Table Of ContentA L L I G A T OR M E T A B O L I SM
STUDIES ON CHEMICAL REACTIONS
IN VIVO
ROLAND A. COULSON
AND
THOMAS HERNANDEZ
PERGAMON PRESS
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Comp. Biochem. Physiol. Vol. 74, No. 1, pp. i to 182, 1983 0305-0491 /83/01 OOOi-186S03.00/0
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ALLIGATOR METABOLISM
STUDIES ON CHEMICAL REACTIONS IN V I VO
Roland A. Coulson* and Thomas HERNANDEzf
*Departments of Biochemistry and tPharmacology, Louisiana State University Medical Center
1100 Florida Avenue, New Orleans, LA 70119, U.S.A.
[Received 19 March m i)
PREFACE
The results of our earlier investigations were summarized in 1964 in Biochemistry of the Alligator, a Study of
Metabolism in Slow Motion. Since then, with the aid of better equipment and better methods, we have learnt
more and it seemed time to correlate and summarize our findings and those of others who have used this
remarkable experimental animal with profit. This monograph differs too much from the one of 1964 to be
considered, or called, a second edition. A section on natural history was included for those scientists, wild-life
experts, alligator farmers, zoo keepers etc., whose primary interest is in the nature and habits of the intact
alligator. As few would be interested in all the aspects of the reported research, an effort has been made to make
each chapter intelligible by itself. This necessitated a small amount of repetition which we hope will not prove a
burden to the reader.
It is not possible to have done research on alligators for many years without having gained a reputation for
eccentricity as a consequence of the choice of experimental animal. One accepts this and learns to live with it.
Yet, the primary purpose of almost all the research was not to determine the nature of the alligator, but to
understand biochemical reactions in vivo and the alligator was a means to that end. Scientists may work with
squid, horseshoe crabs, turtles, fish, frogs, molds, fungi, dogs, rats, microbes etc., and be identified not with the
organism, but with the process or reactions under study, but they become "alligator men" the day they use that
animal. By some, an alligator man is tolerated (as a harmless eccentric should be), and by others he is admired
for the fearless manner in which he confronts such a "terrifying" beast as a 1 kg alligator. Had we kept record of
the questions visiting scientists have asked about the nature of this much maligned reptile, they would have
been worthy of publication.
A desire not to further endanger a species that had become rare forced us to return to physiological
chemistry, an area that had been largely abandoned by biochemists. Within the first year it became apparent
that several reactions of which we had knowledge in the live alligator were not what one might have predicted
from reference to a text in biochemistry. Naturally enough, we concluded that the alligator did not react in the
same way as other more familiar animals, believing species differences responsible for the aberrant results. We
persisted in this view long after it had become untenable. Although the reasons for some of the differences in
the results of experiments in vivo compared with those in vitro are not known in detail, it is probable that most
of the variations concern different degrees of organization. Disintegration of a cell will inevitably lead to
disruption of membranes, various cellular components etc., and enzymes that were probably packaged inside
Publication of this monograph was made possible by a grant from the Louisiana Department of Wildlife and Fisheries.
David C. Treen, Governor
Jesse J. Guidry, Secretary
Gregory A. Weimer, Undersecretary
Ted Ford, Assistant Secretary
John D. Newsom, Assistant Secretary
Marian Pendley, Executive Assistant
Wildlife and Fisheries Commissioners
Jesse Knowles, Chairman
James C. Farrelly, Vice-Chairman
Wayne C. Ducote
J. C. Gilbert
George N. Gray
Bobby Orgeron
Charles A. Riggs
Division Chiefs
Allan Ensminger, Refuge/Fur
Joe Herring, Game
Harry Schδfer, Seafood
Ray Montet, Enforcement
Bennie Fontenot, Fish
i
ii ROLAND A. COULSON and THOMAS HERNANDEZ
the cells are released and then termed "soluble enzymes'", even though they may have been attached formerly to
solid structures. Homogenization destroys cellular organization and substrates which may have been prevented
from contacting their respective enzymes in the intact cell may react readily when the cells fragment.
