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KOENIG AND LIVINGSTON-KILLIFISH EMBRYOLOGY KOENIG AND LIVINGSTON-KILLIFISH EMBRYOLOGY

. 1967. Fundulus, p. 113-122. In: Methods in developmental biology. F. Wilt and N. Wessels (eds.). Thomas Y. Crowell Co., New York.

Wourms, J. P. 1967. Annual fishes, p. 123-137. In: Methods in Developmental Biology, F. Wilt and N. Wessels (eds.). Thomas Y. Crowell Co., New York.

. 1972a. Developmental biology of annual fishes. I. Stages in the normal development of Austrofundulus myersi Dahl. J. Exp. Zool. 182: 143-153.

. 1972b. The developmental biology of an- nual fishes. II. Naturally occurring dispersion and reaggregation of blastomeres during the development of annual fish eggs. J. Exp. Zool. 182:169-200.

. 1967. Fundulus, p. 113-122. In: Methods in developmental biology. F. Wilt and N. Wessels (eds.). Thomas Y. Crowell Co., New York.

Wourms, J. P. 1967. Annual fishes, p. 123-137. In: Methods in Developmental Biology, F. Wilt and N. Wessels (eds.). Thomas Y. Crowell Co., New York.

. 1972a. Developmental biology of annual fishes. I. Stages in the normal development of Austrofundulus myersi Dahl. J. Exp. Zool. 182: 143-153.

. 1972b. The developmental biology of an- nual fishes. II. Naturally occurring dispersion and reaggregation of blastomeres during the development of annual fish eggs. J. Exp. Zool. 182:169-200.

. 1972c. The developmental biology of an- nual fishes. III. Pre-embryonic and embryonic diapause of variable duration in the eggs of annual fishes. J. Exp. Zool. 182:389-414.

YAMAMOTO, T. 1967. Medaka, p. 101-111. In: Methods in developmental biology, F. Wilt and N. Wessels (eds.). Thomas Y. Crowell Co., New York.

DEPARTMENT OF BIOLOGICAL SCIENCE, FLORIDA STATE UNIVERSITY, TALLAHASSEE, FLORIDA 32306. PRESENT ADDRESS (CCK): GRICE MA- RINE BIOLOGICAL LABORATORY, COLLEGE OF CHARLESTON, CHARLESTON, SOUTH CAROLINA 29412. Accepted 8 May 1975.

. 1972c. The developmental biology of an- nual fishes. III. Pre-embryonic and embryonic diapause of variable duration in the eggs of annual fishes. J. Exp. Zool. 182:389-414.

YAMAMOTO, T. 1967. Medaka, p. 101-111. In: Methods in developmental biology, F. Wilt and N. Wessels (eds.). Thomas Y. Crowell Co., New York.

DEPARTMENT OF BIOLOGICAL SCIENCE, FLORIDA STATE UNIVERSITY, TALLAHASSEE, FLORIDA 32306. PRESENT ADDRESS (CCK): GRICE MA- RINE BIOLOGICAL LABORATORY, COLLEGE OF CHARLESTON, CHARLESTON, SOUTH CAROLINA 29412. Accepted 8 May 1975.

Embryonic Mortality in Pseudophryne (Anura: Leptodactylidae)

DAVID S. WOODRUFF

Australian toadlets Pseudophryne bibroni, P. dendyi and P. semi- marmorata lay medium-sized telolecithal eggs in depressions on the ground in recognizable batches of 70-90 ova. Observation of saprovoric fungal infestations in 50 field-collected batches led to the retrospective determination of natural embryonic mortality patterns. 98-100% of the ova were fertilized and had commenced development. Embryonic mortality was generally less than 5% (range 0-11%) and most failures occurred during gastrulation. Hatching occurs after 4-6 weeks when the hind limb bud appears.

Quantitative estimates of embryonic mortality in nature are almost non-existent. There is some evidence that the proportion of eggs that are fertilized is lower in anurans that deposit their eggs in water than in Pseudophryne. Comparable studies of two ranids support the conclusion that survival of encapsulated embryos is high except in cases where en- vironmental factors act catastrophically. Thus, the survivorship curves of these anurans do not become highly concave until the aquatic larval stage. The significance of this fact on the evolution of the relative dura- tion of the three stages of the anuran life cycle does not appear to have received much attention.

