THE OXYGEN CONSUMPTION OF EPHEMERID NYMPHS FROM FLOWING AND FROM STILL WATERS IN RELATION TO THE CONCENTRA- TION OF OXYGEN IN THE WATER

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1 THE OXYGEN CONSUMPTION OF EPHEMERID NYMPHS FROM FLOWING AND FROM STILL WATERS IN RELATION TO THE CONCENTRA- TION OF OXYGEN IN THE WATER BY H. MUNRO FOX, C. A. WINGFIELD AND B. G. SIMMONDS From the Zoology Department, Universy of Birmingham (Received 7 November ) (Wh One Text-figure) Fox & SIMMONDS () and Fox et al. (5) have shown that certain may-fly nymphs, a caddis larva and an isopod from swift streams have a higher oxygen than nearly related forms from still waters or slow-flowing streams. Their results were summarized in Table IV of Fox et al. (5). It has since been shown by Washbourn () that the oxygen of trout fry reared in swiftly flowing water is greater than that of fry reared in slow water. Wolsky & Holmes () found the oxygen s of four individuals of the crayfish Astacus leptodactylus Eschscholtz, from Lake Balaton, to be 0,, and 5 of oxygen per kg. of animal per hour at - C, the animals weighing,, and g. respectively. The mean of these values for oxygen is. Whout studying the problem we are now considering, Wolsky () later found that the oxygen s of seven individuals of A. torrentiutn (Schrank), living in a swift stream in Hungary, were,, 57, 57, 0, and oxygen per kg. of animal per hour at - C, the animals weighing,, 5,,, and g. respectively. The mean of these values for oxygen is 5. The oxygen of A. torrentium is thus 50 per cent greater than that of A. leptodactylus, and the relation between oxygen and suggests that habat, not size, was responsible for this difference. The species of ephemerid nymphs which we have studied were the following. Cloeon dipterum L. from the pond at Selly Park, Birmingham; Ephemera vulgata L. from a pond at Beam Brook, Newdigate, Surrey; Leptophlebia vesperttna L. and L. marginata L. from Lake Windermere; Baetis scambus Eaton and Baetis sp. from swift streams at Alvechurch, Worcestershire, and at California, near Birmingham. B. scambus were taken from the Alvechurch stream in May shortly before emergence. The mean dry of ten individuals was 0 Baetis sp. were small nymphs There are two misprints in the table: the of ten animals, both of Cloion and Baltis, should be 0, not We have to thank Mr R. S. A. Beauchamp and Mr L. Haig for sending the Leptophlebia and the Ephemera to Birmingham, and Mr N. D. Riley for identifying B. tcambut and L. vetpertina.

2 Consumption of Ephemerid Nymphs from both streams, selected for uniformy of size, the mean dry of ten individuals being They may be young stages of B. scambus. Baetis sp. was Table I. The oxygen of Baetis sp. Jlxp. c.c /I. c.mm./g./hr. i 5 7 II O 5 7 O June n June» July June, f July July Oct. Oct. 0 Nov. Nov. Nov. May May Nov. 7 Nov. s IO I- 5- ' ' I5-I I- I I'0 II o ' 7-7' 7' 7-5'5 S- 5'i -0 - I' 7-7 S SO O O O IO I7O is found in the rapid water in the middle of the streams; our specimens of.. scambus were taken in less swift water near the banks of the stream. The alkali reserves of the waters in which the animals lived were as follows:

3 H. MUNRO Fox, C. A. WINGFIELD and B. G. SIMMONDS Windermere, N; Newdigate, 0-00 N\ Selly Park, N; California, N'> Alvechurch, 0-00 N. All experiments were done at io C, on the day following that on which the animals arrived in the laboratory. The animals were not anaesthetized. For each set of experiments an appropriate quanty of sodium bicarbonate was added to Birmingham tap water (which has an alkali reserve of N) to bring to the normaly of the natural water in which the particular species lives. The water was then eher saturated wh air at C, or nrogen or oxygen was passed through until had approximately the required oxygen content. This was done by passing the gas through a measured volume of water at a known rate for a previously determined time, the rate of flow of the gas being measured wh Beckett's () glass Table II. The oxygen of Baetis scambus Exp. animals c.c./l. c.mm./g./hr. S 7 May }»»»» May May May May 7 > a i i i 0 I-I ' ' 5-o 7- ' 0 5O 'S7O meter. For each experiment the prepared water was siphoned into a small widemouthed bottle provided wh a stopper, and a sample of the water was taken for analysis of s oxygen content. A number of animals was put in the bottle, which was then stoppered and placed in a thermostat. Every 5 min. the bottle was turned upside-down sharply to stir the water inside. Each experiment lasted - hours, the bottle being of such a size that the oxygen content of the water was reduced by about -5 P er cent in that time. At the end of the experiment a further water sample was taken from the bottle and analysed for oxygen, after which the total amount of water in the bottle was measured. The animals were then dried at io and weighed. In the earlier experiments, oxygen was analysed by Nicloux's (0) modification of the Winkler method. The procedure can be simplified whout loss of

