Biological Journal u/the Lznnean Society (1989), 38: 369-388. With 4 figures
Developmental differences in visceral
morphology of megophryine pelobatid tadpoles
in relation to their body form and mode of life
EDWARDINE NODZENSKI, RICHARD J. WASSERSUG" AND
ROBERT F. INGER
Division of Amphibians and Reptiles, Field Museum of Natural History, Chicago,
60605, Illinois, 1J.S.A.
Received I 1 October 1988, accepted f o r publication 28 April 1989
Tadpoles face severe packing constraints on viscera within the pleuro-peritoneal cavity bccause of
their extremely short torsos--a feature they sharc with adult anurans-and the concomitant need
for relatively slender torsos for efficient locomo~ion.We examined the effects of differences in body
form and habits on the size, shape and development of viscera in three kinds of sympatric, streamassociated pelobatid tadpoles. Leptobrachium montanum larvae are generalized, wide, deep-bodicd
tadpoles. Larval Leptolalax gracilis arc very slender and live in thc crc-vices bctwecn rocks 011 the
bottom of riffles. Larval Megophvs nasuta are intcrmediate between the other two in body form, and
live with L. montanum in a variety of microhabitats but feed at the surface film.
I n all three specics, liver, gall bladder, arid kidneys begin development early and grow
isometrically throughout larval life. The gut and pancreas havc a growth spurt shortly after
hatching, then grow at a constant rate until near metamorphosis when both shrink drastically. 'Ihe
spleen grows at a slower rate than the body throughout the larval period. Lungs do not appcar in
I,. gracilis until the tadpole approaches metamorphosis, which accords with its benthic habits,
whereas they grow throughout the larval period in L. montanum and M . nasuta. I n M . nasuta, however,
the lungs are unusually wide anteriorly; this shifts buoyancy forward and facilitates the head-up
feeding posture characteristic of that species. Gonads appear early in L. montanum and I,. gmcilis, but
not until near metamorphosis in M . nasuta. We suggest that accelerated gonadal development in
tadpoles characterizes species that metamorphose close to their sizc at first reproduction.
Leptobrachhm montnnum, with the bulkiest body and most generalized habits, has relatively and
ahsolutely the largest gut, liver ( x of combined gut and liver volurne=24"4, of total volume), and
kidneys. Leptolalax gracilis, the most slender tadpole, has rclativcly the smallest combined gut and
liver volume ( x = 10% of total volume). Other premetamorphic difrerences among the species were
observed in gut coiling, liver, pancreas and kidney shape and Ieft/right asymmetry of urogenital
organs. The major interspccific differences we observed in the size, shape, and developmental
patterns of viscera in tadpoles are clearly related to intcrspccific diffcrcrices in torso shape,
microhabitat distrihutioii and mode of feeding.
KEY WORDS:-Tadpoles - viscera
ecology Anura Pelobatidae.
-
-
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functional morphology
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development
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packing constraints
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C O N T EN TS
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Introduction .
Materials and methods
General description
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370
37 1
373
*Present address: Department of Anatomy, Dalhousir IJnivrrsity, Halifax, Nova Scotia, B3H 4H7, Canada.
369
0024-4066/89/120369+ 20 $03.00/0
0 1989 Th e Lirinean Society of London
E. NODZENSKI E'T AL.
370
Results
. . . . . .
Alimentary tract .
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Biliary system.
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Pancreas .
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Spleen
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Urogenital system .
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Lungs
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Discussion.
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Growth patterns ol" viscera.
Interspecific differences
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Conclusion
Acknowledgements
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References
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Appmdix .
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387
I N I R O D U C I ION
The radiation of tadpoles into a variety of microhabitats and modes of life has
been accompanied by modifications of their ovoidal body form (Orton, 1953;
Mertens, 1960; Duellman & Trueb, 1986). Although these modifications affect
all portions of the body, there are inherent constraints on the kinds and amounts
of adjustments possible for the visceral mass. These constraints result from two
factors. First, the relative dimensions of the trunk region cannot increase greatly.
The need to retain a fusiform shape for aquatic locomotion sets a limit on how
wide the body can be relative to its length. The length of the trunk itself seems to
be constrained developmentally by the locomotor specialization of the postmetamorphic frog; that is, efficient saltatory locomotion in the adult requires a
relatively compact, inflexible trunk. Indeed, frogs and their pre-metamorphic
larvae share the shortest vertebral column in the vertebrate world.
Secondly, within the pleuro-peritoneal cavity proper the size of the visceral
organs relative to one another is limited physiologically by the need to maintain
coordinated vital functions and, mechanically, by the size of neighbouring
organs. The organ system that occupies most of the volume within the pleuroperitoneal cavity is the digestive system; most tadpoles are herbivorous and
require a large gut surface area. T h e sheer bulk of the alimentary tract restricts
possible adjustments in size and shape of other organs. As tadpoles have evolved
divergent shapes, they have faced packing problems with viscera. In this paper
we consider two questions: ( 1 ) How do related tadpoles differing in body form
differ in size and pattern of development of visceral organs? (2) How do those
differences relate to differences in microhabitat utilization and habits?
We have chosen to examine tadpoles of three Bornean species of pelobatid
frogs living in rain forests. These three, Megophrys nasuta (Schlegel), Leptobrachium
montunum Fischer, and Leptolalax graciliJ (Giinther), all belong to the subfamily
Megophryinae (Frost, 1985), although details of their phylogenetic relations are
not known. The three larvae often occur in the same small forest streams. Larval
Megophrys nasula and Leplohrachium montanum use a broad array of stream
microhabitats, such as riffles, open pools and side pools (Inger, Voris & Frogner,
1986), but M . nasuta feeds at the surface and L. montunum at the bottom (Inger,
1986). Lefitolalax gracilis is restricted to riffles and torrents (Inger et al., 1986), and
lives in the crevices between rocks on the bottom.
The tadpole of Leptohrachium monlanum diverges the least from a gencralized
ovoid form, having the widest and deepest body and shortest, deepest tail. It is a
VISCERAL ORGANIZAI'ION IN TADPOLES
371
Figurc 1. Thrcc vicws of the tadpolrs of 1,eptobrachium montanum (top), Mep$hr_ys nasula (middle) and
Leptolalaxgraci/i.c. (bottom). Dorsal view on lrft, lateral view on right. I n thr middle are cross scctions
through each at thc widest point of the plcuro-pcritonral ravity (peritoneal linings represented by
heavy linc; viscera removed). Th e figurcs have been reproduced at the same length to illustrate the
rrlative diflcrcnrcs in thc size of the body cavity. Notr how much larger is the body ravity of
L. montanum relative to that of either M . nasuta or Z., g r a d i s . Scale lines for each spccics=4.0 mm.
large, rotund tadpole (Fig. l ) , and clearly the bulkiest. Tadpoles of Leptolalax
gracilis are very slender-bodied, but have thick, though shallow, tails. The
tadpole of Megophrys nasuta is intermediate between the others in body girth,
though closer to L. montanum (Fig. 1). Like L. gracilis, M . naruta has a low, long
tail, which is not as thick as that of L. gracilis (Inger, 1985). The differences in
body form among the three larvae are evident in the ratio of cube root of total
volume, a linear measure of bulk, to head-body length. This ratio is largest in
L. montanum ( 1.04) and significantly different ( P <0.05) from those of L. gracilir
(0.71) and M . nasuta (0.60). T h e diets of Leptobrachiurn montanum and Leptolalax
gracilis consist mainly of relatively large tracheoid plant fragments and that of
Megophrys nasuta mainly of small algae (Inger, 1986).
