age estimation, growth rates, and population structure in missouri bullfrogs

Age Estimation, Growth Rates, and Population Structure in Missouri BullfrogsAuthor(s): Eugene E. Schroeder and Thomas S. BaskettSource: Copeia, Vol. 1968, No. 3 (Aug. 31, 1968), pp. 583-592Published by: American Society of Ichthyologists and Herpetologists (ASIH)Stable URL: http://www.jstor.org/stable/1442029 .

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SCHROEDER AND BASKETT-AGE OF BULLFROGS SCHROEDER AND BASKETT-AGE OF BULLFROGS

vocal sac; ovary packed with heavily pigmented eggs each approximately 1.5 mm in diameter. Skin of head not co-ossified with skull, roof of skull not exostosed.

Dimensions.-Head and body 57.0 mm; head length 20.5 mm; head width 19.8 mm; femur 32.3 mm; tibia 32.2 mm; heel-to-toe 40.0 mm; hand 17.0 mm.

Color in alcohol.-A dingy white with tiny melanophores scattered over all dorsal surfaces but restricted to a narrow band on top of the thigh.

Notes.-When we examined this specimen in Paramaribo just a few weeks after it was preserved it still retained some of the dark green dorsal pigmentation it had in life but by the time it was shipped to us from Pitts- burgh nearly a year later the green color- ation had completely faded and all that re- mained of pigment or pattern was minute, scattered melanophores on the dorsum and dorsal surfaces of the limbs. These have the effect of making the specimen a dirty white rather than clear milky white.

The type was taken at night from a large aroid plant beside a house in the Arawak vil- lage of Powakka. A diligent search by five of us in the same area a few weeks later failed to turn up any more specimens.

vocal sac; ovary packed with heavily pigmented eggs each approximately 1.5 mm in diameter. Skin of head not co-ossified with skull, roof of skull not exostosed.

Dimensions.-Head and body 57.0 mm; head length 20.5 mm; head width 19.8 mm; femur 32.3 mm; tibia 32.2 mm; heel-to-toe 40.0 mm; hand 17.0 mm.

Color in alcohol.-A dingy white with tiny melanophores scattered over all dorsal surfaces but restricted to a narrow band on top of the thigh.

Notes.-When we examined this specimen in Paramaribo just a few weeks after it was preserved it still retained some of the dark green dorsal pigmentation it had in life but by the time it was shipped to us from Pitts- burgh nearly a year later the green color- ation had completely faded and all that re- mained of pigment or pattern was minute, scattered melanophores on the dorsum and dorsal surfaces of the limbs. These have the effect of making the specimen a dirty white rather than clear milky white.

The type was taken at night from a large aroid plant beside a house in the Arawak vil- lage of Powakka. A diligent search by five of us in the same area a few weeks later failed to turn up any more specimens.

Mr. Walter Polder of Paramaribo, who is well acquainted with the local fauna, told us that he caught an individual of what he be- lieves is the same species in the suburbs of Paramaribo but that it escaped before he was ready to preserve it.

The type-specimen is filled with mature, pigmented eggs and apparently was ready for amplexus.

The species is named in honor of our friend, Murray de la Fuente, who collected the type.

ACKNOWLEDGMENTS

Murray de la Fuente, Walter N. Polder, Duvall A. Jones, and Steven A. Bass were pleasant companions in the field and aided appreciably in collecting; the figure of the type is from the pen of Paul Laessle; Clar- ence McCoy forwarded the type and other Suriname material to Gainesville for study; our work on Suriname frogs is supported by grant GB-3644 from the National Science Foundation. To all of these we are ex- tremely grateful.

DEPARTMENT OF ZOOLOGY, UNIVERSITY OF

FLORIDA, GAINESVILLE, FLORIDA 32601.

Mr. Walter Polder of Paramaribo, who is well acquainted with the local fauna, told us that he caught an individual of what he be- lieves is the same species in the suburbs of Paramaribo but that it escaped before he was ready to preserve it.

The type-specimen is filled with mature, pigmented eggs and apparently was ready for amplexus.

The species is named in honor of our friend, Murray de la Fuente, who collected the type.

