i
THE REPRODUCTIVE. AND DEVELOPMENTAL HISTORY OF THE CALIFORNIA TIGER SALAMANDER
A thesis submitted in partial fulfillment of the requirements for the degree of
Master of Arts in the Department of Biology
Fresno State College
June, 1968 iv
TABLE OF CONTENTS
LIST OF TABLES ...... v
LIST OF FIGURES • ...... vi LIST OF PLATES ...... vii INTRODUCTION ...... 1
AREA OF STUDY • • • • • • • • • • • • • • • 4
ME11HOD OF S'rUDY • • • • • • • • • • • • 12
FORMATION AND DURATION OF THE PONDS • • • • • • • 14
ADULT MIGRATION AND EGG LAYING • • • • • • • • • 17
EGG INCUBATION • • • • • • • • • • • • • • )0
LARVAL GROWTH • • • • • • • • • • • • • • • • • • • 37
METAMORPROSIS • • • • • . • • • • • • • • 47
LARVAL NUTRITION • • • • • • • • • • • • • • • • 6)
LARVAL COMPETITORS AND PREDATORS • • • • • • • • 72
SUMMARY AND SUGGESTIONS • • • • • • • • • • • • • 76
LITERATURE CITED • • • • • • • • • • • • • • • • • • 81 v
LIST OF TABLES
Table Page 1. Precipitation During Pond Formation • . . . 15
2. Preci pita tion During Spawning • • • • . . . 20
3. Dimensions of Eggs and Egg Capsules in mm. 27
4. Dimensions of Embryos and Egg Capsules in mm. • • • • • • • . . . . 28 5. Incubation Rates ...... 31
6. Air and . Water Temperatures, Water Depths, and Chemical Analyses, Pond c • . • . • . . 52
Larval Measurements During the Pe iod of Rapid Water Loss from Pond c . • . . . • . . 53
8. Larval Measurements During the Period of Rapid Water Loss from Pond B . . . . • . 59
9· Air and Water Temperatures, Water Depths, and Chemical Analyses, 'Pond B ••••• . . 60
10. I1easurements of Oldest Larval Group During Metamorphosis, Pond A • • • • • • • • 61
11. Air and -later Temperatures, Water Depths, and Chemical Analyses, Pond A •••• 62
12. Stomach Contents of Various Sized Larvae 65
13. Appearance of New Food Organisms ••••• 66
14. Depths at Which Principal Food Organisms Occurred • • • • • • • • • • • • • 67
15. Principal Food Organism Densities in Pond C
16. Principal Food Organisms; Frequency of Ingestion by fute in Pond C •••••• 70
17. Deviations from the Usual Larval Diet ...... 71
18. Water Turbidity of Ponds A, B, and C on April 1 • • • • • • • • • • • • • • • • 75 vi
LIST OF FIGURES
Figure Page 1. Larval growth rates in Pond A • ...... 39
2. Larval growth rates in Pond B • • • 40
3- Larval growth rates in Pond C • • • • • 41
4. Comparative growth rates in Ponds A, B, and c . • . . . . • • . • . . . . . 42
5· Comparative growth rates of larvae in Ponds A, B, and c . . • . . • ...... 43
6. Comparative growth rates of larvae in Ponds A, B, and c . . . . • . • • ...... • 44
?. Metamorphic rates of larval groups in Pond C expressed as a ratio between front limb length and back limb length plotted against total length. Mar. 13 data . . 50
8. Metamorphic rates of larval groups in Pond C expressed as a ratio between total length and gill length plotted against total length Data from :Mar. 13 • • • • • • • • • • • • 51
9. Average gill lengths in Pond C. Ihta from April 16 to May 4 • • • • • • 54
10. Metamorphic rates of larval groups in Pond B expressed as a ratio between front limb length and back limb length plotted against total length. l\1ay 12 data • • • • • • • • 57
11. Metamorphic rates of larval groups in Pond B expressed as a ratio between total length and gill length plotted against total length. :May 12 data • • • • • • • • • • • • • • • • • • 58 vii
LIST OF PLATES
Plate Page I. Range of Ambystoma tigrinum californiense in Relation to the Range of the Continuous Tiger Salamander Population 2
II. Relative Locations and Surrounding Topographies of Ponds A, B, and C 6
III. Depression Forming Pond B During Early November • • • • • . . . 7
IV. Pond B After the First Winter Rain • . . . 9
v. Dimensions of Ponds A, B, and C on Dates of Initial Spawnings •• . . . 16
VI. Distribution of Eggs on Willow Branch 23
VII. Attachment of Eggs on Vegetation • • • • • • • 25
VIII. Embryonic Development at Field Temperatures Which Induced Hatching in 12 Days • • • • • 34 1
INTRODUCTION
The California Tiger Salamander, Ambystoma tigrinum californiense (Gray) is isolated from all other tiger salamanders by an area several hundred miles wide which includes the Sierra Nevada Mountains and the Great Basin. The range of the subspecies is shown in relation to the range of the continuous tiger salamander population on
Plate I. As a result of its geographic isolation, the life history of the disjunct subspecies differs from that of the continuous population reviewed by Dunn (1940). In parts of its range the subspecific variations of the California tiger salamander appear to be reproductively advantageous. This report describes the reproductive and developmental variations and their ad ptive value in the hot, dry San Joaquin Valley of Central California. The investigation was conducted in the field between
November 15, 1967 and May 31, 1968. Unless indicated, all data and discussions describe the re roductive attern under natural conditions.
PLATE I
RANGE OF AM8YSTOMA TIGRINUM CALIFORNIENSE IN RELATION TO THE RANGE OF THE CONTINUOUS TIGER SALAMANDER POPULATION
Redrawn from Stebbins (1951) .I I I I I 1:::0 I I" IS!. Jf Ill I' I I I I I
4
AREA OF STUDY
In order to observe the reproductive activjties and the course of egg and larval development under several sets of environmental conditions, three pools were chosen for the study. The ponds varied in size and were designated in order of decreasing depth as Ponds A, B, and C. The ponds were located in Madera County within three miles of Friant, California. Ponds A and B were within
42 feet of each other, at an. elevation of approximately 475
feet above sea level. Pond C was about two miles from Ponds A and B, at an elevation of about 420 feet above sea level. The relative locations of Ponds A, B, and C and their surrounding topographies 'are illustrated on Plate II. The depressions forming Ponds A and B appeared to have been either created or modified by road building exca• vations. These depressions had been used previously as garbage dumps. Similarly, the depressions forming Pond C appeared to have been created by the removal of earth in construct• ing the nearby Madera Canal.
Plates III and IV show one of the pond beds during the early part of November, 1967, and after the first winter rain. 5
PLATE II
RELATIVE LOCATIONS AND SURROUNDING TOPOGRAPHIES OF PONDS A, B, AND C 6
PLATE III
DEPRESSION FORMING PO D B DURING EARLY NOVEMBER
PLATE IV
POND B AFTER THE FIRST WI T
--
11
The ponds were filled through a natural accumulation of rain water. Throughout the breeding season, the physical, chemical, and biological composition of the water was analyzed. Where appropriate, these data are considered in the discussions of egg incubation, larval feeding habits, growth developmenand metamorphosis.
During the previous five years, there had been periodic evidence of tiger salamander spawning in Ponds
A and B. Information concerning previous use of Pond C was not available.
