Larval growth in three sympatric Ambystoma salamander species: species differences and the effects of temperature

W. HUBERT KEEN Department of Biological Science, State University of New York, College tit Cortland, Cortland, N Y, U.S.A . 13045

AND

JOSEPH TRAVIS AND JOHN JUILIANNA Department of Biological Science, Florida State University, Tcillaha.ssee, FL, U.S.A. 32306

Received July 25, 1983

KEEN, W. H., J. TRAVIS, and J . JUILIANNA. 1984. Larval growth in three sympatric Amby.stoma salamander species: species differences and the effects of temperature. Can. J. Zool. 62: 1043 - 1047.

Differences in the larval growth of three Ambystoma salamander species that breed in close proximity to each other in space and time in north Florida were investigated under standardized regimes of controlled food levels and temperature. The order of species growth rates was as follows: Ambystoma tigrinum > A. talpoideum > A. opcicum. This order is exactly the reverse of the order in which the species breed. Growth of A. talpoideum larvae was strongly dependent on temperature, whereas A. opacum larval growth was only weakly affected by temperature. Based on these growth rate differences, it is unlikely that A. talpoideum larvae could survive to metamorphosis without special behavioral mechanisms for predator avoidance in habitats with the rapidly growing predatory A. tigrinum larvae. Furthermore, A. opacum larvae would be favored in their growth over those of A. talpoideum at low temperature, while the reverse would be true at higher temperature.

KEEN, W. H., J. TRAVIS et J. JUILIANNA. 1984. Larval growth in three sympatric Amb~l.stoma salamander species: species differences and the effects of temperature. Can. J. Zool. 62: 1043- 104.7.

Les differences dans la croissance larvaire ont fait I'objet d'une etude chez trois especes de salamandres du genre Ambystoma qui se reproduisent dans des regions tres voisines a des periodes tres rapprochees dans le Nord de la Floride; des larves des trois expeces ont CtC gardees a des regimes standardises de nourriture et de temperature. Les taux de croissance suivent cet ordre d'importance: Ambystoma tigrinum > A. talpoideum > A. opacum. Cet ordre est exactement a l'inverse de I'ordre dans lequel les especes commencent a se reproduire. La croissance des larves d'A. talpoideum est fortement reliee a la temperature, alors que celle des larves d'A. opacum ne l'est que faiblement. D'apres ces differences dans les taux de croissance, i l semble evident que les larves d'A. talpoideum seraient incapables de survivre jusqu'a la mktamorphose sans les mkcanismes particu- liers de comportement qui leur permettent d'kviter la prkdation dans les habitats oh elles cohabitent avec les larves predatrices a croissance rapide d'A. tigrinum. 11 ressort aussi qu'a basse temperature. le dkveloppement d'A. opcltum serait favorise au detriment de celui d'A. talpoideum, alors que I'inverse serait vrai aux temperatures plus klevkes.

[Traduit par le journal]

Introduction Timing of life history events such as breeding, development,

and larval or juvenile growth can be of critical importance in the survivorship of cohorts of young. If young animals are particularly susceptible to intra- or inter-specific predation by larger juveniles, then timing of breeding, subsequent growth rates, and consequent body size differences among age groups or species will be major determinants of the nature of any predator-prey relationship. Differences in growth rates between the young of two contemporaneous predatory species can result in the more rapidly growing individuals avoiding predation or even becoming predators on the more slowly growing ones.

These issues are especially critical among salamanders in the genus Ambystoma, in which smaller larvae of one species or cohort may become the prey of larger larvae occurring in the same aquatic habitats. Throughout eastern North America, two or more species of Ambystoma commonly breed in succession in the same ponds (Bishop 1943; Anderson and Graham 1967; Worthington 1968, 1969; Hassinger et al. 1970; Wilbur 1972; Keen 1975; Patterson 1978), and reports of intrageneric preda- tion and cannibalism are common (Stewart 1956; Stine et al. 1954; Hassinger et al. 1970; Anderson et al. 197 1). Such predation is size limited; potential prey can avoid predation by achieving a body size that is sufficiently large relative to the size of the predator (Wilbur 1972). Predator - prey re- lationships in young larvae are important because much evi- dence suggests that amphibian populations are regulated in part

through mortality in the larval stage (Wilbur 1980). Predator-prey relationships among Ambystoma species are

complicated by the temperature dependence of larval growth (cf. Smith-Gill and Berven 1979). If contemporaneously breed- ing species differ in their temperature dependence, then one species may well grow fast enough to become a predator on the other. For species that breed in succession, as temperatures are changing seasonally, the nature of any predator-prey re- lationship depends not only on the phenology of breeding but on the differences among species in temperature dependence. To escape predation by their predecessors, later-breeding spe- cies must be able to outgrow their predecessors over whatever range of temperatures they may encounter. However, smaller larvae may also avoid predation by behavioral mechanisms or by having access to refuges from predation.

