Marine ecology progress series 235:127

Vol. 235: 127–134, 2002
Published June 19
Mar Ecol Prog Ser
Species differences, origins and functions of
fatty alcohols and fatty acids in the wax esters and
phospholipids of Calanus hyperboreus, C. glacialis
and C. finmarchicus from Arctic waters
Catherine L. Scott1, Slawomir Kwasniewski3, Stig Falk-Petersen4, John R. Sargent2,*
1 Department of Biological Sciences and 2Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, UK
3 Institute of Oceanology, Polish Academy of Sciences, Powstancow Warszawy St 55, 81-712 Sopot, Poland
4 Norwegian Polar Institute, 9296 Tromsø, Norway
ABSTRACT: The percentage (%) fatty alcohol and fatty acid compositions of the wax esters of largenumbers of Stage V and females of Calanus hyperboreus, C. glacialis and C. finmarchicus taken inlate August to late September from Arctic waters (Kongsfjord in Svalbard, 78° 57’ N, 11° 50’ E) arepresented. The data reveal that these stages of development of the 3 species can be discriminated onthe basis of the % of 22:1n-11 fatty alcohol in their large levels of wax esters, with C. hyperboreushaving the highest % followed by C. finmarchicus and then C. glacialis. Equally, C. hyperboreus hasthe lowest % of 20:1n-9 fatty alcohol in its wax esters with C. finmarchicus having a higher % andC. glacialis the highest %. Relatively minor differences occur in the fatty acid compositions of the waxesters of the 3 species, which consisted principally of 20:1n-9 (15 to 18%) and 22:1n-11 (10 to 15%),together with the diatom-derived fatty acids 16:1n-7 (20 to 23%) and 20:5n-3 (11 to 13%). Theflagellate-derived fatty acids, 18:4n-3 (3 to 6%) and 22:6n-3 (1 to 3%), were minor constituents. Thefatty acid compositions of the small amounts of polar lipid in the 3 species were indistinguishable with22:6n-3 (41 to 46%) and 20:5n-3 (22 to 24%) being the major components. We conclude that Stage Vand females of the species can be distinguished in autumn on the basis of the different % of 22:1n-11and 20:1n-9 fatty alcohols in their wax esters and that de novo lipid biosynthetic activity in the cope-pods increases in the order C. finmarchicus < C. glacialis < C. hyperboreus. We discuss the results interms of the contributions of fatty acids and fatty alcohols biosynthesised de novo and fatty acidsderived from the diet to the copepods’ lipids, the role of 20:1 and 22:1 fatty alcohols and fatty acids asenergy sources, and the possible role of 22:6n-3 in the copepods’ physiology.
KEY WORDS: Calanus · Arctic · Wax esters · Phospholipids · Acids · Alcohols Resale or republication not permitted without written consent of the publisher INTRODUCTION
1999). C. glacialis is primarily an Arctic shelf species(Conover 1988, Hirche & Kwasniewski 1997). C. fin- Calanus hyperboreus, C. glacialis and C. finmarchi- marchicus is primarily a North Atlantic species (Flem- cus can all be abundant in Arctic waters. C. hyper- inger & Hülsemann 1977) which is exported to the boreus is primarily a deep-water species found espe- Arctic (Hirche 1991). However, all 3 species can be cially in the Greenland Sea and the Arctic Ocean found in the same location, as for example in the Arctic (Hirche 1991, Hirche & Mumm 1992, Thibault et al.
fjord studied in the present investigation. All 3 speciesaccumulate large amounts of oil, which consists princi-pally of wax esters (Lee et al. 1971a,b, Lee & Hirota *Corresponding author. E-mail: [email protected] 1973, Sargent et al. 1976, Sargent & Henderson 1986).
