Data from: Temperature-dependent oxygen limitation and the rise of Bergmann’s Rule in species with aquatic respiration

Bergmann’s Rule is the propensity for species-mean body size to decrease
with increasing temperature. Temperature-dependent oxygen limitation has
been hypothesized to help drive temperature–size relationships among
ectotherms, including Bergmann’s Rule, where organisms reduce body size
under warm oxygen-limited conditions, thereby maintaining aerobic scope.
Temperature-dependent oxygen limitation should be most pronounced among
aquatic ectotherms that cannot breathe aerially, as oxygen solubility in
water decreases with increasing temperature. We use
phylogenetically-explicit analyses to show that species-mean adult size of
aquatic salamanders with branchial or cutaneous oxygen uptake becomes
small in warm environments and large in cool environments, whereas body
size of aquatic species with lungs (i.e., that respire aerially), as well
as size of semi aquatic and terrestrial species do not decrease with
temperature. We argue that oxygen limitation drives the evolution of small
size in warm aquatic environments for species with aquatic respiration.
More broadly, the stronger decline in size with temperature observed in
aquatic vs terrestrial salamander species mirrors the relatively strong
plastic declines in size observed previously among aquatic vs terrestrial
invertebrates, suggesting that temperature-dependent oxygen availability
can help drive patterns of plasticity, micro- and macroevolution.