Metabolic Correlates of Activity in the Caecilian Geotnjpetes Seraphini

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Metabolic Correlates of Activity in the Caecilian Geotnjpetes seraphini

Reprinted from COPEIA,1974, No. 3, October 18 pp. 764-769 Made in United States of America Metabolic Correlates of Activity in the Caecilian Geotrypetes semphini

Metabolic factors involved in energy production during activity were examined in the West African caecilian Geotrypetes seraphini occidentalis. This species exhibits violent escape behavior during stimulation but fatigues rapidly. Measurements of oxygen consumption and lactate production during activity indicate that nearly 90% of the energy produced during 2 min of activity is derived from anaerobic sources. The pattern of oxygen consumption during activity and the morphology of the integument and lungs of caecilians suggest that oxygen uptake is primarily pulmonary rather than cutaneous.

HE Amphibia, once a much larger and with superficial annulae caused by the pull T more diverse group, is now represented of muscle-connective tissue elements on the by only three extant orders: Anura (frogs skin. Geotlyp~tes is a member of the and toads), Urodela (salamanders) and Caeciliidae, a relatively generalized family. Gymnophiona (caecilians). Information con- cerning the interrelations and derivations of these groups is of considerable evolutionary Juvenile specimens of Geotrypetes sera- importance, but at present their phylogeny phini occidentalis (mean weight, 1.93 g) were is only a subject of speculation. One of the collected in Tafo, Ghana. They were trans- principal dilficulties in elucidating these ported to the United States and housed at relationships is tlie almost total lack of in- 20-25 C in either aquaria with damp soil formation about the Gymnophiona, in con- or plastic containers with moist paper towels trast to the data available for anurans and for several months belore experimentation. salamanders. This paper presents some of The animals remained healthy, constructed the first comparative physiological observa- burrow systems in the soil or hid under the tions among these three groups. Such com- paper towels, and fed regularly on earth- parative studies will eventually produce a worms. Animals were fasted for at least broader picture of the biology of these ani- two days before experimentation. mals and hopefully clarify their relationships. Oxygen corlsumption at 20 C was measured Caecilians are blind and limbless bur- in a small manometric chamber connected to rowing animals, confined to tropical regions. a Warburg manometer, as previously de- Because of their propensity for life in bur- scribed by Bennett and Licht (1973). The rows, stream banks or murky water, they chamber contained wet filter paper to pro- are seldom seen or collected by biologists. vide an atmosphere saturated with water Virtually no physiological measurements have vapor; a small dish containing 15% KOH been made on caecilians. Resting metabolic absorbed carbon dioxide. The animal sat rate, a fundamental measurement of ener- within a small wire cage on an electrical grid getic expenditure, has been reported for through which electrical shocks could be only one species (Sawayi, 1947). The present delivered. The chamber was immersed in a study examines metabolism during rest and constant temperature water bath set at 20 2 stimulated activity, the relative contributions 0.2 C. Appropriate thermobarometric con- of aerobic and anaerobic metabolism to this trols were made with each determination. activity and tlie pattern of oxygen debt Oxygen consumption during rest and in the West African caecilian Geotrypetes during and after activity was measured in- se~aphinioccidentalis. This species lives in dividually in four animals. burrows in sandy mud banks of forest streams An animal was in the lowland humid tropics. Adult animals weighed, placed in the metabolism chamber, are rather small, attaining a maximal length and permitted at least two hours to attain of 400 mm and a diameter of 10-15 mm. a resting condition and thermal equilibrium. They are a dull purplish-gray and are marked Oxygen consumption was then measured