In north Florida, three species of Ambystoma breed in close proximity to each other in space and time, and their larvae may develop in the same pond. The earliest breeding of the three species, Ambystoma opacum, is near the southern edge of its range in the Tallahassee area (Stevenson 1976). It deposits its eggs during autumn in depressions of dry pond basins, where larvae hatch upon filling of the ponds by winter rains. Adults of the second species, Ambystoma talpoideum, migrate into breeding ponds during rainy periods between December and February (Carr 1940; Shoop 1960; Mount 1975). Deposition and development of eggs and larvae therefore occur later than for A. opacum. The third species, Ambystoma tigrinum, breeds during the winter in a shorter temporal period than

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Dep

osito

ry S

ervi

ces

Prog

ram

on

10/0

7/14

For

pers

onal

use

onl

y.

C A N J ZOOL. VOL 62 . 1984

A opocum ( 20 O C )

a tolpoideum (20°C) opocum ( 1 0 . 6 O C )

o tolpoideum ( 1 0.6 O C

DAYS SINCE INlTlATlaN FIG. I . Growth of A . rulpoideurn and A . opucurn larvae at constant

low ( 10.6"C) and constant high (20°C) temperatures.

A . tcdpoideum, but within the limits of the breeding period of A . talpoideum. Although actual times of breeding depend on temperature and rainfall, and thus may vary considerably from year to year and even among locales in the same year, the sequence outlined above is maintained. Clearly, however, degree of temporal separation among the three species will show a wide variation over years. Thus, the nature of the relationships among species, whether predator and prey, poten- tial competitors, or merely noninteracting sequential exploiters of the same habitat, depends on breeding phenology, species- specific growth rates, and temperature dependence of those growth rates.

This study was designed to investigate species differences in growth under standardized regimes of controlled food levels and temperature. For a pair of species separated in time of breeding, A . opacwm and A . tulpoicieum, we investigated whether the later breeding species, A . tulpoideum, could out- grow its potential predator at temperatures characteristic of its own breeding period as well as at temperatures characteristic of the hatching period of A . opacaum. An inability to outgrow a predecessor at the lower temperature characteristic of its hatch- ing period would impose a limit on initiation of reproduction that is based on a requirement for a minimum water tem- perature. For a pair of species that can breed at the same time, A . tulpoideum and A . tigrinum, we investigated whether the species displayed any difference in growth rate at a constant temperature characteristic of their breeding period.

Materials and methods Eggs and larvae of the three Amby.srorntl species used in the experi-

ments were collected in January and February of 1983 from ponds in Leon County, Florida. Arnbysrornu opuc-urn were collected as small

larvae, and A . rtrlpoideurn and A . rigrirlurn larvae were hatched in the laboratory from eggs collected from ponds. Prior to initiation of the experiments. eggs and larvae were maintained in polyethylene pans containing 6 L of well water: water was replaceti every 2-3 days, and larvae were fed equal aliquots of plankton obtained from ponds.

To test for effects of species and temperature on growth, larvae of A . rtrlpoidcurn and A . opticam were grown for 62 days in a 2 x 2 (species x temperature) factorial design with 15 larvae of each species within each temperature. Larvae were raised individually in I I x I I x 4 cm polyethylene containers with 450 mL of well water which was changed every 10 or I I days at the time of measurement.

Larvae in the low tc~nperaturc ( 10.6 -+ 1°C) were maintained in an environmental chamber under a 12 h light : 12 h dark regime syn- chronized approximately with the natural light cycle. Larvae in the high temperature (20 -+ 1°C) were kept in a controlled environment room under the same light regime described for the low temperature. All larvae were fed equal aliquots of pond plankton or equal numbers of equal-sized hylid tadpoles (Hvltr c.ruc./fer, P.seudtrc.ri.s orntrrtl). Plankton was collected and concentrated using a plankton net, and, to assure homogeneous distributions of plankton among aliquots during a feeding. cultures were mixed thoroughly before each aliquot was extracted. All larvae were given food daily, although quantities pro- vided in the latter days of the experiment probably did not sustain maximum growth rates.

