Data from: When Bergmann's rule fails: evidences of environmental selection pressures shaping phenotypic diversification in a widespread seabird

Organisms tend to exhibit phenotypes that can be shaped by climate,
commonly demonstrating clinal variations along latitudinal gradients. In
vertebrates, air temperature plays a major role in shaping body size in
both ectothermic and endothermic animals. However, additional small-scale
environmental factors can also act as selection pressures in the marine
ecosystem (e.g. primary productivity), evidencing multi-scale processes
acting on marine organisms. In this study, we tested Bergmann's rule
in a widely distributed seabird, the brown booby Sula leucogaster, in
addition to evaluating the relationship of sea surface temperature and
chlorophyll α with phenotypes. We used traits from a morphometric dataset
(culmen, wing chord, and tarsus length) and body mass of 276 brown boobies
distributed on six breeding sites along a latitudinal gradient in the
South Atlantic Ocean (0–27°S). We found significant differentiation among
colonies, but phenotypic similarities were observed between colonies
located at the extremes of the latitudinal gradient. As the colony nearest
to the Equator, Saint Peter and Saint Paul archipelago, had the largest
and heaviest individuals, the model containing only air temperature
explained < 5% of the allometric variation, providing no
substantial support for Bergmann's rule. However, when we added the
interaction of chlorophyll α and sea surface temperature the deviance
explained rose to over 80%. Primary productivity and sea surface
temperature do not follow a latitudinal gradient in the ocean and,
therefore, the role of small-scale oceanographic processes in shaping body
size and the importance of considering additional environmental variables
when testing Bergmann's rule in marine organisms are evident.