Female SVL Research Articles

Reproductive Traits of a High Elevation Viviparous Lizard Sceloporus bicanthalis (Lacertilia: Phrynosomatidae) from Mexico

Several species of lizards exhibit significant annual variation in reproductive traits; however, most work in this area focused on populations from temperate latitudes or low to medium elevations. We examined annual variation in litter size, neonate size, and relative litter mass in a high elevation (4200 m) population of the viviparous lizard, Sceloporus bicanthalis from the Volcano Nevado de Toluca, México. We found little evidence for annual variation in reproduction in this population. Female body size influenced litter size and litter mass. Relative litter mass in this population (0.47) was among the highest reported for any Sceloporus and may be a consequence of a nearly “annual” life cycle. Mean neonate size was not affected by female SVL or litter size, suggesting it may be optimized in this population.

Sexual Dimorphism, Diet, and Reproduction in the Swamp Skink, Egernia coventryi

The Swamp Skink, Egernia coventryi, is an uncommon species that inhabits wetlands and swampy heaths in predominantly coastal regions of southeastern Australia. We examined museum specimens to quantify the diet, reproduction, and sexual dimorphism of E. coventryi. The mean SVL of both adult males and females was 85–86 mm, and individuals attain sexual maturity at about 72–74 mm SVL. Although the sexes did not differ in body size (SVL), males have longer and broader heads than females, both in terms of absolute head size and head size relative to body size. Females ovulate in September and October with parturition occurring in late January or early February. However, not all adult females collected during the breeding season were pregnant, suggesting that female E. coventryi may not always breed annually. Litter size in E. coventryi ranged from 1–4, with a mean litter size of 2.6. Egernia coventryi is omnivorous and a largely opportunistic forager, with spiders (found in 16 of 47 individuals, 34%), beetles (26%), lepidopterans (17%), ants (11%), hemipterans (9%) and aquatic amphipods (9%) the most common animal prey items found in the alimentary canals of individuals. However, plant materials (e.g., fruits/berries, seeds, other vegetation) also were found in the stomachs of the majority of the specimens (66%). Sloughed skin (26%) and the tail fragment of another E. coventryi were found in the alimentary tracts of preserved specimens. The majority of specimens (76%) were infested with endoparasites, with one specimen containing 130 nematodes, although the mean number of nematodes per specimen was 8.87.

NATURAL HISTORY OF THE MASSASAUGA, SISTRURUS CATENATUS EDWARDSII, IN SOUTHEASTERN COLORADO

A BSTRACT Studies of natural history are important for determining baseline information, particularly for species that might be threatened or endangered. We collected 254 (141M:94F:19UNK) massasauga, Sistrurus catenatus edwardsii, from May 1995 through October 1996. The average snoutvent length (SVL 6 SD) for adult males (355 6 45 mm) was not significantly different than the SVL of adult females (364 6 24 mm). Habitat descriptions indicate that the massasauga in Colorado is a semi-arid grassland species that utilizes areas of relatively open shortgrass prairie. Massasaugas were active between 14 and 308C, with an average ambient temperature during activity of 22.1 6 2.58C. The time of observed activity shifted through the season, with primarily diurnal activity during the cooler months (April and late September to October) and primarily early evening activity during the hotter months (May through August). Massasaugas in Colorado gave birth to litters of 5 to 7 young between late August and late September, and reproduction appeared to be biennial. Populations of S. c. edwardsii in Colorado are scattered but population size appeared to be relatively large based on number of captures and low recapture rates, particularly in Lincoln County. However, due to habitat loss and fragmentation resulting from agricultural expansion, these populations might become increasingly threatened in the future.

Diet of sympatric Gaboon Vipers (Bitis gabonica) and Nose‐horned Vipers (Bitis nasicornis) in southern Nigeria

The stomach content of 524 Gaboon Vipers, Bitis gabonica gabonica (53 subadults, 222 males and 249 females) and 392 Nose‐horned Vipers, Bitis nasicornis (48 subadults, 163 males and 161 females), from a number of forest‐plantation mosaic areas of southern Nigeria (West Africa) were recorded. Adult sex ratio was close to 1:1 in both species. In both Gaboon and Nose‐horned vipers, mean SVL of females significantly exceeded that of males. 30.7% of the total sample of Gaboon Vipers and 26% of the total sample of Nose‐horned Vipers contained identifiable food in the stomach. The stomachs of gravid females of both species never contained food. The stomach contents of the Gaboon Vipers consisted mainly of small mammals, followed by birds, lizards and, occasonally frogs. Males and females had similar diets. The diet of subadults differed from that of adults in that there were significantly more newborn mice and more lizards consumed. Nose‐horned Vipers also fed mainly upon small mammals, but amphibians were also eaten. Males and females had similar diets, and the diet of subadults differed from that of adults and consisted largely of newborn mice.