Inter-Research 2002 · The large C. hyperboreus and the intermediate-sized ferences in maximal levels of wax esters in the differ- C. glacialis contain higher levels of oil per unit body ent species. We have recently determined levels of mass than the small C. finmarchicus (Scott et al. 2000). total lipid and wax esters in large numbers of Stage V The fatty acid compositions of the wax esters of and female Calanus hyperboreus, C. glacialis and C. Calanus hyperboreus, C. glacialis and C. finmarchicus finmarchicus taken in late summer-autumn at a single reflect the fatty acid compositions of their phytoplank- station in Kongsfjord, Svalbard (Scott et al. 2000). We tonic diet, particularly in their % of 16:1n-7 and various present here the fatty alcohol and fatty acid composi- polyunsaturated fatty acids (PUFA), whereas the fatty tions of the wax esters, together with the fatty acid alcohols of the esters are invariably dominated by compositions of the phospholipids of the same speci- 20:1n-9 and 22:1n-11 units not found in phytoplankton mens. We discuss the results in terms of the contribu- (Lee et al. 1971a,b, Lee & Hirota 1973, Sargent et al.
tions of fatty acids and fatty alcohols biosynthesised 1976, Sargent & Henderson 1986, Sargent & Falk- de novo and fatty acids derived from the diet to the Petersen 1988, Tande & Henderson 1988, Graeve et al.
copepods’ lipids, and the roles of 20:1n-9, 22:1n-11 and 1994, Albers et al. 1996). It has been proposed, there- fore, that calanoid copepods accumulate large stores ofwax esters by efficiently assimilating and retainingdietary, phytoplanktonic fatty acids and esterifying MATERIALS AND METHODS
them with fatty alcohols biosynthesised de novo fromdietary phytoplanktonic protein and carbohydrate The copepods were sampled during an expedition (Sargent & Henderson 1986). Earlier literature sug- (BIODAFF 97) from Ny Ålesund Large Scale Facility gests that Stage V and adult C. hyperboreus have a in Kongsfjorden, Svalbard, in 1997 as previously de- substantially higher % of 22:1n-11 than 20:1n-9 in their scribed by Scott et al. (2000). Sampling was performed wax esters (Lee 1974, 1975). Comparable stages of C. at Stn K3 in Kongsfjord (78° 57’ N, 11° 50’ E) from a 2 m glacialis have a substantially lower % of 22:1n-11 than metal dory with an outboard engine. The water column 20:1n-9 (Clarke et al. 1987, Tande & Henderson 1988).
in the fjord was formed of local waters overlaying a mix Comparable stages of C. finmarchicus have only a of Spitzbergen shelf water and transformed Atlantic slightly lower % of 22:1n-11 than 20:1n-9 (Kattner & water with a layer of intermediate water in between.
Krause 1987, Falk-Petersen et al. 1987, Kattner 1989).
Hauls were taken with 2 conical WP-2 (Working Party One difficulty in elucidating inter-species differences 2, UNESCO) plankton nets to obtain samples every from these studies is that they all considered only a 48 h when conditions allowed, from 24 August to 20 single species at a given time, with the different spe- September 1997. A WP-2 net of 57 cm opening dia- cies being taken from different locations. However, meter with a 180 µm mesh size and a WP-2 net of 57 cm Kattner et al. (1989) analysed Stages IV and V and opening diameter with a 500 µm mesh size were used.
females of C. hyperboreus and C. finmarchicus in the Both nets were towed vertically from 200 m depth to Fram Strait in the summer of a single year. Albers et al.
the surface at a rate of 45 m min–1 (UNESCO 1968). (1996) presented analyses of females of all 3 species Individual copepods were identified to species and taken in the Fram Strait between 78° and 80° N in the to stage of development, and both Stage V individuals, summer of 2 successive years. These more extensive i.e. the stage immediately preceding full sexual devel- analyses (Kattner et al. 1989, Albers et al. 1996) opment to males or females, and females were se- showed the same trends for differences in the % of lected. At least 10 individuals of each of these 2 stages 22:1n-1 and 20:1n-9 in the wax esters of the 3 species from each of the 3 species were pooled to constitute a single sample. Total lipid was extracted from separate Such results strongly suggest species differences in samples by the method of Folch et al. (1957) and the fatty alcohol compositions of the wax esters of the fractionated into lipid classes by thin layer chromato- 3 species, consistent with their having different pro- graphy (Olsen & Henderson 1989). Wax esters and pensities to biosynthesise long-chain fatty alcohols.