The approach in vivo subjected us to criticism from our colleagues in biochemistry, who favored fragmenting
the alligators to a state of disintegration below the cellular level. Had we done this, it is safe to predict that
almost all the enzymes familiar to those studying mammalian fragments would have been found in the alligator,
and in the same parts of the cells. Oxidative phosphorylation would prove to occur in the mitochondria,
glycolysis in the cytosol, protein synthesis at the microsomes etc. The research would probably have been less
rewarding and it certainly would have been less interesting.
Most of the alligators that were used weighed more than a rat but less than a rabbit, and had their metabolic
rates been comparable to those of mammals of the same size, our research in vivo would have been discon
tinued within months for the same reason that others before us had stopped trying to follow reactions that
proceed so rapidly. The low metabolic rate allowed ample time in which to observe a reaction, but this
advantage was not an unmixed blessing since most experiments lasted for many days (and nights too).
Usually, if a particular reaction had been shown to occur in the flask, that same reaction could be demon
strated in the intact animal, but in many cases the yield was not what would have been predicted. The yield of a
reaction in vivo had been assumed to be proportional to the tissue enzyme content as determined in vitro. For
example, if a substrate could be removed through either of two pathways, it was accepted that the principal
route would be the one shown to have been provided with the greatest amount of the relevant enzyme.
Conclusions based on differences in K were also common on the assumption that if one enzyme could catalyze
m
the conversion A to B, and if another could catalyze conversion of A to C, the reaction with the lowest K
m
would be favored. For a number of reasons, in the intact animal neither of the assumptions is necessarily
correct.
Most of us have a natural desire to classify people and scientific subject matter, and scientists are probably
more inclined this way than others. Yet, we hope not too much misdirected effort is expended in classifying this
monograph. It is not intended to be a thorough study in comparative biochemistry and physiology, and indeed
it could not have been even if that had been our intent, for our personal knowledge of reactions is limited to
only a few species. When we used animals other than alligators and caimans, the choice was motivated by a
desire to spare the alligators, or equally compelling, a desire to reduce the cost of isotopes etc. by resorting
to the use of smaller animals. Occasionally, when the results of an experiment on alligators deviated consider
ably from what was expected, the experiments were repeated at once on other species. The reason was less
a desire to compare animals than to verify the existence of reactions in vivo which had not been observed
in vitro.
It would be difficult to conceive a better animal for metabolic studies than an alligator. They thrive when
crowded, they eat willingly, they are subject to few diseases, and compared with many laboratory animals, they
are not only easy to handle, but also easy to bleed or catheterize. Perhaps most important, the alligator is hardy
as an experimental animal, being able to tolerate large doses of drugs, salts, water, massive amounts of food,
hormones etc. This is not a property common to mammals or even to many reptiles that often prove quite
delicate.
Another factor of considerable importance is the remarkable increase in the plasma concentration of reac-
tants in this animal after injection of certain drugs, hormones and metabolites. For example, some sympathomi
metics will increase blood glucose from a fasting level of about 5 up to 45 mM (810 mg/100 ml) and the plasma
concentration will remain high for days. In man, the same drugs will elevate glucose by about 2 mmol/1 for less
than an hour. Any single metabolite derived from the usual foods will also have a half-life sufficiently long to
permit a study of the effect of various conditions or factors on both the rate of its removal and on its metabolic
fate.
Inevitably, the monograph will be criticized for what appears to be a capricious selection of references to
quote. We fear that it will be said that we have not always given due credit to a number of important
contributors, considering the fact that the research reported here deals with scores of biochemical reactions. In
truth, we could not do justice to even a considerable minority in less than 1000 references, and were the book
intended to be a review after the manner of the Annual Reviews, several times that number would be needed.
We do quote standard texts in biochemistry and physiology, and for this we make no apology. Many readers
may not have ready access to some of the literature, but most will be able to obtain texts commonly used in
universities. (For a survey of many aspects of reptilian metabolism the reader should consult Biology of the
Reptilia, edited by Carl Gans, Academic Press, New York.)
In recent years there has been such an increase in the use of jargon in scientific and medical communication
that many articles require translation before they can be understood. Medicine is probably the worst offender,
but several of the life sciences are almost as guilty as can be verified by a glance at the abstracts published by
the Federation of American Societies of Experimental Biology. In opposition to the trend, we have tried to
substitute a simple English word or phrase for words of unnecessary complexity as much as possible. Unfortu
nately, some of our own jargon will probably have crept in, and for this we apologize.
