ENERGY METABOLISM IN THE LOCOMOTOR MUSCLES OF THE COMMON MURRE (URIA AALGE) AND THE ATLANTIC PUFFIN (FRATERCULA ARCTICA)

M. BENJAMIN DAVIS AND HELGA GUDERLEY D•partementde biologie,Universit• Laval, Quebec, Quebec GIK 7P4, Canada

ABSTRACT.--Tocompare the metabolicsystems that supportthe combinationof flying and diving with thoseused to supportburst flying and sustainedflying, myoglobinconcentrations and maximum enzyme activitieswere determined for selectedenzymes of glycolysis,the Krebs cycle, and amino acid metabolism in the pectoral, supracoracoideus,and sartorius musclesof the Common Murre (Uria aalge),Atlantic Puffin (Fraterculaarctica), Rock Dove (Columbalivia; hereafter "pigeon"), and Ring-neckedPheasant (Phasianus colchicus). Glycolytic enzyme levels in the flight muscleswere lower in the murre and the puffin than in the pheasant,while both glycolyticand Krebs-cycleenzyme levels resembledthose in the pigeon. We believe puffinsand murresdo not rely extensivelyon anaerobicglycolysis during diving. In concordancewith a role in oxygenstorage for diving, the levels of myoglobin in the flight musclesof murres and puffins were higher than those in pigeons or pheasants.They were lower than publishedvalues for penguins,however. In contrastto the trends for pigeon and pheasant muscles,the alcid sartorius muscleshad a considerably lower aerobic orientation than the flight muscles.Received 21 November1986, accepted 9 June1987.

