Climate is changing at accelerated rates across the globe, and under these novel environmental conditions species will need to adapt or perish. For the 3rd year of the Pollinator in Changing Climates NSF-IRES course, we have continued investigating the physiological and functional traits of plants and pollinators to better predict species responses to the rapid ongoing environmental changes. In 2023, we worked with 9 students from the USA and Colombia and 4 mentors from Penn State (USA) on the following four projects:
1. How does shade impact plant vegetative, reproductive, and floral traits?
2. Does within-species variation in body size and color offer an advantage to bees across elevation and temperature gradients?
3. Does variation in body and appendage size across elevation and temperature gradients in bee communities?
4. Can barcodes and raspberry pis be implemented to study foraging behavior in social bees?
To investigate question 1, Lizeth (Liz) Russy and Maya Zepeda investigated how shade affects vegetative (plant height, leaf canopy area, leaf temperature), floral (number of flowers), reproductive (number of fruits), and photosynthetic (stomatal conductance, transpiration, internal CO2 concentration) traits in four key crops in Colombia (blueberry, raspberry, strawberry, and goldenberry). The results of this study revealed that crops have diverse responses to the reduction of sunlight (shade). Specifically, blueberries and strawberries benefit from shade conditions as they showed increased plant height, canopy area, and photosynthetic rates compared to plants exposed to full sun. In contrast, raspberries and goldenberries overall underperformed in shade conditions. Many high-elevation areas in tropical ecosystems will experience increased precipitation and cloudiness with climate change. Under these conditions, crops such as blueberries and strawberries will be better suited for cultivation in these areas. Liz and Maya explain all the details of what they did and found in the video below.
For question 2, Sabrina Scothorn and Owen Akiyama investigated how color and body size affect the thermoregulatory capacity of two widespread Andean bees: the social bumble bee Bombus pauloensis and the solitary long-horned bee Thygater aethiops. Specifically, they tested the thermal melanism hypothesis—poses that dark coloration facilitates higher and faster heating up—and Bergman’s rule—which states that individuals of larger size are found in colder environments than in warmer regions. Using specimens from insect collections and freshly collected individuals, they found that both color and body size impact the thermoregulatory capacity of these but in different ways. For the social bumble bee B. pauloensis, size but not color increased the thoracic temperature of the bees in flight. However, darker colors heat up faster in this species but only for small individuals. These results suggest that the importance of color and body size interact and it is likely advantageous for colonies to have large within-colony variations for both of these traits. In contrast, for the solitary long-horned bee T. aethiops, color but not size was associated with higher thoracic temperatures of individuals at flight. Similarly, darker individuals of T. aethiops were found more frequently at higher elevations. Taken all together, results from this study suggest that social species may have more plasticity to adapt to changes in temperature and that darker morphs may be at a disadvantage as temperatures continue to increase. Check out the video below where Owen and Sabrina explain in detail the results of their experiments.
Question 3 was investigated by Gabriella (Gabbie) Hoffmann, Daniel Nossa, and Harold Pulido. They investigated how bee communities and their functional traits change along elevational gradients that have steep changes in average ambient temperature. Specifically, they tested three hypotheses:
(1) the species-energy hypothesis posits that the amount of available energy limits species richness thus, high-elevation sites with decreased solar energy are less species-rich,
(2) Bergman’s rule which states that overall species that inhabit colder environments exhibit larger body sizes than species in warmer regions, and
(3) Allen’s rule posits that animals adapted to cold climates have shorter limbs and bodily appendages than animals adapted to warm climates.
They tested these hypotheses by comparing community diversity (species richness) and functional traits (body size, wing relative length, and tibia relative size) across sites varying in elevation from 700 to 3700 meters above sea level. Their results show support for all of these hypotheses in Andean bee communities: there is lower species diversity in higher elevations, average body size increases with elevation, and appendages are shorter in higher elevations. These findings strongly indicate that bee biodiversity shows strong responses to variations in elevation and temperature, and implies that ongoing rising temperatures will have dramatic effects on the species composition and traits of these critical pollinators. Check out details about their project here.
The last group (composed by Sofia Jordan and María Alejandra Chavez) investigated the possibility of implementing Apriltags connected to the body of the bees and used cameras as automated readers to study whether larger body size is advantageous for bumble bee foraging early in the morning when ambient temperatures are low. This group successfully designed and implemented an automated system to study foraging behavior in bumble bees. Using the Andean species Bombus pauloensis, they marked large and small individuals within one colony to investigate the frequency of foraging throughout the day. Their preliminary results suggest that larger individuals begin flying out of the colony earlier in the day than individuals of small body sizes. These technologies will greatly facilitate studies of bumble bee foraging behavior in the context of climate change.
Projects from this year’s IRES course have revealed strong evidence that the diversity of plant and bee pollinator traits may facilitate adaptations to ongoing climate changes, at least in some species. This course was a huge success and had the participation of students from the United States and Colombia working in collaboration on all of these independent studies. We will continue to work on these studies to share our results with the scientific community through peer-review publications.
Project funded by NSF OISE-1952470 and administered by the López-Uribe Lab in the Department of Entomology at Penn State University
Contributed post by
Margarita M. López-Uribe
Associate Professor in Pollinator Health
Pennsylvania State University
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