MAI'EKIALS AND ME7 HODS
Length and volume measurements were made on intact animals. A cut was
made in the skin of the throat, down the midline of the abdomen as far as the
vent, and a second, transverse, cut made around the tail so that the skin and
musculature of the abdominal wall could be pulled forward, exposing the entire
visceral mass. At this point, the numbers of gut coils along both transverse and
rostral-caudal axes were counted using the centre of the visceral mass as the
origin and the position of the centre of the coil noted (Fig. 2). The position of the
switchback, which is where the path of the intestine reverses itself, was recorded
and the gut diameter was measured 90" back from the switchback on both thc
oral and ahoral sides. An estimate was made of the percentage of the surface of
the visceral mass occupied by the liver and pancreas. T h e alimentary tract was
372
E. NODZENSKI E T A L .
Figure 2. Veni.ral view of a Leptohrachium monlanum tadpole with skin and muscles of the body wall
rrmovrd. L = exposed portion of the right lobe of livrr; I'= tail tip of pancreas; S =switchback point
for gut coils. 'The two linrs crossing the grit coils (near the tip of' the pancrras in this specimen)
indicate places whcrc the diameter of thr gut was measurrd in rrlation to the position of thc
switctihack. The heavier of thr lines rquals thr more oral rnd of the alimentary tract. Scale
b a r = 10.0 mm.
cut at the anus, the gut tube was lifted up and the major mesenteric vessels were
clipped.
The hepatic veins were cut from the posterior caval vein just caudal to the
heart. T h e oesophagus and gastric vessels to the foregut and liver were severed.
At that point i he alimentary tract, liver and pancreas could be lifted out in one
piece. T h e liver and pancreas were dissected away from the gut tube and the
liver and pancreas separated from each other by a cut in the recess where the
pancreas adjoins the liver. The volume of the liver and alimentary tract were
taken. Smaller mesenteric vessels of the gut were cut so that the intestines could
be uncoiled and their length measured. Maximum length and width were
recorded for the liver. Lung length was measured in situ. The vessels to and from
the kidneys and the peritoneum along the edges of the kidneys wcre cut and the
kidneys lifted free of the dorsal abdominal wall along with gonadal tissue, fat
bodies and spleen. Maximum length, breadth and depth were measured on
kidneys and gonads, and the length and width of the spleen recorded. T h e
pancreas was too small in most tadpoles for us to measure its volume reliably and
only linear measurements were taken (maximum length, depth of head at level
of hepatic process and maximum width of head and tail).
VISCERAL ORGANIZAlION I N 1ADPOLES
373
Fat bodies in tadpoles are fairly uniform in thickness and vary mostly in area,
and in the number and length of finger-like projections. Consequently, to assess
the size of fat bodies, they were treated as two-dimensional structures. They were
dissected out, placed on slides and traced with a camera lucida. Their area was
then measured with an IBAS image analyzer.
Finally, the volume of the eviscerated animal was measured.
All linear measurements of the viscera, except for length of the gut, were made
using an ocular micrometer. Volumes of the intact and eviscerated animal and of
the gut were made by fluid displacement using three volumetric flasks of
precisely known volumes and a microburette. Volumes of liver, and of the coils of
gut, were measured by displacement of water in notched pipette tips using
Hamilton gas syringes graduated to 0.2 pl.
For each organ for which we had dimensional data, plots were made of raw
measurements against Gosner ( 1960) developmental stage. Within a single stage,
specimens were always ordered by head-body length. T o identify growth
patterns, raw measurements were divided by head-body length, total tadpole
volume or the cube root of total volume (depending on whether the
measurements were linear dimensions or volumes) and, again, plotted against
stage. If, on inspection, there was any suggestion of an ontogenetic trend in the
growth pattern, the derived character was regressed on stage and compared
either non-parametrically using a Spearman rank correlation or parametrically
within stage using standard linear regression.
Where no regression was observed, comparisons between species were made
with Mann-Whitney U tests. I n cases where allometric developmental trends
were observed, the regressions of characters against size were compared among
species with analyses of covariance (ANCOVA). These analyses were run on the
SAS System (SAS Institute Inc., Cary, North Carolina). Where appropriate,
Chi square, T- and Wilcoxon runs tests were also used.
Sample sizes are given in Tables 1 and 2. Differences between sample sizes for
measures of different organs reflect removal of specimens because of stage effects
(see Results) or simply missing data because of losses in dissection or preservation
artifacts.
GENERAL DESCRIPTION
With the skin of the tadpole pulled completely away from the ventral surface
of the body, only three abdominal organs are visible: the coiled intestine, the
liver and the pancreas. The gut takes up a t least 80% of the field of view. I n all
three species the alimentary tract is a tightly packed double spiral that fills most
of the pleuro-peritoneal cavity. The switchback always points in a counterclockwise direction in ventral view. Before metamorphosis, the foregut is
undeveloped and does not differ grossly from the oesophagus or small intestine.
Only the position of the pancreas and bile duct distinguish foregut from midgut
in these tadpoles (as in both Kana temporaria and Sufo bufo (Barrington, 1945)).
Similarly, only in larger tadpoles is the ampulla of the rectum expanded
compared to the small bowel before it; otherwise the relationship of the intestine
to the neighbouring organs, specifically its proximity to the spleen, is the only
macroscopic indicator of the boundary between the midgut and the hindgut.
T h e liver has three lobes, the right and left of which extend over the right
374
E. NODZENSKI Ei' A L
rostral portion of the coiled gut. The pancreas is usually visible for its whole
length, with its head, the expanded portion closest to the liver, lying tightly
nestled within a curve of the intestine that by definition forms the duodenum.
The attenuate tail of thc pancreas lies over the gut coils along the right side of
the animal. There is variation among species in the shape of the pancreas and
the position of its large hepatic process, but not in the general placement of the
organ or the degree of visibility (e.g. the tail of the pancreas is never tucked
under the gut coils). The gall bladder, which appears as a large, distended,
transparent sac, lies medially between thc right lobe and the caudal lobe of the
liver. In our preserved tadpoles it was distended by a clear fluid.
All three species develop lungs before metamorphosis. T h e lungs are thinwalled sacs arising directly from short bronchi and lie dorsal or dorsolateral to
the liver and gut coils. Lung shape, Gosner stage at first appearance, and rate of
development differ greatly among species.
All the other viscera lie along the dorsal abdominal wall, either immediately
ventral or lateral to the dorsal aorta. Starting at the extreme caudal end and
working forward we find the paired metanephric kidncys, developing gonads, if
any are present, fat bodies, and the spleen. The kidneys are broad and thick at
the caudal end and taper rostrally. They may extend 1/4 to 1/3 of the length of
the pleuro-peritoneal cavity. There are species differences in the shape of the
kidneys, but kidneys were present in all species at all stages we examined.
Gonadal tissue begins as a narrow strip that may or may not bc scparatcd
from the kidneys. It grows laterally from the midline, developing frills and folds,
but does not differentiate into grossly distinguishable ovaries or testes until
metamorphosis.
