Hydrobiologia 186/187: 109-117, 1989.C. Ricci, T. W. Snell and C. E. King (eds), Rotifer Symposium V. 109© 1989 Kluwer Academic Publishers. Printed in Belgium.

Morphological variation in Kellicottia longispina

W. T. Edmondson & Arni H. LittDepartment of Zoology, NJ-15, University of Washington, Seattle, Washington 98195 U.S.A.

Key words: zooplankton, Rotifera, biogeography, arctic limnology

Abstract

The lengths of the body, the posterior spine and the three longest anterior spines were measured for 25specimens of Kellicottia longispina from each of the eight lakes distributed from Imikpuk at Point Barrow,Alaska (latitude 71 15') to Lake Washington (latitude 47 38'). Collections were available for more thantwo dates from six of the lakes. Temperature ranged from 1.2° to 18 C. Mean lengths and ratios wereexamined in relation to latitude and temperature. Each population differed from the others in some aspectof absolute size, variability, or shape as expressed by the ratios of the dimensions. The population fromPoint Barrow is similar but not identical to Olofsson's var. heterospina.

Introduction

Kellicottia longispina is a widespread, commonplanktonic rotifer that can become very abundant.It is strikingly different in appearance from allother rotifers, even from its only congener,K. bostoniensis. Interestingly, both species weredescribed from North America. Kellicottia bos-toniensis was confined to that continent untilabout 1943 when it was first noticed in Sweden(Arnemo et al., 1968). It subsequently spread toFinland (Dr. Pertti Eloranta, personal communi-cation).

Kellicottia longispina was found in 'Niagarawater' near Buffalo, N.Y. and assigned to Anuraeaby Kellicott in 1879 (Fig. 1-a). Following Hudson& Gosse (1886) it was known as Notholca until1938 when Ahlstrom created Kellicottia to recog-nize its unusual structure. The species was noticedin England and Europe soon after its discovery inNorth America. Hood's Ertemias tetrathrix (1888)probably was this species (Fig. 1-b). Some

species described as Ertemia may have beenrhizopod shells into which a rotifer had crept (seeHudson & Gosse).

Although K. longispina is easily recognized,even causal examination shows that there are dif-ferences in size and shape among different popu-lations. A form from arctic Norway is so differentthat it was given the varietal name heterospina byOlofsson (1917) (Fig. 1-c). A similar form wasrelatively abundant in samples collected by thelate G.W. Comita from Imikpuk (FreshwaterLake) near Point Barrow, Alaska in 1951. Itsoccurrence in this small arctic lake raisedquestions about its distribution in the Arctic andthe occurrence of forms resembling the ones intemperate regions. Therefore we examined col-lections from other lakes in northern Alaska andmaterial from five lakes at lower latitudes (Fig. 2,Table 1). We measured major anatomical struc-tures in an attempt to define objectively whatmade the populations look so different (Fig. -d,Fig. 3, Table 2). We also examined correlations

110

A

b

C

C dFig. 1. Four drawings of Kellicottia longispina. a. Anuraea longispina, from original drawing by Kellicott (1879). b. Ertemiastetrathrix from Hood (1888). c. K. longispina var. heterospina after Olofsson (1917). d. Diagram indicating symbols used throughout

the text.

among the various dimensions and between mor-phometric features and the location and environ-mental conditions of the lakes.

Materials and methods

Collections from two arctic lakes in addition toImikpuk were made by Comita in 1951. Imikpukwas studied more in detail in 1952 (Comita, 1956;

Edmondson, 1955). For reasons not understood,Kellicottia was extremely scarce in that year. Inaddition to our own material from Bare Lake,Hall Lake and Lake Washington, we were kindlyprovided with material from Great Slave by thelate Donald S. Rawson and from Lake PendOreille by Raymond A. Stross.

The three arctic lakes are small tundra ponds.Great Slave Lake is very large and oligotrophic(Rawson, 1956). Bare Lake is small and oligo-

B

a

111

Fig. 2. Location map.

trophic, but was fertilized on June 11, 1952(Nelson & Edmondson, 1955). Lake Pend Oreilleis large and mesotrophic. Hall Lake is small andslightly dystrophic. Lake Washington is moder-ately large and mesotrophic (Edmondson, 1963).

Twenty-five specimens from each collectionwere measured under light compression.

Measurements were made of the three longestanterior spines (A,D,E), the posterior spine (C),and the length (B) and width (W) of the body(Fig. l-d). After a preliminary graphical analysisof the dimensions and their ratios to each other,we selected dimensions or proportions thatshowed distinct relation to location or strong cor-

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Table 1. Data on collections used for measurements of Kellicottia longispina.

