6. Seasonal Dynamics of Lipids
119
Another similar situation occurs in the aquatic soldier fly larvae, Hedriodiscus
truquii, which was studied for ecological energetics modeling in thermal springs
(Stockner, 1971). The algivorous larvae pass through four instars from egg to
adult. Total lipid levels of H. truquii may double or quadruple from the second to
fourth instar (pupae) and finally reach a maximum lipid level of approximately
20% of dry mass (Stockner, 1971). Energy expenditure during metamorphosis is
revealed in the adult's lower lipid levels of 11-12% of dry mass. In addition, the
short-lived adults (i.e., a few days) probably do not feed, therefore relying on the
lipid acquired as larvae to complete their reproductive cycle.
Mayfly nymphs, members of the order Ephemeroptera, live in diverse habitats
from fast-running streams to slow-moving rivers and lakes. Most mayflies are
herbivores and detritivores, but a few may be true carnivores (Edmunds, 1978). In
addition, they are very sensitive to poor water-quality conditions. Thus, many
species were eliminated from their natural habitats due to cultural eutrophication.
Lipid content has been analyzed for studies of mayfly toxicokinetics (Landrum
and Poore, 1988) and biochemical composition (Meyer, 1990). Lipid content of
the mayfly nymphs varies seasonally. The stream mayfly Epeorus sylvicola had
its highest values in lipid level, dry mass, and body length in June, just prior to
mature nymph emergence to the sub imago or preadult stage. The maximum mean
lipid level was 12% of dry mass, and the range throughout the year for E. sylvicola
was from 2 to 20% of dry mass (Meyer, 1990). Hexagenia limbata, a burrowing
mayfly nymph, had a similar lipid range from 2.4 to 17.7% of dry mass. Like E.
sylvicola, the mean maximum lipid level in H. limbata occurred in June (Landrum
and Poore, 1988). In several species of mayflies from a Scottish stream, TAG was
determined to be the most abundant lipid class (i.e., 50-60% of total lipid),
whereas PL ranked second (i.e., 30% of total lipid) during August (Bell et aI.,
1994).
Sexual differences in lipid level were found in large nymphs of E. sylvicola.
Male lipid levels were approximately 15% of dry mass, whereas female lipid
levels were approximately lO% of dry mass in individuals> 15 mg dry mass
(Meyer, 1990). The lower lipid level in females may be due to production of eggs
when stored lipid is used for the synthesis of yolk proteins (Meyer, 1990). In
compliance with this, protein levels were higher in the> 15-mg dry mass female
than in male nymphs of the same size.
6.2.2.4. Mollusca: Bivalvia
The mollusk Diplodon patagonicus lives in Lake Nahuel Huapi located in the
Patagonian Andes Mountains. Total lipid levels varied seasonally in D. patagonicus. Lipid values of 4.1 % of dry mass (percentage dry mass was converted
from wet mass data by assuming that dry mass is 15% of wet mass) occurred in
winter, whereas lipid values of9.7% of dry mass occurred in the spring (Pollero et
aI., 1981). This lipid increase was likely due to an increase in D. patagonicus
feeding in the spring but not on a diatom bloom. The spring-melt runoff is low in
nutrients in Lake Nahuel Huapi and does not promote a spring diatom bloom. In
addition, the lack of seasonal variation in D. patagonicus fatty acid (FA) compos i-
119
Another similar situation occurs in the aquatic soldier fly larvae, Hedriodiscus
truquii, which was studied for ecological energetics modeling in thermal springs
(Stockner, 1971). The algivorous larvae pass through four instars from egg to
adult. Total lipid levels of H. truquii may double or quadruple from the second to
fourth instar (pupae) and finally reach a maximum lipid level of approximately
20% of dry mass (Stockner, 1971). Energy expenditure during metamorphosis is
revealed in the adult's lower lipid levels of 11-12% of dry mass. In addition, the
short-lived adults (i.e., a few days) probably do not feed, therefore relying on the
lipid acquired as larvae to complete their reproductive cycle.
Mayfly nymphs, members of the order Ephemeroptera, live in diverse habitats
from fast-running streams to slow-moving rivers and lakes. Most mayflies are
herbivores and detritivores, but a few may be true carnivores (Edmunds, 1978). In
addition, they are very sensitive to poor water-quality conditions. Thus, many
species were eliminated from their natural habitats due to cultural eutrophication.
Lipid content has been analyzed for studies of mayfly toxicokinetics (Landrum
and Poore, 1988) and biochemical composition (Meyer, 1990). Lipid content of
the mayfly nymphs varies seasonally. The stream mayfly Epeorus sylvicola had
its highest values in lipid level, dry mass, and body length in June, just prior to
mature nymph emergence to the sub imago or preadult stage. The maximum mean
lipid level was 12% of dry mass, and the range throughout the year for E. sylvicola
was from 2 to 20% of dry mass (Meyer, 1990). Hexagenia limbata, a burrowing
mayfly nymph, had a similar lipid range from 2.4 to 17.7% of dry mass. Like E.
sylvicola, the mean maximum lipid level in H. limbata occurred in June (Landrum
and Poore, 1988). In several species of mayflies from a Scottish stream, TAG was
determined to be the most abundant lipid class (i.e., 50-60% of total lipid),
whereas PL ranked second (i.e., 30% of total lipid) during August (Bell et aI.,
1994).
Sexual differences in lipid level were found in large nymphs of E. sylvicola.
Male lipid levels were approximately 15% of dry mass, whereas female lipid
levels were approximately lO% of dry mass in individuals> 15 mg dry mass
(Meyer, 1990). The lower lipid level in females may be due to production of eggs
when stored lipid is used for the synthesis of yolk proteins (Meyer, 1990). In
compliance with this, protein levels were higher in the> 15-mg dry mass female
than in male nymphs of the same size.
6.2.2.4. Mollusca: Bivalvia
The mollusk Diplodon patagonicus lives in Lake Nahuel Huapi located in the
Patagonian Andes Mountains. Total lipid levels varied seasonally in D. patagonicus. Lipid values of 4.1 % of dry mass (percentage dry mass was converted
from wet mass data by assuming that dry mass is 15% of wet mass) occurred in
winter, whereas lipid values of9.7% of dry mass occurred in the spring (Pollero et
aI., 1981). This lipid increase was likely due to an increase in D. patagonicus
feeding in the spring but not on a diatom bloom. The spring-melt runoff is low in
nutrients in Lake Nahuel Huapi and does not promote a spring diatom bloom. In
addition, the lack of seasonal variation in D. patagonicus fatty acid (FA) compos i-