The role of trematode parasites as a nutritional food source for higher trophic level consumers

Recently, there has been a call for the inclusion of free-living stages of trematode parasites in food web models as they are present in high numbers in aquatic ecosystems and serve as prey for higher trophic levels. I investigated the presence of lipids in cercariae, specifically neutral energy reserve lipid stores and long-chain polyunsaturated fatty acids (LC-PUFA), as they are considered the primary energy currency in aquatic ecosystems. Cercariae of all investigated taxa contained distinct neutral lipid compositions and Ribeiroia ondatrae cercariae had significant quantities of total lipids, as well as essential fatty acids (EFA). I also investigated the viability of cercariae as prey items for dragonfly larvae (Leucorrhinia intacta) and detected indistinguishable proportions of EFA in larvae subsisting on equivalent quantities of R. ondatrae and Daphnia spp. This suggests that cercariae may contribute to nutrient subsidies in aquatic ecosystems, thereby supporting aquatic organism growth and fitness.

The role of trematode parasites as a nutritional food source for higher trophic level consumers

Recently, there has been a call for the inclusion of free-living stages of trematode parasites in food web models as they are present in high numbers in aquatic ecosystems and serve as prey for higher trophic levels. I investigated the presence of lipids in cercariae, specifically neutral energy reserve lipid stores and long-chain polyunsaturated fatty acids (LC-PUFA), as they are considered the primary energy currency in aquatic ecosystems. Cercariae of all investigated taxa contained distinct neutral lipid compositions and Ribeiroia ondatrae cercariae had significant quantities of total lipids, as well as essential fatty acids (EFA). I also investigated the viability of cercariae as prey items for dragonfly larvae (Leucorrhinia intacta) and detected indistinguishable proportions of EFA in larvae subsisting on equivalent quantities of R. ondatrae and Daphnia spp. This suggests that cercariae may contribute to nutrient subsidies in aquatic ecosystems, thereby supporting aquatic organism growth and fitness.

Energy Reserve Lipids of Zooplanktonic Crustaceans from an Oligotrophic Saline Lake In Relation to Food Resources and Temperature

In three zooplankton species examined over a 2-yr period in an oligotrophic saline (22 g∙L−1) lake, triacylglycerols (energy reserve lipids) were the most abundant lipid class followed by phospholipids and sterols. Marked seasonal differences in patterns of total and energy reserve lipid content in the herbivorous calanoid Leptodiaptomus sicilis were correlated with temporal patterns in edible algal biomass and temperature. The appearance of particular algal species, or groups of similar-sized species, occurred synchronously with changes in lipid content of both L. sicilis and Daphnia pulex. These periods of changing lipid content were used to infer nutritional suitability or inadequacy (unavailability) of specific algae for wild populations of zooplankton. Energy transfer from phytoplankton to the carnivorous calanoid Hesperodiaptomus nevadensis through L. sicilis involved a time lag of approximately 1–2 mo; this was hypothesized to result from a feeding dependency on L. sicilis copepodites due to a gape limitation of the predator. Demographics of D. pulex in this lake were unusual because the species was consistently absent during spring. In addition, total lipids and triacylglycerols were low (<15% and <4.5 μg∙animal−1, respectively), suggesting that D. pulex had been pushed into a subsistence niche by the rising salinity levels.

Lipid Mobilization in Dormant and Nondormant Caryopses of Yellow Foxtail (Setaria lutescens)

The major reserve lipid of yellow foxtail [Setaria lutescens(Weigel) Hubb.] caryopses is triacylglyceride stored in lipid bodies. Lipid bodies are heavily concentrated in the cells of the embryo axis, scutellum, and aleurone layer and are roughly spherical (average diam 0.5μm). Percentage lipid (hot isopropanol extract) on a fresh-weight basis of mature, unimbibed seed and caryopses collected locally was about 6.4 and 11%, respectively. About 95% of the total (0.23 mg/caryopsis) was saponifiable and distributed among fatty acid classes as follows: 16:0, 5.8%; 18:0, 1.5%; 18:1, 16.2%; 18:2, 73.7%; and 18:3, 2.8%. In nondormant caryopses, saponifiable lipid content declined (18:1 and 18:2 only) about 23% during the first 6 days after imbibition in the dark at 25 C. This modest decline was preceded by the appearance of an alkaline lipase at about 24 h after the onset of imbibition. Free fatty acids accumulated during these early stages of germination and accounted for about 22% of the total saponifiable lipid remaining (0.17 mg/caryopsis) 6 days after the onset of imbibition. Lipid content and lipase activity did not change in dormant caryopses treated similarly. The delayed initiation of lipid mobilization in germinating caryopses suggests that triacylglyceride degradation is not a pivotal metabolic pathway controlling dormancy.

Étude en microscopie électronique de Conidiobolus obscurus. I. Formation et germination des azygospores

The multinucleate hyphal bodies of Conidiobolus obscurus are characterized by a striated wall which does not react with Thiéry's stain used to detect free α glycol groups. In the developing mycelial zone, the protoplasm contains microvesicles and electron-dense corpuscles; during ageing of the mycelium, lipid globules varying in size according to the age of the cell and vesicles with dense inclusions are observed in large numbers, whereas the endoplasmic reticulum shows little development. The onset of sporulation is characterized by protoplasmic condensation at a particular point in the hyphal body through successive accumulations of cicatricial partitions. The young prespore is a spherical organ; its wall has the same structure as that of the mycelium, and it contains more or less the same organelles as the hyphal protoplasm. The first sign that the prespore is developing into a spore is the deposition of a very thick inner wall layer (tripartite layer). The inner makeup of the azygospore has all the features of a dormant spore of low metabolic activity having a huge reserve lipid globule. At the onset of germination, the spore wall and the central lipid globule are progressively digested. A new wall entity is synthesized. There is a proliferation of multivesicular and multilaminate bodies. The emergence of the germ tube results from the rupture of the original outer layer of the spore. Results are compared with those observed in various resistance organs of zygomycetes and oomycetes, and discussed in relation to functional metabolic pathways during sporogenesis or germination. [Journal translation]