36
G.E. Napolitano
and C22 0)3 PUFA, arising from dietary sources or derived via elongation and
de saturation of 18:30)3. A significant dietary effect on the fatty acid composition
of beavers and muskrats is that the liver of beavers, which are exclusively herbivorous, contained very low concentrations (~O.2% of the total fatty acids) of
22:60)3, a typical component of the lipids of fish and aquatic invertebrates. By
contrast, the liver of the muskrats, which not only feed on plants but also prey on
fish and mussels, contained high proportions of 22:60)3 (6.9% of the total fatty
acids) (KakeHi and Hyvarinen, 1996).
2.5. Research Needs
Future research in the area of fatty acids markers in freshwater environments
should expand the database on primary sources of lipids, extend their use to
unexplored trophic relationships, and optimize the use of statistical treatments on
new and existing data. An examination of the available information of the fatty
acid composition of freshwater algae reveals an uneven coverage of the different
algal taxa and, in particular, a lack of adequate studies on diatoms, often the major
primary producer of planktonic and benthic communities.
Fatty acids markers should be used to evaluate the transference of nutrients and
metabolites in unconventional trophic linkages, such as in the case of organisms
involved in symbiotic relationships. There are only a few studies on the translocation of photosynthetic products from symbiotic algae to the host in marine (see
Bishop et aI., 1976, and references therein) and freshwater species (Caudales et
aI., 1992). Because the species involved in symbiotic relationships are often from
philogenetically unrelated taxa, it would be possible to detect symbiosis by the
study of fatty acid signatures in lipid extracts of the host.
'
Studies should also address the quantitative aspects of the trophic transference
of fatty acids and the assessments of organic matter pools in aquatic ecosystems.
The bulk of the detailed quantitative information on fatty acid composition of
aquatic lipids is presented as percentages rather than actual pool sizes. This type
of data precludes the possibility of evaluating net transfer of biomass and energy
from one trophic level to the next, limiting the use of biochemical markers to a
qualitative evaluation of trophic relationships. Further work should integrate the
use of complementary information derived from other lipid and nonlipid materials. The information from different sources, in particular from the large number
of fatty acids identified in each matrix analyzed, should be integrated by means
of statistical analyses to produce unambiguous patterns or chemical marker
signatures.
2.6. Conclusions
The information presented in this chapter illustrates that the analysis of the fatty
acid composition of organisms and the identification of potential biochemical
G.E. Napolitano
and C22 0)3 PUFA, arising from dietary sources or derived via elongation and
de saturation of 18:30)3. A significant dietary effect on the fatty acid composition
of beavers and muskrats is that the liver of beavers, which are exclusively herbivorous, contained very low concentrations (~O.2% of the total fatty acids) of
22:60)3, a typical component of the lipids of fish and aquatic invertebrates. By
contrast, the liver of the muskrats, which not only feed on plants but also prey on
fish and mussels, contained high proportions of 22:60)3 (6.9% of the total fatty
acids) (KakeHi and Hyvarinen, 1996).
2.5. Research Needs
Future research in the area of fatty acids markers in freshwater environments
should expand the database on primary sources of lipids, extend their use to
unexplored trophic relationships, and optimize the use of statistical treatments on
new and existing data. An examination of the available information of the fatty
acid composition of freshwater algae reveals an uneven coverage of the different
algal taxa and, in particular, a lack of adequate studies on diatoms, often the major
primary producer of planktonic and benthic communities.
Fatty acids markers should be used to evaluate the transference of nutrients and
metabolites in unconventional trophic linkages, such as in the case of organisms
involved in symbiotic relationships. There are only a few studies on the translocation of photosynthetic products from symbiotic algae to the host in marine (see
Bishop et aI., 1976, and references therein) and freshwater species (Caudales et
aI., 1992). Because the species involved in symbiotic relationships are often from
philogenetically unrelated taxa, it would be possible to detect symbiosis by the
study of fatty acid signatures in lipid extracts of the host.
'
Studies should also address the quantitative aspects of the trophic transference
of fatty acids and the assessments of organic matter pools in aquatic ecosystems.
The bulk of the detailed quantitative information on fatty acid composition of
aquatic lipids is presented as percentages rather than actual pool sizes. This type
of data precludes the possibility of evaluating net transfer of biomass and energy
from one trophic level to the next, limiting the use of biochemical markers to a
qualitative evaluation of trophic relationships. Further work should integrate the
use of complementary information derived from other lipid and nonlipid materials. The information from different sources, in particular from the large number
of fatty acids identified in each matrix analyzed, should be integrated by means
of statistical analyses to produce unambiguous patterns or chemical marker
signatures.
2.6. Conclusions
The information presented in this chapter illustrates that the analysis of the fatty
acid composition of organisms and the identification of potential biochemical