IN birds a high anaerobiccapacity, as indi- dives (Scholander 1940), voluntary dives in catedby typesand levels of glycolyticenzymes, pondsare aerobic(Butler and Woakes 1984) and is correlated positively with locomotory pat- free-ranging dives are generally short (re- ternsdemanding burst flying, extensivediving, viewed by Baldwin et al. 1984).The studiesthat or quick maneuvering (Wilson et al. 1963,Kies- established the correlation between diving sling 1977,Mill and Baldwin 1983,Baldwin et depth and glycolyticcapacity for penguins(Mill al. 1984).During theseactivities oxygen tension and Baldwin 1983, Baldwin et al. 1984), how- in musclemay be reducedto the point where ever, did not directly compareenzyme activities ATP is produced from substrate-level phos- in penguinswith thosein terrestrial birds with phorylations coupled to lactateproduction. An- varying locomotorstrategies. The need for such aerobicglycolysis seems the primary sourceof an integrated approach is underlined by the ATP during flight for burst fliers like the Ring- data from mammals. Although early studies necked Pheasant (Phasianuscolchicus; Wilson et suggestedthat diving mammalshad exception- al. 1963, Kiessling 1977). Similarly, the take-off, al glycolytic capacities(Simon et al. 1974), an hovering,and quick directionalchanges of Rock extensive comparison of pyruvate kinase and Doves (Columbalivia; hereafter "pigeon") are lactate dehydrogenaselevels in terrestrial and thought to be anaerobically supported (Pen- marine mammals showed no differences (Cas- nycuick 1968, Parker and George 1975). The tellini et al. 1981).In addition, becauseenzyme functionalutility of the high glycolyticcapacity activities are markedly affected by assaycon- of diving birds is less clear. Anaerobic glycol- ditions,simultaneous determination of enzyme ysiscould fully supportdiving, in analogywith activities in the different speciesis a prerequi- pheasant flight, or it could permit rapid direc- site for rigorous comparison. tional changesduring diving, in analogy with Severalalcid speciesare the ecologicalcoun- pigeonflight. Deeper-divingbirds also may have terparts of penguins in the Northern Hemi- a greater glycolytic capacityrelative to shallow- sphere. Two of these, the Atlantic Puffin (Fra- diving birds as a backup system proportional tercula arctica) and the Common Murre (Uria to the depths to which they dive. While most aalge),dive to depths of 60 m and 180 m, re- penguin specieshave anaerobiccapacities that spectively (Piatt and Nettleship 1985), using are proportional to their diving depths (Bald- their wings and legs for propulsion and steer- win et al. 1984) and show marked bradycardia ing (Tuck 1961,Spring 1971).Besides being pro- and lactateproduction during forcedlaboratory ficient divers, the alcids migrate over long dis- 733 The Auk 104: 733-739. October 1987 734 DAVISAND GUDERLEY [Auk,Vol. 104 tancesfrom overwintering areas at sea to land shooting as they surfaced (Environment Canada/Ca- for the breeding season.Just as their morphol- nadian Wildlife Permit ASK 18-84 and with the per- ogy representsa compromisebetween the op- mission of the Newfoundland Wildlife Division). The posingrequirements of diving and flying, their carcasseswere placed in -2øC seawaterduring trans- port back to the wharf (maximum 2 h). There tissues metabolicorganization must be compatiblewith were dissected,wrapped in aluminum foil, and fro- both. For alcids flying and diving are closely zen in 2-methylbutane (EastmanKodak, Rochester, associatedactivities. During the breeding sea- New York) previously chilled in a liquid nitrogen son, foraging dives are sandwiched between bath. Samples were stored at -25øC until assayed. flights between the nest and feeding areas(Har- Five pheasantsand 5 pigeonswere obtainedlive from ris and Hislop 1978). commercialsuppliers, decapitated,and dissectedim- We examined the metabolic organization of mediately. Tissueswere stored as above. the locomotormuscles in puffins and tourresto Enzymeassays.--Muscle samples were freed of con- elucidate the metabolic strategiesthat support nectivetissue and fat, weighed, mincedwith a scalpel, the combinationof diving and flying. To com- and homogenizedwith a Polytron (Brinkman Instru- ments) for 30 s in 10 ml/g ice-cold extraction buffer. pare the metaboliccapacities of thesealcids with For all enzymes except NADP+-linked isocitratede- those of birds whose metabolic strategies are hydrogenase,the extraction buffer was 50 mM im- reasonablywell defined, we studied the Ring- idazole-HC1, 50 mM KC1, 1 mM EDTA, 2 mM 2-mer- necked Pheasant, a burst flyer (Wilson et al. captoethanol(omitted for citrate synthaseassay), pH 1963, Kiessling 1977), and the pigeon, a bird 7.4. For NADP+-linked isocitratedehydrogenase, the capable of sustainedflight (Pennycuick 1968, extraction buffer was 50 mM Pipes [piperazine-NN'- Parker and George 1975).Our specificaims were bis(2-ethanesuphonicacid)], 10 mM MgCI2, 5 mM to compare the metabolic systemsthat support 2-mercaptoethanol,1 mM EDTA, 5 mM MnC12,2 mM extensiveflying and diving with those used to ADP, 5 M glycerol, 0.1 mM phenylmethylsulphonyl support burst or sustainedflying, to examine fluoride, pH 7.4. The homogenatewas centrifugedat whether glycolyticcapacity was proportional to 25,000 x g for 40 min at 4øC(600 x g for 3 min for NADP + isocitratedehydrogenase) in a Sorvall SS-34 diving depth in these alcids, and to compare rotor. The supernatantwas used immediately for the the metabolic organization of the major flight assays.All biochemicalswere obtained from Sigma muscles(pectoral and supracoracoideus)and an ChemicalCo. (St. Louis, Missouri).Enzymes were as- important leg muscle (sartorius) becauseboth sayed with a UV/Vis recording spectrophotometer wings and legs are used in underwater pro- (Varian Cary 210).The cuvettetemperature was main- pulsion. tained at 38 +_ 0.5øCthroughout the assaysusing a Puffinsand tourresare logisticallydifficult to circulatingwater bath.Determinations of activitywere obtain, making determination of in situ meta- done in triplicate. Enzyme activities are expressedas bolic flux impossible.Instead, we measuredthe •tmol of substrate transformed.min •.g • wet mass maximal activitiesof glycolyticand Krebs-cycle of tissue.Enzymes were assayedby following changes in absorbanceat 340 nm, exceptcitrate synthase, which enzymesto assessanaerobic and aerobicpoten- wasassayed at 412 nm. Preliminary experimentswere tial; this has been done in previous studies,in- run to determine the substrate concentrations re- cluding those on penguins (Crabtree and quired to give maximal activities. All pH values were Newsholme 1972,Kiessling 1977, Castellini and adjustedat 38øC.The compositionof the reactionmix- Somero 1981, Mill and Baldwin 1983, Baldwin tures is given below. et al. 1984). We measured myoglobin concen- Aldolase(ALD) (E.C. 4.1.2.13): 0.2 mM NADH, 1.5 trations as an indication of the oxygen stores mM fructose-l,6-bisphosphate, 50 mM triethanol- availableto the muscles(Weber et al. 1974,Pages amine/HC1, excess glycerol-3-phosphatedehydro- and Planas1983) and the levels of enzymesthat genase,triose phosphateisomerase, pH 7.4. Fructose- 1,6-bisphosphatewas omitted for the control.Pyruvate contributeintermediates to the Krebscycle. Be- kinase(PK) (E.C. 2.7.1.40):100 mM KC1,10 mM MgC12, cause we worked with frozen tissues, we mea- 0.2 mM NADH, 5 mM ADP, 5 mM phosphoenolpy- sured only enzymes that are stable to freezing ruvate, 50 mM triethanolamine/HC1, excess lactate (Farrar and Farrar 1983). dehydrogenase,pH 7.4. Phosphoenolpyruvatewas omitted for the control. Lactatedehydrogenase (LDH) MATERIALS AND METHODS (E.C. 1.1.1.27):0.2 mM NADH, 1.5 mM pyruvate for pheasantand pigeon muscleand 2 mM pyruvatefor Experimentalanimals.--Five Common Murres and 5 murre and puffin muscle, 50 mM triethanolamine/ Atlantic Puffins were collectedin early July 1984 at HC1, pH 7.4. Pyruvate was omitted for the control. Witless Bay, Newfoundland (47ø15'N, 52ø40'W) by Citratesynthase (CS) (E.C. 4.1.3.7): 50 mM triethanol- October1987] MetabolicAdaptations toDiving 735

