Herpetologists' League

The Reproductive Cycle of Barisia monticola: A Unique Variation among Viviparous LizardsAuthor(s): James L. Vial and James R. StewartSource: Herpetologica, Vol. 41, No. 1 (Mar., 1985), pp. 51-57Published by: Herpetologists' LeagueStable URL: http://www.jstor.org/stable/3892128Accessed: 08/12/2009 15:03

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March 1985] HERPETOLOGICA 51

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LICHT, P., AND G. C. GORMAN. 1970. Reproductive and fat cycles in Caribbean Anolis lizards. Univ. California Publ. Zool. 95:1-52.

MACCULLOCH, R. D., AND D. M. SECOY. 1983. Demography, growth, and food of western painted turtles, Chrysemys picta bellii (Gray) from south- ern Saskatchewan. Can. J. Zool. 61:1499-1509.

MCPHERSON, R. J., AND K. R. MARION. 1981. Sea- sonal testicular cycle of the stinkpot turtle (Ster- notherus odoratus) in central Alabama. Herpeto- logica 37:33-40.

MOLL, E. 0. 1973. Latitudinal and intersubspecific variation in reproduction of the painted turtle, Chrysemys picta. Herpetologica 29:307-318.

. 1979. Reproductive cycles and adapta- tions. Pp. 305-331. In M. Harless and H. Morelock (Eds.), Turtles: Perspectives and Research. John Wiley and Sons, New York.

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SEXTON, 0. J. 1959. A method for estimating age of painted turtles for use in demographic studies. Ecology 40:716-718.

SHINE, R. 1977. Reproduction in Australian elapid snakes I. Testicular cycles and mating seasons. Aust. J. Zool. 25:647-653.

STEEL, R. G. D., AND J. H. TORRIE. 1960. Princi- ples and Procedures of Statistics. McGraw-Hill Book Co., New York.

WILBUR, H. M. 1975. The evolutionary and math- ematical demography of the turtle Chrysemys pic- ta. Ecology 56:64-77.

ZAR, J. H. 1974. Biostatistical Analysis. Prentice- Hall, Englewood Cliffs, New Jersey.

Accepted: 20 July 1984 Associate Editor: James Spotila

Department of Biology, University of Richmond, Richmond, VA 23173, USA

Herpetologica, 41(1), 1985, 51-57 ? 1985 by The Herpetologists' League, Inc.

THE REPRODUCTIVE CYCLE OF BARISIA MONTICOLA: A UNIQUE VARIATION AMONG VIVIPAROUS LIZARDS

JAMES L. VIAL AND JAMES R. STEWART

ABSTRACT: Among the several reproductive patterns previously known for viviparous tropical lizards, populations of Barisia monticola from the Cordillera de Talamanca in Costa Rica dem- onstrate a unique variation. The males are continuously spermatogenic without any seasonal changes in size or activity of the testes and seminiferous tubules, and gonadal size is correlated with body size. Our evidence indicates that the ovarian cycle is probably biennial, in contrast to any other known viviparous lizard. Further, the gestation period is also greatly prolonged. While females demonstrate some degree of seasonal synchrony in parturition, the birth period may extend over an interval of at least 5 mo. We suggest that the climatic factors characterizing this montane tropical region can be exploited only by reptiles having extended egg retention and probably represents a thermal environment that favors the evolution of viviparity.

Key words: Reptilia; Sauria; Anguidae; Barisia monticola; Tropical lizards; Reproduction; Vi- viparity

WHEREAS reproductive activity for temperate zone lizards is invariably sea- sonal and cyclic, a diversity of reproduc- tive patterns has been reported for species inhabiting tropical regions (Alcala, 1966; Gorman and Licht, 1975; Kitada and As- ana, 1951; Smith, 1968; Vitt, 1982a,b, 1983; Wilhoft, 1963a,b).