We are indebted to the following for financial aid over the years: N.I.H. Grant H.E. 02062, The Schlieder
Foundation, and the Louisiana Department of Wildlife and Fisheries, particularly the latter. This organization
has supplied us with funds, alligators, and also with fish with which to feed them. Without the help and
cooperation of Alan Ensminger of the Refuge Division, and Ted Joanen and Larry McNease of the Rockefeller
refuge at Grand Chenier, Louisiana, progress would have been slow.
Alligator metabolism iii
A number of people have been involved in the research over the more than 30 year span. We gratefully
acknowledge the contributions of Herbert C. Dessauer, Harley Bearden, James K. Williams, Jackson Beebe,
Octavia Stevenson, Fred G. Brazda, Rosa Floro, Charles Martinez, Emery Williams, Virgil Byers, Jacob V.
Watson, Jr., Monty Holland, Sid Henderson, Sally Clingman and Thomas D. Coulson. Of course, credit is
always owed to the institution, Louisiana State University Medical Center, for providing the facilities, some of
the equipment and much encouragement.
We wish to also acknowledge the invaluable contributions of J.D. Herbert to results and discussion presented
in the chapters on metabolic rate and amino acid metabolism, and to Llewellyn Densmore and Herbert C.
Dessauer for supplying most of the information for the section on alligator phylogeny and genetics. So many of
our colleagues have reviewed sections of the monograph that it is difficult to recall them all. We are particularly
grateful to J. D. Herbert, Nestor Flodin, Lewis Mokrasch, R. E. Reeves, Paul Cook, Robert Roskoski and the
late Gφsta Ehrensvδrd for helpful criticism.
Over the several months that the manuscript was in preparation our wives, Nancy Coulson and Dorothy
Hernandez, gave generously of their time with the illustrations, the proofreading and with the typing.
Chapter 1
NATURAL HISTORY
It may seem strange to spend a considerable amount Bartram (1791) during his travels in the late 18th
of space describing the nature and habits of an experi century wrote:
mental animal but experience has taught us that inter
"Alligators feeding in a river in Florida were in such
est in the alligator is universal. Time and again at the
incredible numbers and so close together from shore to
conclusion of a scientific presentation on some facet of
shore that it would have been easy to have walked across
biochemistry in vivo, the first question was "Do they
on their heads."
bite?" Visitors to the laboratory (and they have in
cluded men in occupations from ornithology to theor With the increase in human population their
etical physics), usually ask the age of the alligators numbers dwindled as they were killed supposedly to
first, followed by questions about longevity and diet. I protect livestock, for sport, for food and for their
suppose we could claim to be experts in how to grow hides. Around 1850 their destruction was accelerated
alligators in captivity, but we are amateurs in Natural by an increase in demand for leather goods and many
History. However, by a combination of library thousands more were killed for the same reason dur
research and personal communications with experts ing the Civil War to supply the Confederate army
such as Joanen and McNease, and Dessauer and (Chabreck, 1967). From 1870 to modern times, it is
Densmore, we composed the following section which estimated that of the 10 million alligators killed, 3-3.5
we hope will answer some of the obvious questions. million came from Louisiana alone between 1880 and
The American alligator (Alligator mississippiensis) is 1933 (Mcllhenny, 1935). Tax records of the Louisiana
found in the wetlands of southeastern United States Department of Wildlife and Fisheries show that only
from North Carolina along the Gulf Coast to Texas. a little over 300,000 skins were sold in Louisiana from
Another member of the order Crocodilia, Crocodilis 1939 to 1955, a period of decline for the alligator.