ACKNOWLEDGMENTS

Murray de la Fuente, Walter N. Polder, Duvall A. Jones, and Steven A. Bass were pleasant companions in the field and aided appreciably in collecting; the figure of the type is from the pen of Paul Laessle; Clar- ence McCoy forwarded the type and other Suriname material to Gainesville for study; our work on Suriname frogs is supported by grant GB-3644 from the National Science Foundation. To all of these we are ex- tremely grateful.

DEPARTMENT OF ZOOLOGY, UNIVERSITY OF

FLORIDA, GAINESVILLE, FLORIDA 32601.

Age Estimation, Growth Rates, and Population Structure in Missouri Bullfrogs

EUGENE E. SCHROEDER AND THOMAS S. BASKETT

Growth marks on the posterior limb of the pterygoid bone of the bullfrog (Rana catesbeiana) are useful in estimating postmetamorphic age up to six years. Validity of age estimation was checked on 42 frogs of known age. Growth rates were quite similar for frogs of five different populations, a fact probably related to their ability to use many different kinds of foods. The sex ratio of 426 bullfrogs did not differ significantly from 1:1. Frogs from areas under moderate hunting pressure maintained a constant percentage of older age groups but areas presumed to be heavily hunted had markedly fewer or no representatives of older age groups.

Age Estimation, Growth Rates, and Population Structure in Missouri Bullfrogs

EUGENE E. SCHROEDER AND THOMAS S. BASKETT

Growth marks on the posterior limb of the pterygoid bone of the bullfrog (Rana catesbeiana) are useful in estimating postmetamorphic age up to six years. Validity of age estimation was checked on 42 frogs of known age. Growth rates were quite similar for frogs of five different populations, a fact probably related to their ability to use many different kinds of foods. The sex ratio of 426 bullfrogs did not differ significantly from 1:1. Frogs from areas under moderate hunting pressure maintained a constant percentage of older age groups but areas presumed to be heavily hunted had markedly fewer or no representatives of older age groups.

INTRODUCTION

A few researchers have used morphological features to determine age of amphib-

ians (Humphrey, 1922; Senning, 1940; Organ, 1961). Others have translated length-frequency modes into age groups (Blanchard and Blanchard, 1931; Bannikov, 1949, 1950;

INTRODUCTION

A few researchers have used morphological features to determine age of amphib-

ians (Humphrey, 1922; Senning, 1940; Organ, 1961). Others have translated length-frequency modes into age groups (Blanchard and Blanchard, 1931; Bannikov, 1949, 1950;

Stebbins, 1954; Green, 1957; Tamsitt, 1962). Nevertheless, population studies of amphib- ians have often been handicapped by the lack of suitable techniques for determining age (Cagle, 1956; Turner, 1962).

In his review of demographic studies of anurans, Turner (1962) emphasized the need

Stebbins, 1954; Green, 1957; Tamsitt, 1962). Nevertheless, population studies of amphib- ians have often been handicapped by the lack of suitable techniques for determining age (Cagle, 1956; Turner, 1962).

In his review of demographic studies of anurans, Turner (1962) emphasized the need

583 583



COPEIA, 1968, NO. 3

Fig. 1. Left pterygoid bone of Rana catesbeiana, posterior limb at left (1.6 X; age group 5).

for morphological criteria that would be useful in determining the age of individual animals. One objective of the present study was to satisfy this need in the case of the bullfrog (Rana catesbeiana). This paper pre- sents information about testing the useful- ness of pterygoid bones, zygapophyses, and eye lenses for estimating age in this species. The paper also contains data on growth rates and demographic characteristics of several Missouri populations of bullfrogs.

Our emphasis on pterygoid bones resulted directly from our own preliminary examina- tions of many bony structures. However, annual marks on cranial bones have been reported for a salamander (Senning, 1940), snakes (Bryuzgin, 1939; Petter-Rousseaux, 1953; Peabody, 1958), and certain living and fossil poikilothermic tetrapods (Peabody, 1961). Use of zygapophyses for age determination was suggested by Willis's (1954) work with bullfrogs. Lord's (1959) work with cottontails (Sylvilagus floridanus) prompted our studies of bullfrog lenses.

MATERIALS AND METHODS

Bullfrogs were collected twice monthly during the summer of 1962 and 1963 at the University of Missouri's Ashland Wildlife Area in central Missouri. Others were collected from surrounding farm ponds in Boone County. Large collections of frogs were made during July 1963 and 1964 at the James A. Reed Wildlife Area in Jackson County, and during August 1964 bullfrogs were also taken from the Meramec River beginning at the Highway 19 bridge north of Steelville to the confluence of Huzzah Creek and the Meramec River in Crawford County. Bullfrogs were also collected from Big Piney River from Mineral Springs to Boiling Springs in Texas County.

