Exposure to elevated temperature during development affects bumblebee foraging behavior.

Bee foraging behavior provides a pollination service that has both ecological and economic benefits. However, bee population decline could directly affect the efficiency of this interaction. Among the drivers of this decline, global warming has been implicated as an emerging threat but exactly how increasing temperatures affect bee foraging behavior remains unexplored. Here, we assessed how exposure to elevated temperatures during development affects the foraging behavior and morphology of workers from commercial and wild Bombus terrestris colonies. Workers reared at 33 °C had a higher visiting rate and shorter visiting time than those reared at 27°C. In addition, far fewer workers reared at 33 °C engaged in foraging activities and this is potentially related to the drastic reduction in the number of individuals produced in colonies exposed to 33 °C. The impact of elevated developmental temperature on wild colonies was even stronger as none of the workers from these colonies performed any foraging trips. We also found that rearing temperature affected wing size and shape. Our results provide the first evidence that colony temperature can have striking effects on bumblebee foraging behavior. Of particular importance is the drastic reduction in the number of workers performing foraging trips, and the total number of foraging trips made by workers reared in high temperatures. Further studies should explore if, ultimately, these observed effects of exposure to elevated temperature during development lead to a reduction in pollination efficiency.

Climate Change-Induced Stress Reduce Quantity and Alter Composition of Nectar and Pollen From a Bee-Pollinated Species (Borago officinalis, Boraginaceae).

In temperate ecosystems, elevated temperatures, and drought occur especially during spring and summer, which are crucial periods for flowering, pollination, and reproduction of a majority of temperate plants. While many mechanisms may underlie pollinator decline in the wake of climate change, the interactive effects of temperature and water stress on the quantity and quality of floral nectar and pollen resources remain poorly studied. We investigated the impact of temperature rise (+3 and +6°C) and water stress (soil humidity lower than 15%) on the floral resources produced by the bee-pollinated species Borago officinalis. Nectar volume decreased with both temperature rise and water stress (6.1 ± 0.5 µl per flower under control conditions, 0.8 ± 0.1 µl per flower under high temperature and water stress conditions), resulting in a 60% decrease in the total quantity of nectar sugars (mg) produced per flower. Temperature rise but not water stress also induced a 50% decrease in pollen weight per flower but a 65% increase in pollen polypeptide concentration. Both temperature rise and water stress increased the total amino acid concentration and the essential amino acid percentage in nectar but not in pollen. In both pollen and nectar, the relative percentage of the different amino acids were modified under stresses. We discuss these modifications in floral resources in regards to plant-pollinator interactions and consequences on plant pollination success and on insect nutritional needs.

Growing and Flowering in a Changing Climate: Effects of Higher Temperatures and Drought Stress on the Bee-Pollinated Species Impatiens glandulifera Royle.

Drought and higher temperatures caused by climate change are common stress conditions affecting plant growth and development. The reproductive phase is particularly sensitive to stress, but plants also need to allocate their limited resources to produce floral traits and resources to attract pollinators. We investigated the physiological and floral consequences of abiotic stress during the flowering period of Impatiens glandulifera, a bee-pollinated species. Plants were exposed to three temperatures (21, 24, 27 °C) and two watering regimes (well-watered, water stress) for 3 weeks. Not all parameters measured responded in the same manner to drought and/or heat stress. Drought stress induced leaf senescence, decreasing leaf number by 15-30% depending on growth temperature. Drought also reduced photosynthetic output, while temperature rise affected stomatal conductance. The number of flowers produced dropped 40-90% in response to drought stress, while higher temperatures shortened flower life span. Both stresses affected floral traits, but flower resources diminished in response to higher temperatures, with lower nectar volume and pollen protein content. We conclude that increased temperatures and drought stress, which are becoming more frequent with climate change, can negatively affect flowering, even if plants deploy physiological resistance strategies.

Warm Temperatures Reduce Flower Attractiveness and Bumblebee Foraging.

(1) Background: Plants attract pollinators using several visual signals, mainly involving the display, size, shape, and color of flowers. Each signal is relevant for pollinators foraging for floral rewards, pollen, and nectar. Changes in floral signals and rewards can be induced by an increase in temperature, drought, or other abiotic stresses and are expected to increase as global temperatures rise. In this study, we explored how pollinators respond to modified floral signals and rewards following an increase in temperature; (2) Methods: We tested the effects of warmer temperatures on bee-pollinated starflower (Borago officinalis, Boraginaceae) and determined the behavior of one of its main pollinators, the buff-tailed bumblebee (Bombus terrestris). We measured visual floral traits (display and size) and rewards (nectar and pollen) for plants cultivated at 21 °C or 26 °C. We investigated bumblebee behavior by tracking insect visits in a binary choice experiment in an indoor flight arena; (3) Results: Plants cultivated at 26 °C exhibited a smaller floral area (i.e., corolla sizes summed for all flowers per plant, 34.4 ± 2.3 cm2 versus 71.2 ± 2.7 cm2) and a greater flower height (i.e., height of the last inflorescence on the stem, 87 ± 1 cm versus 75 ± 1 cm) compared to plants grown at 21 °C. Nectar production per flower was lower in plants grown at 26 °C than in plants grown at 21 °C (2.67 ± 0.37 µL versus 4.15 ± 0.22 µL), and bumblebees visited flowers from plants grown at 26 °C four times less frequently than they visited those from plants grown at 21 °C; (4) Conclusions: These results show that warmer temperatures affect floral signals and reduce overall floral resources accessible to pollinators. Thus, the global increases in temperature caused by climate change could reduce plant pollination rates and reproductive success by reducing flower visitation.