acutus, is limited to southern Florida. Some 21 species The rapid decrease in the alligator population coin
of crocodilians are recognized throughout the world cided with a developing fur industry as well as with
(Ditmars, 1964; Brazaitis, 1973; Densmore, 1981) but the rapid expansion of oil exploration in South Loui
only one other species of alligator (A. sinensis), a siana. The Louisiana Department of Conservation,
native of China, is known to exist. At one time south now known as the Department of Wildlife and Fish
eastern United States was the home of millions of eries, in its first year of record keeping (1913-1914)
these reptiles and in some accounts the population reported a harvest of more than 4.25 million muskrat
was almost too great for safety. The following is an skins, and at the peak (about 1945) over 8 million
excerpt from a letter written over a century ago pelts were harvested. With the introduction of the
(reported in Louisiana Conservation Review, 1931) nutria in 1939 and the recognition of its value for fur,
concerning Audubon's observations on the abun trapping and hunting resulted in more frequent tres
dance of alligators in Louisiana: passing on alligator territory, endangering them
further. Concurrently, in the search for oil, canals
were dredged into remote swamps leaving few areas
"In Louisiana, all lagoons, bayous, creeks, ponds, lakes,
and rivers, are well stocked with them—they are found inaccessible to man.
wherever there is sufficient quantity of water to hide them,
Conservation laws
or to furnish them with food, and they continue thus, in
great numbers, as high as the mouth of the Arkansas River, The alligator population reached a record low
extending east to North Carolina, and as far west as I have about 1960 when man finally became concerned with
penetrated. On the Red River (Louisiana), before it was
the possibility of their extinction. At that time the
navigated by steam-vessels, they were so extremely abun
Lousiana legislature prohibited killing those less than
dant, that, to see hundreds at á sight along the shore, or on
the immense rafts of floating or stranded timber was quite 5 ft long, and authorized the Louisiana Wildlife and
a common occurrence, the smaller on the backs of the Fisheries Commission to establish seasons and to
larger, groaning and uttering their bellowing noise, like limit the areas and the methods used for harvesting.
thousands of irritated bulls about to meet in fight, but all In 1964 the commercial harvest was stopped, and in
so careless of man, that unless shot at, or positively dis 1966 the alligator was placed on the federal list of rare
turbed, they remained motionless, suffering boats or canoes and endangered species. In 1970 the US Congress
to pass within a few yards of them, without noticing them
amended the 1906 Lacey Act, prohibiting the inter
in the least. The shores are yet trampled by them, in such a
state shipment of illegally taken alligators (Nichols et
manner that their large tracks are seen as plentiful as
ai, 1976). Other amendments concentrated on law en
those of sheep in a fold. It was on that river, particularly,
that thousands of the largest size were killed, when the forcement at both the state and federal levels. These
mania of having either shoes, boots or saddlebags, made of Acts, coupled with the research activities of the Loui
their hides, lasted. It had become an article of trade, and siana Department of Wildlife and Fisheries, (Joanen
many of the squatters, and strolling Indians, followed, for a 6 McNease, 1971; Palmisano, 1972), led to an in
time, no other business." crease in alligator population in a few short years so
1
2 ROLAND A. COULSON and THOMAS HERNANDEZ
great that Louisiana petitioned the Federal Govern 1979) with the interval between fertilization and lay
ment to remove them from the list of endangered spe ing 3-3.5 weeks. Joanen (1969) and Joanen &
cies. In 1975 the Endangered Species Act was McNease (1975, 1976, 1977, 1979) have spent years in
amended and the alligator received a "threatened observing the size of animals at sexual maturity,
status" classification. This allowed the state more flex courtship and nesting habits, time of nest building
ibility and the Department of Wildlife and Fisheries and egg laying, fetility rates, growth rates etc., and
was able to put into practice its theory of game man they have made a number of comparisons of animals
agement over the opposition of those conservationists in the wild with those in captivity. Their observations
demanding permanent prohibition of all hunting. The on the time of breeding are in concert with the
Department was vindicated by the success of a decade reported plasma titers for testosterone in the male
of alligator harvests, first in a few areas, and then and of estradiol in the female (Lance, 1981). Lance
statewide, during which the alligator population found that plasma testosterone was highest in early
actually increased (Palmisano et al., 1973; McNease April and lowest in July and August when the testes
& Joanen, 1978). had fully regressed. In the breeding female peak
plasma estradiol also occurred in early April coincid
Habitat of the alligator ing with the period of rapid egg growth in the ovaries.