Fat bodies develop rostral to the gonads, with two large ones having long and
short finger-like projections being most common, although a third smaller one
may appear centrally. The orientation of the fat bodies is primarily rostralcaudal, although their fingers may intertwine among other organs.
The spleen lies embedded in the dorsal mesentery of the gut rostral to the
gonads and dorsal to the intestinal coils. I t first appears as a sphere. As the
tadpole develops, the spleen becomes more elongate, with the largest tadpoles
having the most elongate spleen.
KESUL'I
s
Alimenlary tract
As has long been known, gut length in anuran larvae decreases drastically
with metamorphosis (e.g. Hourdry & Beaumont, 1985). In addition we observed
that the amount of the intestinal mass compared to the overall mass of the
tadpoles changes markedly during early and late larval development. It
increases shortly after hatching to plateau through most of the larval period then
abruptly decreases with metamorphosis.
When the developmentally youngest and oldest larvae (stages < 26, > 39) are
excluded from comparison, the species difier in a variety of intestinal features
(Table 1 ) . Leplobrachium montanum has the largest gut overall, amounting to a n
average of 22.37(" of total volume, almost twice that of M . nasuta and 2.4 times
that of L. gracilis. In non-parametric pairwise comparisons, L. monlanum differs at
VISCERAL ORGANIZATION IN TADPOLOS
375
P<0.005 from both I,. gracilis or M . nasuta, which do not differ from each other
(P=O. 123). Analysis of covariance for intestinal volume against total volume
reveals homogeneity of slopes (P=O.91), but a significant species effect when
total volume is controlled (P<O.OOl). Once again, the singular cause of the
difference is the large intestinal mass of L. montanum.
The type of preservation (ethanol us. formalin) alters gut dimensions relative
to tadpole body size in ways that may not be the same for all species or sizes of
tadpole. With that cautionary note, we report species differences in both mean
gut diameter and gut length. The absolute diameter of the intestine of
L. montanum is approximately twice that of L. gracilis, and three times that of
M.nasula. Differences between L. montnnurn and each of the other two are
statistically significant ( P < 0.01); M . nasuta and L. gracilis, however, do not differ
( P > 0.15). The same relationships hold when relative gut diameter (i.e. diameter
divided by cube root of volume) is analysed. Similarly, the average gut length of
L. monlanum is 7 1yo larger than that of L. gracilis, which is itself 28% longer than
that of M . nasuta. Regression of gut length on cube root of volume for the three
species revealed no differences in slope ( P = 0.32) but a highly significant
ANCOVA (P<O.O001) with L. montanum separating from the other two species.
These size differences are reflected in the coiling pattern proper. T h e species
with the narrowest intestine, M . nasutn, has the most coils in the superficial layer
of the gut (Table I ) , but did not differ from L. gracilis (P=0.22). Both, however,
differed from L. montanum, (P<O.OOl). T h e actual arrangement of the coils
differs among the species and this is reflected in several features. For all of the
species, transverse counts of superficial intestinal coils were higher by one to
three coils than rostral-caudal counts. However, only in M . nasula is the
discrepancy between the two counts great enough (i.e. % =2.3 coils) to be
statistically significant (P<0.002). I n all of these species, the intestine is in a
double spiral, with a superficial ventral and a deeper dorsal layer, but in
M , nasula, some of the coils of the deeper spiral are visible in the ventral view.
Megophps nasula apparently has a shorter dorsal mesentery and, therefore, a
more constrained gut. For example, the switchback always lies directly over the
centre of the gut coils, on the midline, a layer below the superficial layer of coils.
In the other species the mesentery is longer and the switchback can be displaced
from the centre of the spiral by up to seven coils (in L.gracilis) (Table 1 ) .
Leptobrachium monlanum and L. gracilis differ significantly ( P < 0.01) in this feature.
TABLE
1. Features of thc alimentary tract in tadpoles of Leptobrachiurn montanum, Leptolalax gracilis,
and Meguphrys nasuta. Data in form of mean
standard error with sarnplc sizes in parenthescs
Species
Leplolalax
gracilis
Mepphrys
moiltanurn
0.223f0.017 (20)
1.09k0.12 (20)
268k17.5 (16)
11.5k0.2 (15)
3.2k0.2 (23)
0.091f0.014 (9)
0.55k0.10 (9)
157f31.4 (9)
13.3+_0.5(9)
4.0k0.4 (10)
0.123&0.013 (14)
0.38f0.03 (14)
123+ 10.5 (13)
13.9k0.5 (14)
0.0+0.0 (14)
Leptobrachium
Feature
Relative volumc of gut”
Gut diameter (mm)
Gut length (mm)
Number of gut roils”
Displacement of switchback‘
“Volume of gut divided by total volume.
bCoilsin superficial layer of gut counted along rostrdl-caudal axis.
‘Displacement of switchback from centrc of coils couritcd in number of coils.
na.cula
376
E. NOUZENSKI E 7 A L .
Intercstingly, the switchback tends to lie caudal to the transverse plane through
the centre of the gut coils in both species (six out of eight times in L. gracilis and
13 out of 17 times in L. montanum:
test; 0.05 < P<O.I) and is more than twice
as common in the lower right quadrant ofthe abdomen than would be expected
on chance alone.
x2
Biliary system
Variation in livcr size is great at any stage within a single species and,
consequently, we could identify no significant correlations between various
measures of liver size relative to body size when plotted against stage for the
individual species. However, for the species with the largest sample size,
L. montanum, the liver volume grows in pace with the rest of the tadpole u p to and
through metamorphosis (correlation of liver volume with total volume: r = 0.92,
P < O . O O O l , n = 18).
It is not suprising that L.montanum has a liver volume that is larger absolutely
than either that of L. gracilis or M . nasuta, or that the livers of the latter two
species do not differ significantly in size, given the overall size differences of the
species (Table 2). Less obvious are relative size and shape differences among the
species once overall size is factored out. Comparisons of regression of liver
volume against total volume (both converted to natural logs) reveal no
differenccs in slopes ( P = 0.84). There is, however, a significant ANCOVA
(P<O.OOl) with L.graci1i.r having a smaller liver relative to body size than either
I,. montanum or M . nasuta, which did not separate from each other in this analysis.
In contrast, pairwise comparisons of a single dimension of the liver, namely,
maximum liver length, divided by the head-body length separated all the species
from each other at P=O.O1 or highcr level. Megophrys nasuta has an extremely
attenuate liver compared to the other species; in this species the liver averages a
third of the head-body length (Table2) and extends most the length of the
pleuro-peritoneal cavity. Although the average A4.nasuta liver is a sixth of the
volume of a L. montanum's liver, it is only about 20% shorter. The liver of larval
'I'ABLE2. Features of t h e biliary system and pancreas i n tadpoles of I,eptobrachium montanum,
Leptvlalax gracilis, a n d Megophrys nasuta. Data in form of m e a n f s t a n d a r d e r r o r with s a m p l e size i n
parentheses
Species
Fcaturc
Liver volumr (plj
Rclative liver volume"
Liver length ( m m )
Relative liver lenqthb
Gall bladder (mm)
Relative diameter of gall bladder'
Pancreas length (mm)
Relative pancreas length'
Leptobrachium
m on tan um
Leptvlalax
gracilis
Megophy
nasuta
21.4+4.30 (23)
0.013+0.002 (12)
4.54k0.41 (21)
0.234+0.010 (21)
2.02k0.21 ( 2 3 )
0.104f0.006 (23)
8.20k0.80 (18)
0.420k0.022 (18)
2.50rf-0.88 (10)
0.006f0.001 (10)
2.42k0.26 (10)
0.184+0.013 (10)
1.24+0.07 (10)
0.092f0.008 (10)
5.85k0.91 (9)
0.454k0.056 (9)
3.42k0.87 (13)
0.012+0.002 (13)
3.63k0.21 (14)
0.334+0.010 (14)
1.72k0.10 (11)
0.163+0.00 ( 1 1 )
4.75k0.41 (14)
0.435 k0.027 (14)
"Liver volume dividcd by total volumr.
