Jm. Starck, Phenotypic flexibility of the avian gizzard: Rapid, reversible and repeated chances of organ size in response to changes in dietary fibre content, J EXP BIOL, 202(22), 1999, pp. 3171-3179
Evolutionary biology presumes that organ capacities match their natural loa
ds. Therefore, in fluctuating conditions, organ systems are expected to sho
w a reversible, repeatable and rapid phenotypic response that is directiona
l and scaled. In this study, phenotypic responses of the gizzard of adult J
apanese quail (Coturnix japonica) to experimental mismatches of load and ca
pacity were tested by a series of diet-switching experiments, involving an
increased content of non-digestable fibre (NDF) in the diet. The results of
all experiments were in accordance with the predictions of the hypothesis
that there is matching between loads and capacities. (1) The observed pheno
typic responses are directional and scaled to the demands, i.e. increasing
NDF elicits an increase in gizzard size. When the proportion of NDF in the
diet was raised from 1 % to 45 %, the gizzard was more than twice as large
as in the control group. (2) Size responses were reversible, and reduced ND
F was followed by a decrease of gizzard size. (3) Phenotypic responses coul
d be elicited repeatedly in three successive trials. (4) Excess capacities
were downregulated and insufficient capacities mere upregulated. (5) The re
sponses followed changes of loads with almost no time lag, with size change
s measurable within 24 h.