The alligator is amphibious and prefers fresh to In studies at the Rockefeller Refuge (Grand Che-
brackish water. Information from telemetric studies nier, LA), the egg laying season was from 12 June to
on the habits of adult alligators (Joanen & McNease, the first week of July, about the same time as for
1970, 1972) revealed differences in habitat preference alligators in the wild. Temperature and humidity are
between males and females. In the spring both sexes undoubtedly important factors affecting nesting, egg
gather in courting groups in deep-water areas. During laying, hatching viability etc. The average number of
courtship females are more sociable than males, but eggs was 38.9 for 266 nests observed over a period of
after mating, males remain in open water while the years (Joanen, 1969). The following record (Table 1.1)
females move to dense cover and small isolated ponds of three nestings of alligators at Avery Island, LA, is
in the interior marshes to begin nest construction. interesting (Mcllhenny, 1935).
Females generally remain isolated in the marshes In one study on hatching in the wild, Mcllhenny
until the following spring when courtship again brings (1935) reported nest temperatures ranging from 32.2
them into open water. to 38.9°C, values considerably higher than the
According to Mcllhenny (1935), alligators dug deep 23.3-32.8°C reported by Joanen (1969). Eggs were
holes interconnected with underground dens in which hatched in incubators at temperatures from 28 to
they spent the cold months, coming out to sun them 34°C (82.4^93.2°F) with the best hatching success
selves when the air temperature was warmer than that occurring at 31-31.7°C (87.8-89.1°F). The incubation
of the water. More recently, the close proximity of temperatures for alligator eggs are similar to those
numerous deep channels seems to have induced large reported for the Nile crocodile by Modha (1967).
numbers to abandon their winter dens in favor of Recently, Ferguson (1981) reported on the structure
man-made canals. The location of alligator holes or and chemical composition of the alligator eggshell
dens still in use can be recognized from a considerable throughout the 65-day incubation period. He con
distance by the lush growth of grass surrounding the cluded that acidic by-products from microbial metab
hole. This is not surprising in view of the excretion of olism eroded the shell by reacting with the calcite
large amounts of NH HC0 , an excellent fetilizer for crystals. The degradation increased shell porosity as
4 3
plant growth. incubation progressed, facilitating the exchange of
respiratory gases and water vapor in the developing
Nest and nest building, egg laying and incubation embryo, and hatching.
The average size of an alligator's nest is approx The issue of "temperature-dependent sex de
2.4-3.0 m (8-10 ft) wide and about 0.6 m (2 ft) high at termination" has long been controversial, but recent
the center. Once each season females deposit their studies by Ferguson & Joanen (personal communi
eggs in a hollowed out area in the top center of the cation) seemed to have dispelled doubts of the im
nest and cover them by placing loose weeds and mud portance of temperature in the alligator nest. In
on top. Nest building is an elaborate process well extensive field and laboratory experiments they
described by Mcllhenny (1935). reported that sex is fully determined at the time of
In southwest Louisiana courtship and bellowing hatching, an incubation temperature of 30°C or below
beings in early April and gradually increases in inten resulting in 100% females and 34°C or above, 100%
sity into May. Copulation is most frequent from late males. The temperature sensitive period was between
May to the first week in June (Joanen & McNease, the 7th and the 21st day of incubation. Eggs hatched
Table 1.1. Hatching record at three nests at Avery Island, LA*
Incub. Average Length of Wt of Length of Wt of
Nest Laying Hatch. period No. of egg wt hatchling hatchling mother mother
No. date date (days) eggs (g) (cm) (g) (m) (kg)
1 6/21 8/22 63 42 87 23.9 - 2.78 74.1
2 6/23 8/28 67 34 60 22.2 50 2.21 52.8
3 6/2 8/7 66 41 64 23.4 55 2.34 58.7
* Mcllhenny (1935).
Alligator metabolism 3
Length-age relationships between males and females
are shown in Fig. 1.2. Their mathematical model pro
jected 4.2 m (14 ft) at 80 years for males and 2.73 m
200 (9 ft) at 45 years for females. In 10 years wild males
reached 2.55 m and females 2.10 m. Both sexes in
crease in length greatly during the first year after
hatching and the rate gradually declines after that.
Coulson et al. (1973) studied growth rates of alliga
tors kept in temperature controlled concrete tanks.
Temperatures were generally kept at about 30°C
except in very cold weather when water temperatures
as low as 23°C were recorded. These animals were fed
daily 5 days a week and were allowed to eat ad lib.