"Livcr lrngth divided by hcad-body length.
'Gall bladder diamrter divided by head-body length
'Pancreas lengi h divided by head-body length.
377
1
Heod-body length (rnrn)
Figure 3 . Plot of liver length us. head-body lcngth of tadpoles of Leplululax grucilis, 1,eptobmchium
montanum and Mesophrys nasuta. All regression lines differ significantly. I n contrast, M. namtu arid
L. montanum do not differ in terms of relative liver volume (see tcxt and Table 5). 'l'hus thc plot
reflects differences in shape as opposed to differenccs in volumc.
L. gracilis is, by comparison, both smaller in volume and more compact in shape
than livers of the other two species. These differences in relative liver length are
documented in Table 2 and Fig. 3. The elongated liver of M . nasuta is in close
relation to loops of the narrow intestine; the loops of intestine cause a scalloping
of caudal surfaces on the preserved livers not observed in L. montanum or
L.gracilir. Besides differences in size and shape, the species also differ in liver
colour. For example, the liver appears to darken with flecks of melanin pigment
developmentally earlier in L. gracilis than in the other species.
Since the liver and alimentary tract function in concert to process digested
nutrients, we would expect the species with the largest liver also to have the
largest intestinal mass, both absolutely and relative to body size. Leptobrachium
montanum meets that expectation. Leptolalax gracilis has both the smallest liver and
smallest intestinal volume relative to body size, again consistent with our
expectation. The combined liver plus intestinal volume of L. montanum ranges as
high as 34% of total volume, whereas the combined volume never exceeds 16%
in L. gracilis. Leptobrachium montanum differs significantly from both L. gracilis and
M . nasuta in this proportion in separate pairwise comparisons ( P t 0 . 0 0 0 5 ) .
Megophrys nasuta falls between the two (maximum= 25%), differing from
L.gracilis at the P=0.07 level.
Gall bladders in these megophryine tadpoles are extremely large, spherical
sacs. We found no ontogenetic trends in the diameter of the gall bladder
compared to head-body length in any of the three species. In absolute size,
L. montanum has the largest gall bladder and L. gracilis the smallest (Table 2).
However, relative to the head-body length, M . nasuta has a gigantic gall bladder,
one comparable in volume to a quarter of the liver itself. T h e mean ratio of gall
bladder diameter to head-body length of M . nasuta differs from that of both
L.gracilis and L. montanum at P<O.001. Relative to body size, the gall bladder is
378
E. NODZENSKI E‘T A L
smallest in L,y~acilis,but not so small that it differs significantly from that of
L. montanum ( P > 0 . 2 ) .
Pancreas
After a growth spurt in small stage 25 tadpoles, pancreas length (absolute and
relative to head-body length or to cube root of volume) shows no allometric
trend until just prior to metamorphosis (stage 39-40). The pancreas has been
reported to shrink greatly during metamorphosis in other anurans (Gillois 8r
Beaumont, 1964; Frieden &Just, 1970), so our observations simply confirm this
for pelohatitis. Metamorphic individuals ( > stage 39) were excluded from
further analyses involving the pancreas.
Slopes for pancreas length plotted against cube root of volume arc
homogeneous among species ( P = 0.96) but an ANCOVA is significant
(P<0.0001) indicating a species effect when size is factored out of the
relationship. Leptobrachium monlanum has a significantly larger pancreas
( P = 0.039) than M . nasula, but I,. gracilis, with a intermediate-size pancreas,
differs from neither of thc other species ( P > 0 . 2 9 ) . However, when pancreas
length is examined as either a proportion of head-body length (Table 2) or cube
root of volume, differences between pairs of species fail to reach statistically
significant levels ( P > 0.1). Thus thc amount of pancreas, measured indirectly as
its length, seems to be a relatively fixed proportion ofthe size of the tadpole. This
proportion seems little affected by species differences in the relative proportion of
other abdominal viscera, such as liver or intestines.
Gross shape of the pancreas clearly differs among the three species. I n
L. m o n h u m the larval pancreas is shaped like an apostrophe with the head
( =hepatic process) slightly offsct from the curved body-tail. In L. gracilis the
pancreas is thinner with a proportionally smaller head, which tapers into the
body-tail. Megophrys nasula has the most attenuate pancreas, which follows the
curve of the gut loops caudally along the intestinal coils and curves toward the
vent. Also, the head of the pancreas is not at the anterior tip of the organ as it is
in the other species, but is about one-third of the way down from the anterior tip.
In both L. gracilis arid M . nasuta the deep surface of preserved pancreatic tails
retains the scalloped impressions of ad.jacent intestinal coils. This sculpturing is
particularly deep and conspicuous in M . nasuta where the pancreas travels across
many coils.
Spleen
‘The spleen grows as the tadpole grows; correlation of average linear dimension
of spleen against cube root of volume lor L. monlanum is significant (r, = 0.80,
n = 14, P<0.01). However, it does not grow nearly as fast as the body so that the
average dimension of the spleen decreases relative to body si,x as tadpoles get
larger (for I-. montanum r = -0.51, P<0.05).
In absolute size, L. montanum has a significantly larger splccn (P<O.Ol) than
either of the olhcr two species, which do not differ (Table 3). Relative to headbody length, however, I,. gracilzs has a disproportionately small spleen, comIiared
to that of L.montanum (P<0.02) or M.nasula ( P < 0 . 0 5 ) . In this f’eature,
L. monlanum and M . rial-ula do not differ ( P > O . l ) .
VISCERAL ORGANIZATION I N TADPOLES
379
The species differ slightly in width: length ratios for their spleens. O n average
the diameter of the spleen is 40.7% of its length in L. montanum, 55.6% in
L. gracilis and 62.3% in A4.nasuta. These differences, however, reflect little more
than the fact that smaller spleens are rounder regardless of species. L. montanum
appears to have a more attenuate spleen simply because it has a larger spleen.
Urogenital system
As in the case of the pancreas, we were able to make only linear measurements
of the kidneys. Relative kidney size (Table 3 ) , measured as the average of
length x width x depth of the two kidneys divided by total tadpole volume,
shows no clear relationship to either size or developmental stage. Within stage
25, in which these animals achieve a large part of their larval growth, there is no
significant correlation between relative kidney size and total volume
(L. rnontanum: n=9, r,=0.42, P>0.05;Lgracilis: n = 5 , r,= -0.55, P>0.05; too
few M . nasuta to warrant calculation). For all stages, no significant correlation of
relative kidney size to total volume is shown by L. montanum ( n = 18, r,=0.13,
P> 0.05) or L. gracilis (n = 9, r, = -0.43, P> 0.05). I n contrast, A4.nasuta has a
statistically significant negative correlation ( t i = 13, rs= -0.80, P<O.Ol), which
we frankly suspect is spurious.