Embryonic Mortality in Pseudophryne (Anura: Leptodactylidae)

DAVID S. WOODRUFF

Australian toadlets Pseudophryne bibroni, P. dendyi and P. semi- marmorata lay medium-sized telolecithal eggs in depressions on the ground in recognizable batches of 70-90 ova. Observation of saprovoric fungal infestations in 50 field-collected batches led to the retrospective determination of natural embryonic mortality patterns. 98-100% of the ova were fertilized and had commenced development. Embryonic mortality was generally less than 5% (range 0-11%) and most failures occurred during gastrulation. Hatching occurs after 4-6 weeks when the hind limb bud appears.

Quantitative estimates of embryonic mortality in nature are almost non-existent. There is some evidence that the proportion of eggs that are fertilized is lower in anurans that deposit their eggs in water than in Pseudophryne. Comparable studies of two ranids support the conclusion that survival of encapsulated embryos is high except in cases where en- vironmental factors act catastrophically. Thus, the survivorship curves of these anurans do not become highly concave until the aquatic larval stage. The significance of this fact on the evolution of the relative dura- tion of the three stages of the anuran life cycle does not appear to have received much attention.

OUR understanding of the considerable vari- ation in life history strategies among

anurans is still at a relatively descriptive stage (Salthe and Duellman, 1973; Salthe and Mecham, 1974). This is partly because of the lack of reliable quantitative data on survivor- ship in nature (Turner, 1962; Porter, 1973) and is especially true for the embryonic stage where only a few estimates of survival rates in nature appear in the literature. Four estimates known to me concern anurans which deposit their eggs in water: Bufo cognatus (Bragg and Bressler, 1951), Discoglossus pictus (Knoepffler, 1962), Rana sylvatica (Herreid and Kinney, 1966) and

OUR understanding of the considerable vari- ation in life history strategies among

anurans is still at a relatively descriptive stage (Salthe and Duellman, 1973; Salthe and Mecham, 1974). This is partly because of the lack of reliable quantitative data on survivor- ship in nature (Turner, 1962; Porter, 1973) and is especially true for the embryonic stage where only a few estimates of survival rates in nature appear in the literature. Four estimates known to me concern anurans which deposit their eggs in water: Bufo cognatus (Bragg and Bressler, 1951), Discoglossus pictus (Knoepffler, 1962), Rana sylvatica (Herreid and Kinney, 1966) and

Rana aurora (Calef, 1973); a fifth concerns Eleutherodactylus decoratus a terrestrial breeder. In this paper I report studies of embryonic mortality in three closely related species of Pseudophryne (Anura: Leptodactylidae) which lay their eggs on land.

Pseudophryne bibroni, P. dendyi and P. semi- marmorata occur in southeastern Australia. The noun, toadlet, has been widely employed to describe these small leptodactylids for nearly 50 years (Waite, 1927). Their morphological variation, breeding biology, developmental bi- ology and interactions with one another have been studied in some detail (Woodruff, 1972).

Rana aurora (Calef, 1973); a fifth concerns Eleutherodactylus decoratus a terrestrial breeder. In this paper I report studies of embryonic mortality in three closely related species of Pseudophryne (Anura: Leptodactylidae) which lay their eggs on land.

Pseudophryne bibroni, P. dendyi and P. semi- marmorata occur in southeastern Australia. The noun, toadlet, has been widely employed to describe these small leptodactylids for nearly 50 years (Waite, 1927). Their morphological variation, breeding biology, developmental bi- ology and interactions with one another have been studied in some detail (Woodruff, 1972).

445 445

COPEIA, 1976, NO. 3

TABLE 1. EMBRYONIC MORTALITY IN THREE SPECIES OF

Pseudophryne. N is the number of batches within each group. Locality designations are generalized; for precise information see Woodruff (1972).