Transformed frogs of the year from the Ozark Fish Hatchery at Stoutland, Missouri, and 12 transforming tadpoles collected in Boone County, comprised our source of known-age animals. All frogs were finger- and toe-clipped for later identification.

Frogs of known age were confined in four pens at the Ashland Wildlife Area. Each pen measured 20 X 16 X 6 ft. Hardware cloth of 1/4-inch mesh covered the tops and sides of the pens. The sides were extended to 18 inches below the soil surface. Each enclosure had a pool of water 10 X 10 X 5 ft with dirt sides and bottom. Lights were attached to the pens to attract insects, and crayfish were added for supplementary food from time to time during the summer.

Frogs were pithed and measured on a fishery measuring board. The sex of large frogs was determined by tympanum size; in questionable cases, and for all small frogs, sex was confirmed by dissection.

All bones of the bullfrog were examined for growth marks by gross or microscopic in- spection. In preliminary trials, many bones were sectioned as outlined by Peabody (1961), and many were stained with alizarin red S (Hollister, 1934). Neither sectioning nor staining substantially improved discern- ment of marks on the most promising structures. Many bony structures, including zygapophyses, transverse processes, centra of the vertebrae, mandibles, scapulae, and pterygoids, had marks. However, we scruti- nized the pterygoids most intensely because they consistently exhibited the clearest patterns.

The pterygoid is a triradiate bone of the skull (Fig. 1). The anterior limb attaches to the maxilla, the medial limb joins the pro- otic bone, and the posterior limb joins the quadratojugal and the squamosal bones to form the posterior angle of the jaw.

Paired pterygoid bones were detached, fleshed by hand, and placed in boiling water for 40-60 sec to free them of remaining flesh. After the bones had dried they were either stored in numbered envelopes or examined directly under a dissection micro- scope with transmitted light. Presumed growth marks were observed on the posterior limb. Many of the marks were difficult to see, and to locate them accurately required varying the position of the bone with respect to the light source, using low-

584



SCHROEDER AND BASKETT-AGE OF BULLFROGS

power magnification, and sometimes, wetting the bone with 30% alcohol.

Lenses were prepared for weighing as de- scribed by Lord (1959). Eyeballs were preserved for two weeks to five months in 10% formalin before the lenses were removed. Each lens was freed of the ciliary apparatus and oven-dried at 80? C for at least 96 hr. A torsion balance was used to weigh the lenses.

RESULTS AND DISCUSSION

Age Estimation

Marks on zygapophyses.-In a study related to ours, Willis (1954) concluded that marks on the zygapophyses of the vertebrae of bullfrogs held promise for age determination. In order for these marks to be distinguished, it was necessary to clear and stain the vertebrae with alizarin red S (Hollister, 1934). Marks on the zygapophyses were of two types: "distinct marks" and "indistinct marks." Each "distinct mark" was interpreted by Willis as possibly representing one year of postmetamorphic existence. Willis lacked known-age material, but the numbers of "distinct marks" appeared to correlate rea- sonably well with the rather fragmentary information about growth rates that was available to him.

Our investigations confirmed the presence of marks on the zygapophyses. Although thin white lines or marks became more numerous with increased body length, Schroeder, who studied them intensively, could not duplicate Willis's interpretations for large zygapophyses. Because the zygapophyses rarely were more than four mm long in even the largest frogs, growth marks toward the periphery were very close to- gether. Thus, determining their number was progressively more difficult as the postmetamorphic age of the frog increased.

Marks on the pterygoid bones.-Pterygoid bones were more suitable for age determination studies in the bullfrog because they consistently exhibited the clearest marks. More- over, their large size facilitated analysis.

When viewed under transmitted light, the posterior limbs of the pterygoids were light gray or white, and had narrow opaque marks alternating with broad translucent bands. The narrow marks varied in distinctness, but the most distinct ones usually extended to edges of the pterygoid. We hypothesized that

these distinct marks resulted from periods of arrested growth during winter, and that the broad translucent bands represented growth during more favorable periods. Patterns of the distinct marks that we assumed to be annual growth marks were quite similar on paired pterygoids.

