Climate change is affecting our native pollinators, but not in ways we understand mechanistically. What happens if temperature alters their nesting biology? I study the effects of rising temperatures on the nesting of a common desert native bee, the Desert Carpenter Bee (Xylocopa californica). Read on to learn about my projects:
Dissertation Work: Can carpenter bees tolerate temperatures projected in the next 50 years in the Sky Islands?
What temperatures can carpenter bees tolerate?
Adult carpenter bees die between 50-51ºC (122-124ºF). But–Do developing larvae have the same thermal tolerances as adults? Could projected extreme temperatures place the species at risk during a previously unobserved life stage? I used flow-through thermolimit respirometry to assess the critical thermal maxima (CTmax) of carpenter bees at all life stages, and found them to be significantly lower in early-instar larvae than in pupae.
Insects can survive extreme temperatures briefly, but could lower sustained average temperatures still be lethal over extended time periods? Barring extreme temperature events, this could be a more ecologically relevant way of approaching thermal tolerance. I raised carpenter bees from egg to adult at 25, 30, and 40ºC, and measured survival, growth rate, and ultimate adult size. Interestingly, no bees survived to adulthood at 40ºC (104ºF), indicating that there could be a much lower long-term thermal limit than that indicated by the CTmax experiments described above. Growth rate and adult size were also influenced by temperature, suggesting indirect ecological effects of a warmer climate.
What temperatures do carpenter bees actually experience during development?
To find out, I enlisted the help of Flowing Wells High School students via a 4-week lecture/lab series during their Advanced Biotech class. Four students enjoyed their project so much that we developed an internship to allow them to continue over the summer. With the help of these students, we built Arduino-based devices that can measure temperatures inside and outside the nests of carpenter bees, using 8 thermocouple probes each. The students learned to solder in order to assemble the devices, and later learned to successfully calibrate the thermocouples. We are now in the troubleshooting stage of programming these devices, and plan to use them to collect temperature data inside carpenter bee nests in the next season.
You can see a photo of our devices here:
Where do we find carpenter bees’ thermal niche in the Sky Islands? Where will we still find it in 50 years?
To determine how projected temperatures in the Southwest will impact where carpenter bees and their sotol nest plants can survive, I will construct a Species Distribution model using the ‘dismo’ package in R. This will project carpenter bee and sotol distributions over the next 50 years under a range of climate scenarios. Updates coming in fall 2020!
Birds and Bees: Are carpenter bees evolving behavioral adaptations to avoid predation from woodpeckers? With Chloe Burkholder. Carpenter bees build their nests in the woody flower stalk of plants like sotol (Dasylirion wheeleri), where they are subject to predation during development. The densely packed, barbed leaves of the sotol plant could offer protection from woodpecker predators. To test this, we measured locations of bird pecks (evident from damage on the outside of sotol stalks), leaf height of the sotol plant, and entrance heights of carpenter bee nests. We found that most nests are placed below the leaf height, that most pecks occur above the leaf height, and that nests that avoided predation were placed lower than those that were pecked. Results suggest that woodpeckers may place selective pressure on bees to build their nests lower.
Inside Cells: Can we use ventilatory rates to accurately identify sleep in honey bees while they are mostly hidden within comb cells? With Barrett A. Klein.
Klein, B. A. & Kathryn Busby, M. Slumber in a cell: honeycomb used by honey bees for food, brood, heating… and sleeping. PeerJ. 8, e9583 (2020).
Honey bees pump their gaster when they breathe, which can be visually tracked. We used JWatcher to analyze the ventilatory pumps of honey bees performing each of four behaviors: discontinuously ventilating (sleeping), feeding, cleaning, and heating. To observe their behaviors inside cells, we used a cross-section of an observation colony covered with a thin layer of plastic wrap. This thin covering enabled temperature measurements using a FLIR thermal video camera, to verify differentiation of heaters from other behaviors. Sleep had a distinct ventilatory rate from the other behaviors, and heater bees had a significantly different body temperature from other behaviors.