In all three species there is a consistent left/right asymmetry in the size of the
kidneys with the right one, on average, 35% to 76% larger than the left. In only
four individuals, two I,. montanum and two L. gracilis, was the left kidney equal to
or larger than the right. The asymmetry is accounted for more by differences in
widths than in lengths of kidneys in I,. montanum and hl.nasuta. A Wilcoxon test
shows that the percentage difference in widths is greater than percentage
TABLE
3. Size of thc spleen, fat bodies, and urogenital organs in tadpoles of Leptobrachium moritanum,
Leptolalax gracilis, and Megofihrys nasula. Data in form of mean & standard error with sample size in
parcntheses
Species
Feature
Avrragr spleen dimension (mm)"
Relative splren sizcb
Fat body sizc (mm')'
Relative tat body sizrd
Kidnry volume (PI)'
Relativr kidncy volume'
Kidnry width/length
Gonad size (mm)g
Relative gonad sizeh
Leptohmclzium
montanum
Leptolalax
gracilis
MegophryJ
0.90f0.08 (15)
0.47 f0.06 (8)
0.033k0.004 ( 8 )
2.08k0.44 (5)
0.121 k0.003 (5)
1 . 6 i 0 . 4 (9)
0.0040 i0.0005 (9)
0.528k0.029 (9)
1.32f0.26 (5)
1.62 k 0.25 (5)
0.49k0.03 (12)
0.045 0.003 (1 2)
1.38k0.17 ( 7 )
0.126k0.014 ( 7 )
1.2f0.1 ( 1 2 )
0.0047+_0.0007(12)
0.287 k 0.038 (1 3 )
0.0 (14)
0.0 (14)
0.050k0.004
(15)
2.74k0.31 (12)
0.117k0.009 (12)
12.7+2.0 (18)
0.0073~0.0006(18)
0.397k0.038 (18)
2.87f0.18 (9)
2.19k0.08 (9)
"Length plus width divided by 2.
"Average spleen dimension dividrd hy hcad-body length.
'Square root of arcas of fat bodies.
'Fat body size divided by head-body length.
'Lrngth x width x depth of right plus left kidneys divided by 2.
'Kidney volume (as dcfined in previous footnote) divided by total volumc
"Length plus width of right plus left gonads divided by 4.
"Gonad sizr divided by cube root of volumr.
nasuta
+
380
E NODZENSKI E T AZ,.
difference in lengths in both these species ( P< 0 . 0 2 ) , but not in Lgracilis
( P >0.10).
Leptobrachium montanum predictably has the largest absolute kidney size
(Table 3 ) , differing from the others significantly (P<0.02). It also has the largest
relative kidney size ( P < 0.02). Leptolalax gracilis and M . nasuta do not differ from
one another. Kidney shape also varies among these species. Leptolalax gracilis has
the widest kidney and M . naJuta the narrowest (Table 3 ) . Differences between
pairs of species in kidney width : length ratio are statistically significant
( P < 0.02).
A small consolidated mass of connective tissue, the anlage of the urinary
bladder, can be seen immediately anterior to the terminal portion of the bowel in
some of the larger, more mature tadpoles, but we did not observe a bladder with
an open lumen in any of these pelobatid larvae until near the end of
metamorphosis. This observation is consistent with results from Powell & Just
( 1987) showing that the bladder does not become endocrinologically functional
in anurans until metamorphosis.
Although reproductive organs do not function in tadpoles and one might
suppose that their development could and would be delayed until
metamorphosis, two of the three species that we examined show substantial
gonadal growth during the tadpole period. T h e exception is M . nasuta where
distinct gonads are not discernible until metamorphosis (stage 4 2 ) . T h e smallest
three to five stage 25 L. gracilis and L. montanum also lack gonads, but
development in both species accelerates within that stage. From stage 26 to
initiation of metamorphosis gonadal development relative to either head-body
length or the cube root of volume remains approximately constant in
L. montanum. The growth pattern through these same stages is less clcar in
L. gracilis because of greater variation and smaller sample size. After the initial
growth spurt during stage 25, Leptobrachium montanum has absolutely and
relatively larger gonads than L. gracilis (Table 3 ) ; the difference between these
two species in relative gonad size is statistically significant a t P < 0.02.
In both L. gracilis and L.montanum the left gonad is larger than the right in all
but one individual. I n the latter species the average dimension of the left gonad
is about 1.8 times that of the right. Testes were not seen in any of the tadpoles
examined until metamorphosis. Since no histology was attempted, it is not
evident whether the organs present are true ovaries or ‘progonads’ (Swingle,
1926), which will later degenerate and be replaced by testes.
For all species fat bodies first appear in middle to late stage 25 and then grow
rapidly within that stage. We did not, however, find a clear correlation of fat
body size with tadpole stage in the limited sample that we had after stage 25.
Species differences were more obvious, but only in terms of the absolute size of
the fat bodies, (Table 3 ) . Not surprisingly, Leptobrachium montanum has the largest
fat bodies throughout its larval period; they are almost exactly twice the size of
those of M . nasuta. Those of L. gracilis are, in turn, intermediate. All t-test
comparisons between species were not significant (P>0.54) when fat body size
was adjusted to either the length or volume of the tadpoles.
Lungs
Previous studies (e.g. Wassersug & Heyer, 1988) have reported gross,
interspecific variation in lung development among tadpoles that correlates with
VISCERAL ORGANIZATION IN TADPOLES
38 1
2018-
16 -
Lepto/a/ax gracilis
Leptobrachium montunum
+ Megophrys nosuta
14 -
I
E
12-
f
P
l0-
P
8-
-
-I
64-
3
Figure 4. Plot of lung length us. head-body length of tadpoles of Leptolalax gracilis, Leptobrachium
montanum arid Megophrys nasuta. Leptolulux larvae do not dcvelop inflated lungs until late in larval life.
T h e regression lines for L. montanum and M . nasuta differ significantly in ANCOVA (see text and
'lable 5).
microhabitat utilization. O u r observations fit expected patterns. Leptolalax
gracilis, with its obligate benthic larva, shows no lung development before stage
36, and even at stage 39 the lungs are very small and uninflated. Megophrys
nasuta, the surface feeding form, and L. montanum, the most generalized tadpole of
the three, have accelerated lung development in early stage 25, and the lungs
continue to grow throughout the larval period. In L.montanum, for which we
have the most data, lung growth is disproportionately great compared to body
growth throughout the whole larval period u p until metamorphosis. This growth
pattern is confirmed with both linear regression of lung length against head-body
length within stage 25 ( n = 9 , r=0.82, P=0.003) and across stages (n=24,
r=0.65, P<O.Ol). By the time L. montanum reaches maturity as a larva (c. stages
35-36), the lungs are approximately the length of the whole coelomic cavity.
Differences between species in size of lungs are shown in Fig. 4. T h e regression
lines for L.montanum and M . nasutu do not differ in slope (P=0.42) but do differ
in ANCOVA (P<O.OOl).
