Research Note Crustacean species new to Spitsbergen with notes on the polymorphism and the subfossil preservation of Cytherissa lacustris (G. 0. Sars) T A D E U S Z SYWULA. T A D E U S Z NAMIOTKO, JERZY SELL, ANDRZEJ WITKOWSKI and MAREK ZAJACZKOWSKI Sywula. T . , Namiotko, T . , Sell, J . , Witkowski, A. & Zajaczkowski, M . 1994: Crustacean species new to Spitsbergen with notes on the polymorphism and the subfossil preservation of Cytherissa lacustris (G. 0. Sars). Polar Research 13(2), 233-235. The copepods Limnoralanus macrurus G. 0 . Sars and Eucyclops serrulatus (Fisch.) and the ostracode Cytherissa lacustris (G. 0 . Sars). hitherto unknown on Spitsbergen, were found in Lake Rewatnet. the last species also in Lake Svartvatnet. Samples from parthenogenetic populations of C. lacustris showed a complete lack of electrophoretically detectable variability at four enzyme-encoding loci, two of which are highly variable in mainland populations. However, morphological variation in the carapace length and nodation was no less than in the mainland populations. The carapace valves of C . lacustris d o not preserve well in the sediments of Revvatnet. “ ~ ~ o ~ ~ ~ ~ N S “ ’ T . Sywula, Marine Biology Centre, Polish Academy of Sciences, 81-347 Gdynia, s w . Wojciecha 5 , Poland: T . Namiotko and J . Sell, Department of Genetics, University of Gdansk, 80-822 Gdatisk. Kladki24. Poland; A . Witkowski, Institute of Oceanography, University of Gdatisk, 81-378 Gdynia, Pitsudtkiego 46, Poland; M . Zajqczkowski, Institute of Oceanology, Polish Academy of Sciences, 81-967 Sopot, Powstancdw Warszawy 55, Poland. An interesting crustacean community was found in samples taken with a dredge on 31 August 1990 from Lake Revvatnet in Spitsbergen (Wedel Jarlsberg Land, 77”02‘N, 15’23’E). This lake is approximately 0.9 km2 in area, with a maximum depth of 27 m, and does not freeze to the bottom. The profundal zone is extensive, its area being ca. 64% of the lake’s surface area; its upper border coincides more or less with the 7 m isobath (Kuziemski 1959). The bottom sediment is an organogenic silty mud containing ca. 5.03% organic matter, 0.32% calcium, 3.6% magnesium and 6.0% iron d. w.; 86.6% of particles are of $J < 0.063 mm. As many as 7 species of Crustacea were found: a cladoceran Macrothrix hirsuticornis Norm. et Br. (not very abundant); copepods, Limno- calanus rnacrurus G . 0. Sars (very abundant), Eucyclops serrulatus (Fisch.) f. typica (not very abundant), Diacyclops crassicaudis (G. 0. Sars) (not very abundant), Harpacticus uniremis Kroyer (single specimens); and ostracodes Can- dona rectangulata Alm (abundant) and Cytherissa lacustris (G. 0 . Sars) (abundant). Of these species, E. serrulatus and C . lacustris are new to Spitsbergen. L . macrurus was previously col- lected on Spitsbergen in 1977 by I. J ~ r g e n s e n and J. A. Eie ( J ~ r g e n s e n & Eie 1993). The occurrence of L . macrurus and E. ser- rulatus on Spitsbergen is not unexpected. Both species are widely distributed in the Arctic. On the other hand, the presence of C . lacustris was a great surprise. C . lacustris, which has come to be known meta- phorically as “The Drosophila of paleolimnology” (Danielopol et al. 1990), is a strictly specialised lacustrine species with a Holarctic distribution which prefers the muddy bottom of a profundal habitat. Neither adults nor any larval stages are capable of swimming, nor do they penetrate the littoral zone. The dispersal of C . lacustris between lakes is presumably effected in two stages: a speci- men is first swallowed by a fish or macrobenthic invertebrate which itself then becomes the prey of 234 T. Sywula et al. a water bird (Sywula 1990). However, considering the rapid passage of food through a bird's digestive tract, such long-distance transport over the Barents Sea hardly seems possible. Hence the statement that the occurrence of C. lacustris on Spitsbergen was absolutely unexpected. The relatively thick and strongly calcified valves of C. lacustris are usually well preserved in the sediments of mainland lakes: C. lacushis is thus considered a very significant species in pale- olimnology. It is noteworthy, however, that in the sediment of Rewatnet the valves of this species do not preserve well. This is due to the dissolution of the calcite crystals in the valve's external wall immediately after the animal's death. This decalcification is difficult to explain. Although one measurement indicated the water to be slightly acidic (pH 6.8), the composition of the diatom assemblage inhabiting this lake indicates that the water is neutral or slightly alka- line: among the 68 taxa found in samples by one of us (A. W.), 34 were alkaliphilous, one was even alkalibiontic (Denticula fenuis Kutz.), but only 3 were acidophilous. In 1991, an abundant population of C. lacustris was found in another deep Spitsbergen lake - Svartvatnet ( S ~ k a p p Land, 76"53'N, 15'40'E); this lake, like Rewatnet, does not freeze to the bottom either. Except in Lake Baykal (Bronshtein 1947), C. lacustris reproduces parthenogenetically. This is also true of both Spitsbergen populations (the presence of males would be conspicuous owing to the pronounced sexual dimorphism in the cara- pace structure - a characteristic of the family Cytherideidae in general). We considered it interesting to compare the degree of morphological polymorphism in the two Spitsbergen populations of C. lucustris with that of the Central European populations and to assess the genetic relationship between both Spitsbergen populations. To do so, we examined patterns of morphological polymorphism in carapace size and nodation