% embryonic mortality

N Mean Range

P. bibroni You Yangs, central Victoria 8 4.4 1.0-10.7 Cherrypool, western Vic. 3 4.0 0.0-9.9 Gosford, eastern New South

Wales 3 2.8 1.4-4.9 Intraspecific in vitro crosses 8 5.7 0.0-10.5

P. dendyi Walhalla, eastern Vic. 4 5.8 0.0-8.8 Khancoban, southern N.S.W. 3 5.1 3.7-6.2 Other localities 5 4.1 0.0-8.3 Intraspecific in vitro crosses 3 8.3 3.5-12.0 P. semimarmorata Halls Gap, western Vic. 9 4.2 1.3-9.7 Woodstock, central Vic. 6 4.3 0.7-6.6 Bunyip, eastern Vic. 4 1.1 0.0-2.9 Other localities (Vic.) 5 6.7 3.6-9.2 Intraspecific in vitro crosses 3 2.1 0.0-6.2

These toadlets lay their eggs on the ground after the first autumn (March-April) rains in situations which subsequently become flooded during the winter (June-August). The eggs are laid in relatively discrete batches averaging between 70-90 ova. The intracapsular em- bryonic stage of development is protracted, lasting 4-6 weeks, and the larvae are relatively advanced (Gosner, 1960; Stage 27) when they hatch. The larval phase is aquatic and spans about five months. Metamorphosis occurs in the spring and early summer.

Pseudophryne eggs are relatively large (ovi- diameters: 2-3 mm) and individually sur- rounded by tough, transparent capsules (Salthe, 1963). Groups of hydrated eggs average be- tween 4.0 and 5.2 mm in diameter. Abnormal embryos can be identified within each batch and their development and eventual failure can be observed in detail. Although cytolysis commences soon after death (and fungal hyphae rapidly cover the capsule) the egg usually re- mains intact. The stage of development at the time of death can be determined for a week or more after death. It was therefore possible to determine mortality patterns retrospectively in many batches of eggs collected in the field.

METHODS AND MATERIALS

Patterns of embryonic mortality were studied in 50 batches of field-collected eggs from vari- ous localities in southeastern Australia (Table 1). Following transfer to the laboratory, the eggs in each batch were washed briefly to re- move adhering soil particles and then arranged in a single layer in a petri-dish. Care was taken not to put pressure on the eggs at any stage of collection, transportation or culture. To minimize any possible crowding effect, at least a third of the surface area of each petri- dish was kept empty. The eggs were stored in a constantly illuminated chamber at 16.0 + 1.0 C and kept moist with distilled water. Eggs were inspected individually every 24-48 hrs, at which time each egg was rolled gently to a new position in the petri-dish. When a batch of eggs reached stage 27 it was flooded with water and the larvae and empty capsules were removed. In determining the mortality within each batch, unfertilized ova and those acciden- tally damaged by handling were excluded.

Thirty-five batches were collected sufficiently early in their development to permit the de- termination of mortality rates during the dif- ferent phases of the embryonic period. Failures were recorded as occurring in the develop- mental stage during which the abnormality was first noted. No significance was attached to the fact that some embryos would continue to develop abnormally for several days before dying. To facilitate the comparison of the results the embryonic period is divided into six phases: cleavage (stages 2-9), gastrula (10- 12), neurula (13-16), tail-bud (17-19), advanced embryo (20-25) and hatching (26-27). The stage numbers used here correspond to those used by Gosner (1960).

RESULTS

In field-collected batches the proportion of eggs that were fertilized was very high: ranging between 98-100% in 28 batches.

In 50 batches embryonic mortality varied slightly from batch to batch within the range 0- 10.7% (Table 1). The mean values for the various groups of batches vary between 1.1 and 6.75%. There are slight but statistically insig- nificant differences in the mean values for each species.

The time of failure of 150 embryos from 35 batches is shown in Table 2. More than 85% of the mortality occurred before neurulation and more than half the failures occurred during

446

WOODRUFF-PSEUDOPHRYNE EMBRYONIC MORTALITY

TABLE 2. EMBRYONIC MORTALITY: THE STAGE OF FAILURE IN FIELD-COLLECTED Pseudophryne sPP. The per- centage mortality during each of the six phases of embryonic life are shown. NB = no. of batches in group. NL = no. of cases of mortality observed.