The data represent the median weights and lengths of
about 200 small alligators for the first year and of 25
0 60 120 180 240 300 360 for the second year (Fig. 1.3). The growth rates in
LENGTH (CM) these experiments were much greater than those
Fig. 1.1. Relationship between weight and length in the reported for wild alligators (Mcllhenny, 1935; Cha
wild alligator. (Chabreck & Joanen, 1979.) breck & Joanen, 1979), at least up to 1.7 m in length.
In later experiments T. D. Coulson (personal com
at 30°C weighed considerably more than those munication) raised an alligator that was 1.3 m long
hatched at 34°C, while incubation below 26°C or and that weighed 7.8 kg in 1 year.
above 36°C was lethal. A number of experiments are Temperature is a most important factor in the rate
currently being conducted to elucidate other factors of growth, and alligators in the wild will not eat dur
involved in sex determination. ing the cold months (October-March). If kept warm
It is difficult to determine sex in the young alligator in environmental chambers there is no sign of hiber
since there are no distinguishing external character nation and the metabolic rate differs little, if any,
istics which may be used with any degree of reliability. between winter and summer (Coulson & Hernandez,
In our experience, and in a study by Joanen & 1964; Joanen & McNease, 1976). Although the opti
McNease there was a considerable error in using the mum temperature is probably 29-31°C (perhaps even
cloacal method for sexing, especially for alligators 32 or 33°C), higher temperatures have a damaging
under 1 year of age. The degree of accuracy increased effect leading to a marked variability in heart rate at
with the size of the alligator, and a high degree of 34°C, and irreversible cardiac damage above 40°C
reliability began with the animals about 60 cm in (Wilbur, 1960). An ample food supply is necessary to
length. keep the plasma amino acids at a level high enough to
assure maximum protein synthesis. About half of the
Rates of growth size and age protein eaten is converted to body protein in the
Much has been written on the large sizes attained rapidly growing immature alligator (Coulson & Her
by various crocodilians (Graham & Beard, 1973). The nandez, 1964). What is not known is the relationship
"biggest croc" is a mythical beast unreliably reported of the development of gout to the quantity and type
to reach 40-50 ft. Actual measurements indicate that of food consumed. Feeding during the winter often
while they are of more modest proportions, they are leads to the deposition of urates throughout the body
still among the largest animals on earth. In Kenya and feeding frequency must be carefully controlled to
and Uganda, a hunt by Graham yielded one specimen prevent the disorder. Another factor for maximum
of C. niloticus 4.72 m long (15 ft 6 in.), another of growth is the availability of water for adequate hy-
4.80 m long (15 ft 9 in.) and of 30,000 crocodiles re
portedly shot by Bousfields, the longest was 5.30 m
(17 ft 4^ in.). The record Nile crocodile was one re
portedly shot by an unknown hunter in 1927, with the
c/) 5
skin measuring 5.94 m (19 ft 6 in.). Mcllhenny (1935)
reported 3 male alligators above 5.49 m (18 ft), the
largest being 5.84 m (19 ft 2 in.), the second 5.63 m
(18 ft 5i in.) and the third 5.56 m (18 ft 3 in.). It was his
opinion that these represented exceptional animals
and that the usual maximum is more like 4.57 m
(15 ft). The largest female caught was 2.78 m (9 ft \j in.)
and weighed 74.07 kg (163.5 lbs). The largest crocodi
lian may be C. porosus, the salt water crocodile of the
Far East. Enough reports of males exceeding 25 ft
have been received to suggest they cannot all be
wrong.
The relationship between weight and total length in 0 tO 20 30 40 50
wild alligators is shown in Fig. 1.1 (Chabreck & Joa AGE IN YEARS
nen, 1979). There was little difference in growth rates Fig. 1.2. Length-age relationship from capture-recapture
between the sexes up to 100 cm in length, but beyond data on 167 males (J) and 137 females (+). Broken lines
100 cm the males grew much faster than the females. represent projected data. (Chabreck & Joanen, 1979.)
