Data from: Altitude sickness in pollinators: Skyward emigration holds consequences for a native bee

With the increasing severity of climate stressors, the elevational ranges
of plant and animal species are pushing skyward. The channeling and
redistribution of species is expected to increase in frequency and
magnitude globally. However, any elevational gradient will be associated
with decreasing air pressure, which will impose a degree of hypoxia on
colonizing organisms. Insect species developing under depleted oxygen (O2)
concentrations in controlled laboratory conditions are known to exhibit
smaller adult sizes, reduced reproductive capacity, and lower survival
rates, all of which represent major fitness consequences for insects. This
begs the question as to whether altitudinal hypoxia might produce the same
types of consequences as artificially reduced O2 in laboratory
experiments. With this question in mind, we observed the development of a
native bee species, Osmia lignaria across an elevational gradient
in the Rocky Mountains, USA. Known commonly as the blue orchard bee, O.
lignaria is a univoltine (single generation per year) solitary
(non-social) bee that nests within hollow stems and reeds. Fully
provisioned reeds were collected in the foothills of the Rocky
Mountains in Salt Lake City, UT, and were distributed among three sites
representing an elevational gradient: 1300 m, 1900 m, and 2500 m. The
fully provisioned reeds were placed within unsealed plastic containers, in
climate-controlled indoor spaces at each of the three elevations. Here we
report a series of observations that reveal a surprising pattern of
uneaten pollen-provisions, increased mortality, and markedly reduced sizes
among the bees at higher elevations. The incidence of uneaten pollen
increased with rising altitude, while pupal (or adult) weights declined
with altitude, suggesting that with increasing altitude, the bee larvae
ceased feeding prematurely, becoming smaller pupae/adults. As pollinator
populations emigrate skyward, these communities will likely exhibit a
diversity of responses to altitudinal hypoxia, with each species
potentially experiencing its own ‘hypoxia ceiling.’ Given that bees are
key players in the foundational mutualisms between microbes and flowering
plants and that declining pollinator diversity has been linked to reduced
plant diversity, the basic functioning of high-elevation ecosystems may be
constrained by the ceilings imposed upon pollinator populations.