Evidence of egg laying was not observed in any other temporary ponds in the area. Compared to Ponds A, B, or C, the unused pools were very similar in both chemical and biological composition, but they were neither as deep nor as long lasting as Ponds A, B, or C. Unlike the tiger salamanders east of the Sierra
Nevada Mountains, the California subspecies uses only temporary rain pools for reproductive activities. There• fore, it is dependent on seasonal rains for successful spawning. Only a few permanent ponds were located in the area of study and none of them showed evidence of spawning by · tigrinum californiens . These observations which indicate the exclusive use of temporary ponds agree with findings made by Storer (1925) in Bellota, California, and
Twitty (1941) in Palo Alto, California. 12
METHOD OF STUDY
During the period of pond formation, egg laying, incubation, and hatching, data on the physical nature of the ponds were gathered at weekly intervals. Data concern•
ing the course of reproductive events were gathered at the
same frequency; supplementary data were collected after each
rain and during egg incubation. Data concerning larval
growth, development, and feeding habits were gathered
weekly. During the period of larval development, chemical
and biological analyses of all three ponds were made every
two weeks.
Pond plankton and stomach contents were identified
in Prescott (1954) and Pennak (195J). The Saprolegnia
was identified in Krueger and Johansson (1959). At Fresno State College, Dr. Weiler identified the vascular plants used for egg deposition and Dr. Harmon identified the
Trichomonas.
Chemical analyses were made by the following methods:
' Electronic Method; gxygen, Azide Modification of the
Winkler Test; carbon dioxide, Titrimetric Method; Cloride,
Mercuric Nitrate Titrimetric Method; calcium, EDTTitri•
metric Method; total hardn ss, EDTA Compleximetric Method;
magnesium, determined from calcium and total hardness values. 13
The above techniques are described in Farber (1962).
All the amphibians were measured as unpreserved specimens. The measurements were made according to the procedures described by Storer (1925) and were expressed in the metric system.
Climatological data for the entire study came from the Fresno Air Terminal and the Bureau of Reclamation in Friant. The former source of information is about 23 miles from the ponds, while the latter source is about two miles away. The sources gave similar data. The Fresno Air Terminal, however, was able to supply hourly data on pre• cipitation and temperature. In the following discussions, all information on
temperature and total rain came from the Friant area. References to hourly trends have been inferred through the use of data from the Fresno Air Terminal. 14 FORMATION AND DURATION OF THE PONDS
Throughout the early fall of 1967, the Friant area received only .26 inch of rain. During this period, dry, shallow depressions existed where Ponds A, B, and C were eventually formed. From November 18 to January·10, the area received J.58 inches of precipitation which accumu•
lated to form Ponds A and B. Pond C, however, lost water quickly through evaporation and seepage and dried up a few days after each rain. It was not until February 17, 1968, that Pond C became favorable for egg laying. Table 1 shows an account of daily precipitation and weather conditions during the period of pond formation. When the ponds were first used for spawning, their depths were as follows:
Pond A, 92 em.; Pond B, 41 em.; Pond C, JO em. The dimen• sions of the ponds at these depths are illustrated on
Plate 5. Due to variations in the shapes of the depressions that formed the pools during the . breeding season, Ponds A, B , and c differed radically in both depth and duration. Ponds B and C lasted 192 days and 78 days, respectively; while Pond A was J4 em. deep at the end of the study. 15
TABLE 1
PRECIPITATION DURING POND FORMATION
r.a te Mean Air Total Approximate Approximate Temperature* Rain Hours of Temperature* Greatest During Hours Rain of Greatest Rain
Nov. 18 18.5 .23 6-7 PM 18.5
Nov. 19 14.0 .so 6-9 PM 13.5
Nov. 29 19.0 .65 10-12 PM 10.0
Nov. 30 17.0 .38 1-2 PM 10.0
Dec. 12.4 .54 4-6 AM 10.0 5
19.0 .10 7-10 AM 7.8 Dec. 7 1.0 .22 9-11 PM 6.0 Dec. 17
.so 5-8 AM 6.0 Dec. 18 s.o .46 8-11 AM 10.0 Jan. 10 5-5
11.8 .11 2-4 AM 3·5 Jan. 15 .29 7-8 PM 1.5 Jan. 27 21-5 .38 11-12 PM 9.0 Jan. 30 9·0 .23 10-12 AM 10.5 Feb. 9 10.0 1-3 PM 11.5 Feb. 13 s.o .17 1-4 PM 15.0 Feb. 16 10.0 .25 .29 10-12 AM 15.0 Feb. 17 13·0
centigrade. *Temperatures in degrees 16
PLATE V
DIHE NSIONS OF PONDS A. B .A ND C ON DAT2:S OF Hfi'riAL SPAW N INGS
64 feet1----7
0) 00
c
17
ADULT MIGRATION AND EGG-LAYING
Migration
It appears that the warm winter rains which form the temporary ponds play an additional role in the reproductive behavior of the salamander. With the advent of rains and the proper physiological readiness both sexes leave their underground burrows and migrate toward suitable breeding sites.
Mass migrations have been described by Twitty (1941); throughout this investigation, however, no mass migrations were observed. On February 25, 1968, two adult females were found trapped in an old kettle which was cupped in a depression in the ground. Perhaps these animals were attracted to the small quantity of rain water which had accumulated in the kettle. No tiger salamanders were found in water-free containers which could have served similarly as traps.
Migrations of adults probably cover a limited area.
The salamanders' selective spawning in certain long-lasting temporary pools indicates that populations of tiger salamanders might occur only in scatterd areas within the habitat. The late seasonal development of Pond C, and the extent of egg-laying in that pond as compared to that of 18
Ponds A and B, offer some insights into the probable extent of migration. Spawning was extensive in Pond c as soon as conditions for egg-laying became suitable. Concurrent spawnings were meager in Ponds A and B, which had been used previously. This would indicate that the salamander popu- lation using Pond C had not made use of earlier-developing ponds and that migratory movements were probably limited to an area extending less than the two-mile distance between
Pond C and Pond A or Pond B.
Cortelation Between ftains and Spawning
During the study, no salamanders were observed in the act of egg-laying. On the rainy evening of March 7 one adult salamander was seen in Pond B.This animal swam away from the shore line, preventing a close observation of its activities. An account of the egg-laying process under natural conditions is given by Twitty (1941).
All newly-laid eggs which were located were found within 12 hours following the rains which promoted spawning.
Thus, most eggs were found in an early cleavage stage of development. The first evidence of egg-laying was observed on January 28 in Ponds A and B. The early stage of egg development indicated that spawning probably occurred during or following the preceding rainy evening. This spawning was preceded by a period of 15 rain-free days.
Table 2 shows spawning frequency and its relationship to the 19 quantity and periodicity of the rains.
The rain which initiated spawning was the first winter rain which occurred during the early evening hours.
Most subsequent rains which promoted spawning occurred during, or were followed by, periods of darkness. See
Table 2.
After breeding had begun, there was evidence of spawning in Ponds A and B following all rains amounting to
.18 inch or over. The last evidence of spawning was observed following the rain of April 1. In one case a light rain amounting to .23 inch was accompanied by exten• sive spawning. This rain was preceded by several weeks of dry weather. Conversely, in another case a moderately heavy rain amounting to .)8 inch failed to stimulate spawn• ing. This rain was preceded by extensive egg-laying only three days before. The events following the rains of
February 9 and January )0, respectively, illustrate these situations. These deviations from the expected reproductive behavior indicate that the same population of animals may have spawned successively in their respective ponds.