The less distinct marks were generally in- complete and their patterns were dissimilar on paired pterygoids. We term them false growth marks. An additional type of narrow, opaque mark, associated with transformation, was usually found near the medial limb of the pterygoid. This mark was sometimes obliterated in older frogs.

Examination of a series of pterygoid bones over a complete season indicated that growth was accomplished by deposition of bone at the distal edge of the posterior limb and by lesser deposition of bone along the shaft. Pterygoid bones from frogs captured at the beginning of the growing season (May) had the past winter's marks at the tips of the bones. As the growing season progressed, these distinct, complete marks (hereafter termed growth marks) were progressively far- ther from the tips. In general, marks denot- ing the first two or three years' growth after transformation were relatively more widely separated than growth marks laid down in later years.

Pterygoid bones of frogs collected at or just before transformation contained no marks on the posterior limb (Fig. 2A). How- ever, the pterygoid bones of known-age frogs captured in August 1963, soon after transformation but before the first winter, showed a distinct mark several mm from the tip. Evidently this was the mark of transformation, and bone distal to it represented growth to the time of capture (Fig. 2B).

Pterygoids taken from frogs sacrificed in September 1964 and known to have overwintered once had two marks: a mark of transformation, and a growth mark corre- sponding to the first winter after transformation (Fig. 2C). Frogs known to have overwintered twice after metamorphosis, and collected during June 1965, had two marks: one growth mark for each winter after transformation (Fig. 2D). Several frogs collected soon after transforming in 1960 were sam- pled during August 1963, August 1964, and June 1965. Depending on the year these frogs were killed, pterygoid bones had three, four, or five growth marks (Figs. 2E, 2F,

585



COPEIA, 1968, NO. 3

Fig. 2. Pterygoid bones of bullfrogs of known age. A. Transforming (17.2 X). B. Immature, show- ing transformation mark T (12.0 X). C. Known age, one winter; note single growth mark I, false growth mark F, and transformation mark T (9.2 X). D. Known age, two winters (9.2 X). E. Known age, three winters (9.0 X). F. Known age, four winters (9.0 X). G. Known age, five winters (8.6 X).

586




2G). Bones from these older frogs had undergone more ossification, with the result that growth marks of years 1 and 2 and the mark of transformation were rendered less distinct. However, the mark of transformation when present was recognizable by its close proximity to the medial limb.

Thus, our assumptions about the identity of growth marks were confirmed by the known-age material. Frogs with no growth marks belonged to post-transformation age group 0 and had not overwintered since transformation. Frogs with two growth marks belonged to age group 2 and had lived through two winters post-transformation, but had only one full season of postmetamorphic growth. Growth marks were recognized at least through five years postmetamorphosis. Data about known-age frogs are summarized in Table 1.

To check the method, attempts were made to determine the accuracy of readings by three other persons, all of whom had some experience in reading annuli of scales and bones of fishes. In a 45-min session readers studied the growth marks of known-age frogs and then analyzed another series of pterygoid bones. Their readings of these were compared with Schroeder's age determinations. In a series of 15 bones, one reader agreed with Schroeder 14 times. Ten of these bones were from frogs three years or younger, postmetamorphosis. Two other readers, each furnished with a series of 17 bones, showed 40% correspondence with Schroeder's readings. However, 12 of these bones were from frogs four, five, and six years or older, postmetamorphosis. In only two instances were deviations greater than one year from Schroeder's determinations. There were consistent indications that the mark of transformation in younger frogs was being counted as a growth mark; several times in older frogs the last-formed growth mark was not counted. False and true growth marks were sometimes confused.

Despite these problems, with careful study the technique is satisfactory for estimating the age of bullfrogs through the fifth year after transformation. Validity of the method is indicated by the uniformity in both number and position of the growth marks on paired pterygoids from individual frogs. The technique might be applied successfully to anurans with life spans shorter than that of the bullfrog.

TABLE 1. GROWTH MARKS ON PTERYGOID BONES OF BULLFROGS OF KNOWN AGE. Numbers in parentheses refer to sample size. (All frogs not killed soon after capture were held in fenced

pools.)