T h e lungs of M . nasuta never grow as long as and differ in shape and size from
those of L. montanum. In L. montanum the lungs typically bellow out from short
bronchi into cylindrical structures with either blunt or nipple-like ends. Left/
right asymmetry is common. Lung inflation is variable in preserved tadpoles, but
there is no doubt that the lungs were capable of inflation in all larger specimens.
In M . nasuta the lungs are widest rostrally and taper toward the tail. Thus, they
are triangular when uninflated and conical or pyramidal when inflated. Left/
right asymmetry is not uncommon, and where present, the left lung is usually
larger. Inflation was common. This lung morphology is consistent with the headup swimming posture of M . nasuta; an implication of the shorter and rostrally
wider lungs in this species is that the centre of buoyancy is shifted forward
compared to more typical cylindrical lungs, like those in L. montanum.
382
E. NODZENSKI E T AI,.
DISCUSSION
There are several ways to organize our observations on viscera. One is to
group viscera according to patterns of development common across species. This
obliges consideration of functional significancc of differences within and between
organ systems. A second way of viewing our data is to focus on differences
between specics in organ systems. ‘This leads to evaluating differences in terms of
general size and shape of the tadpoles and in terms of ecological constraints on
the separate species.
Growth pakerns of viscera
Growth palterns of major organs differ greatly in the larval stages. For certain
organs the growth pattern is probably the same for all species. For example, for
all three of the larval forms we examined, livers, gall bladders and kidneys begin
development very early and then grow at a constant rate throughout larval life
and probably beyond. The gut and pancreas have a growth spurt early in stage
25, then grow at a constant rate until stage 39-40 (for pancreas) or stage 42 (for
gut), when both organs shrink markedly. These patterns for pancreas, liver and
alimentary tract are consistent with what has been reported before for other
species (reviewed in Frieden & Just, 1970; Hourdry & Beaumont, 1985). T h e
spleen grows at a slower ratc than the body, becoming progressively smaller
relative to the body size as the tadpole develops.
Developmental patterns of lungs and gonads, in contrast, are not the same
across all three species. In I,. montanunz and M . nasuta, although lungs appear
early in stage 25 and grow throughout the larval stages, they develop at different
rates. Specifically, the lungs grow faster than the body in L. montanum. I n
L. gracilis, however, lungs do not appear until stage 36.
Gonads, on the other hand, begin to develop early in L.graci1i.r and
L. montanum, growing at a constant rate from the middle of stage 25. They do not,
however, appear until near metamorphosis in M . nasuta. The pattern of gonadal
development in larval and metamorphic anurans is highly variable, including:
( 1 ) early larbal differentiation of testes and ovaries (e.g. in some Rana cateJbeiana
(Swingle, 1926)); ( 2 ) differentiation of testes from larval ovaries at or after
metamorphosis (e.g., in some Rana pipiens, (Christensen, 1930)); (3)
differentiation of testes and ovaries from “progonads” or “intersexual” gonads
(e.g. in Rana pipiens (Christensen, 1930) and R. rugosa (Takahashi, 1971)). T h e
pelobatids appear to fit the second or third pattern.
These differences between organs in growth patterns can be understood in
three ways. First, isometry of liver, gall bladder, and kidney presumably relates
to a constant functional demand placed on these organs that is directly
proportional to the animal’s mass and independent of its gross body form or
microhabitat ecology. Secondly, abrupt changes in function at critical points in
development account for the growth patterns of gut and pancreas. Although the
gut processes food throughout life, the change after hatching from use of yolk to
a diet of plant material and protists requires a much longer alimentary tract.
The change at metamorphosis from microphagous herbivory to macrophagous
carnivory underlies the dramatic shortening of the intestine and differentiation
of the stomach (Hourdry & Beaumont, 1985). T h e pancreas, too, has long been
383
VISCERAL O R G A N I Z A TI O N I N TADPOLES
known to change function at metamorphosis (Frieden & Just, 1970). Thirdly,
the delayed development of lungs in benthic L. gracilis and gonads in M . nasuta
can be explained on the basis of lack of function in the larvae.
Finally, the negative allometry of the spleen remains a puzzle. T h e spleen is
considered the major erythropoietic organ in adult anurans (Duellman & Trueb,
1986). However, it can share these functions with bone marrow in adults and
with the liver in transforming tadpoles and froglets. It may be that the
coordinated maturation of splenic tissue in relationship to other haemopoietic
sites may allow the spleen to increase in functional significance at the same time
it decreases in relative size. Without a clearer understanding, though, of possible
physiological roles of the premetamorphic spleen, this is merely speculative.
Interspecijic dzferences
Interspecific variation in visceral organ shape and size is summarized in
Tables 4 and 5. Interpretation of these differences requires consideration of the
constraints imposed by the general form of each tadpole and the ecological
demands of the microhabit it inhabits.
Given the greater size of L. montanum, it is not surprising that it has the
absolutely largest gut (volume, diameter and length), liver (volume and length),
gall bladder, spleen, fat bodies, kidney and gonads and the longest pancreas.
However, sheer bulk of the animal does not explain interspecific differences in
relative organ size or differences in organ shapes. Some of these differences seem
to be related to problems of packing organs in a limited space. Bear in mind the
differences in body shape of the three larval types: L. montanum has a wide and
deep body; L. gracilis has a slender body, and M . nasuta is intermediate between
the two. Packing constraints are more likely to be severe in L.gracilis and
M . nasuta than in I,. montanum. As L. montanum has a very generalized, robust body
form, its viscera are evidently least limited by space constraints.
TABLE4. S u m m a r y of interspecific differences in s h a p e of visceral o r g a n s in ta d p o lc s of
Leptobrachium rnontanum ( = m), Leptolalax gracilis ( = g), and Megobhrys nasuta ( = n)
Feature
Gut coils:
No. of coils along rostrocaudal axis
No. of coils rostrocaudal us. transverse
Switchback
Liver length"
Pancreas shape
Spleen: width/length
Lungs
Kidneys: width/length
Specific relationships
n%g>m
n: significant difference
n: central, not superficial
g & m: superficial, not central
n>m>g
n: shaped like apostrophe
g: smaller head
n: most attenuate, head position
different
n>g>m
m: cylindrical
n: triangular
g>m>n
"Relative to head-body length as an index of attenuation
Statistically
significant
at P<0.05
n>m,g>m
n > m, n > g, m > g
No significant
differences
g > m, g > n, m > n
E. NODZENSKI E T AL.
384
TABLE
5. Summary of interspecific differences in size of visceral organs in
tadpoles of. Leptobrachiurn montanum ( = m), Leptolalax gracilis ( = g ) and
Megophrys nasuta ( = n)
Interspecific
relationships"
Feature
Gut volume
Gut diameter
Gut length
Liver volume
+
Gut
liver volumes
Liver length
Gall bladder diameter
Pancreas length
Spleen size"
Lung length
Kidney size"
Fat body sizeb
m >n
m >g
m >g
m >g
Statistically
significant a t P < 0.05
> g (relative)
m>n, m > g
> n (absolute)
> n (relative)
m>n, m > g
> n (absolute)
m > n > g (absolute)
m =n >g
m >n >g
m >n >g
n >m >g
m >n >g
n >m >g
m >g >n
g>n >m
m >n >g
m >n >g
m >g >n
m >n >g
m >g>n
n >g >m
(relative)
(relative)
(absolute)
(relative)
(absolute)
(relative)
(absolute)
(relative)
(absolute)
(relative)
(absolute)
(relative)
(absolute)
(relative)
m>n, m > g
m>n, m>g
m>n, m > g
m>g, n > g
m>n, m > g
m>g, n > g
n>m, n>g, m > g
mzg, n>g
n>m,n>g
m>n
m>n,m>g
n>g, m z g , m > n
m>g, m > n
m>n, m>g
m>n
~~
"'Relative' equals absolute values divided by total volume or head-body length (see
trxt).