The first appearance of eggs in Pond C occurred under unique conditions. As stated above, Pond C dried up after each rain preceding the first spawning. However, eggs were found in Pond· c immediately following the first rain which permanently filled the pond. This would indicate that fertilization and egg-laying occurred within a 12-hour 20
TABLE 2
PRECIPITATION DURING SPAWNING
Approxi- Mean Air Approxi- mate Spawning Tempera- mate Tempera- in Ponds rate ture on Total Time of tures !ate of Bain Majority During Rain of Bain Majority A B c of Rain
** Jan. 27 21.5 .29 7-8 PM 1.5* * X* X X
Jan. 30 17.0 .J8 11-12 PM 10.0
Feb. 9 10.0 .2J 10-12 AM 10.5 X X
Feb. 17 13.0 .29 10-12 AM 15.0 X X X
Feb. 20 15.0 .14 3-6 AM 14.5 X X X l'flar. 7 10.0 -39 6-9 PM 10.5 X X
Mar. 13 12.0 -59 3-7 AM 10.0 X X
Mar. 16 8.0 .64 2-4 PM 12.0 X
X X X Apr. 1 20.0 .47 7-9 PM 10.0
*x indicates spawning• **Temperatures are in degrees centigrade. 21
As emphasized, newly-laid eggs were found only following periods of rain. But the capture of six adult salamanders in Pond A during the dry weather of April 21 to
April 28 indicates that some egg laying might have occurred independent of rain. If this was so, spawning was so meager that eggs and larvae were not observed.
Egg Deposition
Eggs were found attached to the submerged section of tree branches, weed stems, and aquatic plants. The objects chosen for egg deposition varied from 2 mm. to 5 mm. in diameter. Turkey mullein (Eremocarous setigerus), marsh grass (Heleocharis Palustris), poplar (Populus .),and willow (Salix -) were used extensively. The objects chosen for egg-laying Nere either completely submerged or projected out of the water. In either case, these objects formed angles of 0 degrees to 90 degrees with the surface of thwater; however, most eggs were found on objects which formed a 45 degree angle
(estimated) with the surface of the water.
Most egg deposits were found along the edge of the pool, 15 em. to 25 em. below the surface of the water, and between 7 em. and 25 em. from the bottom of the pond. All eggs were deposited deep enough below the surface to remain submerged in spite of fluctuating pond depths during the incubation period. The eggs of Ambystoma tigrinum californiense were usually deposited singly or in groups of three to five. The 22 maximum number of eggs per group was seven. Single egg deposits were more common than egg clusters. Single eggs and egg clusters were spaced at distances of 0.5 em. to
20.0 em. These observations on egg deposition agree with
Twitty (1941). Plates 6 and 7 show the distribution of eggs and the manner in which they are attached to the vegetation.
Egg deposition of the California tiger salamander differs greatly from that of the eastern population which deposits large egg masses containing 50 to 75 eggs. These egg masses are described by Bishop (1943).
Description of Eggs
The individual eggs of the California subspecies are surrounded by three gelatinous envelopes. The two inner capsules are usually more spherical and less viscid than the outer capsule. The egg masses were not easily located because of the debris which collected on their surfaces.
Table 3 gives dimensions of the eggs and egg capsules at late blastula. Table 4 gives dimensions for embryo and egg capsules at a later stage of development. These dimensions are slightly less than those reported by Storer (1925). The eggs and surrounding capsules are similar to those of the Eastern subspecies. The animal and vegetal poles of the California tiger salamander eggs are more lightly pigmented than the corresponding poles of the east• ern subspecies and their outer gelatinous envelope is
•
PLATE VI
DISTRIBUTION OF EGGS ON WILLOW B CH
The numerical graduations on the ruler are in centimeters.
PLATE VII
ATTACHMENT OF EGGS ON VEGETATION
The numerical graduations on the ruler are in centimeters.
27
TABLE J
DIMENSIONS OF EGGS AND EGG CAPSULES IN MM.
Egg Inner Middle Outer Jelly Coat Jelly Coat Jelly Coat
Minimum 2.3 J.O J.J 4.0 Maximum 2.6 J.J 4.0 4.) Average of 5 2.5 J.l ).6 4.2 28
TABLE 4
DIMENSIONS OF EMBRYOS AND EGG CAPSULES IN MM.
Einbryo Inner· Middle Outer Jelly Coat Jelly Coat Jelly Coat
Minimum 6.2 4.1 4.J 4.8
Maximum 7·7 5·7 6.1* 8.5*
Average of 5 7·0 4.9 5.2 6.6
*Elongated capsule. 29 considerably more sticky. Unlike the egg capsule of the eastern subspecies, the egg capsule of . tigrinum calif• orniense did not become impregnated with algae during incubation. )0
EGG INCUBATION
Incubation Bates
Because of the salamander's long breeding season, the egg incubation period was determined under the influence of different temperature ranges. The minimum and maximum incubation periods were 10 and 14 days respectively. Data comparing incubation rates with water and air temperatures are presented in Table 5.
Differences in the sizes of the ponds demand that comparisons of incubation rates with temperature be inter• preted with care. Throughout the study, Pond A was considerably larger than Ponds B and C, and its early after• noon temperature was almost always a few degrees lower than the temperatures of Ponds B and C. During the night this relationship between size and temperature was reversed.
Therefore, the temperature of Pond A was more constant than the temperatures of Ponds B and C.
A consideration of these factors helps to explain the nearly uniform incubation periods in Pond A throughout a wide variety of recorded temperatures and indicates that a large water volume buffered against fluctuating air temperatures, while the very different incubation rate in
Pond c indicates that the temperature of a stable pond is 31
TABLE 5
INCUBATION RATES
Mean Temperature in oc Pond Incubation Incubation Periods Rates Air Water Water at Surface 25 em.
A Jan. 27 to Feb. 10 14 days 10 13.6 9·3
B Jan. 27 to Feb. 10 14 days 10 14.4 10.9
A Feb. 9 to Feb. 23 14 days 13.5 16.3 13.5
B Feb. 9 to Feb. 23 14 days 13.5 16.6 13.2
A Feb. 17 to 16.6 Feb. 29 13 days 16 17-5
B Feb. 17 to 22.8 15.8 Feb. 29 13 days 16
c Feb. 17 to 24.6 18.9 Feb. 29 13 days 16
A Feb. 20 to 21.7 16.0 Mar. 4 13 days 15
B Feb. 20 to 21.5 15.5 Mar. 4 13 days 15
20 to c Feb. 15 24.7 19.1 Mar. 5 14 days
A Mar. 7 to 11 14.7 13-9 Mar. 20 13 days
to B Mar. 7 11 24.2 15.1 Mar. 20 13 days .32
TABLE 5--Continued.
Mean Temperature in oc Pond Incubation Incubation Periods Bates Air Water Water at Surface 25 em.
c Mar. 7 to Mar. 19 1.3 days 11 22.5 16.7
A Mar. 1.3 to Mar. 25 12 days 11.5 17.2 14.8
B Mar. 1.3 to Mar. 25 12 days 11.5 22.8 14.0
c Mar. 1.3 to Mar. 25 12 days 11.5 22.0 16.9
c Mar. 16 to Mar. 26 10 days 15 2.3.0 18.2
A Apr. 1 to 20.0 17.2 Apr. 14 1.3 days
c Apr. 1 to Apr. 11 10 days 24.7 18.8 JJ greatly influenced by air temperatures. Incubation rates of intermediate ranges were observed in Pond B.
Stages of embryo development are illustrated on
Plate VIII. Ninety-seven percent of the embryos observed were curved so both their anterior and posterior ends curved inward to the larva's right side. The drawings show developmental rates at field temperatures which induced hatching in 12 days.
The incubation period of the eggs of the California tiger salamander is considerably less than the incubation period of the eastern subspecies' eggs. Pope (1964) reports that the natural incubation period of A· tigrinum tigrinum eggs is about 28 days. Data concerning the natural incubation temperatures are not available; however, at room temperatures the eggs of the eastern subspecies hatch in
14 to 18 days.
Egg Viability and Predators
The occurrence of egg deposits on turkey mullein
(Eremocarpus setigerus) is of special interest because the plant is reported by Jepson (1960) to have a toxic effect which appears to stupefy fish in slowly moving streams.