No. of No. of Times Growth Date Date Overwintered Marks Captulred Killed

0 (Transforming 0 (12) June 1965 next day tadpoles)

0 (Newly 0 (3)1 Aug. 1963 Aug. 1963 transformed) 0 (5)1 June 1964 Sept. 1964

I 1 (14)1 Aug. 1963 Sept. 1964 2 2 (3) Aug. 1963 June 1965 3 3 (1) Summer 1960 Aug. 1963 4 4 (2) Summer 1960 Aug. 1964 5 5 (2) Summer 1960 June 1965

1 Transformation marks evident.

Growth of lenses.-Lenses were obtained from 32 transformed bullfrogs of known age to determine whether lens weights could be used for age determination. Lenses were also obtained from 126 frogs whose age was estimated by growth marks on the pterygoids.

Although lens weights increased with age, overlapping of the weights for all age groups (except age group 0) rendered these data useless for determining yearly age groups (Fig. 3). Usually frogs belonging to age group 0 (the exceptional group) can be recognized directly by their body size. Bullfrog lenses continue to grow at least to the fifth year after transformation, but no distinct group- ings could be discerned.

The great variation in lens weights probably results from the long breeding season, long season of transformation, and the slowing of growth in later postmetamorphic years.

Growth Rates

Bullfrog body lengths in mm were tallied against ages, as estimated by growth marks on the pterygoid bones, up to six postmetamorphic years for each of five collecting sites (Table 2). Frogs older than five years were placed in age group 6, because of the diffi- culty in estimating the age of older frogs. The mean body length values for age group 0 from four collecting sites are probably not representative, because no attempt was made to collect adequate numbers of these young frogs.

587



COPEIA, 1968, NO. 3

TABLE 2. MEAN BODY LENGTH ACCORDING TO AGE GROUPS AND THE PERCENTAGE OF THE TOTAL

GROWTH IN RELATIONSHIP TO MAXIMAL BODY LENGTH OF BULLFROGS FOR FIVE SITES IN MISSOURI.

(Length measurements in mm; age estimated by marks on pterygoid bones.)

Age Group

N x Length

1 Range SD

% of the Total Growth

N x Length

2 Range SD


N x Length

3 Range SD % of the Total Growth

N x Length

4 Range SD


N x Length

5 Range SD


N x Length

6+ Range SD % of the Total Growth

Length of Largest Frog from Each Site

Ashland Wildlife

Area

31

102 83-127

9.8 61.8

45 122

111-133 5.4

12.1

20 132

119-138 5.7 6.1

17 143

134-160 7.3 6.7

14 150

131-164 9.6 4.2

10 156

144-165 12.9 3.6

165

The uniformity in the growth rates of bullfrogs from various habitats in Missouri, including frogs from new impoundments at the Schell-Osage and Reed Wildlife Areas, is remarkable. Growth rates of bullfrogs from the five collecting sites were compared after computing for each age group a percentage of the total growth. The largest frog of each site was considered the largest frog of the population (Table 2). There was no evi- dence that transformed bullfrogs exhibit increased growth in fertile new impoundments as do most fishes. Unlike tadpoles and

Reed Schell-Osage Wildlife Wildlife

Area Area

3 74 105 102

87-116 80-121 - 10.6

58.0 58.0

21 124

111-135 6.6

10.5

16 136

127-145 6.8 6.6

10 148

139-162 7.0 6.6

5 155

143-168 108 3.9

5 164

153-181 10.3 50

181

Big Piney River

33 104

88-119 8.7

60.4

Meramec River

42 104

85-119 8.2

73.2

2 3 10 129 123 121

125-133 121-124 113-131 - - 2.3

15.3 11.1 12.0

1 4 5 130 135 131 130 134-135 126-139

- 1.0 4.7 .5 7.0 7.0

5 11 2 147 149 138

136-155 136-155 133-142 6.3 5.6 - 9.7 8.1 4.9

2 5 -

150 152 - 149-151 140-161 -

- 8.8 - 1.7 1.7 -

2 4 - 175 170 -

173-176 169-172 - - 1.4 -

14.2 10.5 -

176 172 142

fishes, transformed bullfrogs forage beyond the confines of a pond. They eat many foods from terrestrial and aquatic habitats (see Korschgen and Moyle, 1955; Korschgen and Baskett, 1963). That patterns of feeding are similar for bullfrogs in Missouri impoundments, rivers, and farm ponds (Korschgen and Baskett, 1963) may explain the uniformity of growth rates in bullfrogs from different habitats.