Size of each larva was measured from photographs taken every 10 or I I days of each individual larva in its container. Total length was scaled to mass as follows. Twenty A . opticurn larvae not in the experi- ment were photographed as above and killed by freezing. Carcasses were vacuum dried for 48 h at 60°C, and dry weights were taken to 0 . I -mg precision. Ilry weights varied from 2.5 to 28.5 mg, and total lengths varied from 19.30 to 37.09 mm. Since there was a strong correlation between these measures of body size ( r = 0.91, P < 0.005). we used our photographic measures of total length to estimate mass. Decrease in sample sizes during experiments were caused in part by loss of measurements using the photographic tech- nique and in part by mortality.

Variances aniong experimental groups were homogeneous. Anal- yses of variance were used to test two hypotheses: ( i ) total length (TL) was not significantly different between species and temperatures at the six measurement times; ( i i ) size-specific growth rate of TL was not significantly different between species and temperatures over the five time intervals. Size-specific growth rates were calculated following Travis (1980); this method yields growth rate per millimetre TL. Statistical analyses based on growth rate are independent of absolute sizes, thus avoiding confounded analyses if species differences in size exist.

To evaluate species differences in growth rates of A . rtrlpoideurn and A . tigrinurn larvae. 20 individuals of each (obtained from eggs as described above) were grown at 20.0 2 I "C for 29 days. 'These larvae were kept individually in 13.5 cm diameter x 8.5 cm high poly- ethylene containers with 750 mL of well water. Larvae were fed equivalent quantities of plankton anti, after some growth. hylid tad- poles. Variances among experimental groups were not homogeneous and TL values were squared to equalize variances before analyses (Box et ( 1 1 . 1978). One-way analyses of variance of TL and size- specific growth rate of TL were used to test the hypotheses of no difference in size and growth rates between species.

Results Compcrrison qf' A. opacum and A. talpoideum

Growth trajectories of salamander larvae varied with tem- perature and species identity (Fig. 1). Mean sizes of the four species- temperature groups were not significantly different at day 10, although a species difference ( P < 0.05) was apparent on days 20, 30, 5 1, and 62, and temperature had a significant effect on days 30 and 4.1 (Table I ) . The species differences result from a consistently larger average TL of A . talpoideum and the temperature differences result from a larger average TL

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Dep

osito

ry S

ervi

ces

Prog

ram

on

10/0

7/14

For

pers

onal

use

onl

y.

KEEN ET AL

TABLE I. Analyses of variance with respect to species and temperature for total length at six times (days) and size-specific growth rates over five time intervals for A. talpoideum and

A. opacwm

Total length Growth rate

Time interval

Day F df P (days) F df P

10 Species Temperature Interaction

20 Species Temperature lnteraction

30 Species Temperature lnteraction

41 Species Temperature lnteraction

51 Species Temperature lnteraction

62 Species Temperature lnteraction

10 - 20 Species Temperature Interaction

20-30 Species Temperature Interaction

30-4 1 Species Temperature lnteraction

41 -5 1 Species Temperature Interaction

5 1-62 Species Temperature lnteract ion

at the high temperature than at the low temperature. Interaction between species and temperature was significant for TL of larvae at day 30, as well as for TL at each of the three sub- sequent measurements. This interaction is caused mainly by a stronger temperature dependence in A. talpoideurn. The tem- perature dependence of A. opacurn was quite weak (Fig. 1 ), as indicated by similar slopes for larvae grown at high and low temperatures.

In the analysis of variance, no main effects of species iden- tity were detected in size-specific growth rate (Table 1). Effect of the temperature difference was significant over four of five intervals. Species identity did have an effect on size-specific growth rate, however, by interacting strongly with tempera- ture during the interval from day 20 to day 30. The effect of this significant species- temperature interaction would persist as a difference in total lengths over subsequent time intervals, even though growth rates were not different in the later measurements.

The quantity of food provided late in the experiment was insufficient to sustain maximum growth rate in the larvae. This effect is noticeable in the slowing of growth in both species in the high-temperature treatments (Fig. 1). At this point in the experiment, individuals in the low-temperature treatment con- tinued to grow and attained the same average size as individuals in the high-temperature treatment. Our feeding records sug- gested that animals in the low-temperature treatment were being fed to near satiation while high-temperature animals were consuming food rapidly but not growing. We concluded, there- fore, that prolongation of the experiment would lead to an artifactual increase in growth of the low-temperature animals, so we stopped the experiment.