No toxic conditions, however, were observed during the development of either eggs or larvae in ponds containing this herb.
PLATE VIII
EMBRYONIC DEVELOPMENT AT FIELD TEMPERATU ES WHICH INDUCED HATCHING IN 12 DAY
Illustrations show embryos after the follow1n periods of incubation: A, 1 day; B, 2 days; C , 4 days ; D, 5 days; E, 6 days; F, 8 days; G, newly-emerged larvae . A- are 15x, G is lOx. F illustrates an atypical embryonic curve .
D
F
36 Nearly all of the eggs which were located developed successfully. Out of the hundred embryos that were observed, only two failed to emerge from the egg, and these had become infected with a fungus. This organism was cultured and identified as Saprolegnia, a common fungus which invades amphibian eggs. Because the eggs were deposited singly, or in small groups, Saprolegnia infestations did not spread readily. Thus, there seemed to be a definite selective advantage in A· tigrinum callforniense's manner of egg
deposition.
regilla and Scaphiopus hammondii adults were
common members of the aquatic community during the period of embryo development. Evidence of predation by these amphibians was not observed. It appeared that the eggs and developing embryos had few enemies. 37 LARVAL GROWTH
Methods of Determining Growth Rates
In order to determine the sizes of newly hatched and day-old larvae, ten egg masses containing advanced embryos were taken into the laboratory. Four of the embryos from this sampling hatched on the way to the laboratory; the remaining six hatched within two hours at 30.5 degrees c. Growth rates reflecting natural field conditions were determined by sampling the larval population in each pond at weekly intervals. Examining the lengths of the individual larvae in each pond's sample permitted grouping the salamander larvae into well-defined size categories. A prior knowledge of larval hatching dates permitted age determinations of these groups. This system worked best for Pond C. It was particularly successful here because of the age differences between the larvae and because the small size of the pond permitted a thorough sampling. Age differ• ences between certain groups allowed this method to work well in Ponds A and B also•
ijesults
The total lengths of the newly-hatched larvae aver• aged 12.6 mm. The minimum length was 11.5 mm., the maximum was 14.2 mm. Within 24 hours these larvae had attained an average total length of 14.1 mm. The minimum length was
1).8 mm.; the maximum was 14.3 mm. 38
Under natural conditi.ons, numerous factors influenced the growth of salamander larvae. It appears that the most important factors were larval diet, pond age, pond tempera- tures, pond depth, and metamorphosis.
Effects of Larval Diet
During the first six weeks of growth, the larvae fed entirely on small crustaceans and algae. Later, the utiliza• tion of additional food sources such as anuran tadpoles, tiger salamander larvae, and aquatic insects was evidenced in many larval diets and correlated with periods of rapid growth. The relationships between larval age and growth rate are shown in Figures 1, 2, and 3·
Effects of Pond Age
Because Ponds A and B were established about three months earlier than Pond C and, therefore, contained a greater variety and abundance of food organisms earlier in the breeding season, some growth rate variations may be attributed to differences in the age of the ponds. Figures 4,
5 and 6 compare growth rates in each pond throughout the
same time period.
Effects of Pond Temperature
In each pond, the later-hatching larvae grew more
s groups, as long as conditions for rapidly than all Previou
growth remained favorable. This variation probably· is Fig. 1.--Larval rowt rates in Fond A
140
130
120
110
100 t-' (\) 90 c+ ;s f-'" 80 :::s Hatching Dates
70 0 Feb. 10 • 0 Feb. 23
b. Feb. 29
X r ar. 4 @ I· ar. 19
40 E9 Har. 29
30 Apr. 13
/ 20
JO _so 6o 70 80 90 100 Age in d.qys Fig . 2 .--La rva l gr o"'It rates j!l Fond B
130 • 120
110
Beginning 100 Metamorphosis t-' (\) m 90 cT ::> ...... Hatching Dates ::s ;:js •Feb. 10 • 0 Feb. 23 Feb. 29 X t ar.- 4 @ J'l1.ar . 19 40 E9 r·1ar . 24
30
20
10 20 30 40 50 60 ?0 80 100 Age in da ys Fig. J.--Larval sz:rowth rates in Fond C
140
130
120
110
100 t1 (1) Beginning 64 90 Metamorphosis :c:ts• 0 m ..... 80 ::s s8 70 • Hatching Dates • Feb• 29 0 Mar. 5 r> ar . 1Q 8 X !'1ar. 24 & 26
20 1 00 Age ln days Fig . 4.--Compa rative gro'li-rth rates of larvae in Ponds A, B, & C.
140
130
...... ::s :::1 s • Hatching Dates
A Feb. 29 B Feb. 29 c Feb. 2Q
100 10 20 JO 40 50 60 70 Age in days Fig. 5.--Comparative grov;th rates of la rvae in Ponds A, B , & C.
140
130
120
110 B
Hatching Dates
A Iv'Iar. 4 B i'lar . 4 c ·ta r. 5
10 70 80 90 100 in days
Fig. 6.--Comparative growtrates of larve in Pons A, B, & C.
140 A 130
120
110
100 t-1 (I) 90 61 c+ ;:s 80 1-'" ::s e 70 Hatching Dates (:l • 60 A Mar. 19 50 8 Mar. 19 40 c Mar. 19
30
20
70 90 Age in days
45 due to temperature differences within the ponds throughout the breeding season. Figures 1, 2, and 3 compare the growth rates of the larvae inhabiting Ponds A, B, and c.
The Effects of Pond Depth
Larvae were found in greatest abundance in the shallow, warm water during the day, and in the deep, warm water during the night. These observations, which agree with the findings of Prosser (1911), indicate that the depth of a pond and its heat retaining capacity may regulate the thermal factors influencing larval growth. The effects of pond depth are indicated by comparing growth rates in each pond throughout the same time period. Figures 4, 5, and 6 show that in general growth progressed most rapidly in the large pond which allowed the larvae to move into deep, warm water during the night, and least rapidly in the small pond which restricted the larvae to water of rather uniform depths and temperatures. An intermediate growth rate occurred in the intermediate-sized pond.
The Effects of M tamorphosis
Figures 2 and 3 show that metamorphosing larvae of all ages exhibited decreasing growth rates. The decrease occurred during the initial stages of metamorphosis, indi• cating that growth rate data were based on random samplings and did not include an abundance of small, slowly meta- morphosing animals. 46
Stomach contents of metamor hosing larvae seldom contained the usual quantity of food organisms. This suggests that feeding habits may have influenced the growth rate. 47
ME'rAMORPHOS IS
Method of Determining Metamorphic Rates
Many morphological changes may be considered as indications of larval metamorphosis. However, only external structural modifications which equipped the larvae for a terrestrial existence have been considered here. The development of limbs and the absorpti.on of gills were the most apparent indications of metamorphosis. The front legs of the larvae appeared during the early stages of development. Throughout most of the larvae's existence, the front legs exceeded the hind legs in total length. However, as development progressed, the limb lengths became more nearly equal. A comparison of limb length gave a good indication of larval development. This .comparison was expressed as a ratio by dividing front limb length by hind limb length. In early stages of development, before the appearance of hind limbs, the ratio equaled infinity. Later, as metamorphosis progressed, the ratio dropped down to one or less.
Prior to metamorphosis, the larvae's gills grew in proportion to their total length. However, as metamorphosis began the gills were absorbed. A comparison of gill length with total length gave a good indication of larval 48 development. The relationship was expressed by dividing total length by gill length.