Body length values of females were tallied separately from males, but no differential growth by sex was detected. The results of

588




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Age after Transformation (Years) Fig. 3. Relationship between lens weight and age of 158 bullfrogs.

Moyle (1952) and Durham and Bennett (1963) were similar. In our study the largest females were 165, 172, and 181 mm long. The largest males were 164 and 170 mm long.

Data obtained in this study represent maximum growth for all age groups, because most frogs were captured late in the growing season. Frogs assigned to age group 1 had grown in parts of two seasons: (i) in the season of transformation, until first hibernation, and (ii) in the growth season following first hibernation, until captured. Other investigators (George, 1940; Raney and Ingram, 1941; Ryan, 1953; Durham and Bennett, 1963) reported bullfrog growth rates based on the mark-recapture method; they

could correlate growth more precisely with the frog's postmetamorphic age.

However, our results are directly compar- able with those of earlier studies (Table 3) when lengths of our frogs of age group 1 are compared with those said to be in the first full season after transformation, those of our age group 2 with those in the second full season after transformation, etc. When com- parisons are made in this fashion, the growth rates for Missouri bullfrogs appear to be similar to those of New York frogs, but not to those of Louisiana frogs. The greater growth rate in Louisiana is probably related to temperature and length of growing season (Turner, 1960b).

The overlap of body lengths among age

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COPEIA, 1968, NO. 3

TABLE 3. MEAN BODY LENGTH OF BULLFROGS IN MM IN RELATION TO AGE AFTER TRANSFORMATION.

Length During 1st Winter Full Seasons after Transformation

after Trans- formation 1 2 3 4 5 6

Ryan, 1953 (N. Y.) 62 107 George, 19401 (La.) 69 129 154 Durham and Bennett, 1963 (Ill.) 35 101 132 137 144 This study (Mo.) 103 124 133 145 152 162

1 Mean lengths based on Turner's (1960b) computations from original source.

groups eliminates length frequency distributions as a means of determining age. The failure of body length frequency distributions to show distinct age groups may be due to the long season of transformation of tadpoles and the slowing of growth after sexual maturity is attained. Moyle (1952) plotted the length frequencies of 288 bullfrogs and observed no definite size groups. However, Turner (1962) indicated that size frequency distributions of frogs and toads could be translated into age groups if the maximum individual size and growth rates for the first few age groups were known. For Missouri bullfrogs this method would be invalid because of the variability in growth of all age groups except the young of the year.

Population Structure

Sex ratios.-Males comprised 51.8% of 426 bullfrogs captured at five sites. The pooled ratio of all age groups did not differ significantly from 1:1. Table 4 summarizes the sex ratio by age groups (with age estimated by marks on the pterygoid). There was no in- dication of differential mortality by sex.

Two studies have shown sex ratios of North American ranids to be approximately 1:1. Martof (1956) reported that of 389 adult

TABLE 4. SEX RATIOS OF 426 BULLFROGS BY

AGE GROUPS.

Age % Group N Males

0 23 47.8 1 185 53.0 2 80 40.0 3 47 34.0 4 44 54.5 5 26 61.5 6 or older 21 52.4

Rana clamitans examined outside the breeding season, 56% were females. However, he thought that the sample was biased and suggested that if a larger area had been studied, the ratio might have been 1:1. Turner (1960a) reported that a 1:1 ratio was maintained in Rana pretiosa until the fifth year after transformation; then females appeared more numerous.

Age distribution.-The age distribution of 397 transformed frogs from five collecting sites is shown in Table 5. Recently transformed frogs of the year were not included in the calculations, because they were not collected consistently. Frogs estimated to be older than five years were assigned to age group 6.

Bullfrogs from the Ashland Area and from the Reed Wildlife Area ponds showed similar age distributions. Both sites had a moderate amount of frog hunting pressure, although night frog hunting was prohibited at the Reed Area. Percentages of frogs in older age groups were constant. However, the percentage of age group 1 in the Reed Area appeared disproportionately low. In 1963 and 1964, collecting in the Reed Area was confined to ponds constructed in the spring of 1963. Tadpoles were observed in these impoundments on the first collecting trip, but these did not transform until the following summer. Their small size in 1964 excluded them from collections. All age groups of postmetamorphic bullfrogs in the Reed Area had to migrate from surrounding ponds to become established in the new impoundments. The data indicate that frogs of all age groups (except age group 1) per- formed such movements.