QuoVidi: An open-source web application for the organization of large-scale biological treasure hunts.

Learning biology, and in particular systematics, requires learning a substantial amount of specific vocabulary, both for botanical and zoological studies. While crucial, the precise identification of structures serving as evolutionary traits and systematic criteria is not per se a highly motivating task for students. Teaching this in a traditional teaching setting is quite challenging especially with a large crowd of students to be kept engaged. This is even more difficult if, as during the COVID-19 crisis, students are not allowed to access laboratories for hands-on observation on fresh specimens and sometimes restricted to short-range movements outside their home. Here, we present QuoVidi, a new open-source web platform for the organization of large-scale treasure hunts. The platform works as follows: students, organized in teams, receive a list of quests that contain morphologic, ecologic, or systematic terms. They have to first understand the meaning of the quests, then go and find them in the environment. Once they find the organism corresponding to a quest, they upload a geotagged picture of their finding and submit this on the platform. The correctness of each submission is evaluated by the staff. During the COVID-19 lockdown, previously validated pictures were also submitted for evaluation to students that were locked in low-biodiversity areas. From a research perspective, the system enables the creation of large image databases by the students, similar to citizen science projects. Beside the enhanced motivation of students to learn the vocabulary and perform observations on self-found specimens, this system allows instructors to remotely follow and assess the work performed by large numbers of students. The interface is freely available, open-source and customizable. Unlike existing naturalist platforms, allows the educators to fully customize the quests of interest. This enables the creation of multiple teaching scenarios, without being bound to a fixed scope. QuoVidi can be used in other disciplines with adapted quests and we expect it to be of interest in many classroom settings.

Species-specific responses to combined water stress and increasing temperatures in two bee-pollinated congeners (Echium, Boraginaceae).

Water stress and increasing temperatures are two main constraints faced by plants in the context of climate change. These constraints affect plant physiology and morphology, including phenology, floral traits, and nectar rewards, thus altering plant-pollinator interactions.We compared the abiotic stress responses of two bee-pollinated Boraginaceae species, Echium plantagineum, an annual, and Echium vulgare, a biennial. Plants were grown for 5 weeks during their flowering period under two watering regimes (well-watered and water-stressed) and three temperature regimes (21, 24, 27°C).We measured physiological traits linked to photosynthesis (chlorophyll content, stomatal conductance, and water use efficiency), and vegetative (leaf number and growth rate) and floral (e.g., flower number, phenology, floral morphology, and nectar production) traits.The physiological and morphological traits of both species were affected by the water and temperature stresses, although the effects were greater for the annual species. Both stresses negatively affected floral traits, accelerating flower phenology, decreasing flower size, and, for the annual species, decreasing nectar rewards. In both species, the number of flowers was reduced by 22%-45% under water stress, limiting the total amount of floral rewards.Under water stress and increasing temperatures, which mimic the effects of climate change, floral traits and resources of bee-pollinated species are affected and can lead to disruptions of pollination and reproductive success.

Temperature and water stress affect plant-pollinator interactions in Borago officinalis (Boraginaceae).

Climate change alters the abiotic constraints faced by plants, including increasing temperature and water stress. These changes may affect flower development and production of flower rewards, thus altering plant-pollinator interactions. Here, we investigated the consequences of increased temperature and water stress on plant growth, floral biology, flower-reward production, and insect visitation of a widespread bee-visited species, Borago officinalis. Plants were grown for 5 weeks under three temperature regimes (21, 24, and 27°C) and two watering regimes (well-watered and water-stressed). Plant growth was more affected by temperature rise than water stress, and the reproductive growth was affected by both stresses. Vegetative traits were stimulated at 24°C, but impaired at 27°C. Flower development was mainly affected by water stress, which decreased flower number (15 ± 2 flowers/plant in well-watered plants vs. 8 ± 1 flowers/plant under water stress). Flowers had a reduced corolla surface under temperature rise and water stress (3.8 ± 0.5 cm2 in well-watered plants at 21°C vs. 2.2 ± 0.1 cm2 in water-stressed plants at 27°C). Both constraints reduced flower-reward production. Nectar sugar content decreased from 3.9 ± 0.3 mg/flower in the well-watered plants at 21°C to 1.3 ± 0.4 mg/flower in the water-stressed plants at 27°C. Total pollen quantity was not affected, but pollen viability decreased from 79 ± 4% in the well-watered plants at 21°C to 25 ± 9% in the water-stressed plants at 27°C. Flowers in the well-watered plants at 21°C received at least twice as many bumblebee visits compared with the other treatments. In conclusion, floral modifications induced by abiotic stresses related to climate change affect insect behavior and alter plant-pollinator interactions.

Diversity of the Insect Visitors on Calluna vulgaris (Ericaceae) in Southern France Heathlands.

As part of an ongoing research project on the pollination networks in European heathlands, the objective of this study was to assess the insect visitor guild on Calluna vulgaris (L.) Hull (Ericaceae). We focused the study on a region renowned for its largely well-preserved heathlands, the Cévennes National Park, Southern France. In 2013, flower visitors were observed over 3 d per site, in four heathland sites at mont Lozère. Honeybees (Apis mellifera L.) were the main visitors (62-88% of total visitors). Besides honeybees, a high diversity of visitors was detected with 57 different species identified (42 Diptera and 15 Hymenoptera). Hoverflies (Syrphidae, Diptera) visitors were abundant and diverse, especially individuals belonging to the genera Eristalis and Episyrphus. The reported diversity of visitors was probably due to the preservation of large heathland areas at mont Lozère and to the generalist pollination system of C. vulgaris.