'Ah defined in 'l'able 3.
It is consistent with these ideas that the relative, as well as absolute, size of gut,
liver and kidneys is greatest in L. montanum. At the other extreme of body form in
this series, L. gracilis has the smallest combined gut and liver volume, the shortest
liver length, and the smallest spleen, all measured on a relative scale. It also lacks
lungs until stage 36.
Differences among these three species in relative gut and liver volumes
(Table 5) can be related to the general body form, which in turn has significance
for ecological distribution. As noted in the introduction, M . nasuta and
L. montanum occur in the same array of microhabitat types, though the former is
more directly exposed to current, while it feeds at the surface film. In contrast,
L. gracilis lives only in crevices between rocks on the bottoms of riffles. Combined
gut and liver volumes place M . nasuta with L. gracilis and separate both from
L. montanum (combined mean organ volumes equal 13.5, 9.7 and 23.6% of total
body volume in each species, respectively). However, these differences are not
evidently related to diet. Leptobrachium montanum and Leptolalax gracilis have very
similar diets and both differ greatly in this regard from Megofhrys nasula (Inger,
1986). Moreover, the first two, being identical in terms of size and shape of beaks
and denticles and radically different from M . nasula in these respects (Inger,
1985), certainly differ from M . nasuta in the manner of obtaining food.
Megophrys nasuta has a more narrowly specialized diet than either of the other
species. Of the three species, M . nasuta feeds on the smallest particles (floating on
the water's surface) and can compensate for a small intestinal volume by, having
a narrower gut. It does not need an alimentary tract with a large luminal
diameter, since it does not ingest large particles. However, in order to gain access
to its specialized diet, it requires inflatable lungs which place packing constraints
VISCERAL ORGANIZATION IN TADPOLES
385
on the other viscera in this species. The short, confining mesentery of the gut,
and the elongated liver and pancreas, which are sculptured by the gut coils,
testify to the tight packing in M . nasuta. T h e increased number of gut coils in
M . nasuta may also be attributed to packing constraints. Kemp (1954) found that
experimental reduction in the coelomic cavity in Rana pipien3 led to increased
coiling of the gut.
The comparatively small gut and liver of L. gracilis presumably are associated
with a cost in terms of longer digestion time or reduced digestive efficiency. Such
costs are ultimately reflected in reduced growth rates. Given such costs, the
crucial question is: are there any compensatory advantages? By having a smaller
overall abdominal volume compared to other megophryine tadpoles, I;. gracilis
can have both a smaller cross section and a proportionally slimmer, more flexible
torso. Both features characterize vertebrates designed for anguilliform/serpentine
motion in structurally complex environments (cf. Gans, 1975; Wassersug, 1989);
Leptolalax gracilis is a thin, sleek tadpole that can insinuate itself into cracks and
crevices. I n contrast, a L. montanum larva of the same total length or same overall
volume could not enter such small recesses simply because its larger abdominal
volume would obstruct passage.
For all the organ systems studied, we found the greatest variation in lung
development. Leptobrachium montanum occupies a wide variety of microhabitats
and feeds in a generalized way. Consequently, there are no obvious ecological or
morphological constraints on lung development as there are in the other species.
Leptobrachium montanum is the only one of these larval types that begins to develop
both lungs and gonads during stage 25. Its long, early-developing lungs
probably represent the primitive pattern in the family. Lungs also develop early
in M . nasuta, but do not appear in L. gracilis until stage 36 and remain very small
until near metamorphosis, For L. gracilis, early development of lungs would
create buoyancy problems for a n animal that spends its larval life under rocks on
the bottoms of riffles. Having inflated lungs would also require a larger total
body volume. Delayed lung development in this species consequently relates
both to the packing problem and to ecological demands. T h e short, triangular
lungs of M . nasuta almost certainly shift buoyancy forward and tip the snout
upward, which is the position of the animal during feeding.
The asymmetry of the lungs, which is most obvious in M . nasuta, is difficult to
explain. If the centre of mass for a live M . nasuta tadpole were on the midline,
then inflation of asymmetrical lungs would induce rolling and would be a clear
handicap in swimming. Other abdominal viscera in tadpoles, however, are not
symmetrical and organs, such as fat bodies and the liver, clearly differ greatly in
density. Given this situation, it is likely that the centre of mass is not on the
midline and the asymmetry of the lungs may help correct this imbalance.
T o the best of our knowledge the rather common asymmetry in the urogenital
system that we observed has not been reported before for either pre- or postmetamorphic Anura. The typical pattern appears to be for the kidney on the
right and the gonad on the left to be larger. We do not know whether the
asymmetry in the megophryine larval urogenital system is maintained after
metamorphosis, but according to Ecker ( 1889) urogenital organs are bilaterally
symmetrical in adult Rana.
Since tadpoles are by definition non-reproductive, the early development of
the gonads in tadpoles, such as those of L. montanum and L.gracilis, may reflect
386
E. NODZENSKI E T AL.
the time t6 or size at sexual maturity for the post-metamorphic frog more than
some aspect of physiology or ecology of the tadpole. Although L. gracilis and
M . nasuta have comparably sized tadpoles, gonad development is far faster and
more extensive in L.gracilis than in M . nasuta. Coincidentally, L. gracilis also
metamorphoses much closer to adult size ( L .gracilis: males 32-36 mm, females
40-52 mm; M . nasuta: males 70-104 mm, females 89-121 mm; data from Inger,
1966). T h e enlargement of gonads in larval L. gracilis may be viewed as another
constraint on space for other organs. It remains to be seen whether the extent of
premetamorphic gonadal development in other anurans correlates with the size
at first reproduction for transformed individuals.
CONCLUSION
Larval Leptobrachium montanum are very close to the typical shape of nonspecialized tadpoles (Orton, 1953: fig. 7). It is likely that, in terms of size, shape
and growth patterns of viscera, L. montanum has very few constraints imposed by
the form of its torso. In view of its generalized feeding habits and the wide array
of microhabitats it occupies, it probably also has very few ecological restrictions
on visceral morphology. We suggest that this tadpole exhibits a ‘typical’, nonspecialized solution for packing viscera within the restriction imposed on the
pleuro-peritoneal space by the evolutionary history of anuran larvae.
In contrast, tadpoles of Leptolalax gracilis and Megophrys nasuta diverge both in
body form and ecology from the generalized type. In different ways, their viscera
reflect the interrelated constraints imposed by ecology and torso shape. For
M . nasuta, reduction in size of gut and liver and, to a lesser extent, delayed
development of gonads constitute partial solutions to the packing problem.