At the Schell-Osage Area, the low water level in an impoundment favored the capture of small bullfrogs exposed on the mud- flats, and 86% of those captured were in age

590




TABLE 5. AGE DISTRIBUTIONS OF BULLFROGS CAPTURED AT FIVE DIFFERENT SITES IN MISSOURI.

Values are percentages.

Age Groups Capture Site

and Date N 1 2 3 4 5 6 and 6+

Ashland Wildlife Area, May-Aug. 1963, 1964 133 21.1 33.8 14.3 10.5 11.3 9.0 Reed Wildlife Area, July 1963, 1964 58 5.2 29.3 31.0 12.1 12.1 10.3 Schell-Osage Wildlife Area, Aug. 1964 87 86.2 2.3 4.6 2.3 2.3 2.3 Meramec R., Aug. 1964 59 71.2 15.2 10.2 1.7 1.7 -

Big Piney R., Aug. 1964 60 55.0 5.0 6.7 18.3 6.7 8.3

group 1. Larger frogs were more wary and avoided capture. Therefore, the numbers of large frogs in the sample were not representative of their true abundance.

Bullfrogs along the Meramec and Big Piney rivers were under heavy human ex- ploitation, and the low percentages of older frogs appeared to reflect this fact.

ACKNOWLEDGMENTS

We are especially indebted to Y. L. Willis, Missouri Department of Conservation, Schell City, for advice and aid and to H. Stanton Hudson and Paul E. Osborn, Ozark Fish- eries, Stoutland, Missouri, for assistance in obtaining materials. Daniel Hatch partici- pated in the field work, and Dr. A. Witt, Jr., Mrs. Margaret S. Dickinson, and Mrs. Jaclyn Schroeder kindly provided editorial aid. The study was supported in part by funds from the University of Missouri Research Council.

LITERATURE CITED

BANNIKOV, A. G. 1949. The biology of Ranodon sibiricus. Doklady Akad. Nauk SSSR 65(2): 237-240. (In Russian.)

. 1950. Age distribution of a population and its dynamics in Bombina bombina L. Ibid. 70(1):101-103. (In Russian.)

BLANCHARD, F. N. AND F. C. BLANCHARD. 1931. Size groups and their characteristics in the salamander Hemidactylium scutatum (Schlegel). Am. Nat. 65(697):149-164.

BRYUZGIN, V. L. 1939. A procedure for investi- gating age and growth in reptilia. C. R. (Dok- lady) Acad. Sci. USSR (N.S.) 23(4):403-405. (In Russian.)

CAGLE, F. R. 1956. An outline for the study of an amphibian life history. Tulane Stud. Zool. 4(3):79-110.

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Delta Marsh region of Lake Manitoba, Can- ada. Ecology 43(1):147-150.

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Delta Marsh region of Lake Manitoba, Can- ada. Ecology 43(1):147-150.

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(Rana catesbeiana Shaw) in Missouri. M.A. thesis, Univ. Missouri, Columbia, Mo.

COOPERATIVE WILDLIFE RESEARCH UNIT, UNI- VERSITY OF MISSOURI AND U. S. BUREAU OF

SPORT FISHERIES AND WILDLIFE, COLUMBIA, MISSOURI 65201. Present address: (E.E.S.) DEPARTMENT OF BIOLOGY, EASTERN KEN-

TUCKY UNIVERSITY, RICHMOND, KENTUCKY

40475.

(Rana catesbeiana Shaw) in Missouri. M.A. thesis, Univ. Missouri, Columbia, Mo.

COOPERATIVE WILDLIFE RESEARCH UNIT, UNI- VERSITY OF MISSOURI AND U. S. BUREAU OF

SPORT FISHERIES AND WILDLIFE, COLUMBIA, MISSOURI 65201. Present address: (E.E.S.) DEPARTMENT OF BIOLOGY, EASTERN KEN-

TUCKY UNIVERSITY, RICHMOND, KENTUCKY

40475.