for BENNETT AND Tl\lAKE-h4ETABOLISM IN A CAECILIAN one hour, during which metabolic rates were low and uniform. Animals were stimulated electrically (5-10 volts) for 2.0 min. Oxygen consumption was measured during and after activity over intervals of 5 to 15 min until postactive oxygen consumption was indistin- guishable from previous resting levels. Mea- surements of oxygen consumption were con- verted to STP and expressed as an3 of oxygen per g body weight per hour. Anaerobic energy production was determined by measurement of total lactate content. Four animals were used to determine the pattern of anaerobic energy generation; Fig. 1. Oxygen consumption in Gcolryfietes their rarity precluded the use of more than sernphini during rest and during and after 2 one animal in each activity state. However, rnin of stimulated activity at 20 C. Resting levels were maintained for one hr before stimu- the variability within an activity group of lation. Measurements of oxygen consumption such measurements on other amphibians and during and after activity were n~easured over on reptiles is small (Bennett and Licht, 1972, 5 to 15 min intervals, indicated by the width of 1974), and these single measurements prob- the vertical bar. Mean values of four animals ably indicate the true parameters fairly ac- are reported; vertical lines indicate 95% confi- dence limits of the means. curately. The animals were weighed and left undisturbed overnight in individual containers containing wet paper towels in a maximal oxygen consumption, in G. scra- plzini is 0.122 cms/(g x hr). Maximal levels constant temperature cabinet at 20 & 0.2 C. Animals were removed the following day of oxygen consumption are attained during and stimulated manually for 30 sec, 2 rnin or immediately after activity; thereafter, it or 10 min. The animals moved rapidly decreases exponentially until it returns to around in their containers at activity levels preactive resting levels in approximately 75 comparable to those obtained by electrical rnin after cessation of activity. The oxygen stimulation. Immediately after activity the debt, the total amount of oxygen in excess animals were deca~itatedand total lactate of resting levels consumed during and after cm3/g. content was measured according to the activity, is 0.062 ~ur-in~activity, Geotrypetes respond vio- method of Bennett and Licht (1972). One lently for the first minute of stimulation. unstimulated animal was used as a resting They move rapidly, coil and uncoil, thrust control. Lactate content is reported as mg with their heads as though seeking shelter. lactate per g body weight. - - They fatigue rapidly, however, and activity The morphology of- the integument of level decreases with sustained stimulation. Geotr>~peteswas examined histologically to They become very lethargic after about five assess its capacity for oxygen exchange. It minutes, but are still capable of slow locomo- was compared to that of a plethodontid sala- tion. The rate of lactate formation parallels mander, Batrachoseps attenuatus, which re- this behavioral sequence. Lactate content lies almost entirely on cutaneous oxygen of the resting animal was 0.20 mglg; animals exchange. stimulated for 30 sec, 2 rnin and 10 min had contents of 0.53, 0.70 and 0.95 mg lactatelg, respectively. The maximum rate The diurnal resting metabolic rate of of lactate formation, the anaerobic scope (see Geotrypetes seraphini is 0.037 & 0.003 cm" Bennett and Licht, 1972), occurs during the O,/(g x hr). The rate of oxygen consump- first 30 sec of activity and equals 0.65 mg tion during two rnin of activity is too low lactate/(g X rnin). The anaerobic capacity, to determine accurately, so it was integrated -. the amount of lactate formed during activity with the first five min postactivity measurement. Oxygen consumption during this to near exhaustion, is 0.74 mg lactatelg in period increases more than 400% above Geotrypetes. resting levels to a mean value of 0.159 & The relative contribution of aerobic and 0.012 cm3 O,/(g x hr) (Fig. 1). Aerobic anaerobic energetics to total energetic out- scope, the difference between resting and put can be estimated by calculation of the COPEIA, 1974, NO. 3