Tail Adv. Species NB NL Cleavage Gastrula Neurula Bud embryo Hatching

P. bibroni 13 54 3.7 57.4 25.9 7.4 1.9 3.7

P. dendyi 10 48 4.2 62.5 27.0 4.2 2.1

P. semimarnorata 12 48 6.2 68.8 10.4 8.3 2.1 4.2

gastrulation. Most abnormal embryos showed some degree of exogastrulation.

DIscUSSION

Embryonic mortality has a number of com- ponents: genetic, developmental and environ- mental. The observed 3-5% mortality in these Pseudophryne would appear to be due to in- trinsic causes. The high frequency of failures during gastrulation suggests that developmental problems become critical during this stage in these telolecithal eggs.

There are of course other factors affecting the survival of Pseudophryne embryos in nature. The terrestrial embryonic phase of the Pseudo- phryne would seem particularly susceptible to desiccation. Adult behavior (egg-laying patterns and oviposition-site selection) coupled with properties of the egg capsules themselves, mini- mize the danger of desiccation under the normal range of environmental conditions. During the course of field work extending over five breeding seasons desiccated eggs were found only once. In that instance many batches failed in one area when the egg-laying period was followed by an abnormally warm, dry spell. These observations suggest that desiccation, ex- cept when it acts catastrophically, is not an important component of embryonic mortality in these species. Freezing is probably also an in- significant factor during most breeding seasons. Eggs are generally not exposed to sub-zero tem- peratures during the course of their develop- ment. Laboratory tests showed that encapsu- lated embryos were able to survive exposure to air temperatures as low as 0 C for at least 12 hrs without apparent harm. A third po- tential factor affecting embryonic survival is predation but at present there is no evidence for this. I conclude that, except when external factors act catastrophically, the Pseudophryne embryos are safe inside their capsules. The esti- mates of embryonic mortality reported here are consequently interpreted as indicative of the

real rates that occur in nature under usual conditions. This conclusion is supported by some additional data on the development of embryos produced by intraspecific in vitro crosses (Woodruff, 1972). Field-collected em- bryos developed at the same rates, when trans- ferred to the laboratory, as the controls of intraspecific crosses. Furthermore, the overall levels of embryonic mortality were similar in the two groups (Table 1).

Although there are considerable data on em- bryonic survival in the laboratory (derived from work on developmental rates, temperature tolerance and hybridization), comparable studies of embryonic survival in nature are almost non- existent. Bragg and Bressler (1951) found 882 unhatched eggs in a batch of 1331 capsules of Bufo cognatus: 66% of the ova either were not fertilized or failed during the embryonic stage of development. Their sample is quite inadequate however to characterize a species which typically deposits 20,000 ova. Knoepffler (1962) states that in Discoglossus pictus (a spe- cies which typically lays 800 eggs at a time) up to 60% of the eggs may not be fertilized. Un- fortunately, he provides no data to support this statement; but does cite one instance in- volving 86 ova of which 41 (48%) were fertilized and commenced to develop in an aquarium. He attributed the low proportion of fertilized eggs to the speed with which the eggs are released and the low motility of the sperm. He did not record embryonic mortality rates. Bogert (1969) reports observations made on three clutches of Eleutherodactylus decoratus: containing 20-32 eggs. In one case it appears that all eggs were fertilized and embryonic survivorship was 100%, in the other cases 0% and 60% of the embryos were developing. Again, the proportion of in- fertile eggs is not estimated. More satisfactory estimates of embryonic survival are available for two North American ranids. In Alaskan Rana sylvatica, Herreid and Kinney (1966) estimated average fertilization success (86%) and em-

447

COPEIA, 1976, NO. 3

bryonic mortality through gastrulation (about 4%). Total mortality during the embryonic period was not estimated; these frogs hatch at stage 20 (Herreid and Kinney, 1967) and total mortality would be higher than that observed through stage 12. A second comparable study concerns Rana aurora in British Columbia (Calef, 1973). Calef noted that 2.4% of the eggs in 35 egg masses failed to hatch and suf- fered fungal infestations. Unfortunately, this figure also includes those eggs that were not fertilized and Calef (pers. comm.) suspects that most cases of fungal infection (and mortality) involved infertile eggs. In addition, Calef ob- served isolated cases of catastrophic mortality due to desiccation or freezing. No egg-mass predation was observed in either study.