Comparison of A. talpoideum and A. tigrinum Larvae of these species were not detectably different in size

at the start of the experiment (Fig. 2, Table 2). At each of the three subsequent measurements, A. tigrinurn TL was signifi- cantly greater than that of A. talpoideurn. Species differences

DAYS FIG. 2. Growth of A. talpoideum and A. tigrinum at 20°C

in size-specific growth rate were highly significant for the first and third time intervals and marginally significant for the second interval (Table 2). This difference clearly results from the more rapid growth rate of A. tigrinurn (Fig. 2).

Discussion We found differences in growth between species in both

experimental pairs of Ambystoma that were independent of

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Dep

osito

ry S

ervi

ces

Prog

ram

on

10/0

7/14

For

pers

onal

use

onl

y.

1046 CAN. J . ZOOL. VOL. 62. 1983

TABLE 2. One-way analyses of variance for total length at four times (days) and for size-specific growth rates of total length over three time

intervals for A . tigrinum and A . talpoideum

Total length Growth rate

Ti me interval

Day F d f P (days) F d f P

temperature. Although we did not test A . opac-um and A . tigri- num in the same experiment, the following order of growth rates determined at 20°C was clear from the experiments: A . tigrinum > A . tulpoideum > A . opucum. The much faster growth of A . tigrinum sets it apart from the more similar, yet still significantly different growth rates of the other two spe- cies. Comparisons with Ambystoma growth rates from other studies are not feasible because the quantity and quality of food provided in different experiments are not standardized.

Temperature affected growth of A . tulpoideum and A . opac- um larvae differently. The former species grew much faster in high than in low temperature, whereas the growth of A . opacum was less influenced by temperature. This species difference would manifest itself in a growth advantage for A . talpoideum as water temperature warms during the late winter and spring. Alternatively, prolonged cold water temperature may increase A . opacum's initial size advantage, which results from its earlier breeding and hatching of larvae. Temperature is more likely to become important in the northernmost portions of the range of A . tulpoideum, where it also occurs in the same habitats with A . opacwm (Smith 1961; Mount 1975; Petranka and Petranka 1980), than in the southern part of its range, where water temperature in winter does not reach such low levels and remains low for a shorter time. Thus, in the northern part of its range, the early limit on A . tcllpoicleum breeding may be set evolutionarily by the inability of larvae to outgrow A . opacum at cooler temperatures, provided A . opacum has a head start.

Examination of the numerous accounts of Ambvstomu life histories in the literature reveals extremely wide variation in breeding times and larval growth between species, between years, and between geographic locations. However, given specified environmental conditions and our information on larval growth, the probable outcome of the cooccurrence of combinations of Ambystoma species can be predicted, as- suming that salamander larval predation is a common occur- rence. Given the similar breeding times of A . tulpoideum and A . tigrinum, and the much more rapid growth of the latter, it seems unlikely that A . talpoideum larvae could survive to meta- morphosis in the presence of A . tigrinum. From the numerous natural history accounts (e.g., Carr 1940; Smith 1961 ; Mount 1975), it appears that, although breeding populations of adults and developing larvae of A . tigrinum and A . talpoideum are occasionally found in the same ponds, the former species typically breeds in larger bodies of water than A . talpoideum. We found neither adults nor larvae of these two species together in the study area and conclude that segregation of breeding sites probably resulted from predation by A . tigrinum larvae on A . talpoideum larvae. Avoidance of predation by

small larvae may, of course, be facilitated through behavioral mechanisms, as Hassinger et u l . ( 1970) believed to be the case for two cooccurring species of Ambystoma larvae in New Jer- sey.

We encountered A . tnlpoicleum eggs in the same ponds with A . opuc.nm larvae but have not found a report of intrageneric predation between these species. Whether A . tulpoideum hatch- lings would be susceptible to predation by A . opucum larvae when the two occupied the same ponds would depend primarily on the size attained by the latter before A . talpoideum larvae hatched. Because of its more rapid growth at warm tempera- tures, A . tcllpoitleurn could attain a size refuge from predation if temperature rises steadily and larvae hatch before A . opuc.um grow to a size permitting predation.

It is apparent that A . t i ~ r i n u m larvae frequently become the dominant predators among assemblages of amphibian larvae (Smith 1961; Wilbur 1972; Mount 1975) when given a brief respite from being preyed upon themselves as hatchlings. Given its rapid growth, A . tigrinum can readily achieve a size refuge from further predation. Whether A . tigrinum can become the dominant predator will depend upon the phenology of events associated with breeding and larval growth, relative densities, and the degree to which it must exceed its prede- cessors in body size to prey on them. This last requirement will be a function not only of size, but also of the allometric growth pattern of jaw size and head width (Morin 1983; Smith 1983).

