinators are attracted to the flower, often indicated by petal colour) both play prominent roles in plant and pollinator success. This study investigated whether floral longevity and floral attraction were mediated by pollination type in arctic lupine (Lupinus arcticus S. Wats.), a common herbaceous perennial in northwestern North America. Flowers were either open to pollinators, cross-pollinated by hand, or bagged to prevent cross-pollination, and floral longevity, seed set, and flower colour were observed. Open and hand-pollinated flowers had significantly shorter floral longevities and higher percent fruit sets than bagged flowers. A colour change of the banner petal marking from white to pink occurred in some flowers and was a signal of floral attraction, as pollinators preferentially visited pre-change flowers. Pre-change flowers contained more pollen and were less likely to have been injured by herbivory than post-change flowers, yet the colour change was not related to pollination type or fruit set. Pollination-induced shortening of floral longevity is likely an adaptation to limited plant resources and pollinator visitation rates. For L. arcticus, this could be influenced by short growing seasons and low annual temperatures in the study area. In the face of climatic changes and shifting species phenologies, the mediation of floral longevity by pollinators could decrease temporal mismatch between plants and their pollinators, yet the many factors at play make this difficult to accurately predict.

Fitness costs of delayed pollination in a mixed-mating plant

Background and Aims To predict the evolutionary consequences of pollinator declines, we need to understand the evolution of delayed autonomous self-pollination, which is expected to evolve as a mechanism of reproductive assurance when cross-pollination becomes unreliable. This involves estimating the costs of increased levels of selfing as well as those associated with floral senescence. Methods We studied the mechanisms and costs of delayed self-pollination in the mixed-mating vine Dalechampia scandens (Euphorbiaceae) by first assessing among-population variation in herkogamy and dichogamy, which together determine the rate and timing of autonomous self-pollination. We then tested whether floral longevity responds plastically to delayed pollination. Finally, we assessed the costs of delayed self-pollination in terms of seed number and size, explicitly separating inbreeding depression from effects of floral senescence. Key Results Herkogamy varied extensively, while variation in dichogamy was more limited. Unpollinated blossoms increased their longevity, but seed quantity and quality decreased with increasing delays in pollination, independently of inbreeding depression. Conclusions In D. scandens, earlier autonomous selfing is facilitated by reduced herkogamy rather than reduced protogyny, providing reproductive assurance while maintaining the possibility for outcrossing events. Effective early autonomous self-pollination may evolve under reduced cross-pollination reliability in response to costs associated with floral senescence.