phospholipids were eluted from the plates, dried and This has implications for the levels and energy con- transmethylated in methanol/toluene (2/1 v/v) contain- tents of the wax esters in the different species. How- ing 1% sulphuric acid for 16 h at 50°C. The reaction ever, possible species differences in the fatty alcohol products were extracted into diethyl ether, dried under compositions of calanoid wax esters have thus far not nitrogen and subjected to thin layer chromatography been investigated in the same stages of different spe- in hexane/diethyl ether/acetic acid (70/30/1 v/v/v) to cies taken at the same location, and in late summer- separate fatty acid methyl esters and, for wax esters, autumn when the copepods have accumulated maxi- free fatty alcohols. The fatty acid methyl esters and the mal levels of wax esters. Nor have possible differences free fatty alcohols were eluted from the plates and the in fatty alcohol composition been clearly related to dif- fatty alcohols converted to fatty alcohol acetates by Scott et al: Wax esters and phopholipids of 3 species of Calanus reacting with acetic anhydride in pyridine (Farquhar Fatty acid compositions of the wax esters
1962). The % compositions of fatty acid methyl estersand fatty alcohol acetates were determined in a Fisons As for the fatty alcohols, the fatty acid data were GC8160 gas chromatograph equipped with a chemi- pooled since there were no clear-cut differences cally bonded CP Wax 52CB fused silica, wall-coated between Stages V and females in any of the 3 species.
capillary column (30 m × 0.32 mm i.d., Chrompack UK) The % compositions of fatty acids (Table 2) reveal that with an on-column injection system and flame ioniza- 16:1n-7 was the major fatty acid in all 3 species, with tion detection. Hydrogen was used as carrier gas with lesser % of 20:1n-9 and 22:1n-11. The clear-cut differ- an oven thermal gradient from an initial 50 to 180°C ences between 20:1 and 22:1 fatty alcohols in the wax at 40°C min–1, and then to a final temperature of 235°C esters (Table 1) were only faintly echoed in the corre- at 2°C min–1. Individual components were identified sponding fatty acids (Table 2). Thus, Calanus hyper- by comparison with known standards, with a well- boreus had the highest % of 22:1 fatty acid of the characterised fish oil and by reference to published 3 species and, although the differences between this data, as described previously by Tande & Henderson species and both C. glacialis and C. finmarchicus were (1988), and were quantified using a PC directly linked significantly different, the difference between the lat- to the detector and operating Chrom-Card Software ter 2 species was not. C. hyperboreus had correspond- (Thermo-Quest Italia). All solvents contained 0.01% ingly and significantly lower % of both 14:0 and 16:0 w/v butylated hydroxytoluene as an antioxidant. than the other 2 species, but the differences between Significances of differences between mean values the % of 14:0 and 16:0 in C. glacialis and C. finmarchi- for % fatty alcohols and % fatty acids were determined cus was only significant for 14:0. C. glacialis had the by 1-way analysis of variance followed, where appro- highest % of 20:1, which was significantly different priate, by Tukey’s multiple range test (Zar 1996).
from C. finmarchicus but not from C. hyperboreus. Incontrast to the situation for the fatty alcohols, the % of20:1 fatty acid exceeded that of 22:1 fatty acid in all 3 species. However, the progressive increase in the sumof the % 20:1 and 22:1 fatty alcohols from C. fin- Fatty alcohol compositions of the wax esters
marchicus to C. glacialis to C. hyperboreus (Table 1)occurred also in the sum of the % of 20:1 and 22:1 fatty There were no clear-cut differences between % acids, which increased progressively from 27.5% to compositions of fatty alcohols in wax esters of Stages V 30.8% and thence to 35.6% in the species, respec- and females in any of the 3 species. Therefore, the data tively. The PUFA present in all 3 species in the same % for samples of Stages V and females of a given species was 20:5n-3. Smaller amounts of 18:4n-3 were present, were pooled. The results (Table 1) show that each spe- in significantly higher % in both C. hyperboreus and cies contained minor % of 16:0 and 16:1n-7 alcoholsand major % of 20:1n-9 and 22:1n-11 alcohols. The % Table 1. Fatty alcohol compositions (mass %) of the wax esters of 20:1n-9 alcohol was significantly different in the of Calanus finmarchicus, C. glacialis and C. hyperboreus.
3 species with the highest % in Calanus glacialis. Like- Data are means ± SD; n = number of samples; V = Stage V; wise, the % of 22:1n-11 alcohol was significantly dif- F = female. Values which share a superscript letter within a ferent in the 3 species with the highest % in C. hyper- given row are not significantly different. Values with differ-ent superscript letters within a given row are significantly boreus. Thus, the ratio of (22:1n-11 + 22:1n-9)/(20:1n-9 + 20:1n-7) alcohols was highest in C. hyperboreus andlowest in C. glacialis. However, the sum of 20:1 alcohol isomers (n-9 + n-7) and 22:1 alcohol isomers (n-11 + (n = 13V + 12F) (n = 9V + 8F) (n = 11V + 14F) n-9) was very similar in the 3 species, increasing pro-gressively from a total of 75.4% in C. finmarchicus to 77.1% in C. glacialis and 82.6% in C. hyperboreus.