Fig. 2. A. Skin of Balrachoseps allenualu! ~rasagittalsection, 100 X. B. Skin of GE . peles sernphinii; parasagittal section, 100 X. Abbrevhtions: d = dermis; e = epidermis; m = mucous gland; niu = muscle; p = poison gland; s = stratified dense dermis. Capillaries are indicated by arrows; these are intended to show structure and not numerical distribution. Note particularly the diffcrences in epidermal thickness, dermal structure, and capillary di~tributionbetween the two species. (Photomicrographs courtesy of P. Hermes.) amount of ATP produced by each metabolic 1.0 cm3 0, (STP) consumed = pathway. These are estimated from mea- 0.290 millimoles ATP surement of lactate content and oxygen con- During a 2-min burst of activity, Geotrypetes sumption according to the equations of Bennett and Licht (1972): forms 8.9 millimoles ATP/g body weight anaerobically and 1.2 millimoles ATP/g 1.0 mg lactate formed = aerobically; the total ATP formation during 0.0 167 millimoles ATP activity is 10.1 millimoles/g. Thus, 88% of BENNETT AND WAKE-METABOLISM IN A CAECILIAN 767

its energetic production is anaerobic, or 7.3 time during which maximal activity can times as much ATP is produced anaerobically be sustained. Endurance is low; high levels as aerobically. During the first 30 sec of of activity cannot be maintained for more activity, 5.4 millimoles ATP/g are produced than two or three minutes. Such a response anaerobically. If oxygen consumption is is not particularly surprising in a vermiform maximal during this time, 0.3 millimoles animal which does not travel long distances ATP/g would be produced aerobically, and and can rely on its burrow as a refuge from 95% of the ATP production would come predation. It is known that the snake from anaerobiosis. Miodon acanthias preys upon G. seraphini, The integuments of both Geotypetes and and that it pursues the caecilian a short Batrachoseps are highly glandular structures distance into ;ts burrows in soft, sandy soil (Fig. 2). Despite this obvious common fea- of streambanks (Cole, 1967). Cole reports ture, there are substantial morphological great activity and fast re-burrowing in a few differences. The skin of the caecilian is over seconds when he unearthed G. seraphini, twice as thick as that of the salamander. and he suggests that disturbance of the bur- The epidermis of Geotypetes is three to six row by predators (human or snake) causes layers deep and is tightly organized; that a rapid retreat deeper into the burrow. of Batrachoseps is much looser and is only Sawaya (1947) reported resting metabolic two cell layers deep. The dermis of rate in two indkiduals of ~~phlonectescom- Geotypetes is thick and is organized as a pressicazcda, members of the aquatic family loose dermis above, containing glands and Typhlonectidae. Rates for each were 0.049 scale pockets, and a dense stratified dermis cm" O,/(g x hr) (137 g; 21.7 C) and 0.149 below. The dermis of Batrachoseps is loose cm3 O,/(g x hr) (64 g; 24.8 C). We have and contains several kinds of skin glands, ako determined that resting oxygen consump- some extending through the entire layer. tion in a 12-g individual of Caecilia oc- Especially noteworthy is the distribution of cidentalis at 15 C was 0.045 cm3 O,/(g x hr). capillaries in the skin. Batrachoseps has An extensive study (Mendes, 1945) on resting many large capillaries at the epidermal- oxygen consumption in Siphonops annulatus dermal junction, and numerous smaller ones cannot unfortunately be compared because throughout the dermis. Geotrypetes has a of the inadequately reported metabolic data few large capillaries at the epidermal-dermal and the lack of control of body temperature. border and essentially none throughout the Our values for resting metabolic rate in deep dermis. Geotypetes, considering differences in body size and temperature, are substantially below those measured for Typhlonectes and Geot?ypetes is revealed by this study to be Caecilia. They are also considerably below primarily dependent on lactate formation for most values reported for anurans and energy during activity. This anaerobiosis urodeles of comparable size (Hutchison, permits a very rapid activity response, such 1971), including Hyla regilla and Batra- as fast withdrawal into a burrow or grabbing choseps attenuatws measured with identical and tearing a prey. Observations on feeding apparatus and techniques (Bennett and and predator avoidance in this species sug- Licht, 197313). However, due to lack of data gest that a rapid response is used in both and standardization of measurement tech- situations. Geotrypetes (and other terrestrial niques, it is impossible to determine at this caecilians) have two modes of prey manipu- time whether the maintenance requirement lation. If an elongate prey item, such as (resting metabolism) of caecilians icdifferent an earthworm, is met head-on, Geotypetes from that of other amphibians. seizes it in its jaws and ingests it by suc- The capacity of Geotrypetes for rapid or cessive bites. If the prey is met laterally, sustained anaerobiosis is not exceptional Geotypetes grabs it with its jaws and retreats when compared with that of some anaerobic further into its burrow, rapidly spinning its anurans and urodeles, even though its ac- body around and around so that the sides of tivity pattern appears limited by anaerobic the burrow are used to shear off parts of factors. Anaerobic scope is within the range the prey protruding from the mouth. This of those of eight species of amphibians second feeding mode requires rapid activity (range:0.12-1.31 mg lactate/@ x min) (Ben- of short duration. Anaerobiosis affords the nett and Licht, 1974). Anaerobic capacity activity response, but limits the length of is also intermediate to those of these same COPEIA, 1974, NO. 3