The proportion of fertilized eggs is ap- parently higher in the small terrestrial batches of Pseudophryne than in the aquatic egg-masses of the ranids which usually contain 500-900 eggs. The available data indicate that even lower proportions of eggs are fertilized in the larger egg-masses of B. cognatus and D. pictus. Despite this variation it appears that once de- velopment commences embryonic mortality is relatively low in all these anurans except when environmental factors act catastrophically. As noted above this conclusion is supported by studies of laboratory-reared anuran embryos (Moore, 1939; Volpe, 1953).

Both Herreid and Kinney (1966) and Calef (1973) associated fungal infestations with dead embryos. They did not establish whether the relationship between the fungi and the eggs was parasitic or saprovoric. Porter (19'72:455) argues that the relationship is saprovoric and my observations support this interpretation. Under laboratory conditions fungal hyphae rapidly cover the capsules of dead embryos. However, even when eggs are closely packed the hyphae do not spread to adjacent capsules until several days later. Fungal growth was always checked by simply removing the dead embryos. Similarly in nature, under conditions far more favorable to fungal growth, healthy embryos were apparently resistant to infection even when close to a moldy capsule. The basis of this resistance is not known but it may be due to substances similar to the antibacterial agents found in the jelly capsules of ranids and inacti- vated after hatching (see Salthe and Mecham, 1974, for a review).

There is no valid reason why the embryonic mortality of anurans has been neglected. The techniques used by the workers cited above and the author are very simple and can be applied

to most other anurans. A perusal of the herpe- tological literature shows that others, such as Van Gelder and Oomen (1970), have noted fungal infestations among batches of eggs in nature. The careful observation of such occur- rences would fill this gap in our understanding of anuran demography. The generalization that anurans have highly concave survivorship curves during the premetamorphic phases of life is apparently incorrect as far as the embryonic stage is concerned. More quantitative data are required from other groups of anurans before we can hope to develop an adequate theory of anuran life history strategies.

ACKNOWLEDGMENTS I am grateful to M. J. Littlejohn, A. A.

Martin, I. Crick, G. F. Watson, J. J. Loftus- Hills and D. F. Gartside for advice and as- sistance on numerous collecting trips. I thank A. Greer and B. Holldobler for their con- structive criticisms of the manuscript. My research was supported, in part, by a Common- wealth of Australia Postgraduate Award.

LITERATURE CITED BOGERT, C. M. 1969. The eggs and hatchlings of

the Mexican leptodactylid frog Eleutherodactylus decoratus Taylor. Amer. Mus. Novit. No. 2376: 1-9.

BRAGG, A. N., AND J. BRESSLER. 1951. Viability of the eggs of Bufo cognatus. Proc. Okla. Acad. Sci. 32:13-14.

CALEF, G. W. 1973. Natural mortality of tadpoles in a population of Rana aurora. Ecology 54:741- 758. GOSNER, K. L. 1960. A simplified table for staging anuran embryos with notes on identification.

Herpetologica 16:183-190. HERREID, C. F., AND S. KINNEY. 1966. Survival of

Alaskan woodfrog (Rana sylvatica) larvae. Ecol- ogy 47:1039-1041.

, AND . 1967. Temperature and de- velopment of the woodfrog, Rana sylvatica, in Alaska. Ecology 48:579-590.

KNOEPFFLER, L. P. 1962. Contribution a l'etude du genre Discoglossus (Amphibia, Anura). Vie et Milieu 13:1-94.

MOORE, J. A. 1939. Temperature tolerance and rates of development in the eggs of Amphibia. Ecology 29:459-478.

PORTER, K. R. 1972. Herpetology. W. B. Saunders, Philadelphia.

SALTHE, S. N. 1963. The egg capsules in the Amphibia. J. Morphol. 113:161-171.

, AND W. E. DUELLMAN. 1973. Quantitative restraints associated with reproductive mode in anurans, p. 229-249. In: Evolutionary Biology of the Anurans. J. L. Vial, (ed.) Univ. Missouri, Columbia.

, AND J. S. MECHAM. 1974. Reproductive and courtship patterns, p. 309-521. In: Physiology of the Amphibia, 2. B. Lofts, (ed.) Academic Press, New York.