The Ecology of Cnemidophorus ocellifer (Squamata, Teiidae) in a Neotropical Savanna

We studied the ecology of the lizard Cnemidophorus ocellifer Spix 1825 in the central Brazilian Cerrado. Cnemidophorus ocellifer was active on open ground, in sandy soils and rocky fields, during the hottest hours of the day. Mean body temperatures (37.5°C) were high, relative to sympatric lizard species, and more associated with substrate temperatures than with air temperatures. The thermal ecology of C. ocellifer seems to be tightly associated with an active mode of foraging. Termites were the most important prey, and there was no significant association between head dimensions and prey dimensions. Cnemidophorus ocellifer showed strong sexual dimorphism in body size and shape, with males having larger bodies and head dimensions, and females having longer and thicker bodies. Clutch size averaged 2.1 and was positively correlated with female SVL. Females were reproductively active during the dry season (May to September) and recruitment occurred from July to November. Males were reproductively active throughout the year, peaking from March to August, coinciding with the period of female reproduction. The reproductive cycle in C. ocellifer may be determined by the greater availability of direct sunlight and its physiological effects upon breeding activities, such as courtship and mating, during the dry season.

Ecology of Mabuya agilis (Raddi) (Lacertilia, Scincidae) at the restinga of Grumari, Rio de Janeiro, southeastern Brazil

Some aspects of the ecology of the skink Mabuya agilis (Raddi, 1823) at the restinga habitat of Grumari, in Rio de Janeiro, Brazil are studied. Most of the lizards were first sighted on the ground, though a few were using perches (mainly cacti) up to 30 cm high. Mean body temperature in activity was 33.1 ± 2.4ºC and was significantly correlated to air temperature. There was sexual dimorphism in size (snout-vent length - SVL), with females growing larger than males. Frequency of broken tails was high overall (83%) and did not differ between sexes. Females and males are sexually mature at 49 mm and 47 mm SVL, respectively. Brood size averaged 3.2 ± 1.0 (range 1-5) and was positively and significantly related to female SVL (r = 0.65, p = 0.001). Relative clutch mass (RCM) of seven gravid females averaged 0.250 ± 0.042, being relatively low compared to those of other congeners. The diet of M. agilis was composed basically of arthropods, with relatively large and soft-bodied arthropods such as spiders, caterpillars and homopterans being the most important prey. The results of our work confirm and expand the knowledge of ecological tendencies previously observed for M. agilis in other areas.

Annual Reproductive Activity of Mabuya mabouya (Squamata, Scincidae)

Abstract Rreproductive features of a population of Mabuya mabouya were studied in a wet tropical habitat with a bimodal precipitation regime. The sex ratio was approximately 1:1, and females were larger than males. Males matured at a SVL of 72 mm and are continuously reproductive throughout their adult life. Two groups of females were found reproducing simultaneously: primiparous females that reached a minimum size at their first reproduction and continued to grow during the gestation period and multiparous females of larger size that exhibited more limited growth. Primiparous females began preovulatory follicular growth and ovulated at juvenile sizes (60–74 mm SVL). Reproductive activity of the females appeared aseasonal. However, births occurred during the dry months, producing a bimodal pattern of neonate recruitment into the population. Gestation of four to seven embryos lasted approximately 10 months. Litter size was related to female SVL. The maximum follicular size corresponded to a microlecithal e...

Growth and Reproduction of Gekko hokouensis (Reptilia: Squamata) on Okinawajima Island of the Ryukyu Archipelago, Japan

Abstract A mark and recapture study was carried out from 1990–1992 for a population of Gekko hokouensis in the southern part of Okinawajima Island, Ryukyu Archipelago. Gonadal states were also examined for 389 preserved specimens from the central part of the island. Results indicate that this species breeds from April to August and that females may lay eggs more than once during a breeding season. Young appeared from July to November, and hatchlings, although they grew somewhat in autumn, scarcely grew in winter. Their growth rate dramatically increased during the next spring and summer. Although some hatchlings grew to the minimum maturity size (43 mm in snout–vent length in both sexes) by the end of the next breeding season, others required a second year to reach maturity. There were no sexual differences in juvenile growth. After reaching maturity, however, growth rate of females was significantly greater than that of males. This seems to account for the significantly greater adult SVL in females than ...

Growth and Reproduction of Gekko hokouensis (Reptilia: Squamata) on Okinawajima Island of the Ryukyu Archipelago, Japan

A mark and recapture study was carried out from 1990–1992 for a population of Gekko hokouensis in the southern part of Okinawajima Island, Ryukyu Archipelago. Gonadal states were also examined for 389 preserved specimens from the central part of the island. Results indicate that this species breeds from April to August and that females may lay eggs more than once during a breeding season. Young appeared from July to November, and hatchlings, although they grew somewhat in autumn, scarcely grew in winter. Their growth rate dramatically increased during the next spring and summer. Although some hatchlings grew to the minimum maturity size (43 mm in snout–vent length in both sexes) by the end of the next breeding season, others required a second year to reach maturity. There were no sexual differences in juvenile growth. After reaching maturity, however, growth rate of females was significantly greater than that of males. This seems to account for the significantly greater adult SVL in females than in males.

