Exogenous environmental changes are known to affect the intrinsic characteristics of
biological organisms. For instance, the synthesis rate of the morphogen decapentaplegic
(Dpp) in a
Drosophila wing imaginal disc has been found to double with an increase
of
C
in ambient temperature. If not compensated, such a change would alter the signaling
Dpp gradient significantly and thereby the development of the wing imaginal disc. To
learn how flies continue to develop “normally” under such an exogenous change,
we formulate in this paper a spatially two-dimensional reaction-diffusion
system of partial differential equations (PDE) that accounts for the biological
processes at work in the
Drosophila wing disc essential for the formation of
signaling Dpp gradient. By way of this PDE model, we investigate the effect
of the apical-basal thickness and anteroposterior span of the wing on the
shape of signaling gradients and the robustness of wing development in an
altered environment (including an enhanced morphogen synthesis rate).
Our principal result is a delineation of the role of wing disc size change in
maintaining the magnitude and shape of the signaling Dpp gradient. The result
provides a theoretical basis for the observed robustness of wing development,
preserving relative but not absolute tissue pattern, when the morphogen
synthesis rate is significantly altered. A similar robustness consideration for
simultaneous changes of multiple intrinsic system characteristics is also discussed
briefly.
Dedicated to Charles and Marie-Louise
Steele for their years of outstanding management of IJSS and
JoMMS,and for their more than forty years of warm friendship
with the last author.