448

WOODRUFF-PSEUDOPHRYNE EMBRYONIC MORTALITY WOODRUFF-PSEUDOPHRYNE EMBRYONIC MORTALITY

TURNER, F. B. 1962. The demography of frogs and toads. Q. Rev. Biol. 37:303-314. VAN GELDER, J. J., AND H. C. J. OOMEN. 1970.

Ecological observations on amphibia in the Netherlands. I. Rana arvalis Nilsson: reproduc- tion, growth, migration, and population fluctua- tions. Neth. J. Zool. 20:238-252.

VOLPE, E. P. 1953. Embryonic temperature adapta- tions and relationships in toads. Physiol. Zool. 26: 344-354.

WAITE, E. R. 1927. The fauna of Kangaroo Island,

TURNER, F. B. 1962. The demography of frogs and toads. Q. Rev. Biol. 37:303-314. VAN GELDER, J. J., AND H. C. J. OOMEN. 1970.

Ecological observations on amphibia in the Netherlands. I. Rana arvalis Nilsson: reproduc- tion, growth, migration, and population fluctua- tions. Neth. J. Zool. 20:238-252.

VOLPE, E. P. 1953. Embryonic temperature adapta- tions and relationships in toads. Physiol. Zool. 26: 344-354.

WAITE, E. R. 1927. The fauna of Kangaroo Island,

South Australia. No. 3. The reptiles and am- phibians. Trans. Roy. Soc. S. Aust. 51:326-329.

WOODRUFF, D. S. 1972. The evolutionary signifi- cance of hybrid zones in Pseudophryne (Anura: Leptodactylidae). Unpubl. Ph.D. Thesis. Dept. of Zoology, Univ. of Melbourne.

DEPARTMENT OF BIOLOGICAL SCIENCES, PURDUE UNIVERSITY, WEST LAFAYETTE, INDIANA 47907. Accepted 1 April 1975.

South Australia. No. 3. The reptiles and am- phibians. Trans. Roy. Soc. S. Aust. 51:326-329.

WOODRUFF, D. S. 1972. The evolutionary signifi- cance of hybrid zones in Pseudophryne (Anura: Leptodactylidae). Unpubl. Ph.D. Thesis. Dept. of Zoology, Univ. of Melbourne.

DEPARTMENT OF BIOLOGICAL SCIENCES, PURDUE UNIVERSITY, WEST LAFAYETTE, INDIANA 47907. Accepted 1 April 1975.

The Reproductive Cycle and its Environmental Control in the Pumpkinseed, Lepomis gibbosus (Pisces: Centrarchidae)

JOHN R. BURNS

The seasonal cycle of gonadal development was studied in pumpkin- seed, Lepomis gibbosus, subject to natural temperatures and day lengths in a local pond. During late May, 1972, gonadal recrudescence in both males and females occurred, as indicated by an increase in the gonosomatic index and the appearance of spermatocytes in the testes and active vitel- logenesis in the ovaries. During this time the pond temperature rose above 12.5 C, while the day length was near 15 hours.

Laboratory experiments with fish exposed to controlled temperatures and photoperiods were performed. The results showed that a minimal temperature between 11.5 and 14.0 C was necessary for recrudescence in males, while one between 14.0 and 16.5 C was necessary for the fe- males. However, the seasonal study indicated that the critical temperature for females is probably lower than 14.0 C. The critical photoperiod for both males and females was probably between 12.0 and 13.5 hrs. Since the critical day length was reached sooner than the increase in pond temperature above the critical level, it appears that temperature is the environmental factor controlling the timing of recrudescence in the spring.

During the early post-spawning period temperatures and day lengths were still above the critical levels. However, no renewed gonadal ac- tivity was observed at this time, suggesting the existence of a post-spawning refractory period.

The Reproductive Cycle and its Environmental Control in the Pumpkinseed, Lepomis gibbosus (Pisces: Centrarchidae)

JOHN R. BURNS

The seasonal cycle of gonadal development was studied in pumpkin- seed, Lepomis gibbosus, subject to natural temperatures and day lengths in a local pond. During late May, 1972, gonadal recrudescence in both males and females occurred, as indicated by an increase in the gonosomatic index and the appearance of spermatocytes in the testes and active vitel- logenesis in the ovaries. During this time the pond temperature rose above 12.5 C, while the day length was near 15 hours.