Name Date Latitude Temperature°C

1 Imikpuk 09 August 1951 71 ° 20' 12.52 Imikpuk 18 August 1951 6.63 Imikpuk 06 September 1951 4.24 Imikpuk 18 September 1951 1.25 Ikroik 01 August 1951 71° 20' 13.06 Ikroik 30 August 1951 5.67 Paddle Lake 22 August 1951 71° 15' 9.28 Great Slave Lake 03 July 1949 62° 00' 4.09 Great Slave Lake 11 August 1949 12.0

10 Great Slave Lake 22 August 1947 8.811 Great Slave Lake 21 September 1947 7.012 Bare Lake 03 June 1952 58° 00' 8.013 Bare Lake 17 June 1952 11.114 Bare Lake 25 June 1952 14.515 Pend Oreille Lake 05 April 1953 48 ° 25' 4.316 Pend Oreille Lake 20 June 1953 13.817 Pend Oreille Lake 06 July 1953 18.218 Pend Oreille Lake 26 October 1953 12.019 Hall Lake 02 January 1952 47 ° 50' 4.420 Hall Lake 24 April 1952 11.521 Hall Lake 07 July 1952 14.222 Lake Washington 23 April 1980 47° 38' 9.823 Lake Washington 27 May 1981 14.224 Lake Washington 04 June 1980 13.625 Lake Washington 09 October 1981 13.7

relations with other features for further statisticalanalysis by standard tests (Table 2). We examinedlength-frequency plots for all of the sets ofmeasurements.

In the following section a selection of the resultsis shown in graphical form, with a brief summary,to substitute for lengthy verbal descriptions.

Results

The clearest generalization that we can make isthat the population of each lake was differentfrom all the others in at least one feature. Someof the features varied among samples taken froma lake at different times. We looked to see whetherthe variation was related to time or temperature,as might be expected of cyclomorphosis.

The following comments call attention to factsshown by Fig. 4 and Table 2. The total length of

the animals varied greatly among the lakes, withthe Imikpuk animals being outstanding (Fig. 4-T).Populations from some of the other lakes showmore variation with temperature than those fromImikpuk. There is a clear tendency for the totallength (T) to decrease in lakes to the south. GreatSlave and Paddle are out of line, but their meanshave large standard deviations and the range ofGreat Slave overlaps that of all the lakes to thesouth of it. Rotifers are larger at higher tempera-ture in three of the lakes and smaller in two, butonly the greatest differences in size are significant.

The variation among lakes is more easily seenin plots of the range of all the samples for eachlake (Fig. 4). Of all the features, the length of spineA shows the clearest geographical pattern(Fig. 4-A). The population of Ikroik is out of lineand shows few similarities to that of the other twoarctic lakes.

Differences in the proportions of spines and

113

Fig. 3. Photograph of representative individuals from each lake.

body determine the different appearances of thepopulation. The way the total length is shared bythe spines and body is shown by ratios A:T,B: T and C: T. The ratio of A: C relates the twomost conspicuous features. In four of the eightlakes values of A:C vary from 1.0 to 1.4. InImikpuk they are nearly equal, varying from 1.0 to1.1, but in Great Salve the ratio is 1.7 to 1.9, as

is consistent with the shorter posterior spine.Within its range of variation in each lake, A: C isnot correlated with body size. The ratio A: B hasa clear relation to latitude as did the absolute sizeof spine A, but the ranges of the ratio are propor-tionately much larger. Body length does not varyas much among the lakes as the spines, and itsvariations have less effect on appearance.

Table 2. Upper. Mean values and ratios of some of the features measured. See Fig. 1-d for symbols. T is total length (A + B + C). W is width of body at widest point. Note: The ratios are means of ratios of individual measurements; the values may be slightly different from the ratios of the tabulated mean lengths. Lower. Standard deviations of the means, n = 25. All measurements are in micrometers. Smallest unit of measure for lakes 1 to 7 was 12 p, for lake 8 was 4 p.

OBS Lake T A B C D E W A : T B : T C : T A : B A : C A : D D : E C : B W : B

Imikpuk Imikpuk Imikpuk Imikpuk Ikroik Ikroik Paddle Great Slave Great Slave Great Slave Great Slave Bare Bare Bare Pend Oreille Pend Oreille Pend Oreille Pend Oreille Hall Hall Hall Washington Washington Washington Washington

OBS Lake T A B C D E W A : T B:T C : T A:B A : C A:D D : E C:B W : B

Imikpuk Imikpuk Imikpuk Imikpuk Ikroik Ikroik Paddle Great Slave Great Slave Great Slave Great Slave Bare Bare Bare Pend Oreille Pend Oreille Pend Oreille Pend Oreille Hall Hall Hall Washington Washington Washington Washington

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Two general patterns emerge, one a trend fromnorth to south, the other humped or depressed inthe middle because of the special features of theGreat Slave population.