L I Rest 1. 20 30 40 50 60 Active Time (min) Pig. 3. Oxygen consumption before, during and after activity at 20 C by Geotrypetes seraphini, Hyla regilln and Batrachoseps attentuatus. Data for Geotrypetes are taken from Fig. 1; data on Hyla and Batraclzoseps are from Bennett and Licht, 1973b. eight species (range:0.12-1.45 mg lactatelg) been determined. Elkan (1958) concluded (Bennett and Licht, 1974). Within the con- that there is no extensive oxygen uptake in text of amphibian metabolism, Geotrypetes the bucco-pharyngeal region of Schisto- appears to possess only moderate capabilities metopurn thomensis. Several authors (Sarasin of both aerobiosis and anaerobiosis. Its and Sarasin, 1887; Fuhrmann, 1912; Sawaya, activity energetics resemble those of 1941; Mendes, 1941; Lawson, 1966) have Hyla regilla in many respects, particu- stated that the presence of integumentary larly in the total amount of energy capillaries suggests that the integument is mobilized during activity and the proportion important in gas exchange. Cutaneous car- of that energy derived anaerobically (Bennett bon dioxide release has been reported in and Licht, 1973). Geotypetes and Hyla are Siphonops and Typhlonectes (Mendes, 1941; moclerate anaerobes, in contrast to the Sawaya, 1947). However, experiments per- strongly anaerobic Batrachoseps and the formed attempting to partition pulmonary aerobic Bufo (Seymour, 1973; Bennett and and cutaneous oxygen uptake suggest that Licht, 1973). Whether the activity physiology the magnitude of the latter is small. In the of Geotypetes is representative of caecilians aquatic-species Typhlonectes compressicauda, as a group is unknown: considerable inter- 94% of the oxygen uptake is pulmonary specific differences occur among both the (Sawaya, 1947). Anaesthetized, and con- urodeles and anurans (Bennett -and Licht, sequently non-ventilating, Siphonops an- 1973, 1974). However, the intermediate posi- nuhtus showed a greatly reduced ,xygen tion which this animal occupies -in the ob- uptake (Mendes, 1945). served range of amphibian activity responses The pattern of oxygen consumption suggests at least that there must be broad during and after activity in Geotypetes overlaps in the physiological capacities of supports the contention that oxygen uptake these three groups. in caecilians is primarily pulmonary and