TABLE1. Glycolyticenzyme activitiesin locomotormuscles. Values represent the mean activity (#tool.rain •. g-1wet mass)+_ SD for eachmuscle type measuredin 5 birds.Data were analyzedas explainedin Materials and Methods,and the resultsare shownby lettersfollowing the values.Values with different lettersdiffer significantly(P < 0.05). Lowercaseletters indicate differencesamong the valuesfor one enzyme in a column (interspecificcomparisons); capital letters indicate significantdifferences among the values in a row (in- traspecificcomparisons).

Pectoral Supracoracoideus Sartorius Aldolase Pheasant 319 _+ 69 a, A 291 +_ 16a, A 126 +_ 20a, B Pigeon 117 +_43 b, A 145 +_ 21 ab, A 60 +_ 6b, B Puffin 62 _+ 20 c, A 86 +_ 29b, A 70 +_ 24b, A Murre 116 _+ 10b, A 103 _+ 29b, A 57 +_ 10b, B Pyruvate kinase Pheasant 1,761 +_ 221 a, A 1,505 +_ 182 a, A 970 +_ 68 a, A Pigeon 568 _+58 b, AB 771 +_ 159 b, A 443 _+ 56 b, B Puffin 369 +_ 25 c, A 412 +_ 143 c, A 464 +_ 134b, A Murre 672 +_ 117 b, A 757 +_ 165 b, A 443 +_ 69 b,B Lactatedehydrogenase Pheasant 2,523 _+ 270 a, A 2,409 +_ 207 a, A 1,039 +_ 100 a, B Pigeon 1,015 _+88 b, B 1,872 +_ 137 ab, A 664 +_ 54 c, B Puffin 666 _+ 24 c, C 1,189 +_ 67 c, A 936 +_ 207 ab, B Murre 1,184 _+ 203 b, A 1,583 +_ 297 bc, A 758 +_ 108 bc, B

