Revista Chilena de Historia Natural 81 (4): 599-612, 2008
REVIEW ARTICLE
Gut size flexibility in rodents: what we know, and don’t know, after a century of
research
Phenotypic plasticity comprises a central concept in the understanding of how organisms
interact with their environment, and thus, is a central topic in ecology and evolution. A particular case of phenotypic plasticity is
phenotypic flexibility, which refers to reversible change in organism traits due to changes in internal or external environmental
conditions. Flexibility of digestive features has been analyzed for more than a century in a myriad of different species and contexts.
Studies in rodents on gut size flexibility have been developed mainly from two different areas of the biological sciences, physiology and
ecology. However, as for several other topics related with physiological ecology, both kinds of studies largely developed along separate
paths. Herein, I evaluate altogether the information belonging to both areas. The major conclusions reached are: (1) there is a clear
match between digestive morphology adjustments and change in environmental conditions, and gut size flexibility could be considered
a widespread physiological mechanism occurring in laboratory and wild species, and under laboratory, semi-natural and natural
conditions. (2) For laboratory species, the experimental factors that have been more investigated are diet quality, reproductive status,
environmental temperature and fasting, while for wild species the more analyzed factors are diet quality and temperature. (3) For wild
rodent species, no differences in small intestine length flexibility between methodological approaches nor species feeding categories
has been identified. (4) It appears that high energetic demands are mainly coped with by changes at the small intestine level, while
changes in the amount of undigestible material in the diet are mainly coped with by changes in the hindgut. (5) Change in gut length
may be related to a decrease in food retention time (e.g., during diet dilution), while change in gut mass appears to be related to a need
of higher specific absorption (e.g., during highly demanding periods). (6) The qualities of an energetic demand (e.g., its relative
intensity) rather than simply its presence or absence can affect the amount of digestive flexibility. (7) Quantitative comparisons of the
existing data are difficult due to several factors, such as the disparity of experimental treatments and differences in the types of data
collected. At the end of this review, further directions for the study of digestive flexibility in rodents are presented.
Key words:
digestive physiology,
phenotypic plasticity, physiological flexibility, rodents