Results
Modifications in limb length and gill length appeared to be influenced by a number of factors in addition to age. A comparison of developmental rates in Ponds A, B, and c indicated that variation in the aquatic environment may affect the rate of larval metamorphosis. Due to an accumu• lated daily loss of water through evaporation, these variations were noticeable in different degrees in all three ponds. The effects of evaporation were numerous and each might have been a factor in determining the rate of larval development. A decrease in pond depth correlated with an increase in the daytime water temperature, with an increase in ionic concentration, and with a decrease in dissolved oxygen. Changes in water temperature and chemistry are discussed in relation to Ponds A, B, and C.
Metamorphosis in a Rapidly Prying Pond Pond c was the most shallow pond, having a large
The pond lost water surface area in relation to its volume•
days of its existence and its rapidly during the last 28 During this period level dropped from 15.2 em. to 1.9 em. the effects of evaporation came into operation rapidly and development was evidenced in an increased rate of 1arVa1 49 limb growth and gill absorption. Chemical and thermal variations appeared to operate on the developmental rates of
larvae of all ages and zes. Figure 7 shows that front and s;• back limb growth began more quickly for the late-hatching larvae which inhabited Pond C's comparatively warm water. Once development began under the above conditions, the front and back limbs reached equal lengths rapidly. Also, as
shown in Figure 8, gill absorption began more rapidly in the late-hatching larvae. Climatological changes and variations in Pond C's watP-r temperature, depth, and chemistry are shown in Table 6.
During the period described above, no completely metamorphosed salamanders were found in or around Pond C. However, the size of the larval population changed radically,. dropping from J64 larvae on April 16 to 1 larva on May 4.
Extensive predation on the pond's shallow water inhabitants had been considered as a possible explanation for the loss of larvae, but an examination of the area revealed no evidence of predation during this critical period.
An examination of the physical condition of the
larvae which remained. longest in the pond indicated that metamorphosis might have occurred • As shown in Table 7 and
Figure 9, the longest-remaining larvae showed the least
evidence of metamorphosis. Unfortunately, a thorough examination of the mud cracks and rodent burrows surrounding
the ponds revealed no metamorphosed salamanders.
Fig. ?.-Metamorphic rates of larval groups in Pond C expressed as a ratio between front limb length and bacl<: limb length plotted aga nst total length. 1\"ar. 13 :lata. ::0 so rt" 0"""'" o'4 r-- (l) rt"
(l) (l) ;:s '"""'l Hatching Dates 1-l 0 3- • Feb • 29 f--' 0 l1ar. 5 ...... s o' A T tar. 19
I-' iar. 24 & 26 CD X ::s (A rt- 2 ;::> -
+ o' '<: a' so xx • xx X 8 •• • - A XX A GO (') "' 1 I-' f-'" 3 o'
f-' (l) ::s CR c-t \J\ ::s- I l I I I I I I I I 0 10 20 30 40 50 60 70 80 90 100 Total length in mm.
Fig. 8 .--Metamorphic rates o f l2rval grn ups in Pond C expr e ssed a s a ratio bet·, e e n tota l le ng t h a nd g ill leng t h plot ted aga l nst t o ta l leng th. Da ta fr om f· r. lJ.
80 - sn 70 - 0 Hatching Dates 0 I-+) <+ 60 - Feb. 29 0 • <+ Mar. \)) 0 5 f--1 A rar. 19 1--' 50 - 30 1-- 1--' • f--J I I I I I I I I I I 'p-" ro 20 JO 40 50 60 70 80 oo 1 00 Tota l l e ng t h in mm. TABLE 6 AIR AND vlATER TEHPERATURES , WATER DEPTHS , AND CHEIUCAL ANALYSES, POND C I•l ean temp. of Pond Hater anal;ysis at 2:00 E·ID · Cl Total Ca Hg 12revious 2 l.reeks depth Temp. pH Oxygen co2 mg/1 hardness mg/1 mg/1 Air iater at in mg/1 1% Sat. as eaco3 Date 2 em. depth em. mg/1 3/1 58 24.1 27 22.0 6.97 6.5 74 4.61 3.90 93.7 17 18.4 3/15 54 21.9 31 22.0 6.95 8..3 94 7..32 7.0 1.15.1 21 22..3 4/l 56 24.1. 24 28.2 6.91 7.3 92 12.3 lL7 132 40 21.8 4/15 60 24.7 15 24.7 6.93 5.04 59 b.5.8 14.0 156 66 21.8 5/l 62 28.1 6 24.0 7..3 5 1.8 47 22.8 72.0 21.2 100 27.2 TABLE 7 LARVAL MEASUREMENTS DURING THE PERIOD OF RAPID WATER LOSS FROM POND C Larval Dimensions* April 16 April 21 April 25 April 28 ¥.ay 1 ·1ay 4 Ma M x - .!f x - x I"lin X ax Min x Max Min Max Min X 1>11n X Total Length 79•<: * 42-IH<- 6o 102 47 67 97 51 68 84 55 65 71 38 57 59 Tail Length 23** 5** 14 43 22 30 40 21 30 35 23 29 30 15 23 24 Axilla to Groin 32 18 · 25 30 13.4 20 28 13 20 22 16 18 18 11 16 17 Front Limb 15 9 12 16 6.) 10 13 8 10 12 9 8.8 10 5 6 9 Back Limb 14 7 11 15 5 9 16 9 11 13 7.3 9.2 9 3.2 7 8 Orbit 1.2 1.1 1.2 1.4 0.9 1.2 1.4 1.1 1.4 1.2 1.1 1.1 1.4 1,0 1.1 1.1 Inter- orbital Space 5·5 4.5 5.0 5.5 3.5 4,2 6.5 3.5 5.0 6.0 4.0 4,6 5.0 2.6 J,4 3.6 Gill 8.0 6.0 ?.0 9.0 4.1 5.6 5- 5 4.2 5.0 2.8 4.2 3.2 5.0 2.0 4.3 4.? l...rl *Measurements in millimeters. **Tail loss. Fig. 9.--Average gill length of larvae in Pond C. Data from April 16 to Iv.ay 4. 8 7 ...... ::S5 s s • 4 3 Apr. 16 Apr. 21 Apr. 25 Apr. 28 fv'ay 1 Fay 4- Sample dates 55 Metamorphos1s in I,png :r..• I.asting Temporary Ponds Unlike Pond c, Ponds A and B failed to evaporate rapidly. Yet a difference in the stabilities of their environments existed due to variations in their initial depths. Thus, in the pool of intermediate depth, Pond B, the effects of water loss were accompanied by metamorphosis earlier than in Pond A. Pond a.--The larvae inhabiting Pond B showed evidence of metamorphosis on May 12. Their metamorphoses indicated that the effects of a slowly-decreasing pond depth operate selectively on the larval population. Unlike the develop- mental changes in Pond C, metamorphosis occurred first in the oldest larvae and was initiated in younger larvae only after the pond depth decreased considerably during the weeks that followed. After gill reduction was first observed on May 12, Pond B's entire larval population was examined each week until the pond evaporated on May 28. During this period, only one newly metamorphosed salamander was found in the pond, indicating that the salamanders left the rapidly drying pool as soon as they were physiologically prepared for the terrestrial environment. During the period of rapid metamorphosis, the larval population dropped from 66 larvae on May 12 to one larva on May 28. In the mud that formed the pond bed, two dead 56 larvae were found with the live larva. Data showing develop ental changes in Pond B's larval populations are presented in Figures 10 and 11 and Table 8. Climatological changes and Pond B's water temper- ature, depth, and chemistry are shown in Table 9. Pond A.