Seasonal Changes In Fatty Acid Composition Research Articles

Correlations between fatty acid composition of seston and zooplankton and effects of environmental parameters in a eutrophic Siberian reservoir

During two sampling seasons we analyzed on weekly basis fatty acid (FA) composition of seston fraction <130 μm and zooplankton fraction >130 μm, and compared them using a multivariate canonical correlation analysis (CCA). Besides, we evaluated a possible impact of water temperature and inorganic nutrients on FA composition of the seston and the zooplankton. In spite of significant differences in percentages of several individual FAs, we found very strong canonical correlation (cross-correlation, 1-week lag) between FA composition of the seston and the zooplankton. The most important factor, providing the overall canonical cross-correlation between FA profiles of the seston and the zooplankton fractions was eicosapentaenoic acid (20:5ω3, EPA). FA composition of the zooplankton fraction had comparatively poor correlations with taxonomic composition of the zooplankton. Thus, seasonal variations of FA composition of the zooplankton were determined primarily by seasonal changes in FA composition of the seston, rather than by taxonomic differences of FA profiles between rotifers, cyclopoids and cladocerans. FA composition of the seston was strongly affected by its taxonomic composition, namely by that of phytoplankton. According to CCA, the highest factor loadings pertained to diatoms interacting with their marker acids, including EPA, and cyanobacteria and greens, interacting with their marker acids. Ciliates and small rotifers composed considerable and sometimes major part of the seston biomass, but according to CCA their contributions to seasonal variations of the total FA profile of the seston were insignificant. This finding indirectly support the conclusion of the other authors, that the main source of FAs presented in ciliates and rotifers must be sought in algae and that they do not modify FA composition of food consumed, apart from repackaging it. Water temperature was the principal environmental parameter which drove the overall variations of FA composition. Factor loadings for the inorganic nutrients were comparatively negligible. The main contribution in the seasonal variation of FA composition of the seston was given by negative interaction between water temperature and percentage of EPA in the seston.

Seasonal distribution and fatty acid composition of littoral microalgae in the Yenisei River

We studied fatty acid (FA) composition of littoral microalgae in the fast-flowing oligotrophic river, the Yenisei, Siberia, monthly for 3 years. Seasonal dynamics of species composition had similar patterns in all the studied years. In springs, a pronounced dominance of filamentous green algae occurred, in summer and autumn diatoms were abundant, and in late autumn and winter epilithic biofilms consisted primarily of cyanobacteria and detritus. In general, FA composition of the algal periphytic community was dominated by 16:0, 16:1ω7, 20:5ω3, 14:0, and 18:3ω3 throughout the studied period. Several groups of FAs, which had peculiar seasonal dynamics, were differentiated by statistical analysis based on a method of correlation graphs. The seasonal changes in FA composition could be partly explained by the seasonal succession of species composition of the community. Besides, we found that populations of both diatom and green algae grown in summer at a higher water temperature were lower in polyunsaturated fatty acids than those in spring, at a lower temperature. Hence, we suppose that the regular seasonal dynamics of FA composition of the studied littoral microalgae was driven both by changes in species composition and by temperature adaptations of the algal populations. The highest content of essential polyunsaturated FAs, eicosapentaenoic and docosahexaenoic acids, in the spring “psychrophilic” populations of diatoms could make them of the higher nutritive value for zoobenthic primary consumers.

Association between seasonal changes in fatty-acid composition, expression of VLDL receptor and bovine sperm quality

Reduced reproductive performance of dairy cows during the summer is often associated with elevated temperature. Semen collected and cryopreserved during the summer may be of low quality and might contribute to the compromised fertility of dairy cows during this season. The present study examined the association between seasonality, semen quality and its potential to survive cryopreservation. A comparison between semen collected during the summer (July to August) and that collected during the winter (November to December) revealed the summer semen to be inferior, as reflected by low motility and high mortality of sperm. Furthermore, samples that were defined as good quality had changes in lipid concentration and fatty-acid composition in both the seminal plasma and cell compartment. In particular, semen collected during the summer had reduced levels of polyunsaturated arachidonic acid (20:4; P < 0.05) and decreased levels of linoleic acid (18:2; P < 0.05) in the cell compartment; corresponding reductions in cholesterol ( P < 0.06) and fatty-acid concentrations ( P < 0.001) were detected in seminal plasma of semen collected during the summer. In addition, we provided the first evidence for the existence of a very-low-density lipoprotein receptor (VLDLr) in bovine sperm, suggesting a mechanism for sperm utilization of extracellular lipids. Interestingly, the expression of VLDLr was three-fold greater in samples collected during the winter than in those collected in the summer ( P < 0.01) and was negatively associated with saturated fatty-acid concentration ( P < 0.018) but not with that of cholesterol. An opposite pattern was noted for samples obtained during the summer; mRNA expression of VLDLr was negatively associated with cholesterol concentration ( P < 0.01) but not with that of saturated fatty acids. Such modifications associated with extracellular lipid utilization and fatty-acid composition might explain, in part, the reduced quality of summer semen.