Anurans and urodeles utilize their inte~u-D not cutaneous. Oxygen consumption rises ment as a site of oxygen uptake and carbon rapidly and reaches maximal values during dioxide release. The proportion of total or immediately after activity (Fig. 3). In oxygen consumption derived by cutaneous contrast, the rise in oxygen uptake in respiration in these groups can be substantial Batrachoseps, an animal reliant entirely (Hutchison et al., 1968; Whitford and Hutch- upon cutaneous oxygen exchange, is slow, ison, 1965), and plethodontid salamanders, and maximal values -are not attained until such as Batrachoseps, rely almost exclusively 5 to 15 min after cessation of activity. Hyla on the skin as the site of oxygen uptake regilla has a factorial increment of oxygen (Elkan, 1955; Czopek, 1962; Whitford and consumption during activity similar to that Hutchison, 1965). The extent of reliance on of Geotypetes, but further increments in cutaneous respiration in caecilians has not oxygen uptake occur after cessation of ac- BENNETT AND WAKE-METABOLISM IN A CAECILIAN 769 tivity. This pattern of delayed aerobic scope , AND -, 1973. Relative contributions of anzerobic and aerobic enerev ~roduction in Hyln and Bntrachoseps was interpreted as "1 n during activity jn amphibians. J. Comp. a reflection of the time necessary to increase Physiol. 87:351-360. cutaneous oxygen uptake (Bennett and Licht, , AND -. 1974. Anaerobic metabolism 1973). Presumably a pulmonary system with during activity in amphibians. Colnp. Bio- a variable respiration rate is capable of a chem. Physiol. In press. COLE,L. R. 1967. The snake Miodon acanlhias more rapid adjustment to changes in oxygen found with Geol~ypelesseraphini (A~nphibia: demand than a non-ventilated cutaneous Caeciliidae) as prey. Copeia. 1967:862. system. CZOPEK,J. 1962. Vascularization of res iratory These conclusions regarding the site of surfaces in some Caudata. Copeia. 1&2:576- 587. oxygen uptake are supported by the mor- ELKAN,E. 1955. The buccal and pharyngeal phological structure of the integument and mucous menlbranes in urodeles. Proc. Zool. lungs of caecilians in contrast to those of Soc. London. 125:685-710. urodeles and anurans. The more compact 1958. Further contributions to the buccal and pharyngeal mucous membrane in and less vascular integument of caecilians urodeles. Ibid. 13 l:li35-355. is less well suited for cutaneous oxygen up- FUHRMANN,0. 1912. Le Genre Typhlonecles. take than is that of a lungless salamander Mth. Soc. neuchflteloise d. Sci. Nat. 5:ll-138. (see Results section). The lungs of caecilians HUTCHISON,V. H. 1971. Oxygen consumption: Amphibians. Table 175, part IV, p. 481485. are complex, highly vascular structures in In: Respiration and Circulation. P. L. Altman contrast to the absence of lungs in plethodon- and D. S. Ditttner (eds.). Fed. Amer. Soc. tids and some other salamanders, and to the Exp. Biol. Bethesda, Md. simple sac-like lungs of the majority of sala- -, W. G. WHITFORDAND M. KOHL. 1968. Relation of body size and surface area to mander and frog species. Terrestrial cae- gas exchange in arlurans. Physiol. Zool. 41: cilians have a single, elongate lung that is 65-85. highly compartmentalized. In many species, LAWSON,R. 1966. The anatolliy of the heart including G. seraphini, the lung compart- of Hypogeophis rostl-alus (Amphibia: Apoda) ments are supported by rings of cartilage to and its possible mode of action. J. Zool. London. 1966:320-336. which smooth muscle tissue is attached, pro- MENDES,E. G. 1941. Sobre a res irag5o viding a passive recoil mechanism to venti- (esoMgica, traqubal e cutinea) do sipRonops late the lung. The pulmonary epithelium is annulalus (Arnphibia-Gymnophiona). Bol. Fac. extensively elaborated, and is highly vascu- Fil. Cien. Let. U. Sao Paulo. 1941:283-304. -. 1945. Contribuiqilo para a Fisiologia dos larized. The presence of a structurally com- sistemas res~iratbrioe circulatorio de Sibho- plex lung and an integument with a mor- nops annul~lus(Amphibia-Gymnopiona). ibid. phology which does not suggest efficient 1945:25-67. SARASIN,P., AND F. SARASIN.1887-1890. ZU~ cutaneous respiration indicates that oxygen Ent.ivicklungsgeschichte und Anatomic der consumption is primarily pulmonary in Ceylonischen Blindwiihle. Ergebn. natunviss. caecilians. Forsch. Ceylon. 4 vols. SAWAYA.P. 1941. Contribuiq50 para o estudo da Fisiologia do Sistema Circulat6rio do Anfibio Siphonops annulalus (Mikan). Bol. Financial support for this study was pro- Fac. Fil. Cien. Let. U. Sao Paulo. 1941:207- 270. vided by a Miller Postdoctoral Fellowship - 1947. Metabolismo respiratdrio de to AFB and a grant from the Committee on ~nfibioG ymnophiona, Typhlonectes compres- Research of the University of California to sicauda (Dum. et Bibr.). Ibid. 1947:SI-56. SEYMOUR,R. S. 1973. Physiological correlates MHW. We wish to thank Theodore Papen- of forced activity and burrowing in the spade- fuss for collecting the animals and John foot toad, Scaphiopus harnrnondii. Copeia. Ruben for his technical assistance during 1973: 103-1 15. WHITFORD,W. G., AND V. H. HUTCHISON.1965. the experiments. Gas exchange in salamanders. Physiol. Zool. 38:228-242.

BENNETT,A. F., AND P. LICHT. 1972. Anaerobic metabolism during activity in lizards. J. Comp. Ph ysiol. 81:277-288.