RESULTS amine/HC1, 0.2 mM acetyl coenzymeA, 0.2 mM 5',5'- dithiobis-(2-nitrobenzoic acid), 0.125 mM oxaloace- Interspecificcomparisons.--Pheasant flight rate,pH 7.4. Oxaloacetatewas omitted for the control. musclesconsistently had the highestglycolytic NADP+-linked isocitratedehydrogenase (ICDH) (E.C. 1.1.1.42): 70 mM Tris/HC1, 0.5 mM NADP +, 1 mM enzyme activities, the lowest myoglobin con- MnC12,8 mM MgC12,1.5 mM isocitrate,10 mM citrate, centrations,and the lowest Krebs-cycleenzyme pH 7.4. Isocitrate and citrate were omitted for the activities (Tables 1 and 2). Pigeon and murre control. Malate dehydrogenase(MDH) (E.C. 1.1.1.37): flight muscleshad similar levels of glycolytic 50 mM K+-phosphatebuffer, 0.2 mM NADH, 0.5 mM and Krebs-cycleenzymes. While puffin flight oxaloacetate,pH 7.4. Oxaloacetatewas omitted for the muscleshad lower levelsof glycolyticenzymes, control. Glutamatedehydrogenase (GDH) (E.C. 1.4.1.3): levels of Krebs-cycle enzymes were similar to 50 mM triethanolamine/HC1, 0.2 mM NADH, 1 mM thoseof pigeon and murre flight muscles.Gen- ADP, 2.5 mM EDTA, 100 mM ammonium acetate, 10 erally, the two diving specieshad significantly mMa ketoglutarate,pH 7.4.a ketoglutaratewas omit- higher myoglobin concentrationsin the pec- ted for the control. Glutamatepyruvate transaminase toral and supracoracoideusmuscles than did the (GPT) (E.C. 2.6.12):0.2 mM NADH, 80 mM K+-phos- phatebuffer, 0.8 mM alanine, 18 mMa ketoglutarate, pigeon and pheasant(Table 2). excessLDH, pH 7.4. a ketoglutaratewas omitted for Enzyme levels showeddifferent interspecific the control. Glutamateoxaloacetate transaminase (GOT) trendsin the sartoriusmuscle than in the flight (E.C. 3.5.1.1): 80 mM K+-phosphatebuffer, 40 mM muscles. Although pheasant muscle again aspartate,0.2 mM NADH, excessMDH, 12 mM a ke- showedthe highest activitiesof glycolytic en- toglutarate,pH 7.4. a ketoglutaratewas omitted for zymes (Table 1), its levels of Krebs-cycle en- the control. zymeswere similar to thoseof pigeon sartorius Myoglobin wasmeasured following the methodof (Table 2). The levels of glycolytic enzymes in Reynafarje(1963) and is expressedas mg/g wet mass. the sartoriusof the pigeon, murre, and puffin Statisticalcomparisons.--Bartlett's test indicated that the variances of the raw data scores were not ho- were similar (Table 1). CS levels imply that the mogeneousfor 7 of the 10 setsof data. The data were sartoriusmuscles of diving birds have a lower ranked,and an ANOVA was performedon the ranks aerobiccapacity than thoseof pigeonsor pheas- followed by a Ryan-Einot-Gabrial-Welschcompari- ants (Table 2). Myoglobin concentrations,how- sonof means(SAS Inst. 1982).The data are presented ever, were similar in the sartorius from the four as means +_ SD (n). species(Table 2). 736 DAVISAND GUDERLEY [Auk,Vol. 104

TABLE2. Levels of Krebs-cycleenzymes and myoglobin in locomotormuscles. Values are presented and comparedas explained in Table I. Lowercaseletters indicate interspecific differences for the enzyme levels in a given locomotormuscle; capital letters indicate intraspecificdifferences.

Pectoral Supracoracoideus Sartorius Citrate synthase Pheasant 10.5 +_ 2.9 b, A 9.7 +_ 0.9 b, A 5.9 +_ 2.8 a, A Pigeon 51.3 +_ 10.9 a, A 29.1 + 6.7 a, B 7.4 +_ 1.2 a, C Puffin 46.3 + 5.4 a, A 31.6 +_ 2.3 a, B 2.2 + 0.9 b, C Murre 51.1 +_ 3.7 a, A 27.0 +_ 4.2 a, B 1.5 + 0.4 b, C NADP*-linked isocitratedehydrogenase Pheasant 3.1 + 1.5 b, A 2.9 ñ 0.1 b, A 11.5 + 5.3 a, A Pigeon 72.5 _+ 16.4 a, A 37.6 _+4.9 a, B 19.4 _+0.8 a, B Puffin 82.6 + 13.7 a, A 44.6 +_ 4.8 a, A 10.2 +_ 3.0 a, B Murre 60.0 _+ 9.1 a, A 35.9 _+ 8.2 a, B 3.8 +_ 0.7 a, B Malate dehydrogenase Pheasant 388 +_ 58 b, AB 377 + 22 c, B 477 +_ 76 b, A Pigeon 1,149 +_ 120 a, A 787 + 125 b, B 524 +_35 ab, C Puffin 1,364 +_ 318 a, A 1,169 +_ 95 a, A 682 _+ 98 a, B Murre 1,213 +_ 81 a, A 852 ñ 74 b, B 257 + 25 c, C Myoglobin (mg/g wet mass) Pheasant 0.51 +_ 0.36 c, B 0.71 _+ 0.24 b, B 5.19 +_ 1.97 a, A Pigeon 7.20 + 2.07 b, AB 1.48 +_0.61 b, B 7.30 + 1.80 a, A Puffin 12.54 +_ 2.58 ab, A 9.38 +_ 4.09 a, A 8.06 +_ 5.54 a, A Murre 14.10 ñ 1.22a, A 11.93 +_ 1.78 a,A 6.31 + 3.25 a,B

