Bergmann’s rule
Bergmann’s rule, which states that body size decreases among congeneric
species with decreasing latitude, has primarily been studied in mammals
and birds. Not all birds and mammals follow the rule, and even fewer
smaller organisms, such as insects, conform to it (Blackburn et
al. 1999a; Meiri & Dayan 2003). However, some evidence supports
Bergmann’s rule in microorganisms, such as bacterioplankton (Meadoret al. 2009), with smaller cells at higher temperatures
(Daufresne et al. 2009).
We found no studies testing a mechanism behind this pattern in
microorganisms, but one explanation for Bergmann’s rule among
prokaryotes may be that as temperature increases, nucleic acid content
decreases, resulting in smaller cells (Huete-Stauffer et al.2016). Though studying this rule in microorganisms may provide useful
insights for the evaluation of the ecological impacts of global change
on microbiota, there are significant challenges in defining the size of
many microorganisms, such as multicellular fungal hyphae, that must be
standardized before rigorous comparisons can be drawn.