Laboratory experiments with fish exposed to controlled temperatures and photoperiods were performed. The results showed that a minimal temperature between 11.5 and 14.0 C was necessary for recrudescence in males, while one between 14.0 and 16.5 C was necessary for the fe- males. However, the seasonal study indicated that the critical temperature for females is probably lower than 14.0 C. The critical photoperiod for both males and females was probably between 12.0 and 13.5 hrs. Since the critical day length was reached sooner than the increase in pond temperature above the critical level, it appears that temperature is the environmental factor controlling the timing of recrudescence in the spring.

During the early post-spawning period temperatures and day lengths were still above the critical levels. However, no renewed gonadal ac- tivity was observed at this time, suggesting the existence of a post-spawning refractory period.

SEASONAL cycles of gonadal development have been described for many species of

teleosts. Such cycles are most readily observed in fishes of temperate regions, where substantial variations in temperature and day length may occur over the course of a year. However, studies on the modulation of reproductive cycling by environmental factors are relatively few.

In nearly all of the species studied, the en- vironmental factors which exert the greatest influence upon the initiation of gonadal de- velopment are temperature and day length. In many fishes gonadal recrudescence appears to

SEASONAL cycles of gonadal development have been described for many species of

teleosts. Such cycles are most readily observed in fishes of temperate regions, where substantial variations in temperature and day length may occur over the course of a year. However, studies on the modulation of reproductive cycling by environmental factors are relatively few.

In nearly all of the species studied, the en- vironmental factors which exert the greatest influence upon the initiation of gonadal de- velopment are temperature and day length. In many fishes gonadal recrudescence appears to

depend upon the attainment of both a certain temperature and day length. Included among fishes with this type of gonadal regulation are Phoxinus laevis (Bullough, 1939, 1940; Harring- ton, 1959), Oryzias latipes (Yoshioka, 1963; Kasuga and Takahashi, 1971), Gasterosteus aculeatus (Baggerman, 1957), Culaea inconstans (Reisman and Cade, 1967), Lepomis cyanellus (Kaya and Hasler, 1972) and female Ennea- canthus obesus (Harrington, 1956, 1959).

In the present investigation, seasonal changes in the gonads of male and female pumpkinseed, Lepomis gibbosus, held under natural condi- tions in a local pond were studied. Further

depend upon the attainment of both a certain temperature and day length. Included among fishes with this type of gonadal regulation are Phoxinus laevis (Bullough, 1939, 1940; Harring- ton, 1959), Oryzias latipes (Yoshioka, 1963; Kasuga and Takahashi, 1971), Gasterosteus aculeatus (Baggerman, 1957), Culaea inconstans (Reisman and Cade, 1967), Lepomis cyanellus (Kaya and Hasler, 1972) and female Ennea- canthus obesus (Harrington, 1956, 1959).

In the present investigation, seasonal changes in the gonads of male and female pumpkinseed, Lepomis gibbosus, held under natural condi- tions in a local pond were studied. Further

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Article Contentsp. 445p. 446p. 447p. 448p. 449