as well as genetic variation at enzyme- encoding loci. Samples were taken on 24 July 1991 (Rewat- net) and 27 July 1991 (Svartvatnet). The cara- paces were measured and their nodation was assessed as described by Sywula & Geiger (1990). Homogenates from single living individuals were prepared 1-2 days after sampling and subjected to electrophoresis on cellulose acetate gels in accordance with the methods of Hebert & Beaton Table 1. Carapace length and nodation of adult Cyrherisso lacl~~hir from two Spitsbergen and two Austrian lakes (data concerning Austrian populations, existing as continuous ones since the Atlanticum, from Sywula & Geiger 1990). Specimens Number Mean Coefficient with smooth of length of variation carapace specimens (pm) (%) (%) Rewatnet 76 a75 5.2 59 Svartvatnet 59 835 2.4 29 blondsee 47 885 3.2 24 Attersee 42 915 3.9 41 (1989). 120 adult specimens from each lake were examined. The following enzyme systems were studied from each specimen: glucose-phosphate isomerase (GPI), leucine aminopeptidase (LAP) and esterases (EST). Both GPI and LAP in C. lacustris are coded for by a single locus. However, the genetic background of esterases is more com- plex; the zymograms from C. lacustris are similar to those from representatives of the genus Cyp- rinotus, for which the esterases are coded for by two loci (Sywula et al. 1991; Sywula 1992). All sampled specimens from both populations proved to be genotypically identical and homo- zygous at all four loci. By contrast, the mor- phological characters were variable (Table 1). At least two of the examined loci - Gpi and Est-1 - are highly variable in Central European populations (Sywula 1990; Sywula & Geiger 1990). Studies of other species of parthenogenetic ostracodes also show that genetic variation is com- mon (Have1 8c Hebert 1989; Sywula 1992) except in very young populations. These data suggest that even though they consist of several thousand specimens, both Spitsbergen populations are still in their initial phase from the population-genetic point of view. They also suggest that the group of successful founders (i.e. those whose genotypes persist in the populations) might be very small and might well be representatives of only one clone. These suggestions seem probable, despite the fact that the present evidence is based on very few loci. Populations are enriched with new clones from two sources - mutation and migration. The possi- bility of successful migration of C. lucustris from the mainland to Spitsbergen may be limited in two ways. Firstly, the ecological conditions in the Crustacean species new to Spitsbergen 235 young Spitsbergen lakes differ considerably from those in the continental lakes inhabited by C. lacustris; thus, strong selection of immigrants might be expected. Secondly, potential immi- grants to the existing abundant populations may have, due to some unknown reasons, restricted access to these populations - an effect suggested for another parthenogenetic ostracode Cyp- rinotus incongruens (Ramd.) (Sywula 1992). Thus, it is possible that genetic differentiation in the Spitsbergen populations of C . lacustris may be attained mainly by mutation. In the future, there will be a special opportunity for testing the above assumptions while studying temporal changes and the mode of increase in genetic vari- ation within and between these large natural populations of this parthenogen. The morphological characters of carapace length and nodation are no less variable in Spits- bergen populations of C. lacustris than in the old Central European ones (Table 1; Sywula & Geiger 1990). In view of the fact that the genetic background in the two Spitsbergen populations seems to be at the most only slightly differentiated, it could be inferred that the mor- phological differences between them are largely the result of environmental modification of the phenotype. Acknowledgements. - The authors express their gratitude to S. KwaSniewski for his assistance with the sampling. References Bronshtein, 2. S. 1947: Ostrawda presnych vod. Fauna SSSR, Moskva, Leningrad. 339 pp. Danielopol, D. L., Carbonel, P. & Colin, J. P. (eds.) 1990: Cytherissa: The Drosophila of paleolimnology . Bull. Insr. Gkol. Bassin d'Aquitaine 47. 310 pp. Havel, J. E. & Hebert, P. D. N. 1989: Apomictic par- thenogenesis and genotypic diversity in Cyprihpsis uidua (Ostracoda: Cyprididae). Heredity 62, 383-392. Hebert, P. D. N. & Beaton, M. J. 1989: Methodologies for allozyme analysis using cellulose acetate electrophoresis. Helena Laboratories, Beaumont, Texas. 32 pp. J@rgensen, I. & Eie, J. S. 1993: Utbredelsen av zooplankton, bunndyr og fisk i i n n s j e r (The distribution of zooplankton, zoobenthos and fish in lakes and ponds of the Mossel penin- sula, Svalbard). NINA Forskningsrapport 045, 1-15. Trondheim, Norway. Kuziemski, J. 1959: Some results of observations of inland waters on Spitsbergen in summer 1958. Przeglad Geofizyczny 4, 179-197. Sywula, T. 1990: The dispersal ability of Cytherissa lacurhis. Bull. Inst. Giol. Bassin d'Aquitaine 47, 135-138. Sywula, T. & Geiger, W. 1990. Genetic and morphological polymorphism in the freshwater ostracod Cyrherissa lacurhis (Sam) of Mondsee and Attersee (Austria). Bull. Insr. GLol. Bassin d'Aquitaine 47, 69-81. Sywula, T., Sell, J., Wotniak, G. & Sobolewska, A. 1991: Non- specific esterase polymorphism in marginal populations of Cyprinotur (Hererocyprir) barbarus (Gauthier et Brehm) (Crustacea, Ostrawda). Bull. Pol. Acad. Sci. Biol. Sci. 39, 353-362. Sywula, T. 1992: The population genetics of the ostracode Cyprinotur incongruens on the basis of esterase loci. Biochem. Svsr. Ecol. 20,735-746.