Becausethe enzymes of amino acid metabo- supracoracoideusmuscles (Tables 1 and 2). These lism can contribute intermediates to the Krebs three species also showed some indication of cycle, the levels of enzymes of amino acid higher glycolytic enzyme activities in the su- metabolismand of the Krebscycle may be cor- pracoracoideusthan in the pectoral muscle (Ta- related. We found little evidence of such cor- ble 1). By contrast,the pheasantmuscles gen- relation, however. Only the interspecific dif- erally had similar enzyme levels. For pigeon ferencesof GPT in the flight musclesresembled and puffin, myoglobin concentrationswere those of Krebs-cycleenzymes (Table 3) as GPT similar in the three muscles(Table 2). In pheas- levels were consistently lowest in pheasant antsthe sartoriushad the highestlevels of myo- flight muscle.In contrastto the equivalenceof globin, while in the murre this order was re- Krebs-cycle enzyme levels in pigeon, murre, versed. and puffin flight muscles,GPT levels were sig- nificantly higher in flight musclesof pigeons DISCUSSION and tourresthan of puffins.Comparison of GPT levels in the sartorius indicated that the pigeon The glycolyticand Krebs-cycleenzyme activ- is highest, followed by the murre, the puffin, ities of the flight musclesof the puffin and the and finally the pheasant.GOT levels were gen- murre more closely resemble those in the pi- erally lower in the musclesof the divers than geon than those in the pheasant. If the alcids in those of the nondivers (Table 3). Although relied extensively on anaerobicmetabolism to GDH levels were higher in flight muscleof di- support diving, the glycolytic enzyme levels vers than nondivers, GDH levels in pheasant should have resembledthose in the pheasant. and murre sartorius were similar and higher Instead,the alcidsseem more like pigeons,which than thoseof puffin or pigeon (Table 3). are thought to usethe anaerobiccapacity in the Intraspecificcomparisons.--For pigeon, puffin, flight musclesto power short-duration,energy- and murre muscle, enzyme activities were gen- intensive activitieslike hovering and taking off erally higher in the flight musclesthan in the (Pennycuick 1968, Parker and George 1975, Au- sartorius.Furthermore, the pectoralmuscles had lie 1983). Anaerobic glycolysisin the puffin and higher levels of Krebs-cycleenzymes than the murre flight musclesshould by analogy serve October1987] MetabolicAdaptations to Diving 737

TABLE3. Enzymesof amino acid metabolismin locomotormuscles. Values are presentedand comparedas explainedin Table 1. Lowercaseletters indicate interspecific differences for enzymelevels in a given locomotormuscle; capital letters indicate intraspecificdifferences.