Another feature that catches the eye is the posi-tion of the body along the total length, determinedby the length of the two spines A and C. GreatSlave specimens have the body further back onthe axis because the C spine is shorter than inother lakes (Fig. 4-C: T). One's subjectivereaction to the appearance of the animals isaffected by the shape of the body as well as by theproportions of the spines. The shape of the bodyvaries considerably, as measured by the ratioW:B, but not with a very clear distributionalpattern (see Table 2). The appearance of the bodyis affected by the fact that in some, as in Imikpuk,the maximum width of the body is well behind thefront of the lorica, while in others it is at the frontend. Our measurement system did not includethat aspect of shape.

We looked for evidence of cyclomorphosis orother form changes in graphs of dimensionsplotted against temperature and time. Some of thedimensions and ratios change between sampling

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Fig. 5. Length-frequency histograms of total length ofK. longispina in Bare Lake. Above - 03 June 1952, Middle -

17 June 1952, Below - 25 June 1952.

dates in some of the lakes, but most of the dif-ferences are small and statistically insignificant(t-test, = 0.05). We examined the samples thatshowed the biggest differences by plotting lengthagainst frequency. The relative frequency of dif-ferent stages is affected by changes in birth anddeath rates. An increase in mean value can becaused either by an increase in the frequency ofthe largest size or by a decrease in the frequencyof the smallest, or both (Fig. 5). However, we maybe seeing simply the replacement of a cohort oflarge animals by a cohort of different size.

Any time the lengths of spines of a rotifer showsystematic changes, we must consider the possi-bility of predation and chemomorphosis, as withBrachionus and Asplanchna. As far as we knoweach of these lakes has a tactile invertebratepredator. In addition to the predatory Limno-calanus, Imikpuk had two species of Anostracawhich are capable of swallowing the bigKellicottia.

Conclusions

The Imikpuk form of Kellicottia longispina is notidentical with Olofsson's var. heterospina whichwas characterized on the basis of large size, ratiosA: D > 3 and D: E > 1.5. The Imikpuk formagrees on the first point, although it is 10 % larger,but ratio A: D is only 2.5 and D: E is 1.25. Theother two arctic populations agree even less withthe description of heterospina. It appears that theKellicottia fauna of the Arctic is diverse morpho-logically (see also Turner, 1987).

The question remains whether Kellicottia exhi-bits cyclomorphosis or chemomorphosis. Oursamples show that some populations vary con-siderably over time, but the samples were nottaken frequently enough to define the time courseof changes. These problems are well worthpursuing in lakes that reliably produce large, varia-ble populations. The study of chemomorphosiswould have two components. First, a field studyto identify lakes with different tactile predators.Then one would do laboratory experiments.These will be difficult because Kellicottia is hard

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to culture, largely because it sicks to the surfaceof the water so easily. Possibly some successcould be achieved by tethering individuals by theposterior spine to the bottom of a culture dish ona microblob of petroleum jelly. We know that thespines are tightly curled around the body in theegg and rapidly straighten after hatching, butnothing seems to be known about the subsequentrate and pattern of growth. It is surprising that ananimal as conspicuous as Kellicottia longispina isnot better known.

Acknowledgements

The work at Point Barrow was supported by theUnited States Office of Naval Research. Prepa-ration of this paper was made possible by theAndrew W. Mellon Foundation.

References

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Hudson, C. T & P. H. Gosse, 1886. The Rotifera; or wheel-animalcules. Longmans, Green & Co. London.

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Nelson, P. R. & W. T. Edmondson, 1955. Limnologicaleffects of fertilizing Bare Lake, Alaska. U.S. Fish andWildlife Service, Fish. Bull. 102: 413-436.

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Pejler, B., 1977. On the global distribution of the familyBrachionidae (Rotatoria). Arch. Hydrobiol./Suppl. 53. 2:255-306.

Rawson, D. S., 1956. The net plankton of Great Slave Lake.J. Fish Res. Bd Can. 13: 53-127.

Turner, P. N., 1987. Some rotifers from Alaska, U.S.A. witha note to researchers. Microscopy 35: 541-548.