This was paralleled by the % 16:1n-7 decreasing pro- gressively from 6.5% to 3.8% and 2.6% in the 3 spe- cies, although the decrease from C. glacialis to C. hyperboreus was not significant. Differences between the remaining fatty alcohols in the 3 species were minor and, although differences for a given alcohol between a given species and the other 2 species were generally significant, in no case were the differences Table 2. Fatty acid compositions (mass %) of the wax esters of C. glacialis than in C. finmarchicus. Minor Calanus finmarchicus, C. glacialis and C. hyperboreus. Data are amounts of C16 PUFA were present in all 3 spe- means ± SD; n = number of samples; V = Stage V; F = female. Val- cies with the % of 16:4 being significantly higher ues which share a superscript letter within a given row are not sig- in C. hyperboreus than in both C. glacialis and C. nificantly different. Values with different superscript letters within a given row are significantly different (p < 0.05) finmarchicus. Minor amounts of 22:6n-3 were alsopresent in all 3 species with, once more, C. hyper-boreus having a significantly higher % than both C. glacialis and C. finmarchicus. Thus, C. hyper-boreus had the highest % of total PUFA of all the 3 species. Overall, however, the fatty acid com- positions of the wax esters of the 3 species were Fatty acid compositions of the polar lipids
The % fatty acid compositions of the polar lipids, largely phospholipids, in the 3 species are shown in Table 3, where data were only available for female Calanus finmarchicus and Stages V of C. glacialis and C. hyperboreus. Despite this limi- tation, the fatty acid compositions of the phospho- lipids of all 3 species were very similar, being dominated by 16:0, 20:5n-3 and 22:6n-3, with the % of 20:5n-3 + 22:6n-3 exceeding 60% of the total fatty acids and the ratio of 22:6n-3/20:5n-3 approaching 2:1. The only difference of note between the species is that C. hyperboreus had a higher but not significantly different % of 22:6n-3 DISCUSSION
Table 3. Fatty acid compositions (mass %) of the polar lipid of The Stage V and female specimens of the 3 Calanus finmarchicus, C. glacialis and C. hyperboreus. Data are Calanus species analysed here were all captured means ± SD; n = number of samples; V = Stage V; F = female from the same site in Kongsfjord. The water struc-ture at the site sampled is complex, being formed of local waters overlaying a mix of Spitzbergen shelf water and transformed Atlantic water witha layer of intermediate water in between. It is improbable that the 3 species had all developed from nauplii to Stages V and females in Kongs- fjord and probable that they had different origins.
For example, it is plausible that C. finmarchicus had been advected into the fjord from the south and C. hyperboreus advected in from the north.
This, together with the different development times for the 3 species, makes it virtually certain that they had developed in different locations at different times and thus had experienced different phytoplankton regimes, whether qualitatively in terms of species composition or quantitatively in terms of species abundance. Moreover, the Stages V and females of the 3 species were cap- Scott et al: Wax esters and phopholipids of 3 species of Calanus tured in late summer-autumn when they had accumu- together with the findings of Albers et al. (1996), led to lated their highest levels of wax esters prior to over- the conclusion that Stages V and females of the 3 wintering. Thus, in relating the fatty alcohol and fatty species have different % of 22:1n-11 and 20:1n-9 fatty acid compositions of the copepods’ wax esters to alcohols and, therefore, different ratios of these fatty dietary input, as is attempted here, it is the cumulative, alcohols in their wax esters. We conclude that, in long-term dietary input into the copepods and their copepods with maximal levels of wax esters, the % of maximal accumulated wax esters that are under dis- 22:1n-11 and 20:1n-9 fatty alcohols in their wax esters cussion. Shorter-term dietary influences can only be assessed by analyses of all of the copepods’ 6 develop- Wax esters are considered to be formed by copepods in response to short periods of plentiful food followed The results here establish that Calanus finmarchicus, by long periods of food scarcity (Lee et al. 1971a, Lee C. glacialis and C. hyperboreus have significantly dif- & Hirota 1973), a situation that applies above all to ferent % of both 20:1n-9 and 22:1n-11 fatty alcohols in herbivorous zooplankton in high latitudes. Further, the their wax esters. Similar differences can be deduced fatty alcohol moieties of zooplankton wax esters are from various studies on single species (Lee 1974, 