4 ROLAND A. COULSON and THOMAS HERNANDEZ
30-
28-
26-
24-
22-
Έ
< 20-
or
o
o
Χ
>-
Ω
O
OD
30 40 5 0 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
BODY LENGTH IN CENTIMETERS
Fig. 1.3. Relationship between total length and body weight in alligators raised in the laboratory. Each
dot represents a single specimen. The crosses represent the average. (Coulson et al., 1973.)
dration and to facilitate NH HC0 excretion, the end Cott (1961), in his review of the ecology of C. nilo-
4 3
product of nitrogen metabolism (along with uric acid). ticus in Uganda and Northern Rhodesia, recorded the
How long alligators live remains an unanswered following observations:
question. Pope (1960) in a study of records of zoos "The Nile crocodile is remarkable for the wide variety of
states: prey taken in the course of its life. Victims range from
terrestrial and aerial to wholly aquatic forms; and in size
"among 55 kinds of reptiles definitely known to have lived
from small organisms such as spiders, ants and termites, up
20 years or more, 31 were turtles, 11 were crocodiles, 10
to the great mammals and including African buffalo, lion,
snakes, 2 lizards and the tuatara. An American alligator
black rhinoceros and camel. Its methods of hunting, cap
was 56 years old, a Chinese alligator 50 years, and a marsh
ture and disposal of prey are as varied as the habits of its
crocodile 31 years."
victims. Thus no general statement regarding feeding tech
He further states that there is no evidence that niques is admissible, though it may be said that nearly
crocodiles ever live as long as man (but then there is always stealth, surprise, and a sudden final burst of speed
are involved."
no evidence they don't). An alligator farmer in South
Louisiana has numbers of females approaching 30 When hungry, the alligator is a voracious feeder
years of age and all are still fertile and producing eggs and to witness a group of laboratory alligators eat is a
(Joanen, personal communication). spectacle not easily forgotten. As freshly thawed fish is
thrown into the water they submerge and scan an
area on either side with their heads until food is
Food and feeding habits
located, churning the water so rapidly that it foams. If
Mcllhenny (1935) recorded the food of the alligator two grab the same fish each goes into a rapid spin to
from the time of hatching to 3.05-4.57 m (10-15 ft). sever a morsel, then they stop spinning, raise their
Quoting from his book: heads above water, and rapidly swallow. In nature,
"It is quite safe to say that the food of the alligator at the alligator has a unique approach to his prey. Mcll
some time of its life, consists of every living thing coming henny (1935) relates the following incident:
in range of its jaws that flies, walks, swims, or crawls that is "On April 8, 1916, I was watching an old hen duck with
small enough for them to kill, and covers a tremendously a brood of eight young ones swimming in the canal near
wide range." my shooting camp in Vermilion Parish (South Louisiana).
Shortly after hatching, the alligator eats insects, The tide was low and the old duck had brought her newly
hatched brood to the water, and was quietly feeding them
small crustaceans and small fish. With increasing size,
along the edge of the canal, whose bank was steep and
his diet may include crabs, frogs and other reptiles,
several feet above the water. I saw a small alligator swim
and above 5 ft, muskrats, rabbits, nutria, ducks, rails,
ming towards the old duck and her brood; when it got
geese, and other birds or mammals. His eating habits near it quickened its pace, and although the old duck
are not much different from those of related crocodi- flapped madly away, calling to her brood, who swam after
lians. Table 1.2 lists the stomach contents of alligators her as fast as they could, the alligator overtook the rear
caught in the Louisiana marsh (McNease & Joanen, young, grabbed one and throwing its head into the air,
1977). swallowed it, and with hardly a pause, swam rapidly after
Alligator metabolism 5
Table 1.2. Foods found in 202 alligator stomachs taken from three marsh types of Southwest Louisiana,
September 1972*
Fresh marsh Intermediate marsh Brackish marsh
(%) (%) (%)
Food typet Frequency Weight Frequency Weight Frequency Weight
Mammals 72.2 79.1 49.1 40.6 22.7 20.7
Nutria 63.9 65.6 41.8 25.7 22.7 20.7
Other 8.3 13.5 7.3 14.9 0 0
Birds 44.4 3.6 50.9 9.5 14.7 4.6
Grackle 11.1 1.2 27.1 7.2 4.0 2.5
Blackbird 22.2 1.1 9.1 0.6 0 0
Other 11.1 1.3 14.6 1.7 10.7 2.1
Reptiles 33.3 1.5 36.4 2.5 9.3 1.0
Turtles 11.1 0.1 7.2 0.1 4.0 0.1
Snakes 19.4 0.7 16.5 1.3 2.6 0
Other 2.8 0.7 12.7 1.1 2.7 0.9
Fish 25.0 4.8 36.4 12.6 58.7 33.2
Mullet 2.8 1.1 1.8 0 14.7 11.0
Garfish 8.3 2.2 9.1 5.7 2.7 0.4
Shad 5.6 0.8 1.8 1.4 13.3 12.1
Other 8.3 0.7 23.7 5.5 28.0 9.7
Arthropods (crawfish, 80.6 6.3 80.0 15.5 86.7 30.7
crabs, shrimp etc.)
