156
5. VERIFYING MODELS
characterize and predict the dynamics of the transport within the hydrozoan
colony discussed in Sect. 4.7.
Several lines of research indicate the dependence of morphological development on characteristics of gastrovascular physiology during phase 3
polyp behavior. As discussed in Sect. 2.2.3, phase 3 behavior is that characterized as the period of maximum volumetric transport of gastrovascular fluid
through the stolonal network. The importance of this phase of behavior is
not surprising. It represents the period in which physiological integration of
the colony is strongest due to the interaction between all (or nearly all) of
the polyps in a colony. Moreover, morphogenetic signals based on maximal
metabolic activities presumably would convey less ambiguous information
to cells compared to signals during other phases of behavior where their
magnitudes are less and their variance is greater.
Experiments perturbing characteristics of gastrovascular flow and/or
redox state during phase 3 strongly influence the timing of polyp and stolon
tip morphogenesis. Blackstone and Buss (1992, 1993) manipulated flow and
redox state by treatment with loose couplers of oxidative phosphorylation,
such as z.a-dinitrophenol (DNP), and assayed the effects on colony development. Such compounds diminish ATP production thereby diminishing the
energy available to transport fluid and, consequently, the volumetric rate
of transport declines. The effects on morphology are dramatic. In Podocoryne carnea , diminished flowaccelerates polyp and stolon tip morphogenesis
so that treated colonies appear much more sheet-like. Manipulation of gastrovascular physiology with loose couplers of oxidative phosphorylation or
excessive overfeeding (which also slows fluid transport) generates a physiological state of relative oxidation, and in all experiments using P. carnea
similarly accelerates the production of polyps and stolon tips. These perturbations also show a dose-response effect: an increase in the level of treatment
increases the effect on morphology (Blackstone 1997).
Treatment with inhibitors of electron transport, such as azide, also diminish flow rate, but have the opposite effect on redox state; colonies become
relatively reduced (Blackstone 1999). In this case, colonies of P. carnea produce fewer,larger polyps and fewer stolon tips and become more runner-like.
This suggests that in P. carnea, variation in redox chemistry associated with
gastrovascular transport regulates morphological development.
The results from perturbation experiments in Podocoryne carnea parallel the patterns of morphology and gastrovascular physiology in phase 3
observed in other studies. Colonies that exhibit higher volumetric rates
of flow also exhibit greater redox variation and are associated with more
rapid elongation of stolons and lower rates of stolon branch and polyp bud
formation (Blackstone 1996, 1998). For instance, colonies of Hydractinia symbiolongicarpus show a more sheet-like form than does P. carnea. They also
show lower rates of flow than P. carnea following the formation of stolonal
mat tissue early in development and thereafter (Blackstone 1996). Finally,
colonies of P. carnea derived from inbred lines and selected on the basis of
morphology show the predicted patterns of flow and redox variation (Blackstone 1998). Runners have both greater volumetric rates of flow and greater
variation in redox state than sheet colonies.
In neither case of reduced flow rate or redox state change is it known
whether both polyp buds and stolon tips are regulated directly. It may be
that they are regulated separately by the different putative causes, or one
5. VERIFYING MODELS
characterize and predict the dynamics of the transport within the hydrozoan
colony discussed in Sect. 4.7.
Several lines of research indicate the dependence of morphological development on characteristics of gastrovascular physiology during phase 3
polyp behavior. As discussed in Sect. 2.2.3, phase 3 behavior is that characterized as the period of maximum volumetric transport of gastrovascular fluid
through the stolonal network. The importance of this phase of behavior is
not surprising. It represents the period in which physiological integration of
the colony is strongest due to the interaction between all (or nearly all) of
the polyps in a colony. Moreover, morphogenetic signals based on maximal
metabolic activities presumably would convey less ambiguous information
to cells compared to signals during other phases of behavior where their
magnitudes are less and their variance is greater.
Experiments perturbing characteristics of gastrovascular flow and/or
redox state during phase 3 strongly influence the timing of polyp and stolon
tip morphogenesis. Blackstone and Buss (1992, 1993) manipulated flow and
redox state by treatment with loose couplers of oxidative phosphorylation,
such as z.a-dinitrophenol (DNP), and assayed the effects on colony development. Such compounds diminish ATP production thereby diminishing the
energy available to transport fluid and, consequently, the volumetric rate
of transport declines. The effects on morphology are dramatic. In Podocoryne carnea , diminished flowaccelerates polyp and stolon tip morphogenesis
so that treated colonies appear much more sheet-like. Manipulation of gastrovascular physiology with loose couplers of oxidative phosphorylation or
excessive overfeeding (which also slows fluid transport) generates a physiological state of relative oxidation, and in all experiments using P. carnea
similarly accelerates the production of polyps and stolon tips. These perturbations also show a dose-response effect: an increase in the level of treatment
increases the effect on morphology (Blackstone 1997).
Treatment with inhibitors of electron transport, such as azide, also diminish flow rate, but have the opposite effect on redox state; colonies become
relatively reduced (Blackstone 1999). In this case, colonies of P. carnea produce fewer,larger polyps and fewer stolon tips and become more runner-like.
This suggests that in P. carnea, variation in redox chemistry associated with
gastrovascular transport regulates morphological development.
The results from perturbation experiments in Podocoryne carnea parallel the patterns of morphology and gastrovascular physiology in phase 3
observed in other studies. Colonies that exhibit higher volumetric rates
of flow also exhibit greater redox variation and are associated with more
rapid elongation of stolons and lower rates of stolon branch and polyp bud
formation (Blackstone 1996, 1998). For instance, colonies of Hydractinia symbiolongicarpus show a more sheet-like form than does P. carnea. They also
show lower rates of flow than P. carnea following the formation of stolonal
mat tissue early in development and thereafter (Blackstone 1996). Finally,
colonies of P. carnea derived from inbred lines and selected on the basis of
morphology show the predicted patterns of flow and redox variation (Blackstone 1998). Runners have both greater volumetric rates of flow and greater
variation in redox state than sheet colonies.
In neither case of reduced flow rate or redox state change is it known
whether both polyp buds and stolon tips are regulated directly. It may be
that they are regulated separately by the different putative causes, or one