4 Consumption of Ephemerid Nymphs accuracy by having a simple analysis tube in place of Nicloux's A-tube. In later experiments a much more convenient variety of the Winkler method due to van Dam (5) was used, which requires only -5 c.c. water for analysis. We improved van Dam's syringe-pipette by replacing the metal collar wh a pair of lock-nuts, the thread of the screw being continued higher up the axis of the screw to accommodate the lock-nuts. The dead space of the syringe-pipette was first filled wh 0 per cent Table III. The oxygen of Leptophlebia vespertina Exp/ animals c.c /I- c.mm.; g./hr. 5 5 r Feb. 5 >» }t»>., Feb. Feb. >>»> >» - Feb. >> Feb. >>»» Mar. 5 t> Mar. " ' 7'5 7'5 7'5 - Q y '5 'I - -O -O 'O O -0 -O O " 0 i manganous chloride solution, then, after having been rinsed, the nozzle of the syringe was plunged into the experimental water and the syringe filled wh this water. The alkaline iodide solution (strength: g. NaOH + g. KI in 0 c.c.) was then taken in and the syringe shaken. The oxygen content of the reagents in the quanties used is negligible. Three minutes were allowed for oxygen absorption, and then o-phosphoric acid was drawn into the syringe to dissolve the precipate. The iodine liberated was trated wh standard sodium thiosulphate, using a o-i c.c. Reyberg (5) burette. This method is accurate to per cent. jeb-xivii

5 H. MUNRO Fox, C. A. WINGFIELD and B. G. SIMMONDS Table IV. The oxygen of Leptophlebia marginata Exp. animals c.c/. cmm./g./hr. i I IO II M Mar is» Mar I Apr j > Apr» i O O O ft «, c.c./l. Fig.. s at C. of ephemerid nymphs at various oxygen s, from the data of Tables I-VI. The vertical line at the oxygen of 7- ex. per lre marks the oxygen content of water in equilibrium wh the atmosphere.

6 Consumption of Ephemerid Nymphs 5 The experimental data are given in Tables I-VI and Fig.. The curves show that, in air-saturated water, most oxygen is consumed by the small nymphs of Baetis sp. The larger B. scambus, of which Baetis sp. may be young forms, use much less oxygen. The pond species Clo'eon dipterum and Ephemera vulgata use less oxygen Table V. The oxygen of Ephemera vulgata Exp. animals. c.c. /l- c.mm./g./hr l Apr. >» tt Dec. ti Feb. Feb. 0 Apr. Dec. )) J> Mar. Mar. Mar. 7 Mar. Mar. 0 >»»» Apr.»»> O O n- ii's n-5 n ' -s -S -S S -S 0 -o -i 5-o ' i- i- o-5 o- 0 n i- o O I7O i mo than eher of the Baetis, as does also Leptophlebia marginata from Lake Windermere. L. vespertina, however, which is also from Lake Windermere, consumes more oxygen than Baetis scambus. From a comparison of Table V wh Table III of Fox et al. (s) is seen that the Winkler method used in the present investigation gives higher values for oxygen than the Barcroft manometer used in the earlier investigations. -

7 H. MUNRO Fox, C. A. WINGFIELD and B. G. SIMMONDS Exp. Table VI. The oxygen of Cloeon dipterum nn ITT! Q IQ c.c/. c.mm./ g./hr. i 5 I IO II Nov. May June 5 Dec. fj Dec. >> >» }) June 7 June June 5 Nov. 0 June July July 5 > j Nov. Nov. 5 Nov. " June July Nov. Nov. >, S o 7" 7 7' ' 5- 'i * '5 '5 '5 7 7 * - i- i* - I - I' i-g \? s I- i- - " - * I-I i'i 0 i-o 7 ' -O i- " mo IOIO IOIO