Issue Table of ContentsCopeia, Vol. 1976, No. 3 (Aug. 20, 1976), pp. 423-644Front MatterHematologic Observations on the Aquatic and Estivating African Lungfish, Protopterus aethiopicus [pp. 423 - 434]The Embryological Development of the Diamond Killifish (Adinia xenica) [pp. 435 - 445]Embryonic Mortality in Pseudophryne (Anura: Leptodactylidae) [pp. 445 - 449]The Reproductive Cycle and Its Environmental Control in the Pumpkinseed, Lepomis gibbosus (Pisces: Centrarchidae) [pp. 449 - 455]Sex Ratios of Larval and Transformed Ambystoma tigrinum Inhabiting the Llano Estacado of West Texas [pp. 455 - 461]Development of the Testis in the Frog Rana nigromaculata, with Special Reference to Germ Cell Maturation [pp. 461 - 467]Seasonal Changes in Reproduction and Social Behavior in the Lizard Anolis aeneus [pp. 467 - 476]Growth Rate in Island and Mainland Anoline Lizards [pp. 477 - 482]Population Dynamics and Reproductive Patterns of Three African Skinks [pp. 483 - 490]Color Change and Reproductive Cycling in Female Collared Lizards (Crotaphytus collaris) [pp. 491 - 494]Paratrimma, a New Genus of Gobiid Fishes and Two New Species [pp. 494 - 497]A New Species of Eviota with Discussion of the Nominal Genera Eviota and Eviotops [pp. 498 - 502]Notes on the Indo-West Pacific Species of the Clupeid Fish Genus Ilisha, with a Key to Their Identification [pp. 503 - 509]Kryptophaneron harveyi, a New Anomalopid Fish from the Eastern Tropical Pacific, and the Evolution of the Anomalopidae [pp. 510 - 515]A New Cyclopterid Fish Liparis coheni from the Western North Atlantic with Notes on Life History [pp. 515 - 521]Status of the Largescale Stoneroller, Campostoma oligolepis [pp. 521 - 531]Variation and Systematics of the Stripetail Darter, Etheostoma kennicotti [pp. 532 - 541]The Allometrics of Rattlesnake Skeletons [pp. 542 - 545]A Preliminary Report on the Superficial Throat Musculature of the Microhylidae and Its Possible Role in Tongue Action [pp. 546 - 551]Structure and Function of the Ocular Conus Papillaris of Anolis equestris (Sauria: Iguanidae) [pp. 552 - 558]Variations of Venom Proteins in Agkistrodon Snakes from North America [pp. 558 - 562]In Vivo and in Vitro Effects of Prolactin on Lipid Metabolism in the Cyprinid Teleost Notemigonus crysoleucas [pp. 563 - 573]Herpetological NotesAuto-Shaping: A Simple Technique for Teaching a Lizard to Perform a Visual Discrimination Task [pp. 574 - 576]Foraging Behavior of Bufo americanus Tadpoles in Response to High Densities of Micro-Organisms [pp. 576 - 578]Terrestrial Movements of the Mud Turtle Kinosternon scorpioides in Costa Rica [pp. 579 - 580]Biogeographical Implications of Pattern Variation in the Salamander Aneides lugubris [pp. 580 - 586]First Description of an Adult Varanus grayi [pp. 586 - 588]An Enigmatic Chelonian Fragment from the Pliocene of Kenya [pp. 589 - 591]On the Occurrence of a Stapedial Foramen in Living Non-Gekkonid Lepidosaurs [pp. 591 - 592]

Ichthyological NotesClarification of the Name and Distribution of the Plotosid Catfish Cnidoglanis macrocephalus [pp. 593 - 594]Some Notes on the Chinese Sucker Myxocyprinus [pp. 594 - 595]Filter Feeding and Predation on the Eggs of Thallasoma sp. by the Scombrid Fish Rastrelliger kanagurta [pp. 596 - 597]Artificial Hybridization between Rainbow (Salmo gairdneri) and Golden Trout (Salmo aguabonita) [pp. 597 - 598]Distribution and Known Life History of Stichaeus punctatus in the Northwest Atlantic [pp. 598 - 602]Inorganic Composition of Gallbladder Bile from Freshwater Fishes [pp. 602 - 605]Photoperiodic Effects on Salinity Selection in the Gulf Killifish, Fundulus grandis [pp. 605 - 608]Diurnal Measurements of Plasma Chloride in Catfish [pp. 608 - 609]Temperature Tolerance and Preference of Immature Channel Catfish (Ictalurus punctatus) [pp. 609 - 612]A Blind Channel Catfish, Ictalurus punctatus [pp. 612 - 613]

Reviews and Commentsuntitled [pp. 614 - 615]untitled [p. 615]untitled [pp. 615 - 616]

Editorial Notes and News [p. 617]A National Plan for Ichthyology: (Abstracted from the Report of the Advisory Committee for the Development of a National Plan for Ichthyology) [pp. 618 - 625]Fish Collections in the United States and Canada [pp. 625 - 642]A List of Undescribed Freshwater Fish Species of Continental United States and Canada, with Additions to the 1970 Checklist [pp. 642 - 644]Back Matter