--Due to Pond A's large initial volume, less rapid changes in water temperature and chemistry accompanied the pond's decreasing depth. Under the persistent condi• tions of a stable environment, the oldest larvae continued to grow with no reduction in gill length until they were about 14 weeks old. Unlike the larvae in Ponds B and C, only the oldest group in . Pond A showed evidence of metamorphosis before the study was concluded. Four completely metamorphosed young salamanders were found in Pond A between May 19 and May 26. Earlier samplings of the metamorphosing age group indicated that the gills were absorbed within a seven-day period. Previous inventories of the larval population inhabiting the neighboring pool, Pond B, showed that largest larvae were considerably smaller than Pond A's largest larvae. Therefore, it appears that the metamorphosed salamanders found in Pond A did not migrate from Pond B. Data showing developmental changes in Pond A's oldest larvae are shown in Table 10. Climatological temperature, depth, changes and variations in Pond A's water and chemistry are shown in Table 11· Fig. 10.--Metamorphic rates or larval groups in Pond B expressed as a ratio between rront limb length and bac1{ limb length plotted a€Cainst total length. t-1ay 12 data. 4 f-- :..d ll'> rt I-'" 0 Hatching Dates 0 l-'l3 f-- Mar. 4 1-'l • li > 0 ' Mar. 19 ::s rt Mar. 24 1-' 8 Is-'" o' + 2 r- o' '<: o' A A () r-' 1--'" 1 A 00 t:l - - 0 o' 0 • • • I I I I I I I I I I 10 20 30 40 50 60 70 90 1('0 Larval legth in mm. Fig. 11.--Metamorphic rates of' larval groups in Pond B expressed as a ratio bet'•!een tota.J_ length and gill length plotted agains t total ]_ength . I1ay 12 da tg_ . ., 80 ;:U PJ • c-t f-'" 0 70 - 0 Hatching Dates 1-1) c-t filar• 4 0 60 • c-t • fl) t·1ar. 19 f-' 0 • f-' ,.-- • (1) 50 A 1ar. 24 ::s (.):! c-t ;J 40 + o' "< (}:! 30 1--- 0 f-'" f-' 0 f-1 0 20 0 c-t ::s A • 10 1- A A \..J\ I I I I I I I I I I co 10 20 )0 40 50 6o 70 80 90 1CO Total lengih in mm . TABLE 8 LARVAL r·1E.I. \.SUR EI' IEN TS DUR I NG THE PERI O D OF RAPI D HATER LOSS : FR O H PO ND B ttlay 12 Nay 19 Hay 25 Hay 27 May 28 {H(- r1ax. T1in. X I'1ax. Bin. X t1ax. Hin. X Hax. Hin. X * * !- Total length :1.05 59 89 98 73 84 82 70 76 70 67 69 70 69 67 Tail 42 26 39 40 34 32 3:1. 30 32 27 26 26 27 27 26 Ax illa to - groin 31 21 26 27 17 22 32 20 2J 17 16 16 17 17 16 Front limb 15 8.0 15 16 14 15 14 13 14 13 13 13 13 13 13 Ba.ck limb 17 5.5 15 21 17 18 15 12 15 13 12 12 13 13 12 Orbit 1..5 1.5 1.6 2 1.5 1.7 1.5 1.2 1.3 Inter orbital space 8.0 4.5 7.0 6.0 4.0 5.0 s.o 4.0 4.1 6 5.5 5.7 6 5.5 5.5 Gill 2 6.7 3.2 1.5 7 3.7 2 5.5 3.3 4 4 4 3.5 4 3.5 *Live larvae in mud; -r.·*Dead larvae. TABLE 9 AIR AND \'1 ATER TENPERATURES, HATER DEPTHS , AND CHEN CJ\L .A.NA.LYS:C: S , POND B Hean temp. of Pond Water anal sis at 2:00 J2.ID. Cl Total Ca Mg previous 2·weeks depth Temp. pH Oxye_en C02 mg/1 hardness mg/1 mg/1 Air Hater at in mg/1 %Sat as eaco3 Date 2 em. depth em. mg/1 3/l 58 20.3 50 20.9 6.81 8.J 91 4.15 3.91 88.1 14 1.8.0 3/15 54 21.7 45 21.0 6.73 8.7 97 4.56 6.13 93.7 17 18.7 4/1 56 23.9 38 29.0 6.55 7.5 96 6.70 7.55 99.7 22 18.9 4/15 60 23.0 31 23.0 6.86 8.01 92 21.1 14.0 76.0 28 1L2 5/l 62 22.0 24 27.0 7.38 7.6 94 15.5 5.0 84.0 26 14.1 5/15 61 27.0 17 32.2 6.81 3.6 49 221. 59.0 408.0 1.20 94.0 5/27 61 28.2 1 28.0 7.12 1.5 19 27.4 108. 336.0 154 9.1 TABLE 10 MEASUREHENTS OF OLDEST LARVAL GROUP DURING METM10RPHOSIS, POND A }1ay 4 1·1ay 12 Hay 19 May 25 Nay 31 Max. Hin. X Hax. Nin. X Nax. run. X Hax. Bin. X Max. Min. X Total length 148 135 134 146 136 140 144 135 139 142 135 139 148 138 146 Tail 70 62 60 67 62 65 64 56 61 65 64 63 67 61. 64 Axilla to groin 43 44 40 45 44 44 40 30 36 32 37 33 39 37 38 Front limb 29 21 21 27 21 23 25 22 23 24 24 24 22 22 22 Back limb 24 24 21 26 20 23 23 25 25 26 26 25 24 25 24 Orbit 2 1.9 2 2 2 2 2 1.8 l.9 2 2.2 2 2 1..8 L9 Inter orbital space :1.0 10 9.9 :1.0 10 :1.0 7 9 8 8 7 7 8.2 7.6 8 Gill 16 15 14 11 15 13 0 7 6 8 0 5 0 2 L6 TABLE 11 AIR AND \vATER TEMPERATURES, WATER DEPTHS , Ai'JD CHEMICAL AN.II...LYSES , POND A Mean temp. of Pond Water anal sis at 2:00 p.m. Cl Total ca Ng previous 2 weeks depth Temp. pH Oxy sen C02 mg/1. hardness mg/1 mg/1. Air \·later at in mg/1 %Sat. as CaC03 Date 2 em. depth em. mg/l 3/l 58 20.2 95 19.0 6.90 8.2 87 4.14 J,80 88.0 14 17.9 3/15 54 16.1 91 16.0 6.80 9.1 90 4.58 6.11. 90.1 1.6 18.0 4/1 56 22.3 88 31.0 6.85 7.1 95 6.20 6.91 92.0 19 22.1 4/15 60 20.0 85 22.1 6.85 8.5 96 .4.1 11.0 72.0 26 8.71 5/l 62 23.2 78 26.0 6.92 7.9 97 .4.5 5.0 76.0 24 12.6 5/15 61. 21.0 42 30.0 7.09 9.2 100 39.4 5.0 196.0 58 26.1. 5/30 61 22.0 37 20.0 7.00 9.2 100 .6.7 6.0 192.0 66 6.30 6J LARVAL NUTRITION Determination of 1arval Nutrition In order to determine the extent to which the larvae relied on their yolk sacs as a reserve food supply, ten newly-hatched larvae were kept in bowls of distilled water at J0.5 degrees C. These larvae were denied access to other food sources during this phase of the study. Natural feeding habits were studied in order to determine dietary preferences of various-sized larvae, and dietary variations due to fluctuations in the density of the food organisms. The stomach contents of a sampling of larvae were examined - at weekly intervals. The samplings were made from each pond and included small, intermediate, and large larvae. During the study, 65 larval stomachs were examined. In the field, the specimens were injected with a solution of 50 percent formaldehyde. Digestion was thus halted immediately and the stomach contents were preserved for future examination. The identification of partly digested organisms was difficult and in most cases they could be identified only to genus. Results Field studies showed that a large part of the larvae's diet consisted of invertebrates and algae. All 64 organisms which were eaten by very young larvae were present early in the ponds. The most commonly occurring organisms in the stomachs of young larvae were eubranchiopods, clado• cerans, copepods, ostracods, volvocales, and hormagonales. The ostracods were numerous in many larval diets, but their value as a food source is questionable since they often came through the digestive tract alive. This was observed in all unpreserved specimens which were examined. Table 12 shows an itemized account of the stomach contents of various sized larvae. In general, these findings agree with Little and Keller (1937), Smith (1934), and Rahn (1941) who reported on the continuous tiger salamander population. As a greater variety of food organisms became estab• lished in the ponds, the larvae often included them in their diets. Table 13 shows the dates at which new food organisms were first observed in the ponds and the dates at which they first appeared in the stomachs of different sized larvae. By examining water samples from various levels of the infer that most larvae were feed• ponds, it was possible to th of 10 em. to 20 em. ing in water