Pectoral Supracoracoideus Sartorius Glutamate-pyruvatetransaminase Pheasant 0.25 + 0.13 c, AB 0.12 + 0.06 c, B 0.26 + 0.15 c, A Pigeon 5.38 + 0.97 a, A 2.89 + 0.35 a, B 1.23 + 0.23 a, C Puffin 1.69 + 0.28 b, A 0.93 + 0.09 b, B 0.29 + 0.06 c, C Murre 3.90 + 0.78 a, A 2.24 + 0.24 a, B 0.90 + 0.04 b, C Glutamate-oxaloacetate transaminase Pheasant 65.1 + 5.4 b, A 65.6 + 9.9 a, A 84.2 + 17.2 a, A Pigeon 166.2 + 29.0 a, A 61.9 + 17.3 ab, C 78.7 + 5.6 a, B Puffin 80.3 + 20.7 b, A 33.7 + 14.7 b,B 6.3 + 1.4b, C Murre 47.8 + 6.1 c, A 26.5 + 3.8 b, A 15.7 + 1.7b, B Glutamatedehydrogenase Pheasant 1.29 + 0.31 c, A 0.93 + 0.60 b, A 1.48 + 0.65 ab, A Pigeon 3.57 + 0.21 b, A 0.42 + 0.13 b, B 0.36 + 0.11 b, B Puffin 19.00 + 2.05 a, A 5.63 + 2.96 a, B 0.73 + 0.27 b, C Murre 14.91 + 1.62 a, A 5.68 + 1.51 a, A 1.91 + 0.75 a, B

primarily for bursts of rapid activity during The levels of GDH, GOT, and GPT can be either flight or diving. Thus, in birds asin mam- interpreted in several,though not mutually ex- mals (Castellini et al. 1981), diving does not clusive,ways. As participantsin anapleurotic require exceptionallyhigh levels of glycolytic reactions,they indicate a tissue'scapacity for enzymes. Nonetheless, in accordancewith their stepping up Krebs-cycleactivity. Furthermore, considerablediving capacities,the alcidshave they can reflecta tissue'scapacity to metabolize higher levelsof myoglobinin their flight mus- amino acids.The high GDH and GPT activities cles than do the terrestrial birds. in the diving birds relative to the pigeon and From enzyme activities, histology, myo- pheasantsuggest that the musclesof the diving globin concentrations,and buffering capacities birdshave a goodcapacity for increasingKrebs- in the swimmingmuscles and from diving times, cycle flux and for amino acid metabolism. The Mill and Baldwin (1983) and Baldwin et al. (1984) levels of GOT do not follow the trends shown concludedthat penguinsdive aerobicallyto in- by GDH and GPT, however. BecauseGOT plays termediatedepths. They suggestedthat the an- a central role in the malate-aspartateshuttle in aerobiccapacity is used during burstsof rapid the absenceof a glycerolphosphateshunt, GOT swimmingand that only larger penguinsrely levels should reflect the importance of aerobic extensivelyon anaerobicglycolysis during long glycolysisas well as the two previouscriteria. dives (Mill and Baldwin 1983).The glycolytic Seen in this context, the lower GOT activities capacityof alcid flight musclesis also related in the flight musclesof puffinsand murressug- to diving depth. Becausepuffin flight muscles gest that they rely less on aerobic glycolysis have lower levels of the three glycolyticen- than the pigeon and pheasantand that lipids zymesthan do pigeon flight muscles,however, and amino acidsare important fuels for the div- the correlationmay be spuriousand cannotin- ing birds. dicatea greateruse of glycolysisin the deeper- Alcids usetheir legsand wings to dive (Tuck diving murre.Puffins and murresfly beforeand 1961, Spring 1971), and we hypothesized that after foraging dives, and lactate accumulation the leg muscleswould show metabolicadap- would curtailtheir capacityfor continuedflight tationssimilar to thoseof the flight muscles.We and feeding. Resolutionof the metabolic strat- found that, relative to the flight muscles,the egies used to support diving in alcids (as well leg musclesgenerally had lower enzymeactiv- as in penguins) will require metabolic studies ities.Comparisons of glycolyticand aerobicen- in voluntarily diving birds, similar to thosecar- zyme activities showed that the alcid sartorius ried out on the Weddell seal (Kooyman et al. has a more pronouncedglycolytic orientation 1983, Guppy et al. 1986). than the flight musclesin the alcids or the sar- 738 DAVISAND GUDERLEY [Auk, Vol. 104

