Biology subjects

Spaethe, J.

Publications and source records attributed to Spaethe, J..

6 recordsLinked to original sources

bioRxiv2026

No need for fat: Nutritional preferences affect pollen foraging networks in alpine pollinator communities

Most flowering plant species rely on insect pollinators for successful cross-pollination. While floral color, scent, and morphology help attract visitors, the primary motivation for visiting a flower is the nutritional reward - nectar and, especially, pollen. Pollen provides a complete set of macro- and micronutrients essential for adult and larval provisioning in many insect flower visitors. However, pollen nutrient composition (i.e., quality) varies widely among plant species, and different visitors may have distinct nutritional requirements. Whether these differences are linked to the selection of plants visited remains poorly understood. In this study, we investigated whether the nutrient composition of pollen is linked to the visitation patterns of two main alpine pollinator groups: bumblebees and hoverflies. We observed flower visits in the field and identified the origin of pollen collected by bumblebees and hoverflies via metabarcoding. In addition, we analyzed the nutrient profiles of alpine flowering plants from the same habitat, including amino acids, fatty acids, and sterols. We hypothesized that both bumblebees and hoverflies (i) differ in the plant spectrum they were observed on/collected from and visited for pollen collection, (ii) and that preferred nutrient profiles differ between the two pollinator groups. We additionally expected (iii) that, in the studied alpine plant communities, the nutrient composition of pollen of plant species collected by flower visitors is more strongly associated with pollinator identity than with plant phylogeny due to competition for pollinators. Our results revealed that alpine bumblebees and hoverflies were more similar in their pollen hosts and nutritional preferences than expected, but, for both groups, the network based on observed flower visits differed significantly from that based on pollen collection. Pollen fatty acids and amino acids content was positively correlated, and both bumblebees and hoverflies preferred pollen with low fatty and amino acid content. Pollen sterols did not differ between plants collected by pollinators and non-collected plants. Neither fatty acid, amino acid, nor sterol composition was linked to plant phylogeny. Our findings suggest that not only amino acid content, but also fatty acid content, plays a key role in shaping pollen-collection patterns of flower visitors in alpine ecosystems.

animal behavior and cognition↗

bioRxiv2026

Differential effectiveness of bee and beetle pollinators creates flower colour polymorphism

Floral diversity is the hallmark of Angiosperms and is often shaped by pollinator-mediated selection, which drives floral divergence as plants evolve traits that attract specific pollinator groups. Mediterranean red, bowl-shaped flowers are specialized on pollination by glaphyrid beetles in areas with beetles and bees but evolved different colours and specialize on bees as pollinators when beetles are absent. What explains this geographic variation in specialization and concomitant flower colour differences? We assessed pollination effectiveness of honeybees and glaphyrids for the colour-polymorphic Anemone pavonina in its natural habitat. We recorded the duration and number of flower visits and quantified single-visit seed set. Per-visit effectiveness (relative seed set) was threefold higher for Pygopleurus (36.3%) than for honeybees (9.5%). Flower visitation lasted substantially longer for beetles (56.3 sec. on average) than for honeybees (2.3 sec.). For beetles, pollinator importance (single-visit seed set x visitation frequency) was highest at low elevations but declined with increasing elevation, whereas for bees pollinator importance remained low yet constant across the elevational gradient. The high pollinator effectiveness of beetles indicates that floral specialization for this pollinator group is advantageous, even to the point that excluding low-quality bee pollinators - by producing inconspicuous flower colours - is beneficial. Non-red flowers may only be beneficial at higher elevations, where bee pollinator importance exceeds that of beetles.

animal behavior and cognition↗

bioRxiv2024

Bumblebees flexibly adjust learning and decision strategies to sensory information content in a foraging task

When making decisions, humans and animals often rely on multiple sensory cues simultaneously. These provide complementary sources of information, which can help overcome ambiguity and noise, and increase the accuracy of decisions. While most studies have focused on the benefits of multimodal and within-mode integration for learning and decision making, their costs have received less attention. Processing, learning and memorizing multiple inputs requires more neural resources than for single cues, and might also require more time. In this study, we tested whether insects trade off the costs and benefits of learning multiple cues in a foraging task, using the buff-tailed bumblebee Bombus terrestris. To maximize comparability between cues, we presented combinations of visual-only features, as found on natural flowers: colours of varying discriminability, paired with shapes or patterns. We found that the bees relied exclusively on colours when these were easy to discriminate, and did not learn pattern or shape features presented simultaneously. With harder to discriminate colours, the bees learned both colour and shape or pattern features. Our results demonstrate that bumblebees flexibly adjust their learning strategies when presented with visual features of varying discriminability, to balance the costs and benefits of multi-cue learning. Our analysis of the learning rates of the bees with multi- and single attribute stimuli suggests that blocking could serve as a mechanism to implement this strategy switch. These results shed light on trade-offs in learning and decision making with multiple cues, and can directly be compared to studies in other insects, animals and humans. Significance StatementWhen making decisions, animals often rely on multiple sensory cues simultaneously. These complementary sources of information can increase decision accuracy. Unlike the benefits of cue integration, their costs have received less attention. In this study, we tested whether insects trade off the costs and benefits of learning multiple cues in a foraging task. We trained buff-tailed bumblebees, Bombus terrestris, to feature combinations of natural flowers. Bees flexibly switched from linear integration to winner-takes-all decision strategies depending on the sensory information available, thereby balancing accuracy and time investment in the task. We find that this switch can be explained by the cognitive phenomenon of blocking; providing the ground for future investigations into the underlying neural mechanisms of flexible decision strategies.