However, the necessity for early development of the lungs to achieve the
buoyancy demanded by feeding at the surface imposes additional spatial
restrictions on other organs.
Leptolalax gracilis seems to have solved the packing problem mainly by
reducing relative size of the gut and liver, a solution that may have
disadvantageous consequences for food processing and growth rates. Delayed
development of the lungs in this species, though probably more directly related
to the animal’s benthic habits, partially alleviates the packing problem. To a
limited extent, early development of the gonads, which have no function in the
larvae, adds to the spatial restrictions of other organs.
In conclusion, differences in the relative size and shape of tadpoles’ pleuroperitoneal cavities are reflected in differences in the size and shape of their
viscera. Given a limited amount of body space, different species have made
radically different choices in how to pack those viscera.
ACKNOMJLEDGEMENTS
This research was supported by The Marshall Field I11 Fund, the Karl P.
Schmidt Fund, the Natural Sciences and Engineering Research Council,
Canada, and the National Science Foundation, U.S.A. We are grateful to the
following persons for technical assistance: Debra K. Moskovits (for statistical
help), Jeanne Jendre and Molly Ozaki (for manuscript preparation), Field
VISCERAL ORGANIZATION I N TADPOLES
387
Museum of Natural History; Tracey Earle and V. Ann King (for literature
search), Dalhousie University.
REFERENCES
BARRINGTON, E. J. W., 1945. The delayed development of the stomach in the frog. Proceedings of the
zoological Society of London, 116: 1-21.
CHRISTENSEN, K., 1930. Sex differentiation and development of oviducts in Rana pipiens. American Journal of
Anatomy, 45: 159-187.
DUELLMAN, W. E. & TRUEB, L., 1986. Biology of Amphibians. New York: McGraw-Hill.
ECKER, A., 1889. The Anatomy o f t h e Frog. Oxford: Clarendon Press.
FRIEDEN, E. & J U S T , J. J., 1970. Hormonal responses in amphibian metamorphosis. In G. Litwak (Ed.),
Biochemical Actions of Hormones, I : 1-52. New York: Academic Press.
FROST, D. R., 1985. Amphibian Species of the World. Lawrence, Kansas: A S G alle en Press.
GANS, C., 1975. Tetrapod limblessness: evolution and functional corollaries. American zoologist, 15: 455-467.
GILLOIS, M. & BEAUMONT, A,, 1964. Etude quantitative du pancreas d’iilytes obstetricans Laur. pendant la
vie larvaire et la mttamorphose. Comptes Rendus Socie‘te‘ Biologigue (Paris), 158: 8-1 1.
GOSNER, K . L., 1960. A simplified tablc for staging anuran embryos and larvae with notes on identification.
Herpetologica, 16: 183-190.
HOURDRY, J. & BEAUMONT, A,, 1985. Les Metamorphoses des Amphibiens. Paris: Fondacion Singer-Polignac
et Masson.
INGER, R . F., 1966. The systematics and zoogeography of the Amphibia of Borneo. Fieldiana: zoology, 52:
1403.
INGER, R. F., 1985. Tadpoles of the forcstcd regions of Borneo. Fieldiana: zoology, (n.s.), 26: 1-89.
INGER, R. F., 1986. Diets of tadpoles living in a Bornean rain forest. Alytes, 5: 153-164.
INGER, R. F., VORIS, H. K. & FROGNER, K., 1986. Organization of a community of tadpoles in rain
forest streams in Borneo. 7ournal of Trobical Ecoloev. 2: 193-205.
KEMP, N. E., 1954. Development of intestinal coiling in anuran larvae. Journal qf Experimental ~ o o l o g 116:
,
259-288.
MERTENS, R., 1960. Die Larven der Amphibien und ihre evolutive Bedeutung. xoologischer Anzeiger, 164:
337-358.
ORTON, G. L., 1953. T h c systematics of vertebrate larvae. Systematic ~ o o l o g y 2;
, 630-675.
POWELL, T. L. &JUST, J. J., 1987. Ultrastructure and function of the developing urinary bladder in Rana
catesbeiana. American zoologist, 27: 3A.
SWINGLE, W. W., 1926. The germ cells of anurans. 11. An embryological study of sex difkrentiation in Rana
catesbeiana. Journal of Morphology, 41: 441-546.
TAKAHASHI, H., 197 1. Sex differentiation and development of the gonad in Rana rugosa. zoological Magazine,
80: 15-21. [In Japanese with English summary.]
WASSERSUG, R . J., 1989. Locomotion in amphibian larvae (or “Why aren’t tadpoles built like fishes?”).
American zoologist, 29: 65-84.
WASSERSUG, R. J. & HEYER, W. R., 1988. A survey of internal oral features of leptodactyloid larvae
(Amphibia: Anura). Smithsonian Contributions to ~ o o l o g y ,457: 1-99.
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APPENDIX
Specimens examined. Specimens are grouped by locality, with FMNH
catalogue number, stage, and head-body length (mm) given for each individual.
Leptobrachium montanum: Sarawak; Kapit Dist., Nanga Tekalit; 222395, 25, 5.6;
222396, 25, 7.8; 139375, 35, 26.0; 139380, 38, 22.0; 139375, 39, 20.8; 139375, 39,
21.0; 195076, 45, 22.0; 195077, 45+
34.8. Sarawak: Belaga Dist., Sungai
Segaham; 222400, 25, 8.3; 222400, 25, 8.9; 222411, 25, 12.1; 222418, 25, 14.0;
222411, 25, 15.0; 222428, 25, 17.5; 222398, 25, 17.5; 222401, 25, 24.2; 222397,
26, 21.2; 222429, 30, 25.8; 222426, 31, 27.2; 222432, 36, 26.7; 222428, 36, 27.5;
222430, 42, 26.7; 222401, 42, 27.5. Sabah; Sipitang Dist., Mendolong; 233216,
28, 19.2. Sabah; Lahad Datu Dist., Danum; 233217, 36, 20.0.
Leptolalax gracilis: Sarawak; Kapit Dist., Nanga Tekalit; 146323, 35, 2 1.7.
Sarawak; Belaga Dist., Sungai Segaham; 222481, 25, 17.1. Sarawak; 7th Div.,
+,
388
E. NODZENSKI E T AL
Baleh River; 77509, 41, 15.8. Sabah; Lahad Datu Dist., Danum; 231418, 25, 9.5;
231417, 25, 10.0; 231419, 25, 10.0; 231420, 25, 12.2; 233222, 25, 15.1; 231421,
39, 15.6; 231416, 42, 15.0. Sabah; Sipitang Dist., Mendolong; 233221, 25, 13.8.
b f e g o p h y rtasuta: Sarawak; Kapit Dist., Nanga Tekalit; 148288, 35, 11.5;
148288, 36, 12.9. Sabah; Lahad Datu Dist., Danum; 231429, 25, 8.1; 231427, 25,
9.5; 231432, 25, 10.0; 231430, 26, 10.0; 231431, 27, 8.3; 231427, 29, 10.2;
231432, 29, 11.5; 231427, 30, 10.8; 231427, 31, 11.1. Sabah; Sipitang Dist.,
Mendolong; 233220, 25, 10.7; 233219, 36, 13.3; 233218, 37, 13.2.