near the shore at a dep food organisms were found at either The most commonly eaten Water less than 25 em. deep. the top or bottom of shallow f d deeper than 30 em. Organisms Few food organisms were oun numerous near the surface tended to be more which were found Table 14. These distributions are shown in in shallow water. TABLE 12 STONACH CONTENTS OF VARIOUS SIZED LARVAE Total LArval Lenth Food Organism 17 23 36 45 52 60 71 83 96 104 121 140 Number of Food Organisms Eaten Rotifer egg 30 15 3 0 0 0 0 0 4 0 0 0 Fairy shrimp Branchinecta 0 2 0 0 16 0 0 0 4 0 9 7 Clam shrimp Caenestheriella 0 0 l 0 0 3 0 0 0 0 0 0 Water flea Dauhnia 1 0 0 0 0 0 45 0 0 0 0 0 Hater flea Nacrothrix l 0 0 1 0 0 23 0 0 0 1 0 \>I ater flea eggs 0 0 0 0 0 0 31 0 0 77 0 0 Copepod 3 0 0 l 28 2 5 0 0 4 4 5 Ostracod 47 26 5 47 18 41 77 740 29 29 44 51 Filamentous green algae strand 0 17 0 0 4 0 0 0 0 0 0 0 Protoderma 0 0 0 30 0 15 16 0 0 0 17 8 Other green non-motile algae X 10 7 0 11 95 4 9 13 47 28 17 3 3 Volvox colony 0 6 0 3 0 0 0 0 0 0 1 3 Haematococcus 8 7 2 3 7 2 9 22 14 18 2 3 Nostoc colony 0 0 0 0 0 0 0 0 76 0 37 25 Other blue green algae X 104 2 2 6 0 23 0 121 30 16 Coleoptera 89 18 19 0 0 0 0 0 0 0 0 8 0 1 l !· tigrinum larvae 0 0 0 0 0 0 0 0 J l J J Urodele tadpole 0 0 0 0 0 0 0 0 1 0 0 0 r1osquito larvae 1 0 2 2 0 2 4 6 0 0 0 1 Dragonfly larvae 0 0 0 0 0 0 0 . o 0 0 1 1 Adult back Sl'l"immer Buenoa 0 0 0 1 0 2 0 0 l 2 0 2 Exponential numbers indicqte estimates. '-" 66 TABLE 13 APPEARANCE OF NEW FOOD ORGANISMS fute of Initial Appearance Total Pond Organism Length of Predating In Pond In Larval larvae Stomach Tree Frog B Tadpole Feb. 18 Apr. 13 83.0 mm. Tiger Sala- c mander Larvae Mar. 1 Mar. )1 37-5 mm. Mosquito c larvae Mar. 15 Mar. 17 22.5 mm. Adult Crawling Water Beetle Mar. 22 Apr. 6 68.0 mm. c Adult Back mm. c Swimmer Apr. 1 Apr. 6 58.0 6? TABLE 14 DEPTHS AT WHICH PRINCIPAL FOOD ORGANISMS OCCURRED Strata Within Water of 25 em Depth Organism 1-5 em. 5-10 em. 10-20 em. 20-25 em. From From From From Surface Surface Surface Surface Clam Shrimp 2 C&.enes the;riell 5 Fairy Shrimp (!2ranchine eta) 1 J Water Flea 5 (I:aphnia) 2 ( MaQrQ b::r:l.x.) 7 15 Copepos 7 25 5 40 20 Ostracod 4 103 68 Some dietary variations correlate positively with fluctuations in the population densities of the food organ• isms. These variations were most pronounced in relation to Eubranchiopod, Cladoceran, Copepod, and Ostracod densities. These relationships are demonstrated by comparing Table 15 which shows food organism densities with Table 16 which shows frequency of ingestion. Some dietary differences appeared to reflect indi• vidual preferences independent of food organism densities. Some of the most striking deviations from the usual diets are presented in Table 17. TABLE- 15 PRINCIPAL FOOD ORGANISM DENSITIES IN POND C Quantity of Organisms in Sample Organism · March March April April May 1 15 1 15 1 Fairy Shrimp aianchlne eta 14 2 0 0 0 Clam Shrimp Caenestherlella 18 6 5 0 59 Water Flea 5x102 3 0 0 0 taphnla 1 0 0 X:Q lll:14 0 0 6 4 9 5 14 Copepod 75 4.2x102 Ostracod 8 16 J2 estimated quantities. Exponential numbers indicate TABLE 16 PRINCIPAL FOOD ORGANISMS, FREQUENCY OF INGESTION BY DATE IN POND C Date of Occurrence 3/9 3/9 3/17 3/17 3/23 3/23 3/31 3/31 3/31 4/6 4/6 Total Length of Larva 22 22.7 22.5 22.7 39.4 50.8 20.5 41 29.7 37·5 33 Food Organisms: Fairy Shrimp Branchinecta 7 3 0 2 2 0 1 0 0 1 0 Clam Shrimp 0 0 0 0 4 0 0 2 0 2 1 Water Fleas Daphnia 0 7 1 0 2 0 1 1 2 0 0 I1acrothrix 2 1 1 0 1 0 0 0 0 0 0 Copepod 1 2 7 0 3 0 1 0 0 0 1 Ostracod 11 1 22 26 0 9 1 45 48 48 26 Water Flea Eggs 14 2 30 15 23 6 0 13 20 1 0 Date of Occurrence 4/6 4/6 4/6 4/6 4/13 4/13 4/13 4/13 4/13 4/21 5/1 Total Length of Larva 29.7 33 58 60 17.2 36 46 89 83 97 71 Food Organisms: Fairy Shrimp Branchinecta 0 0 0 0 0 0 0 0 0 0 0 Clam Shrimp 2 1 0 3 0 1 0 0 0 0 0 Water Fleas Daphnia 0 0 0 0 0 0 0 0 0 0 50 f1acrothrix 0 0 0 0 0 0 0 0 0 1 25 Cop epod 0 1 0 2 1 0 0 0 0 1 5 Ostracod 48 26 5x1o3"'' 41 47 5 6 56 7.4x1o1* 10J 85 Water Flea Eggs 1 0 0 0 0 0 0 0 2 0 35 *The exponential numbers indicate estimated quantities. ---.) 0 71 TABLE 17 DEVIATIONS FROM THE USUAL LARVAL DIET Number of Dietary Total Length of Pond Date of Ingesting larvae Occurence Specialties Food Organism Quantity Ostracod 5x1o3 58 mm. c Apr. 6 Ostracod ?.4x102 83 mm. c Apr. 13 Volvox 97 68.2 mm. B Apr. 6 Ostracod 1.3x102 61 mm. c Apr. 13 Spirogyra 215 cells 58 mm. A Apr. 13 Piece of Apr. Cardboard (2mm.)2 55 mm. A 13 Mud Large Quantity 28.6 mm. A Apr. 13 Exponential numbers indicate estimated quantities. 72 LARVAL COMPETITORS AND PREDATORS The ponds were inhabited by few vertebrate species other than tiger salamander larvae. some of these species may be considered as competitors or predators of the salamander larvae. Competitors Toads, frogs, and anuran tadpoles were frequently found in the ponds. From late February to late May, .H.Yl.g_ regilla adults and their tadpoles were present in all three ponds; Scaphiopus hamrnondii tadpoles were present from late February to late April. In mid-April an inventory of the vertebrate life in Pond C showed that the pond was inhabited by 1,234 anuran tadpoles, the majority of which were Scaph1opus hammond11. Periodic examinations of the stomachs of H· regilla adults and both tadpole species indicated that they competed with the tiger salamander larvae for some foods. H. regilla adults often consumed Buenoa ·and Halipus .; their tadpoles were found to have shared the population of JTotoderma, Yolyox, ftgematococcus.and blue-green algae. Scaphiopus hammondlt tadpoles competed with the salamander larvae by eating eubranchiopods, cladocerans, copepods, volvocales, and hormogonales. 73 The hind-gut of the larvae was frequently infected with Trichomonas. This organism is a non-pathogenic parasite. Its harmfulness as a hind-gut parasite is questionable. Predato s The temporary duration of the ponds prevented the establishment of fish populations and discouraged the presence of many potentially predatory vertebrate species. No avian or mammalian predators were seen or evidenced in or around the ponds. Apparently, the larva population was threatened by only a few vertebrate species. Stebbins (1951)reported that spadefoot tadpoles often consume members of their own species during the later part of their aquatic existence and, since these tadpoles occupied the pond concurrently with various sized larvae, the tadpoles were considered as potential predators. An examination of the stomachs of different sized tadpoles indicated that neither spadefoot toad tadpoles nor salamander larvae had been eaten. However, the manner in which spadefoot toad tadpoles consume vertebrate prey may have made the identifi• cation of the prey impossible. In early April one garter snake (Thamnophis), measuring 46.J em. was found in Pond C• An examination of the snake's stomach gave no evidence Of ts predation on tiger salamander larvae. 