1975, considered to be biosynthesised by the copepods from Clarke et al. 1987, Falk-Petersen et al. 1987, Kattner & the corresponding fatty acids, which are themselves Krause 1987, Tande & Henderson 1988, Kattner 1989) biosynthesised de novo by the copepods, largely from but only Albers et al. (1996) analysed the 3 species protein and carbohydrate precursors in the diet (Sar- simultaneously. It can be calculated from the data of gent & Henderson 1986). Key evidence for this hypoth- Albers et al. (1996) that the ratios of 22:1n-11/20:1n-9 esis is that 20:1 and 22:1 are not significant compo- fatty alcohols in females of C. hyperboreus, C. glacialis nents of phytoplanktonic lipid (Sargent & Henderson and C. finmarchicus were, respectively, 1.98, 0.43 and 1986). Fatty acids and fatty alcohols are energy-rich 0.99. The ratios for Stages V and females of the 3 spe- molecules that are catabolised to CO2 and H2O to gen- cies in the present study were 1.74 for C. hyperboreus erate large amount of energy (ATP) for metabolic (lower than reported by Albers et al. 1996), 0.74 for C. needs, the stoichiometry of oxidation of 1 mol (338 g) of glacialis (higher than reported by Albers et al. 1996) and 1.04 for C. finmarchicus (the same as reported by Albers et al. 1996). Such differences may reflect thesamples in the 2 studies being taken at different times A longer-chain fatty alcohol (or fatty acid) is more and at different places. The samples of females chemically reduced and has a higher energy content analysed by Albers et al. (1996) were captured in June per unit mass than a shorter chain fatty alcohol (or fatty and July-August in 2 successive years in the Fram acid). Therefore, the energy content of wax esters (or Strait between 78° and 80° N. The samples of Stages V triacylglycerols) is maximised by increasing the chain and females analysed here were captured between lengths of their constituent fatty alcohols or fatty acids.
late August and late September in Kongsfjord at Thus, Calanus hyperboreus with the highest % of 78° 57’ N. Thus, it is probable that copepods of a given 22:1n-11 alcohol in its wax ester is the most active of species analysed by Albers et al. (1996) had different the 3 species in biosynthesising lipid de novo and nutritional histories from copepods of the correspond- accumulates wax esters with the highest energy con- ing species analysed here, as well as being at a slightly tent. This is consistent with C. hyperboreus being the earlier stage of development. Therefore, it cannot be most highly adapted of the 3 species, maximising for- concluded that copepods of the same species in the mation of the longest-chain end-product of lipid bio- 2 studies had accumulated maximal levels of wax synthesis, 22:1n-11, reflecting its main location in the esters. The chain lengths of the alcohols of the wax most extreme environment, the Greenland Sea and the esters of C. hyperboreus, C. glacialis and C. finmarchi- Arctic basin. Moreover, the sum of 20:1 and 22:1 fatty cus vary with the levels of wax esters in the copepods, alcohols in the wax esters of the 3 species increases i.e. with their stages of development (Lee 1974, Kattner from C. finmarchicus to C. glacialis to C. hyperboreus & Krause 1987, Tande & Henderson 1988), with lower (Table 1), as does the sum of 20:1 and 22:1 fatty acids in levels of wax esters generally being associated with the wax esters (Table 2). That is, major de novo fatty shorter fatty alcohols. Moreover, as evidenced by the acid/fatty alcohol biosynthetic activity increases pro- large standard deviations, there is considerable varia- gressively from C. finmarchicus to C. glacialis to C. tion in the % of 22:1n-11 and 20:1n-9 fatty alcohols in wax esters between individuals of a given species in As established previously (Scott et al. 2000), the the present study (Table 1), as occurs also in the study large Arctic basin Calanus hyperboreus and the inter- of Albers et al. (1996). Nonetheless, the present results, mediate-sized Arctic shelf C. glacialis contain the based on analyses of very large numbers of samples, same level of lipid per unit body mass (ca. 65%) and contain the same % of wax esters in their total lipid 1987, Graeve et al. 1994), consistent with diatoms pro- (ca. 70%). However, C. glacialis has a lesser ability to viding the main dietary precursors of the wax esters in maximise formation of end product 22:1n-11 and, all 3 species studied. This is supported by C16 PUFA therefore, accumulates wax ester reserves with a lower characteristic of diatoms being present in minor but energy content per unit weight than those in the simi- significant % in all 3 species. The flagellate markers larly sized reserves accumulated by C. hyperboreus.