Acknowledgments This work was supported by National Science Foundation

grants DEB 8 1-02782 to J.T. and DEB 82- 10396 to J.T. and W.H.K.

ANDERSON, J. D., and K. E. GRAHAM. 1967. Vertical migration and stratification of larval Ambystoma. Copeia, 1967: 371 -374.

ANDERSON, J. D., D. D. HASSINGER, and G. H. DALRYMPLE. 197 1. Natural mortality of cggs and larvae of Amb~storntr r . rigrinum. Ecology, 52: 1 107 - 1 1 12.

BISHOP. S . C. 1943. Handbook of salamanders. Comstock Publishing Co.. lthaca, NY.

Box, G. E. P., W. G. HUNTER. and J. S. HLIN'T'ER. 1978. Statistics for experimenters. John Wiley and Sons. New York.

CARR, A. F. 1940. A contribution to the herpetology of Florida. Univ. Fla. Publ. Biol. Sci. Ser. 3: 1 - 118.

HASSINGER. D. D.. J. D. ANDERSON, and G. H. DALRYMPLE. 1970. The early life history and ecology of Ambysrorntr rigrinum and Ambysromtr opacurn in New Jersey. Am. Midl. Nat. 84: 474-495.

KEEN, W. H. 1975. Breeding and larval development of three species of Amb~srorntr in central Kentucky (Amphibia: Urodela). Herpetologica, 31: 18 - 2 1 .

MORIN, P. J. 1983. Predation, competition, and the composition of larval anuran guilds. Ecol. Monogr. 31: 1 19- 138.

MOUNT, R. H. 1975. The reptiles and amphibians of Alabama. Auburn Printing Co., Auburn, AL.

PATTERSON, K. K. 1978. Life history aspects of paedogenic popu- lations of the mole salamander, Ambystoma rtrlpoideum. Copeia, 1978: 649-655.

PETRANKA. J. W., and J. G. PETRANKA. 1980. Selected aspects of the larval ecology of the marbled salamander Ambvsroma opacam in the southern portion of its range. Am. Midl. Nat. 104: 352-363.

SHOOP. C. R. 1960. The breeding habits of the mole salamander in southeastern Louisiana. Tulane Stud. Zool. 8: 65-82.

SMITH, D. C. 1983. Factors controlling tadpole populations of the chorus frog (Pseudtrc.ris trisrritrra ) on Isle Royale, Michigan. Ecology, 64: 50 1 -5 10.

SMITH. P. W. 196 1 . The amphibians and reptiles of Illinois. 111. Nat. Hist. Surv. Bull. No. 28.

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Dep

osito

ry S

ervi

ces

Prog

ram

on

10/0

7/14

For

pers

onal

use

onl

y.

KEEN ET AL. 1047

SMITH-GILL, S. J . , and K. A. BERVEN. 1979. Predicting amphibian metamorphosis. Am. Nat. 113: 563-585.

STEVENSON, H. M. 1976. Vertebrates of Florida. University Press of Florida, Gainesville, FL.

STEWART, M. M. 1956. The separate effects of food and temperature differences on development of marbled salamander larvae. J . Elisha Mitchell Sci. Soc. 72: 47-56.

STINE. C., JR., J. A. FOWLER. and R. S. SIMMONS. 1954. Occurrence of the eastern tiger salamander, Amb~.stoma tigrirlltrn tigrinum (Green) in Maryland, with notes on its life history. Ann. Carnegie Mus. 33: 145-148.

TRAVIS, J . 1980. Genetic variation for larval specific growth rate in the frog Hyla gratiosa. Growth. 44: 167- 18 1.

WILBUR. H. M. 1972. Competition. predation. and the structure of the Ambystoma - Rancl ,sylvcrric*cr community. Ecology, 53: 3-21.

1980. Complex life cycles. Annu. Rev. Ecol. Syst. 11: 67-94.

WORTHINGTON, K. D. 1968. Observations on the relative sizes of three species of salamander larvae in a Maryland pond. Herpetologica. 24: 242-246.

1969. Additional observations on sympatric species of sala- mander larvae in a Maryland pond. Herpetologica, 25: 227-229.

Can

. J. Z

ool.

Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Dep

osito

ry S

ervi

ces

Prog

ram

on

10/0

7/14

For

pers

onal

use

onl

y.