Morphology and Variation of Daphnia Galeata SARS from Lake Biwa and Lake Kizaki in Japan
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Jpn. J. Limnol., 53, 1, 47-54, 1992 Morphology and Variation of Daphnia galeata SARS from Lake Biwa and Lake Kizaki in Japan Susumu TANAKA Abstract In Japan Daphnia galeata SARS has been confused for a long time with Daphnia hyalina or Daphnia longispina due to the confusion in Europe where the three species originally described. In this paper, the Daphnia species from Lake Biwa and Lake Kizaki, which has been assigned various scientific names, are confirmed as Daphnia galeata SARS, 1863, based on the determinative key proposed by FLOBNERand KRAUS (1986), and their morphology and morphological variations are described. Key words: Daphnia galeata, Cladocera, Lake Biwa, Lake Kizaki KRAUS (1986), these taxonomic complications 1. Introduction were caused by the occurrence of numerous Since the excellent classical works by UENO different morphological races or forms, and the (1927, 1937), few contributions has been made presence of many intermediate forms among to the taxonomy of Japanese Cladocera. Even different populations. in Lake Biwa and Lake Kizaki where many Recently the populations of hyaline limnetic limnological investigations were conducted, the species of Daphnia in various European waters cladoceran fauna has not been thoroughly stud- have been successfully divided into separate ied. The populations of limnetic species of the species by careful analysis (CHRISTIE, 1983, genus Daphnia in these lakes, which are inter- FLOSNERand KRAUS,1986; HRBACEK,1987; HUDEC, esting as being dominant in zooplankton com- 1991).In the European literature, D. hyalina munities, are also confused with regard to their LEYDIG was defined as a species with pointed taxonomic status and assignment. Therefore rostrum, long and low antennula mound, and a these populations has long been recorded under relatively low and always evenly rounded hel- various names such as D. longispina (NARITA met. The frons is usually convex or straight. and OKAMOTO, 1984), D. longispina hyalina These characteristics are fundamentally identi- (UENO, 1934a, b, 1937), D. hyalina (UENO, 1973, cal to LEYDIG'S (1860) original description, MIZUNO, 1977), D. longispina galeata (UENO, whereas D. galeata SARS was defined as a 1937) and D. galeata (UENO;1973, MIZUNO,1977). species with blunt rostrum, short and high It was also uncertain whether the populations in antennula mound, and high angulated or typi- these lakes were monotaxic. cally pointed helmet. The frons is distinctly Many species of Daphnia including D. galeata concave or nearly straight and directed back- SARS were described originally in Europe, and wards. the confusion as to taxonomic status or nomen- After the taxonomic criteria proposed, the clature of hyaline limnetic species of Daphnia Daphnia populations of L. Biwa and L. Kizaki (D. hyalina-galeata complex) has continued collected in several years were definitely even in Europe until quite recently. The confu- identified as Daphnia galeata SARS. In the pres- sion in Japan undoubtedly relates to the situa- ent paper the author describe the precise tion in Europe. As pointed out by FLOBNERand morphology of Daphnia galeata SARS from two 48 TANAKA Japanese lakes and discusses some taxonomic problems. 2. Materials and methods Lake Biwa is the largest and the most ancient lake in Japan. It is located in the western part of Honshu Island (35•‹15'N, 136•‹05'E) with a surface area of 674.4 km2 and a maximum depth of 104.0 m, and Lake Kizaki is a small lake located in the central part of Honshu (36•‹33'N, 137•‹50'E) with a surface area of 1.4 km2 and a maximum depth of 29.5 m (HORIE, 1962). Sam- ples were collected from the North Basin of L. Biwa (near Station D in KAWABATA, 1987) on 27 October 1989 and the deepest point of L. Kizaki on 23 August 1984 and 29 August 1990. The samples were obtained by the zooplankton net of 94 ƒÊm in mesh size (Nitex) which were vertically hauled from about 30 m depth (L. Biwa) and from near lake bottom (L. Kizaki) to the surface. The animals were fixed with 4% formalin or 95% ethyl alcohol immediately at collection and preserved in 4% formalin or 70% ethyl alcohol for laboratory use. For Fig.1. Total length frequency distributions of observations, complete individuals and isolated parthenogenetic female of Daphnia galeata parts of the body were mounted on slides with SARS from L. Biwa and L. Kizaki. Total 50% glycerol. Measurements of sizes and line length indicates the length from top of drawings were made on a compound micro- head to base of shell-spine. scope with phase optics, a sliding stage and a drawing tube. long and high, developing crest; helmet variable in size and shape, either elongate triangular 3. Description with sharply pointed apex on the top (most 3-1. Parthenogenetic female (Figs. 2-4) materials in L. Biwa, Fig.2 A-F, a few mate- Size: a medium-sized species; longest axis rials in L. Kizaki,Fig.2 K) or uniformly (exclusive of shell-spine) of egg-carrying rounded or bluntly tapering (most materials in female 0.8-2.0 mm (Fig.1). Carapace color- L. Kizaki, Fig. 2 G-J, L); ventral margin bulged less and hyaline; oval shape in lateral view, in front of the eye, slightly or distinctly concave maximum height about 4/5 of length; ventral between eye and rostrum. Rostrum acute, margin curved and dorsal margin slightly moderately long, distinctly projecting beyond curved; spinulation on ventral margin extend- the sensory hair of the antennules (Fig.3). ing anteriorly about half of the edge and on Antennula mound short and high. Fornix dorsal margin restricted posterior one-third; extending to the edge of the optic vesicle. spinules widely spaced and so minute that they Abdominal processes moderately developed, are difficult to discern. Shell-spine long but first process longest and about two and half highly variable up to half as long as carapace, times as long as second (Fig.4 A, C, D). arising in or slightly dorsally from the longitu- Postabdomen weakly tapering distally, with 8- dinal body axis, slightly directed dorso-poster- 13, usually 10-12 anal teeth which strongly and iorly or straight backwards. Head moderately uniformly decrease in length proximally (Fig.4 49 Daphnia galeata SARS in L. Biwa and L. Kizaki Fig.2. Daphnia galeata SARS, parthenogenetic females: A-F, L. Biwa; G-L., L. Kizaki; F and L, young individuals with eggs. Scales indicate 1 mm. 50 TANAKA Fig.3. Daphnia galeata SARS, variation of female rostrum, A-D, L. Biwa; E-H, L. Kizaki . A). Postabdominal claws long and slender, with three pectens of fine teeth and with two incisions on ventral margin (Fig.4 B, E). 3-2. Male (Fig. 5) Samples from both lakes contained a few immature males. The longest axes of mate- rials were up to 1.3 mm in L. Kizaki and 1.0 mm in L. Biwa. Head in the material of L. Kizaki with low rounded crest or sharply pointed apex (Fig.5 C, D), and in L. Biwa almost all males with thornlike vertex (Fig.5 A, B) . Ventral margin between rostrum and eye slightly con- cave. Rostrum directed ventrally, with apex rounded. Antennules two to three times as long as broad, a lateral sensory hair found subapically and near base of flagellum; flagel- lum shorter than apical sensory hairs (Fig .5 E). First thoracic appendage with a stout hook and a long seta as in Daphnia longispina (Fig.5 F). Carapace oblong, dorsal margin slightly con- vex; maximum width middle anterior border of ventral margin forming thickened rim , bearing no spines or hairs (unlike males of most species Fig.4. Daphnia galeata SARS, A, postabdomen, L. Biwa; B, post abdominal claw, L. Biwa; C, of Daphnia). Posterior half of ventral margin abdominal processes, L. Biwa; D, abdomi- with about 24 wide-spaced spinules. Dorsal nal processes, L. Kizaki; E, post abdominal margin without spinulation. Shell-spine long. claw, L. Kizaki. Abdominal processes rudimentary, second the Daphnia galeata SARS in L. Biwa and L. Kizaki 51 Daphnia, he frequently moved the taxonomic status of particular taxa from species to vari- eties or vice versa in his successive published and unpublished lists (FREY, 1982). D. hyalina, on the other hand, was described by LEYDIG (1860) based on the specimens with low rounded helmets from Lake Constance. According to BROOKS (1957), RICHARD (1896) definitely divided D. galeata as a separate species from D. hyalina, but he included the specimens with taller helmet from L. Constance in D. hyalina. Since then taxonomic complica- tions on both species have continued until quite recently. The historical sketches on the change of taxonomic status or nomenclatures of D. hyalina-galeata complex were shown in CHRISTIE (1983) and FLOSNERand KRAUS (1986). BROOKS(1957) indicated precisely the points of morphological differences between D. hyalina and D. galeata in the assignment of specimens belonging to D. galeata distributed in North America. FLOSNER (1972) and HERBST (1976) followed BROOKS(1957) criteria in their Fig.5. Daphnia galeata SARS, Male: A and B, L. studies of European Daphnia and gave keys for Biwa; C and D, L. Kizaki; E, antennule, L. identification. Most recent publications in Biwa; F, first appendage, L. Biwa. Japan, however, still continue to confuse. It is known that D. galeata distributed widely longest. 9-13 anal teeth. in Holarctic (HRBACEK,1987). Most varieties in D. galeata might be described on the basis of 4. Discussion variation of head shape or different stages of The hyaline limnetic species of Daphnia from cyclomorphosis. These morphological varia- Lake Biwa and Lake Kizaki was identified as tions may also indicate a possibility of hybridi- D. galeata SARS, 1863 emend. FLOBNER and zation of two species or forms (BROOKS,1957, KRAUS, 1986.