18:4n-3 and 22:6n-3 (Sargent et al. 1987, Graeve et al.
Consequently, C. glacialis is less adapted to extreme 1994) were present in small and minor %, respectively, environments than C. hyperboreus, reflecting its main in all 3 species. The % of both 18:4n-3 and 22:6n-3 location in the less extreme Arctic shelf waters. None- were higher in Calanus hyperboreus than in the other theless, C. glacialis is more adapted to Arctic waters 2 species but the difference was significant only for than the smaller, North Atlantic species C. finmarchi- 22:6n-3. Higher % of flagellate markers in the wax cus, whose wax ester reserves account for only ca.
esters of C. finmarchicus and C. glacialis have previ- 33% of its body mass in the waters studied here (Scott ously been reported (Kattner & Krause 1987, Kattner et et al. 2000). The sum of the % of 20:1 and 22:1 alcohols al. 1989, Albers et al. 1996), but % in wax esters in C. (and acids) in the wax esters is greater in C. glacialis glacialis have generally been low (Tande & Henderson than in C. finmarchicus, in line with the former species 1988, Albers et al. 1996). One factor underlying such having the higher levels of wax esters. However, the % apparent species differences is that Calanus copepods of 22:1 alcohols in the wax esters of C. finmarchicus is may feed selectively on diatoms or flagellates includ- greater than in C. glacialis (Table 1) so that the lower ing Phaeocystis (Mullin 1965, Meyer-Harms et al.
levels of wax esters in C. finmarchicus have a higher 1999). However, the abundance of individual algae, energy content than those in C. glacialis. It should also i.e. the species composition of the phytoplankton, be noted that 22:1 has the highest phase transition which depends on the timing and stage of develop- point (melting point) of all the fatty alcohols in copepod ment of the bloom, which in turn differs in open Arctic wax esters. It is present in the highest % in the wax waters from waters adjacent to ice, is probably the esters of C. hyperboreus, the species that is likely to major factor determining which algae the copepods experience the lowest ambient temperatures for the ingest. Although the fatty acid compositions in Table 2 longest period. This is not compatible with the accu- are very similar between the 3 species, the standard mulation of long-chain fatty alcohols/acids in polar deviations indicate that considerable variation existed copepods being an adaptation to low ambient temper- between individual samples for all the species. The Stage V and female copepods studied here had accu- The species differences in fatty alcohol compositions mulated their abundant wax ester reserves at times, (Table 1) are reflected, albeit to a much lesser extent, varying from a few weeks to many months during pre- in the fatty acid compositions of the wax esters of the 3 ceding summer(s) and spring(s), before they were sam- species (Table 2). Thus, the highest % of 22:1 fatty acid pled. Consequently, the similarity of the fatty acid is in Calanus hyperboreus and the highest % of 20:1 is compositions of the wax esters in the 3 species indi- in C. glacialis. Therefore, the ratio of 22:1/20:1 fatty cates that, overall, their historical diets were similar, acids is highest in C. hyperboreus and lowest in C. gla- irrespective of when and in what location these diets cialis, as is the case for the fatty alcohols. However, the were assimilated. This is not to say, however, that their ratios of 22:1/20:1 fatty acids are all substantially less individual diets do not vary significantly in time and than the ratios for the corresponding fatty alcohols in all the species, reflecting a higher abundance of 22:1 Although diatom biomarkers dominated the fatty relative to 20:1 in the alcohols as compared to the acids of the copepods’ wax esters, the flagellate bio- acids. Nonetheless 20:1 and 22:1 fatty acids comprise marker 22:6n-3 consistently dominated the fatty acids ca. one-third of the total fatty acids in the species and, in their polar lipids, i.e. this fatty acid is preferentially as noted above, the sum of 20:1 and 22:1 acids in- directed by the copepods to phospholipids. It is pos- creases progressively from C. finmarchicus to C. gla- sible that dietary 20:5n-3 derived from diatoms is cialis to C. hyperboreus. The abundance of these fatty converted to 22:6n-3 by the copepods, but this is acids in the wax esters, together with the dominance of unlikely because flagellates, including dinoflagellates the corresponding fatty alcohols (formed from the cor- and prymnesiophytes, commonly contain around 4 responding fatty acids), emphasises how highly active times as much 22:6n-3 as 18:4n-3 (Sargent et al.
the 3 Calanus species are in lipid biosynthesis.