8 Consumption of Ephemerid Nymphs Fig. shows that in comparing species in the same genus, the larger form has the lesser oxygen. In air-saturated water, Leptophlebia marginata (mean dry of ten animals, 0 ) uses two-thirds of the oxygen used by L. vespertina ( ), and Baetis scambus (0 ) uses two-thirds of the oxygen used by Baetis sp. ( ). It is seen from Fig. that the oxygen of Baetis sp. falls as soon as the oxygen content of the water diminishes, and continues to fall as a linear function of the oxygen. The oxygen of Baetis is not recorded at oxygen s lower than c.c. per lre because the animals die below this (cf. Fox et al. 5, Table V). When the oxygen of the water is raised above that in equilibrium wh the atmosphere, the oxygen of Baetis sp. continues to rise, but eventually becomes constant, after has attained i\ times s normal value. The larger form, Baetis scambus, however, forms a striking contrast to the small Baetis sp.: between 5 and c.c. oxygen per lre s oxygen intake is almost constant. In the case of Ephemera vulgata the oxygen is seen from Fig. to diminish, as a linear function of oxygen, soon after the oxygen content of the water falls below atmospheric equilibrium, although the line slopes less steeply than that of Baetis sp. Above 7* c.c. per lre the oxygen intake of Ephemera vulgata rises very ltle. Cloeon dipterum forms an extreme contrast to Baetis sp. and Ephemera vulgata. From air-saturated water down to an oxygen content of - c.c. per lre, the oxygen intake of Cloeon dipterum is virtually constant. Beneath - c.c. per lre falls off steeply. The oxygen of Leptophlebia vespertina somewhat resembles that of Cloeon dipterum. It decreases slowly as the oxygen content of the water falls, until -5 c.c. per lre is reached, below which there is a sudden drop. We can now arrange the species studied in the following order, commencing wh that which is most dependent on the oxygen content of the environment and ending wh one whose oxygen is independent of the oxygen in the water: () Baetis sp., () Ephemera vulgata, () Leptophlebia vespertina and Baetis scambus, () Cloeon dipterum. The most dependent species, Baetis sp., lives in streams where the oxygen supply must always be abundant; but so does B. scambus. The most independent form, Cloeon dipterum, was taken from a pond where the oxygen content falls low at night (unpublished data). If the behaviour of Cloeon dipterum is adaptive, however, that of Ephemera vulgata is apparently not so, for the latter species was found buried in mud in a pond, yet s oxygen intake drops as soon as oxygen decreases in the water. A. H. Morgan & J. F. Wilder (Pkyriol. ZoSl.,, 5) measured the oxygen of the nymphs of Htxagema recurvata, a near relation of Ephemera vulgata, which lives in similar habats, confining the nymphs in a closed vessel from which water samples were taken at intervals. They state that "In their rate of oxygen nymphs of Hexagema recurvata are independent of the oxygen tension from -75 to -. c.c." But this is not borne out by their Table II, giving oxygen in milligrams (to four significant figures) per gram body. At iz' 0, for example, in three successive 5-hour intervals, the oxygen consumed by recently collected nymphs was 5 - s, - and -, the inial oxygen content of the water not, however, being stated.

9 H. MUNRO Fox, C. A. WINGFIELD and B. G. SIMMONDS SUMMARY The data are best summarized by reference to Fig. i. An extreme contrast is presented by Cloeon dipterum and Baetis sp. in the relation between oxygen and oxygen in the water. When the oxygen in the water diminishes, the oxygen of Cloeon dipterum does not decrease until the oxygen has fallen below one-fifth air saturation, whereas the oxygen of Baetis sp. falls immediately the oxygen in the water decreases. Above air saturation, the oxygen of Baetis sp. rises until reaches i^ times s value in nature. The oxygen of Baetis scambus is almost independent of oxygen in the water, both above and below air saturation. The oxygen of Ephemera vulgata falls soon after the oxygen in the water begins to diminish. Above air saturation rises slightly. Leptophlebia vespertina somewhat resembles Cloeon dipterum: s oxygen falls slowly until one-third air saturation is reached, below which there is a sudden drop. There is a relation between oxygen and size of animal. The oxygen of the larger species Leptophlebia marginata is lower than that of the smaller species L. vespertina, and the oxygen of the larger Baetis scambus is- lower than that of the smaller Baetis sp. REFERENCES BECKETT, E. G. (). J. Soc. chem. Ind., Lond.,, 5. VAN DAM, L. (5). J. exp. Biol., 0. Fox, H. MUNRO & SIMMONDS, B. G. ()- J. exp. Biol., 7. Fox, H. MUNRO, SIMMONBS, B. G. & WASHBOURN, R. (5). J. exp. Biol.,. NICLOUX, M. (0). Bull. Intt. ocianogr. Monaco, No. 5. REYBERG, P. B. (5). Biochem. J., 70. WASHBOURN, R. C). J. exp. Biol., 5. WOLSKY, A. (). Arb. ung. biol. Forschlnst. 7,. WOLSKY, A. & HOLMES, B. E. (). Arb. ung. biol. Forschlnst.,.