Among those lizards occupying tropical environments, spermatogenesis may be either cyclic, associated with a distinct breeding period, or acyclic (Duvall et al., 1982; Fox, 1977). Many tropical species undergo cyclic changes in testicular mass (Baker, 1947; Daniel, 1960; Marion and Sexton, 1971; Marshall and Hook, 1960;

51

52 HERPETOLOGICA [Vol. 41, No. 1

Ruibal et al., 1972; Sherbrooke, 1975; Wil- hoft and Reiter, 1965) although this vari- ation may be less dramatic than for extra- tropical taxa, and spermatogenesis may continue at a reduced rate during testic- ular regression (Licht and Gorman, 1970). In contrast, continuous spermatogenic ac- tivity accompanied by little or no change in testicular or seminiferous tubule size has been reported for several other tropical lizards (Kitada and Asana, 1951; Smith, 1968; Wilhoft, 1963a,b).

In females, distinct ovarian cycles are exhibited by some oviparous tropical species (Gorman and Licht, 1975; Marion and Sexton, 1971; Marshall and Hook, 1960) while others are acyclic in their re- production (Alcala, 1966; Gorman and Licht, 1975). Tropical viviparous females may give birth to more than one brood each year (Alcala, 1966; Simbotwe, 1980; Somma and Brooks, 1976), whereas extra- tropical species are restricted to a single annual brood (Tinkle et al., 1970). Sher- brooke (1975) defined three types of re- productive cycles among tropical lizards: (1) continuous, no variation in reproduc- tive activity; (2) continuous with seasonal variation in reproductive activity; (3) non- continuous, with distinct periods of repro- ductive inactivity. However, the repro- ductive mode for males and females in a single species need not be the same and, when differences occur, males more fre- quently exhibit continuous reproductive activity than do females (Sherbrooke, 1975).

We present evidence of a previously unreported variation among the repro- ductive cycles detailed above. In the trop- ical Central American anguid lizard, Ba- risia monticola, the spermatogenic cycle is continuous, while the ovarian cycle ex- tends for a period in excess of one year.

METHODS AND MATERIALS

Barisia monticola discontinuously in- habits the montane regions throughout southern Central America. A diurnal non-

hibernator, it combines heliothermic-thig- mothermic behavior in regulating body temperature (Vial, 1975). During periods of inactivity, it generally retreats beneath rocks, vegetation and other debris.

Specimens examined for this report were collected in the Cordillera de Tala- manca of Costa Rica at elevations above 2000 m over a 3 yr period (1961-1964). Climatological data for the Cordillera de Talamanca in Costa Rica exhibit little variation in average annual temperatures, which are relatively cool in the elevations over which B. monticola is to be found (Vial, 1968). There is, however, a distinct bimodality to the distribution of moisture during which a period from December through March, and a shorter interval during July and August, are relatively dry. This regimen of seasonal rainfall and ab- sence of substantial seasonal temperature differences is consistent with the defini- tion of most tropical environments (Rich- ards, 1957).

Ninety-eight specimens (58 males, 40 females) were obtained representing all months of the year except January and August, but the maximum time interval between samples is actually less than 6 wk. The lizards were captured by hand, noosed or taken with 0.22 caliber dust shot, then fixed in 10% formalin and stored in a 6% formalin solution.

All measurements were taken from pre- served materials. Linear measurements of snout-vent length (SVL) (by Helios dial caliper) and the dimensions of gonadal and embryonic stages (by ocular micrometer) were read to the nearest 0.1 mm. The pro- cedures used for preparation and staining of testicular material are essentially those described by Mayhew and Wright (1970). We have also applied their criteria and classification for staging of the spermato- genic cycle. Eggs and embryos were counted, classed as to size and stage of development according to those defined by Dufaure and Hubert (1961), and com- pared to the presence and location of any corpora lutea.

March 1985] HERPETOLOGICA 53

FIG. 1.-Adult testicular size, as measured by width, in representative monthly samples of Barisia monticola.

