We now know that a single tree can not be in microbes the unambiguous, meaningful representation of evolutionary history it is in large organisms.
In contrast to the behavioral models applied to body size evolution in large organisms, most studies of size in microbes are biophysical (e.g., Chisholm 1992) or ecological (e.g., size-specific grazing or predation, Hansen 1997).
The contractile vacuole of protozoans, for example, extracts fluid wastes from the cell and eliminates them from the organism, as does the kidney in larger organisms.
Improvement in robustness by increasing efficiencies through cellular redundancies in larger organisms alleviates some of the damaging effects of cellular specialization, which can be expressed in allometric relationships.
With its short and relatively simple lifestyle, Dictyostelium is often used in research to study phagocytosis, cell movement and other processes that are also found in larger organisms.
The proportion of spore to stalk cells is usually around 4 1, although the fraction of stalk cells decreases to as low as 10% in larger organisms [ 7- 9].
In two series of patients treated for peritoneal carcinomatosis with MMC administered in the form of HIPEC, mean plasma half-lives of 76 and 84 min were found, in agreement with the general pharmacological observation of slower drug metabolism in larger organisms [ 6, 14].
While UV-protective compounds have also been found in larger organisms, including fish and their eggs, the presence of these sunscreens has always been attributed to the animal sequestering the compounds from their environment or partnering with a sunscreen-producing microorganism.
The body doesn't break them down, so they amass in larger levels in larger organisms.
However, some aspects of microbial ecology are substantially easier than in large-organism ecology.
Given that MCPH1 functions in cell cycle regulation and DNA damage repair [ 24], it is plausible that positive selection in mysticetes and other mammals is related to the evolution of other phenotypes such as the rate of growth, absolute number of cells, or tumor suppression in very large organisms with long lifespans, although these hypotheses are currently speculative.