Body Fluid Partitioning in Reptilia' THOMAS B. THORSON

The total body water and its apportionment among the major fluid compartments was studied in fifteen species or subspecies of reptiles, representing four orders and seven families. Five were freshwater forms, five marine, four terrestrial, and one brackish water. No parameter appeared to be related to size of animals employed. Hematocrit as well as specific gravity of both plasma and whole blood were lower in freshwater forms than in marine or terrestrial ones. Body water content of marine and terrestrial species was lower than that of freshwater forms. Extracellular fluid volume was higher in both marine and terrestrial than in freshwater forms, and this pattern was reflected in both sub-compartments, plasma and interstitial fluid, as well as in whole blood volume. Elevation of extracellular fluid volume was entirely at the expense of the intracellular compartment. The departure of marine and terrestrial forms from the pattern of freshwater species was in every case more pronounced in marine than in terrestrial reptiles. The body fluid apportionment of the brackish water diamondback terrapin resembled that of the marine species. How- ever, intracellular water was the lowest of any species studied, and extracellular volume was the highest. The latter was accounted for entirely by an elevated interstitial fluid volume.

Body Fluid Partitioning in Reptilia' THOMAS B. THORSON

The total body water and its apportionment among the major fluid compartments was studied in fifteen species or subspecies of reptiles, representing four orders and seven families. Five were freshwater forms, five marine, four terrestrial, and one brackish water. No parameter appeared to be related to size of animals employed. Hematocrit as well as specific gravity of both plasma and whole blood were lower in freshwater forms than in marine or terrestrial ones. Body water content of marine and terrestrial species was lower than that of freshwater forms. Extracellular fluid volume was higher in both marine and terrestrial than in freshwater forms, and this pattern was reflected in both sub-compartments, plasma and interstitial fluid, as well as in whole blood volume. Elevation of extracellular fluid volume was entirely at the expense of the intracellular compartment. The departure of marine and terrestrial forms from the pattern of freshwater species was in every case more pronounced in marine than in terrestrial reptiles. The body fluid apportionment of the brackish water diamondback terrapin resembled that of the marine species. How- ever, intracellular water was the lowest of any species studied, and extracellular volume was the highest. The latter was accounted for entirely by an elevated interstitial fluid volume.

INTRODUCTION

OSMOREGULATORY studies of vertebrates have largely concerned the chem-

ical anatomy of body fluids under various conditions involving changes in external medium or administration of drugs and excess salt or water loads. Basic as these studies are, they have usually ignored quantitative aspects of the body water, the medium in which all metabolic activities occur, and the apportionment of the total water among the various body fluid compartments.

Such studies as exist on vertebrate fluid partitioning have previously been restricted largely to humans and other mammals. Re- cently I have placed on record measurements

1 Studies from the Department of Zoology, University of Nebraska, No. 389.

INTRODUCTION

OSMOREGULATORY studies of vertebrates have largely concerned the chem-

ical anatomy of body fluids under various conditions involving changes in external medium or administration of drugs and excess salt or water loads. Basic as these studies are, they have usually ignored quantitative aspects of the body water, the medium in which all metabolic activities occur, and the apportionment of the total water among the various body fluid compartments.

Such studies as exist on vertebrate fluid partitioning have previously been restricted largely to humans and other mammals. Re- cently I have placed on record measurements

1 Studies from the Department of Zoology, University of Nebraska, No. 389.

of total body water and its partitioning for four classes of poikilothermous animals, Agnatha, Chondrichthyes, Osteichthyes, and Amphibia (Thorson, 1959, 1958 and 1962, 1961, 1964, respectively). The only major fluid fraction for which data on reptiles appear in the literature is blood volume. All references on reptilian blood volume known to me appear in Table 1. To my knowledge no attempt has previously been made to measure total body water in reptiles and to determine its apportionment among the major fluid compartments.


Reptiles representing four orders and eight families were used (Table 2). Animals were held in cages for at least three days before

of total body water and its partitioning for four classes of poikilothermous animals, Agnatha, Chondrichthyes, Osteichthyes, and Amphibia (Thorson, 1959, 1958 and 1962, 1961, 1964, respectively). The only major fluid fraction for which data on reptiles appear in the literature is blood volume. All references on reptilian blood volume known to me appear in Table 1. To my knowledge no attempt has previously been made to measure total body water in reptiles and to determine its apportionment among the major fluid compartments.


Reptiles representing four orders and eight families were used (Table 2). Animals were held in cages for at least three days before

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age estimation, growth rates, and population structure in missouri bullfrogs

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