94
C.E. Goulden et al.
• Total lipid hypothesis: Food limitation is due to total storage lipid; dietary
supplements of triglycerides or non-EFAs will increase reproduction in adult
daphniids, but other dietary supplements will not.
• Essential fatty acid hypothesis: Food limitation is due to specific EFAs (linoleic
or linolenic); supplements of these will increase reproduction in adult daphniids, but other dietary supplements will not.
• Protein hypothesis: Food limitation is due to protein or essential amino acids;
supplements of these will increase reproduction in adult daphniids, but other
dietary supplements will not.
We supplemented natural zooplankton diets with microcapsules or particles
formulated from purified components and measured subsequent egg production.
The daphniids we studied are prominent grazers in many freshwater systems.
Adult females allocate most of their growth to reproduction (Taylor and Gabriel,
1985). We performed a series of experiments in two lakes in northeastern Pennsylvania, with emphasis on an experiment conducted in a eutrophic lake (Lake
Waynewood) in autumn. In this study, the natural diet was concurrently analyzed
in terms of ingestion rates and nutrient-limited status of the common algal food
items.
5.2. Methods
Chemicals: The following compounds (with their purity, when stated) were purchased from Sigma Chemical Co. (St. Louis, MO): casein (bovine milk) purified
powder; gum arabic; cholesterol (99% +); ergocalciferol; linoleic acid (99% by
capillary gas chromatography [GCl); linolenic acid (98% by capillary GC);
I-monooleoyl-rac-glycerol (99%); palmitic acid (99% by capillary GC); L-aphosphatidylcholine (type V-E) from frozen egg yolk (~99%, prepared chromatographically); retinol palmitate, type IV; alpha-tocopherol (from vegetable oil);
and triolein (99%). Na 2 14 C0 3 solution was made up from a carrier free crystalline
salt (New England Nuclear, Boston, MA) and diluted with ACS grade Na 2 HC0 3 .
NaH 2 P0 4 and NH 4 N0 3 •
5.2.1. Microparticle Preparation
Two types of lipid microcapsules were made by encapsulation in gum arabic (gum
arabic primarily consists of a polymer of galactose, rhamnose, arabinose, and
glycuronic acid): a TAG microcapsule, and a microcapsule that contained EFA.
The EFA microcapsule contained phospholipid, cholesterol, vitamins A, D, and E,
monoolein, and three free fatty acids (palmitic and the two EFAs, linoleic and
linolenic). Phospholipid and monoolein both served as emulsifiers, and the monoolein would also improve absorption of free fatty acids. The vitamins served as
antioxidants. This particle composition was the same as the "FV" particle developed by Conklin and Provasoli (1977), except that an equivalent amount of
C.E. Goulden et al.
• Total lipid hypothesis: Food limitation is due to total storage lipid; dietary
supplements of triglycerides or non-EFAs will increase reproduction in adult
daphniids, but other dietary supplements will not.
• Essential fatty acid hypothesis: Food limitation is due to specific EFAs (linoleic
or linolenic); supplements of these will increase reproduction in adult daphniids, but other dietary supplements will not.
• Protein hypothesis: Food limitation is due to protein or essential amino acids;
supplements of these will increase reproduction in adult daphniids, but other
dietary supplements will not.
We supplemented natural zooplankton diets with microcapsules or particles
formulated from purified components and measured subsequent egg production.
The daphniids we studied are prominent grazers in many freshwater systems.
Adult females allocate most of their growth to reproduction (Taylor and Gabriel,
1985). We performed a series of experiments in two lakes in northeastern Pennsylvania, with emphasis on an experiment conducted in a eutrophic lake (Lake
Waynewood) in autumn. In this study, the natural diet was concurrently analyzed
in terms of ingestion rates and nutrient-limited status of the common algal food
items.
5.2. Methods
Chemicals: The following compounds (with their purity, when stated) were purchased from Sigma Chemical Co. (St. Louis, MO): casein (bovine milk) purified
powder; gum arabic; cholesterol (99% +); ergocalciferol; linoleic acid (99% by
capillary gas chromatography [GCl); linolenic acid (98% by capillary GC);
I-monooleoyl-rac-glycerol (99%); palmitic acid (99% by capillary GC); L-aphosphatidylcholine (type V-E) from frozen egg yolk (~99%, prepared chromatographically); retinol palmitate, type IV; alpha-tocopherol (from vegetable oil);
and triolein (99%). Na 2 14 C0 3 solution was made up from a carrier free crystalline
salt (New England Nuclear, Boston, MA) and diluted with ACS grade Na 2 HC0 3 .
NaH 2 P0 4 and NH 4 N0 3 •
5.2.1. Microparticle Preparation
Two types of lipid microcapsules were made by encapsulation in gum arabic (gum
arabic primarily consists of a polymer of galactose, rhamnose, arabinose, and
glycuronic acid): a TAG microcapsule, and a microcapsule that contained EFA.
The EFA microcapsule contained phospholipid, cholesterol, vitamins A, D, and E,
monoolein, and three free fatty acids (palmitic and the two EFAs, linoleic and
linolenic). Phospholipid and monoolein both served as emulsifiers, and the monoolein would also improve absorption of free fatty acids. The vitamins served as
antioxidants. This particle composition was the same as the "FV" particle developed by Conklin and Provasoli (1977), except that an equivalent amount of