RESULTS

The 58 male B. monticola ranged in size from 31-82 mm SVL. Microscopic sections of gonads from 44 males (60-82 mm SVL) were examined for testicular activity. These latter specimens represent a yearly sample taken at 2-4 wk intervals, and include all but a 6 wk period during August and September. There is no indi- cation of any difference in degree of tes- ticular activity among mature males rang- ing in size from 61-82 mm SVL (x = 71.4; SE = 0.8 mm) all of which were spermio- genic. The two smallest males (both 60 mm SVL) were collected in March; nei- ther was reproductively active. Thus, sex- ual maturity probably is achieved at about 60 mm SVL. There was no apparent sea- sonal variation in testicular size (Fig. 1).

Measurements of testicular widths ob- tained for 39 adult males demonstrate that testicular size is correlated with body size (Fig. 2). Such a correlation is not charac- teristic of temperate zone gerrhonotines with cyclic testicular activity (Goldberg, 1972, 1975).

Forty female specimens (29-84 mm SVL) were examined. The smallest with vitellogenic follicles was 64 mm. Twenty- five (SVL 64-84 mm; x = 72.0; SE = 1.1 mm) had vitellogenic follicles or oviductal eggs. Maximum follicle diameter and de-

I- --

FIG. 2.-Adult testicular size, as measured by width, plotted according to SVL of individual. Dashed line represents points of least squares regression (y =

-0.75 + 0.05x; r = 0.65; n = 39).

velopmental condition of oviductal eggs are plotted in Fig. 3. Females with ovi- ductal eggs (n = 12) were present in the samples taken throughout the year. Among these females, undeveloped eggs occurred

(A)

EBBS A ~~A A A A A000 0

- SEEELSPEI SNIBICTA EBBS A UUNESUETEI EDEESS A- PISEESTEB EBETIS

(B)

0IIJETER 4-_

N 3 -

I I I I I I I I I II _ I I r l ~~~~~~~~~~~~~~I 7 I

FIG. 3.-Reproductive condition of adult female Barisia monticola represented in monthly samples. (A) Condition of oviductal eggs or embryos for grav- id females (n = 12; size range = 65-81 mm SVL). Unpigmented embryos correspond to developmental stages 31-35 of Dufaure and Hubert (1961); pig- mented embryos correspond to stage 40. (B) Maxi- mum follicle diameter for non-gravid females (n= 13; size range = 64-84 mm SVL).

54 HERPETOLOGICA [Vol. 41, No. 1

in July and late September. The embryos found in October and December were at stage 31 of the Dufaure and Hubert (1961) developmental sequence for Lacerta vi- vipara; at stages 35 and 40 in March; at stage 40 in June and July. Three adult fe- males (SVL 68-78 mm) with previtello- genic follicles were captured in July, Sep- tember and November. Other females in the population possessed oviductal eggs or embryos during these same months. A 69 mm SVL female collected on 11 July gave birth to 10 young (24.2-27.5 SVL; x = 25.9; SE = 0.35 mm) within 10 days of capture.

An additional 11 specimens were ob- tained from the Los Angeles County Mu- seum of Natural History and 14 speci- mens from the Museum of Vertebrate Zoology. Two females taken at 3353 m on the Cerro de la Muerte (MVZ 78728, 92522) contained oviductal eggs, consis- tent with the sequence presented in Fig. 3. Recently ovulated eggs were present in one of these collected 22 August 1964; the second female, collected 31 March 1970, contained pigmented embryos.

DISCUSSION

The geographic range of gerrhonotine lizards extends from Canada to Central America (Stebbins, 1954), thus including a variety of habitats in both extratropical and tropical regions. Within this subfam- ily, three reproductive patterns have been reported. California populations of both the viviparous Gerrhonotus coeruleus and oviparous G. multicarinatus mate in the spring after emergence from hibernation (Fitch, 1970; Goldberg, 1972; Vitt, 1973; Volz, 1957). Vitellogenesis and ovulation also take place in spring, as does male spermiogenesis; however, testicular re- gression occurs during the summer. Ger- rhonotus kingi and G. liocephalus copu- late during the fall in the southwestern United States (Fitch, 1970; Flury, 1949; Goldberg, 1975). Spermiogenesis in G. kingi occurs in the fall, as does vitellogen- esis in the oviparous female, but the latter process is not completed until early spring