74 During the first half of April four catesbeiana adults were seen occasionally in Pond C. Two of these were captured; their head-and-body lengths were 7.2 and 7-9 em. The stomach of the larger bull frog contained one tiger salamander larvae and another well-digested, unidentifiable, immature amphibian. The stomach of the smaller bull frog contained no amphibians. The greatest incidence of predation was observed in the feeding habits of the large and middle-sized tiger salamander larvae. Cannibalism was common because the ponds contained larvae of many different hatching dates. Evidence of cannibalism was first observed during the latter part of March. During that period, for the first time within the breeding season, the ponds were occupied by larvae which were at least twice as large as coexisting larvae. Variations in pigmentation may have given the salamander larvae some protection against their predators. The larvae which inhabited the ponds appeared to differ in pigmentation in response to water turbidity. The rain water which formed Pond C was considerably less turbid than that which formed Ponds A and B. The larvae which lived in Pond C's comparatively clear water were olive green; those which lived in Pond A's and Pond B's muddy water were much lighter in color. These differences in turbidity are expressed in ble 18 in terms of the waters' optical densities and Similar correlations quantities of undissolved materials. been observed in between pigmentation and turbidity have Scaphlopus tadpoles by Stebbins (1954). 75 TABLE 18 WATER TURBIDITY OF PONDS A, B, AND C ON APRIL 1 Percent Transmittance (at Wave Length of Grams of Undissolved 3900 Angstroms,· Material in 50 ml. Pond through 10 of Pond Water Percent Pond Water) 27.5 0.1557 B 28.5 0.1284 A 82.0 0.0)43 c 76 SUMMARY AND SUGGESTIONS Summary As corroborated in the findings of others, the California tiger salamander was found to breed only in long-lasting temp?rary pools. This exclusive use of long• lasting ponds indicated that the adults either inhabited only the area surrounding the breeding ponds, or migrated several miles before reaching suitable breeding sites. The former supposition was supported by an extensive initial spawning in the late-developing pond. The salamanders spawned between January 27 and April 1 and appeared to spawn only after rain. Most rains which initiated spawning occurred during, or were soon followed by, the night. During the breeding season the embryo incubation period, which varied from 10-14 days, decreased as the water temperature increased • This relationship was most pronounced in the small pons· Neither the embryos nor the larvae appeared to be affected by the toxic properties of the turkey mullein used Was the only organism which for egg deposition. Saprolegnia was observed to attack the developing embryos. ed to be influenced by diet, Larval growth appear 77 pond age, pond temperature pond depth ' , and metamorphosis. m each pond the utilization of vert b t e ra e food organisms correlated with periods of rapid growth. Comparisons of growth rates in each pond throughout the same period showed that growth generally progressed most rapidly in the large, well-established pond which allowed the larvae to feed on a wide variety of food organisms and to move into deep, warm water during the night. All larval groups exhibited a decreased growth rate during metamorphosis. This change was accompanied by decreased food consumption. Metamorphosis appeared to be influenced by environ- mental changes and larval age. During the period of rapid pond evaporation, chemical and thermal variations appeared to operate on the metamorphic rates of larvae of all ages and sizes. Under the conditions of a stable environment, larval age appeared to be the only factor which initiated metamorphosis. Stomach content analyses showed that small salamander larvae consumed motile and filamentous algae and inverte• brates. As growth progressed, the larvae diet often and smaller salamander consisted of toad and frog tadpoles larvae. The environmental distribution of food organisms indicated that most feeding occurred in shallow water. t d with the salamander Toad and frog tadpoles compe e brate food organisms. The larvae for algal and inverte 78 competitive potentials of the 1 arval hind-gut parasite, Trichomonas, is questionable. Few potentially predatory vertebrates inhabited the temporary ponds. One adult bullfrog was found to have preyed on the larvae, but the greatest incidence of preda• tion was observed in the feeding habits of the middle sized and large tiger salamander larvae. It appeared that the larvae in different ponds varied in pigmentation in response to water turbidity. These variations may have given the larvae some protection against predators. Suggestions Larval growth, metamorphosis, and mortality should be studied during breeding seasons having less or more pre- cipitation. The factors which appeared to infl ence larval growth and metamorphosis should be analyzed under controlled laboratory conditions. The system used to determine larval age is described under Larval Growth. A more certain, error-free method of determining age could employ tagging methods such as toe or fin clipping. As the ponds evaporated, the water became very turbid and it was difficult to detect the end-points of analytical titrations. The Winkler Test for oxygen content gave This may be explained negative results in very muddy water. 79 as an error in technique; however, the test is known to be unreliable in water of high ionic concentration. Perhaps other analytical techniques could be employed in these situations. LITERATURE CITED 81 LITERATURE CITED BISHOP, Sherman C. 1943. Handbook of Sal"' d the Salamander of the United States, C.an=madana, lmtJer earnsd, California . Comstock Publishing co. , Inc. , Ithaca,· N . Y. , :J. 943. 1941. The Salamanders of Ne1-1 York Ne\ll York State Museum Bulletin , No. 324, Publishd by the Univ. of the State of N .Y., Albany, 1941. DUNN, E . R . 1940. The Ra ces of A..TD.byst oma tigrinum. Copeia, 3 : 154-62. GILCREAS, F . H ellington, Gail P. Edwards and Hichael J. Turas . :1.962. Standard Methods for the Examination of Water and Haste-Hater. American Public Health Association , Inc. JEPSON, Willis L. 1960. A !1anual of the Flowering Plants of California . Univ . of Calif. Press, Berkeley . KRUEGER, \{alter \-1 ., and Karl R. Johansson. 1959 . Principles of I'1icrobiology. W. B. Saunders Co., Philadelphia. LITTLE, E. L. Jr., and J . G. Keller . 1.937. 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