46
2. ENVIRONMENTALLY DRIVEN PLASTICITY
the greater extent of stolon branches that connect different parts of a colony
and mitigate the effect of a spatially patchy food supply.
Changes in the timing and placement of polyps and stolon branches
are manifest by experimentally manipulating either the flow rate or the distribution of flow throughout a colony (Blackstone and Buss 1993, Dudgeon
and Buss 1996). Likewise, colony development can be affected by manipulation of redox state independent of gastrovascular flow patterns (Blackstone
1999). The relationship between gastrovascular transport and redox state in
effecting a morphogenetic response is complex and it is likely that they act
in concert.
Both mechanisms hypothesized to regulate morphological plasticity are
products of polyp feeding behavior. The ingestion of food triggers oscillations
by a polyp that pumps fluid and eventually the digested prey to the rest of the
colony (Dudgeon et al. 1999). These oscillations are caused by contraction
of epitheliomuscular cells of the polyp that shifts their redox state such
that active polyps become oxidized relative to inactive polyps (Blackstone
1999). The behavior of polyps clearly varies over time in response to food
availability. Therefore, the dynamics of polyp feeding behavior are an integral
component to models of the regulation of morphological plasticity via the
interplay of gastrovascular flow and redox chemistry.
The importance of polyp oscillations to colony development makes it
necessary to characterize the range of polyp behaviors, both alone and when
interacting with other polyps. If polyp behavior is sufficiently simple and predictable under specified conditions, then quantitative models of that behavior
may enable prediction of gastrovascular flow and redox gradient patterns
within a colony. Polyp behavior can be characterized from the dynamics of
their oscillations with respect to the timing of ingestion of food . Dudgeon
et al. (1999) characterized oscillations in terms of changes in polyp length
and volume over a time course beginning prior to ingestion and terminating
after regurgitation of undigested material. Polyps prior to feeding, or long
after regurgitation, behave simply. Contractions are infrequent, they lack periodicity, and the amplitude of volume exchange with the stolon is small
(Fig. 2.27). The behaviors of polyps between ingestion and regurgitation can
be classified into three distinct phases. These phases of behavior reflect differing input-output relationships between the polyp and either the external
(via the mouth) or internal (via the polyp-stolon junction) environment.
(a)
14
(b)
14 Lag diagram of polyp oscillations
prior to feeding
Fig.2.27. (a) Volume of the polyps of
Podocoryne carnea prior to feeding.
(b) Lagplot of the oscillations in polyp
length and volume of the polyps of
Podocoryne carnea prior to feeding
12
4
2
-35
-30
-25
-20
-15
-10
Time (minutes pr ior to feeding)
....
~ 12
+
- '" 10
.§
til 8
:5~ 6
~ 4
2
2
4
6
8
10
12
14
Volume (nl) at time t
2. ENVIRONMENTALLY DRIVEN PLASTICITY
the greater extent of stolon branches that connect different parts of a colony
and mitigate the effect of a spatially patchy food supply.
Changes in the timing and placement of polyps and stolon branches
are manifest by experimentally manipulating either the flow rate or the distribution of flow throughout a colony (Blackstone and Buss 1993, Dudgeon
and Buss 1996). Likewise, colony development can be affected by manipulation of redox state independent of gastrovascular flow patterns (Blackstone
1999). The relationship between gastrovascular transport and redox state in
effecting a morphogenetic response is complex and it is likely that they act
in concert.
Both mechanisms hypothesized to regulate morphological plasticity are
products of polyp feeding behavior. The ingestion of food triggers oscillations
by a polyp that pumps fluid and eventually the digested prey to the rest of the
colony (Dudgeon et al. 1999). These oscillations are caused by contraction
of epitheliomuscular cells of the polyp that shifts their redox state such
that active polyps become oxidized relative to inactive polyps (Blackstone
1999). The behavior of polyps clearly varies over time in response to food
availability. Therefore, the dynamics of polyp feeding behavior are an integral
component to models of the regulation of morphological plasticity via the
interplay of gastrovascular flow and redox chemistry.
The importance of polyp oscillations to colony development makes it
necessary to characterize the range of polyp behaviors, both alone and when
interacting with other polyps. If polyp behavior is sufficiently simple and predictable under specified conditions, then quantitative models of that behavior
may enable prediction of gastrovascular flow and redox gradient patterns
within a colony. Polyp behavior can be characterized from the dynamics of
their oscillations with respect to the timing of ingestion of food . Dudgeon
et al. (1999) characterized oscillations in terms of changes in polyp length
and volume over a time course beginning prior to ingestion and terminating
after regurgitation of undigested material. Polyps prior to feeding, or long
after regurgitation, behave simply. Contractions are infrequent, they lack periodicity, and the amplitude of volume exchange with the stolon is small
(Fig. 2.27). The behaviors of polyps between ingestion and regurgitation can
be classified into three distinct phases. These phases of behavior reflect differing input-output relationships between the polyp and either the external
(via the mouth) or internal (via the polyp-stolon junction) environment.
(a)
14
(b)
14 Lag diagram of polyp oscillations
prior to feeding
Fig.2.27. (a) Volume of the polyps of
Podocoryne carnea prior to feeding.
(b) Lagplot of the oscillations in polyp
length and volume of the polyps of
Podocoryne carnea prior to feeding
12
4
2
-35
-30
-25
-20
-15
-10
Time (minutes pr ior to feeding)
....
~ 12
+
- '" 10
.§
til 8
:5~ 6
~ 4
2
2
4
6
8
10
12
14
Volume (nl) at time t