of the following year (Goldberg, 1975). Two Central American live-bearing ger- rhonotines, Barisia moreleti and B. mon- ticola, were presumed to have an extend- ed breeding season by Fitch (1970). Fitch (1973b) reported on a sample of female Gerrhonotus (= Barisia) monticola col- lected from the Cerro de la Muerte at three time intervals. Births, he concluded, were concentrated in October and No- vember but occur in lesser numbers throughout the year. His "suspected" es- timate of a 7-10 wk gestation period dem- onstrated in a series of B. monticola taken from the Cordillera Central in Costa Rica is based upon ". . . analogy with the closely related G. coeruleus, similar in size and living at similar temperatures ...." Our data suggest some degree of seasonal syn- chrony in female B. monticola, but they also indicate a mechanism that may result in an extended reproductive cycle.

The reproductive condition of our sam- ple of 25 adult females can be interpreted as representing one of two possible repro- ductive cycles for this population: (1) asynchronous reproduction with some fe- males in the population gravid at all sea- sons, or (2) synchronous reproduction with an extended gestation period. We favor the second hypothesis for the following reasons. (1) The sample of 12 females with oviductal eggs includes the period of an entire year, and (2) the distribution of de- velopmental stages of these eggs through- out the year is not random. We have tested the hypothesis of random occurrence of developmental stage by assigning each fe- male to one of three categories: undevel- oped oviductal eggs; unpigmented em- bryos (actually stages 31 or 35 of Dufaure and Hubert, 1961); or pigmented embryos (stage 40). We partitioned the year into four time intervals (July-September, Oc- tober-December, January-March, and April-June) and then tested for the ran- dom distribution of each developmental stage in the time intervals by using the General Exact Test of Wells and King (1980). The hypothesis of equal distribu- tion of the three stages among these four

March 1985] HERPETOLOGICA 55

intervals was rejected (P = 0.015). There- fore, we interpret the gestation sequence for these 12 females to represent ovulation in summer (June through September), with parturition occurring in late spring (May through June) (refer to Fig. 3A). Addi- tional Cerro de la Muerte females for which we have information confirm this pattern. One female (MVZ 78728; 68 mm SVL) collected 22 August 1964 contained undeveloped oviductal eggs, while a sec- ond (MVZ 92522; 69 mm SVL) collected 31 March 1970 contained pigmented em- bryos. Another taken in February 1978 bore three young on 6 March (W. Van Devender, personal communication).

A second aspect of the reproductive cycle is the frequency with which each female reproduces. The reproductive con- dition of 13 females not carrying young, when compared to the 12 gravid females, indicates that the reproductive cycle for individuals in our sample must exceed one year. For example, females with enlarged follicles (May through July) are present in the population at the same time other fe- males are carrying pigmented embryos or undeveloped oviductal eggs. We also have three adult females (68-78 mm SVL) col- lected in July, September and November that are laden with small follicles, while in these same months others in our sample contain either enlarged follicles, or unde- veloped oviductal eggs, or developing em- bryos. We believe these three to be pre- vitellogenic individuals that would have initiated vitellogenesis in the spring and ovulated the following summer. In fact, these data suggest to us that there is a pat- tern of gradual increase in follicle size, beginning in the fall and terminating with ovulation the following summer. Al- though our sample of females is admitted- ly small, it is most reasonable to deduce that there is an extended ovarian cycle, which is a consequence of prolonged ges- tation. A lengthy gestation period has been reported for other Mesoamerican and South American lizards (Jaksic and Schwenk, 1983; Marion and Sexton, 1971; Vitt and Blackburn, 1983).