animal behavior and cognition↗

bioRxiv2023

Cuticular hydrocarbon profiles of Himalayan bumble bees (Hymenoptera: Bombus Latreille) are species-specific and show local and elevation related variation

Bumble bees are important pollinators in natural environments and agricultural farmlands and are in particular adapted to harsh environments like high mountain habitats. In these environments, animals are exposed to low temperature and face the risk of desiccation. The Eastern Himalayas are one of the recognized biodiversity hotspots worldwide. The area covers subtropical rainforest with warm temperature and high precipitation as well as high mountain ranges with peaks reaching up to 6000 m, shaping a diverse floral and faunal community at the different altitudinal zones. We investigated the cuticular hydrocarbon profiles of four bumble bee species occurring at different elevational ranges in Arunachal Pradesh, the northeast most state in India. At 17 locations along an elevational gradient we collected workers of two species from lower elevations (B. albopleuralis and B. breviceps; [~] 100m - 3000m asl) and two species from higher elevations (B. prshewalskyi and B. mirus; [~] 2800m - 4,500m asl). The CHC profiles of all four species showed a significant degree of variation in the composition of hydrocarbons, indicating species specificity. We also found clear correlation with elevation. The weighted mean chain length of the hydrocarbons significantly differed between the low and high altitudinal species, and the proportion of saturated hydrocarbons in CHC profiles significantly increased with the elevational range of the bumble bee species. Thus, these four species of bumble bees in the eastern Himalayas seem to adapt their CHC composition to elevation by decreasing water permeability of their cuticle, similar to insects living in dry mountains or deserts habitats.

ecology↗

bioRxiv2022

Flower patterns improve foraging efficiency in bumblebees independent of nectary guidance

Colourful patterns on flowers are thought to benefit both pollinators and the plants they visit, by increasing the plants pollination success via an improved foraging efficiency of its pollinators. This increased efficiency is thought to result from a guidance effect of the flower patterns, correspondingly termed nectar guides, which indicate the position of the nectary to visiting pollinators. While it is well established that flower patterns play an important role in flower choice, the mechanisms underlying their function for flower-visiting insects remain poorly understood. In this study, we quantified the contributions of patterns to all phases of flower interaction in the buff-tailed bumblebee (Bombus terrestris). We analysed their flight paths, as well as landing positions and walking tracks on artificial flowers with different pattern types. We reveal that flower patterns improved the overall foraging efficiency of the bees by up to 30%, by guiding their approach flight, landing positions, and departure decisions. Surprisingly, these effects were not related to nectary guidance. Since we conducted the experiments with experienced foragers, which represent the majority of insect pollinators active in nature, the newly described nectary-independent guidance effects of flower patterns are of fundamental importance to plant-pollinator interactions under natural conditions.

ecology↗

bioRxiv2018

Species composition and altitudinal distribution of bumble bees (Hymenoptera: Apidae: Bombus) in the East Himalaya, Arunachal Pradesh, India

The East Himalaya is one of the worlds most biodiverse ecosystems. Yet, very little is known about the abundance and distribution of many plant and animal taxa in this region. Bumble bees are a group of cold-adapted and high altitude insects that fulfill an important ecological and economical function as pollinators of wild and agricultural flowering plants and crops. The Himalayan mountain range provides ample suitable habitats for bumble bees. Himalayan bumble bees have been studied systematically for a few decades now, with the main focus on the western region, while the eastern part of the mountain range received little attention and only a few species are genuinely reported. During a three-year survey, we collected more than 700 bumble bee specimens of 21 species in Arunachal Pradesh, the largest of the north-eastern states of India. We collected a range of species that were previously known from a very limited number of collected specimens, which highlights the unique character of the East Himalayan ecosystem. Our results are an important first step towards a future assessment of species distribution, threat and conservation. We observed clear altitudinal patterns of species diversity, which open important questions about the functional adaptations that allow bumble bees to thrive in this particularly moist region in the East Himalaya.

zoology↗