torius musclesin pheasantsor pigeons. Because enzyme levels in the Little Penguin pectoral alcids walk little (Tuck 1961), the leg muscles and supracoracoideusreflect the capacity to are presumably specialized for bursts of gly- generateforward propulsion during the entire colytic activity during diving, perhaps for the wing cycle (Clark and Bemis 1979), while the directional changesdescribed by Spring (1971). differencesbetween the alcid pectoral and su- By contrast,the aerobiccapacity of the sartorius pracoracoideusreflect the need for the pectoral in pheasantsand pigeonscorrelates well with to generate lift as well as forward propulsion their considerablewalking. during flight. Comparisonof the metabolicorganization of Our data indicate that a pattern of metabolic penguins and alcids suggeststhat the require- organization similar to that of pigeons supports ments of flying and diving have led the alcids the impressive foraging dives of puffins and to maintain a higher aerobiccapacity. The Little murres.Higher myoglobin levels of alcid flight Penguin (Eudyptulaminor) is approximately25% musclesrepresent the major difference between heavier than the murre and 120% heavier than alcids and pigeons. The adaptations that are the puffin. The deepestrecorded dive of the generally thought to facilitate diving, includ- Little Penguin is 60 m (Mill and Baldwin 1983). ing an increasedoxygen storage capacity (Scho- Both murres and puffins have lower glycolytic lander 1940), a fusiform body shape, and re- enzyme activitiesthan does the Little Penguin duced wing area, seemmodified in the murres (Mill and Baldwin 1983), although the Little and puffins to meet the requirementsof flight. Penguin dives only as deep as the puffin. By contrast,CS activitiesin the pectoral muscleof ACKNOWLEDGMENTS the murre and puffin are approximately 100% higher than thosein the Little Penguin (Mill Many thanksare due to Dr. J. Larocheliefor helpful and Baldwin 1983), a difference greater than commentson an earlier version of this manuscript.J. that predictedby scalingconsiderations. Platt helped in collecting the puffins and murres. L. M. Dicks assistedwith the enzyme assays.Dr. G. Herz- Myoglobin levels suggest that Little Pen- berg of Memorial University providedlaboratory fa- guinsare betterdivers than murres,despite the cilitiesduring the collectionof the alcids.This study oppositeimpression from diving depths.Myo- was supportedby a grant from NSERC to H.G. globinconcentration in Little Penguinpectoral muscleis approximatelytwice that in murre and LITERATURE CITED puffin pectoral muscles.Little Penguin supra- coracoideus myoglobin concentration is ap- AULIE,A. 1983. The forelimb muscular system and proximatelytwo timeshigher than that in murre flight. Pp. 117-129in Physiologyand behaviour and three times higher than that in puffin of the pigeon (M. Abs, Ed.). London, Academic (Baldwin et al. 1984).These differencesmay re- Press. flecta compromisein alcidsbetween diving and BALDWIN,J., J.-P. JARDEL,T. MONTAGUE,& R. TOMKIN. flying. The increasedlevels of mitochondrial 1984. Energymetabolism in penguinswimming muscles.Mol. Physiol. 6: 33-42. enzymesneeded to supportflight may limit the BUTLER,P. J., & A. J. WOAKES. 1984. Heart rate and quantity of myoglobin that can be maintained aerobic metabolism in Humboldt Penguins in the flight muscle.During flight myoglobin (Spheniscushumboldti) during voluntary dives. J. functions more in the delivery of oxygen to Exp. Biol. 108: 419-428. mitochondria than in the storage of oxygen. CASTELLINI,M. A., & G. N. SOMERO.1981. Buffering Lessmyoglobin is requiredfor oxygendelivery capacityof vertebratemuscle, correlations with than for oxygenstorage. In alcidflight muscles, potentialfor anaerobicfunction. J. Comp. Phys- myoglobinlevels are equivalent to or higher iol. 143: 191-198. than thosein pigeon musclesand must suffice --, --, & G. L. KOOYMAN. 1981. Glycolytic for the delivery of oxygento mitochondriadur- enzyme activitiesin tissuesof marine and ter- restrial mammals.Physiol. Zool. 54: 242-252. ing flight. CLARK,B. D., & W. BEMIS. 1979. Kinematics of swim- The demands of flight are also reflected in ming of penguinsat the Detroit Zoo. J. Zool. the intermuscular differentiation of metabolic London 188: 411-428. organization.CS levels are similar in Little Pen- CRABTREE,B., & E. A. NEWSHOLME. 1972. The activ- guin pectoral and supracoracoideusmuscles, ities of phosphorylase,hexokinase, phospho- while in the alcids pectoral levels of CS are fructokinase,lactate dehydrogenase and glycerol twice thosein the supracoracoideus.The similar 3-phosphatedehydrogenase in musclesfrom vet- October1987] MetabolicAdaptations to Diving 739

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