Mollusks 6.9 Tr. 5.4 0.1 1.3 Tr.
Plant material 94.4 3.2 74.5 6.1 88.0 7.7
Unidentifiables 20.8 0.9 3.6 0.6 5.3 0.6
* McNease & Joanen (1977).
t Food items from fresh marsh alligator stomachs averaged 552 g, from intermediate marsh 531 g, and
from brackish marsh 224 g. Of the 552 g (fresh marsh), 72.2% of the alligator stomachs contained
mammals making up 79.1% of the total weight.
the others. In a distance less than two hundred feet it over striped mullet, red snapper^ black drum, as well as
took, caught and swallowed one after the other all of these garfish, perch, catfish and carp. Marine fish generally
little ducks. This alligator was not more than three and a contain sufficient amounts of vitamin D to prevent
half feet long."
bone abnormalities but if rats or rabbits are fed,
Mcllhenny recounts further: unless vitamin D or sunlight is made available, the
alligators should be exposed to ultraviolet light for a
"When an alligator catches food that is too large to be
few hours a day.
swallowed with its mouth closed, it raises its head above
When Joanen & McNease (1974) fed synthetic diets
the water, and after pulping the food by numerous crush-
ings between its jaws it is deftly shifted by throwing the from vegetable sources (Purina Commercial Catfish
object into the air until the head part points down its Ration® and Rex Turtle Feed Ration®) the growth
throat, when the whole object is swallowed at one gulp. rate of alligators was far less than that of animals fed
Should the object be too large for the throat, and fail to diets containing animal proteins. We were unable to
pass in, it is ejected and again crushed between the jaws demonstrate digestion of vegetable proteins (Chapter
until it becomes more pliable, and then swallowed. I have
4).
seen a large captive alligator fed, at times, the shoulder
containing the bone, and the backbone in sections as much Telemetrie studies on activity and movement
as two feet long of full grown cattle, and these bones were
crushed between the alligator's jaws as matches would be The 34,425 hectares (85,000 acres) Rockefeller
between the fingers of a man. The crushing power of an Refuge at Grand Chenier, LA, has facilities permitting
alligator's jaws is enormous, and the muscular develop a study of the alligator either in his native habitat or
ment operating the under jaw is tremendously heavy and in the laboratory. Radio telemetry equipment with
strong. When even a three-foot alligator closes its jaws on special tracking transmitters and receivers (Joanen &
an object it is impossible for a man with ordinary strength McNease, 1970, 1972; McNease & Joanen, 1974) was
to open these jaws. When a large alligator closes its jaws
mounted on a neck collar and the apparatus, which
on a victim, it is absolutely impossible, no matter what the
weighed about 600 g, was attached to alligators. Port
strength of the thing grasped, for it to get away. This is the
able VHF tracking receivers were tuned to the fre
closing power of an alligator's jaws. The opening power is
exceedingly small. I have held closed with my left hand the quencies of the transmitters and compass bearings
jaws of the largest alligators I have ever caught." were determined with a Silva Ranger® type compass.
The complete procedure was described by Joanen &
Laboratory diets. Either salt water or fresh water fish McNease (1972). Areas of ranges of four nesting
are adequate for crocodilians kept under laboratory female alligators monitored for 177 days were 2.6, 5.0,
conditions (Coulson et al., 1973). Fish can be fed 9.8 and 16.6 hectares (Joanen & McNease, 1970) with
whole or ground and satisfactory types include south an average daily movement 24.1 m. In another similar
ern kingfish, Atlantic croaker, spotted seatrout, study (Joanen & McNease, 1972; Joanen, personal