Two distinct patterns of ovarian cycles have been previously reported for vivipa- rous Mesoamerican lizards. An annual ovarian cycle consisting of fall vitellogen- esis and ovulation with parturition in the spring or early summer is characteristic of Mexican Sceloporus, Eumeces, Gerrho- notus and Guatemalan Corytophanes (Guillette, 1983; Guillette and Casas-An- dreu, 1980; Guillette et al., 1980; McCoy, 1968; Ortega and Barbault, 1984). Scelop- orus malachiticus from Costa Rica exhibit a second type of annual ovarian cycle in which vitellogenesis and ovulation occur in the late spring and early summer with an extended gestation period and partu- rition the following spring (Marion and Sexton, 1971).

We now describe a third variation ex- hibited by Barisia monticola in which vi- tellogenesis and ovulation occur in late spring and early summer, but the pro- longed gestation interval results in partu- rition the following spring or summer. In this case, the actual ovarian cycle exceeds 1 yr and is most likely biennial.

These three cycles are each differen- tiated by two primary components: (1) the length of the gestation interval, and (2) the timing of ovulation. Interestingly, the seasonal timing of parturition is similar for all viviparous Mesoamerican lizards.

Although the gametogenic patterns are different for male and female B. monti- cola, we cannot yet determine if the two sexes are responding to different external cues. Temperature is well known to be a critical controlling variable for lizard spermatogenic cycles. Therefore, the ab- sence of distinct thermal seasonality could in itself induce aseasonal reproduction (Duvall et al., 1982), and thus the pres- ence of noncyclic spermatogenesis in B. monticola should not be surprising.

Any interpretation of proximate envi- ronmental cues on oogenesis are compli- cated by the additional possible influence of moisture, which has been shown to in- fluence this process in other tropical liz- ards (Licht and Gorman, 1970; Sher- brooke, 1975). However, irrespective of

56 HERPETOLOGICA [Vol. 41, No. 1

the possible direct controls exerted on the ovarian cycle of B. monticola (i.e., timing of ovulation), temperature does appear to control the length of the cycle. While vi- tellogenesis may proceed in the presence of oviductal eggs in oviparous lizards (e.g., Sherbrooke, 1975), there are no records of vitellogenic activity taking place during gestation in viviparous lizards. Marion and Sexton (1971) and Fitch (1973a) noted that altitudinal differences may influence de- velopmental rates in Sceloporus mala- chiticus. The relatively cool thermal en- vironment at high elevations on the Cordillera de Talamanca may prolong embryonic development in B. monticola and result in the observed lengthy ovarian cycle.

Field measurements of thermal pref- erenda for members of this population are lower than those known for any other ger- rhonotine lizard (Vial, 1975). The uni- formly low temperatures may well pro- duce a condition in which females are unable to complete gestation in the 60-90 day interval typified by temperate vivip- arous lizards (e.g., Gerrhonotus coeru- leus) in time for autumn parturition.

Although there may be distinct advan- tages to the observed timing of ovulation and/or parturition in high altitude Me- soamerican environments (Marion and Sexton, 1971), a lengthy gestation period is a conspicuous characteristic in both S. malachiticus and B. monticola. The ad- vantages of viviparity under the consis- tently low thermal conditions on the Cor- dillera de Talamanca may be more dramatic than for those montane environ- ments which have even short intervals of relatively high temperatures. The Cordi- llera de Talamanca probably represents a habitat that can be successfully exploited only by reptiles with extended egg reten- tion and likely exemplifies a thermal en- vironment that favors the evolution of vi- viparity.

Acknowledgments.-We thank Harry Greene (Museum of Vertebrate Zoology) and John Wright (Los Angeles County Museum of Natural History) for the loan of specimens in their custody. Denise

Stephenson, at the University of Tulsa, assisted in the preparation of histological materials. Wayne Van Devender (Appalachian State University) volun- teered unpublished information on his observations. Wilbur Mayhew (University of California-River- side) kindly provided us with original photographic materials from his studies.

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Accepted: 22 August 1984 Associate Editor: Kentwood Wells

Faculty of Biological Science, The University of Tulsa, Tulsa, OK 74104, USA