1995a). The small % of flagellate-derived 18:4n-3 in Other than 20:1n-9 and 22:1n-11, the dominant fatty the copepods’ wax esters fatty acids indicates that acids in the wax esters were 16:1n-7 and 20:5n-3, each the dietary input of flagellate-derived 22:6n-3 is likely present in the same % in the 3 species. Both of these to be sufficiently large to account for its presence fatty acids are abundant in diatoms (Sargent et al.
in phospholipids. Because diatom-derived fatty acids Scott et al: Wax esters and phopholipids of 3 species of Calanus dominate the copepods’ wax esters, the contribution of that 22:6n-3 has special properties in copepods relat- flagellates to the copepods’ diet is underestimated by ing to their mobility and migrations rather than to considering the wax esters alone. Nonetheless, polar adaptation to low temperatures is worthy of future lipid is a minor albeit a very important constituent research. This is but one aspect of the fascinating of the copepods’ total lipid relative to wax esters interplay between environment (including diet) and (accounting for ca. 14% of the total lipid) so that, over- genetics in high-latitude zooplankton.
all, diatoms contribute substantially more fatty acids tothe copepods’ lipids than do flagellates. Very high % of22:6n-3 and the correspondingly high ratio of 22:6n- Acknowledgements. C.L.S. thanks the Norwegian Polar Insti- 3/20:5n-3 (2:1) in the copepods’ polar lipids have been tute for support during her PhD studies. BIODAFF 97 was recorded previously (Lee 1974, Tande & Henderson funded in part by the Access to Large Scale Facilities (LSF) 1988, Albers et al. 1996). This is in contrast to the situ- Training and Mobility of Researchers (TMR) Programme ofthe Commission of the European Communities. Norsk Hydro ation in other polar zooplankton, e.g. gammarids (Scott (Contract 9000000465) supported the work as operator of et al. 1999) and euphausiids (Falk-Petersen et al. 2000), Barents Sea Production Licences 182, 225 and 228. Partners where 20:5n-3 is the dominant fatty acid in polar lipid in the licence and co-sponsors are Statoil, SDOE, Agip, and the ratio of 22:6n-3/20:5n-3 is generally ca. 1:2. Clearly the % of 20:5n-3 and 22:6n-3 in marine in- vertebrate phospholipids are regulated much more tightly than those in neutral lipids, even though thePUFA in question are derived, often in variable Albers CS, Kattner G, Hagen W (1996) The compositions of wax esters, triacylglycerols and phospholipids in Arctic amounts, from the copepods’ diets. Such tight regula- and Antarctic copepods: evidence of energetic adapta- tion is presumably determined genetically and is essential to maintain specific cellular function(s). One Clarke A, Holmes LJ, Hopkins CCE (1987) Lipid in an Arctic such function is the critical role 22:6n-3 has in neural food chain: Calanus, Bolinopsis, Beroe. Sarsia 72:41–48 tissues of vertebrates including fish, where it is con- Conover RJ (1988) Comparative life histories in the genera Calanus and Neocalanus in high latitudes of the northern centrated in nerve synaptosomal junctions (Sargent et al. 1993). Some copepods have recently been shown, Davis AD, Weatherby TM, Hartline DK, Lenz PH (1999) unusually for invertebrates, to have myelinated nerves Myelin-like sheaths in copepod axons. Nature 398:571 (Davis et al. 1999) which facilitate their fast strike and Falk-Petersen S, Sargent JR, Tande K (1987) Food pathways and life strategy in relation to the lipid composition of sub- escape responses. Interestingly, Lee (1974) reported Arctic zooplankton. Polar Biol 8:115–120 that the phospholipids of Calanus hyperboreus con- Falk-Petersen S, Hagen W, Kattner G, Clarke A, Sargent JR tained high levels (15 to 19%) of sphingomyelin, a (2000) Lipids, trophic relationships and biodiversity in major lipid in myelin. 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