Centris pallida reflectance and hair density dataset

Incoming solar radiation (wavelengths 290–2500 nm) significantly affects
an organism’s thermal balance via radiative heat gain. Species adapted to
different environments can differ in solar reflectance profiles. We
hypothesized that conspecific individuals using thermally distinct
microhabitats to engage in fitness-relevant behaviors would show
intraspecific differences in reflectance: we predicted individuals that
use hot microclimates (where radiative heat gain represents a greater
thermoregulatory challenge) would be more reflective across the entire
solar spectrum than those using cooler microclimates. Differences in
near-infrared (NIR) reflectance (700–2500 nm) are strongly indicative of
thermoregulatory adaptation as, unlike differences in visible reflectance
(400–700 nm), they are not perceived by ecological or social partners. We
tested these predictions in male Centris pallida (Hymenoptera: Apidae)
bees from the Sonoran Desert. Male C. pallida use alternative reproductive
tactics that are associated with distinct microclimates: large-morph
males, with paler visible coloration, behave in an extremely hot
microclimate close to the ground, while small-morph males, with a dark
brown dorsal coloration, frequently use cooler microclimates above the
ground near vegetation. We found that large-morph males had higher
reflectance of solar radiation (UV through NIR) resulting in lower solar
absorption coefficients. This thermoregulatory adaptation was specific to
the dorsal surface and produced by differences in hair, not cuticle,
characteristics. Our results showed that intraspecific variation in
behavior, particularly in relation to microclimate use, can generate
unique thermal adaptations that change the reflectance of shortwave
radiation among individuals within the same population.