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Abstract Historical data suggest that many bee species have declined in body size. Larger‐bodied bees with narrow phenological and dietary breadth are most prone to declines in body size over time. This may be especially true in solitary, desert‐adapted species that are vulnerable to climate change such asCentris pallida(Hymenoptera: Apidae). In addition, body size changes in species with size‐linked behaviours could threaten the prevalence of certain behavioural phenotypes long‐term.C. pallidasolitary bees are found in the Sonoran Desert. Males use alternative reproductive tactics (ARTs) and are dimorphic in both morphology and behaviour.C. pallidamale body size has been studied since the 1970s in the same population. The authors collected body size data in 2022 and combined it with published records from 1974–2022. The authors find a persistent decline in the mean head width of patrolling males, and shifts towards smaller body sizes in the populations of males found foraging and hovering. Both morphs declined in average body size, and the proportion of large‐morph males in the population decreased by 8%. Mating males did not decline in mean body size over the last five decades. The authors discuss hypotheses related to the decline inC. pallidamale head width. Finally, the authors advocate forC. pallidaas an excellent study system for understanding the stability of ARTs with size‐linked behavioural phenotypes.
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Individual reflectance of solar radiation confers a thermoregulatory benefit to dimorphic males bees (Centris pallida) using distinct microclimates
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 maleCentris pallida(Hymenoptera: Apidae) bees from the Sonoran Desert. MaleC.pallidause 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, particular in relation to microclimate use, can generate unique thermal adaptations that changes the reflectance of shortwave radiation among individuals within the same population.
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- Award ID(s):
- 2109399
- PAR ID:
- 10471861
- Editor(s):
- Cini, Alessandro
- Publisher / Repository:
- PLoS
- Date Published:
- Journal Name:
- PLOS ONE
- Volume:
- 18
- Issue:
- 3
- ISSN:
- 1932-6203
- Page Range / eLocation ID:
- e0271250
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1371/journal.pone.0271250
