5. Lipid Dietary Dependencies in Zooplankton
99
Animals maintained on the ambient epilimnial phytoplankton without supplementations were considered controls. A clutch size response to the addition of algae
(AnkistrodesmusJalcatus) would imply food limitation, which could be due either
to food quantity (total food hypothesis) or to food quality. Response to TAG
supplements but not to EFAs or protein would suggest that energy reserves limited
reproduction (total lipid hypothesis). Response to the EFA supplements (linoleic
and linolenic) but not to TAG or protein would suggest that these fatty acids were
limiting in the diet (EFA hypothesis). A response to protein but not to TAG or
EFAs suggests that protein may be the limiting factor (protein hypothesis). We
also monitored clutch sizes of the ambient populations throughout the experiment,
and averages of these data are given in the table legends for each experiment.
The results of the first experiment with algae and TAG supplements suggest
Daphnia catawba from Lake Lacawac were food limited, as both clutch size and
lipid reserves increased with increased food concentration (Table 5.2). TAG microcapsule supplements caused a substantial increase in visible lipid in the body
but did not enhance fecundity. The results of this experiment prompted us to
develop the EFA microcapsules and protein microparticles used in subsequent
experiments.
As in the previous experiment, Daphnia catawba collected from Lake Lacawac
in late June 1989 responded to algal supplements by increasing clutch size (Table
5.3). Protein alone produced a statistically significant response. In July (Table
5.4), a slight but statistically significant food limitation was apparent, but the
protein effect was not statistically significant. The lower fecundities in the control
and treatment bottles versus the lake population may have been caused by the use
of three animals per vessel, a decision made to counteract increased clutch size
when single Daphnia catawba were placed in vessels.
Daphnia pulicaria was studied in Lake Waynewood in August 1989, when it
was the dominant large zooplankter (three to four individuals per liter) and cyanobacteria were abundant, especially Anabaena planktonica and Aphanizomenon
flos-aquae. D. pulicaria responded to protein supplements with a slight but statistically significant increased clutch size (Table 5.5). The algal supplement, repreTABLE 5.2. Supplement experiment started on May 24, 1988, with Daphnia catawba
from Lake Lacawac, pA.a
Clutch size
Lipid index
Treatment
n
X
SD
ph
X
SD
Control
19
1.2
0.4
0.8
0.3
pc'
+TAG
20
I.Sd
1.2
NS
2.1
0.5
<.05
+Algae
6
5.1
1.9
<.001
1.67
0.4
NS
a+ TAG, triacylglycerol microcapsules; +Algae, A. faleatus; NS, not significant. Mean body length of
lake adults during experiment is 1.5 mm (SD, 0.12).
bLinear contrasts with the control following ANOYA.
'Fisher's exact test of medians.
dlncludes degenerate eggs.
99
Animals maintained on the ambient epilimnial phytoplankton without supplementations were considered controls. A clutch size response to the addition of algae
(AnkistrodesmusJalcatus) would imply food limitation, which could be due either
to food quantity (total food hypothesis) or to food quality. Response to TAG
supplements but not to EFAs or protein would suggest that energy reserves limited
reproduction (total lipid hypothesis). Response to the EFA supplements (linoleic
and linolenic) but not to TAG or protein would suggest that these fatty acids were
limiting in the diet (EFA hypothesis). A response to protein but not to TAG or
EFAs suggests that protein may be the limiting factor (protein hypothesis). We
also monitored clutch sizes of the ambient populations throughout the experiment,
and averages of these data are given in the table legends for each experiment.
The results of the first experiment with algae and TAG supplements suggest
Daphnia catawba from Lake Lacawac were food limited, as both clutch size and
lipid reserves increased with increased food concentration (Table 5.2). TAG microcapsule supplements caused a substantial increase in visible lipid in the body
but did not enhance fecundity. The results of this experiment prompted us to
develop the EFA microcapsules and protein microparticles used in subsequent
experiments.
As in the previous experiment, Daphnia catawba collected from Lake Lacawac
in late June 1989 responded to algal supplements by increasing clutch size (Table
5.3). Protein alone produced a statistically significant response. In July (Table
5.4), a slight but statistically significant food limitation was apparent, but the
protein effect was not statistically significant. The lower fecundities in the control
and treatment bottles versus the lake population may have been caused by the use
of three animals per vessel, a decision made to counteract increased clutch size
when single Daphnia catawba were placed in vessels.
Daphnia pulicaria was studied in Lake Waynewood in August 1989, when it
was the dominant large zooplankter (three to four individuals per liter) and cyanobacteria were abundant, especially Anabaena planktonica and Aphanizomenon
flos-aquae. D. pulicaria responded to protein supplements with a slight but statistically significant increased clutch size (Table 5.5). The algal supplement, repreTABLE 5.2. Supplement experiment started on May 24, 1988, with Daphnia catawba
from Lake Lacawac, pA.a
Clutch size
Lipid index
Treatment
n
X
SD
ph
X
SD
Control
19
1.2
0.4
0.8
0.3
pc'
+TAG
20
I.Sd
1.2
NS
2.1
0.5
<.05
+Algae
6
5.1
1.9
<.001
1.67
0.4
NS
a+ TAG, triacylglycerol microcapsules; +Algae, A. faleatus; NS, not significant. Mean body length of
lake adults during experiment is 1.5 mm (SD, 0.12).
bLinear contrasts with the control following ANOYA.
'Fisher's exact test of medians.
dlncludes degenerate eggs.