Interpopulational Variation in Litter Size of the Skink Mabuya agilis in Southeastern Brazil

We compared litter size (and its relationship with female SVL), minimum size of females at sexual maturity, and minimum adult size of females, among different populations [from eight coastal sea level and two midelevation (600–800 m) sites] of the live-bearing skink Mabuya agilis in the southeastern Brazilian states of Espírito Santo and Rio de Janeiro. There were no apparent differences in litter size among populations within either lowland or highland groups, but each group differed significantly from the other: highland females had larger litters (mean = 5.6, range 2–9) than those from lowland sites (mean = 3.3, range 1–6). There was a significant positive relationship between litter size and female SVL for each group, but the slope of the regression differed between lowland and highland females, with the latter tending to have larger litters for a given SVL. Highland females also reach larger body sizes, although their minimum size at sexual maturity and minimum adult size are just slightly greater than those from lowland populations. We interpret such intraspecific variation relative to possible effects of the physical environment and of genetic factors on reproduction.

Reproductive Cycle of the Spiny Lizard Sceloporus jarrovii (Sauria: Phrynosomatidae) from North-Central México

Abstract We studied the reproductive cycle of Sceloporus “jarrovii” from a temperate environment of the Sierra Madre Oriental in Mexico. Males reached sexual maturity at a smaller snout vent length (SVL; 46 mm) than females (60 mm). Reproductive activity of both sexes was asynchronous, similar to other species inhabiting montane zones. Testes increased in size from June to November and declined rapidly in November. Vitellogenesis occurred from August to October, with ovulation occurring between November and December. Embryonic development was observed from December to early May. There was a significant positive correlation between litter size and female SVL. The reproductive cycle of S. “jarrovii” is similar to other montane species of several families (Anguidae, Scincidae, Phrynosomatidae). Vitellogenesis, ovulation, and gestation time are shorter in northern (Arizona) than southern populations (Mexico). Females from northern populations are larger in SVL and have larger litter sizes than southern popula...

Reproductive Cycle of the Spiny Lizard Sceloporus jarrovii (Sauria: Phrynosomatidae) from North-Central México

We studied the reproductive cycle of Sceloporus “jarrovii” from a temperate environment of the Sierra Madre Oriental in México. Males reached sexual maturity at a smaller snout vent length (SVL; 46 mm) than females (60 mm). Reproductive activity of both sexes was asynchronous, similar to other species inhabiting montane zones. Testes increased in size from June to November and declined rapidly in November. Vitellogenesis occurred from August to October, with ovulation occurring between November and December. Embryonic development was observed from December to early May. There was a significant positive correlation between litter size and female SVL. The reproductive cycle of S. “jarrovii” is similar to other montane species of several families (Anguidae, Scincidae, Phrynosomatidae). Vitellogenesis, ovulation, and gestation time are shorter in northern (Arizona) than southern populations (México). Females from northern populations are larger in SVL and have larger litter sizes than southern populations. Our study suggests that the montane environment (cool temperatures, short growing season, rainfall during the summer) of S. “jarrovii” has played a role in the evolution of a set of reproductive characteristics shared by evolutionarily distant viviparous lizard species inhabiting the montane zone.

Is sexual size dimorphism in relative head size correlated with intersexual dietary divergence in West African forest cobras, Naja melanoleuca?

Sex-biased differences in dietary habits of snakes are often linked to pronounced sexual size dimorphism in absolute body size or in relative head size. We studied the food habits of free-ranging forest cobras (Naja melanoleuca) in southern Nigeria to find whether any intersexual dietary divergence is present in this species, and measured both museum vouchers and free-ranging specimens to find whether any intersexual divergence in relative head size is present. We demonstrated that: (1) head sizes increases more rapidly with SVL in females than in males, with a result that, at the same body length, the females tended to have significantly larger heads; (2) males and females were nearly identical in dietary habits, both if we consider prey size or prey type; (3) both sexes tended to prey upon relatively little sized preys. It is concluded that traditional evolutionary scenarios for explaining sexual dimorphism and food niche divergence are hardly valid in this case, and we need to look for entirely different hypotheses (e.g. linked to the sexual preference of males for females with larger heads).

Among Clutch Variation in Reproductive Output and Egg Size in the Wall Lizard (Podarcis muralis) from a Lowland Population of Northern Spain

Among clutch variation in reproductive output and egg size of the wall lizard (Podarcis muralis) are reported. Females under semi-natural conditions laid eggs from late April to early July. The smallest reproductive female in our sample was 51.2 mm SVL, and all females larger than this size produced at least one clutch per season. Of the 53 females, 13 laid three clutches, 27 laid two clutches, and 13 laid one clutch. Females that laid only one clutch were smaller than those laying two or three clutches. Ovipo- sition frequency was 16.8-54.7 (mean = 30.4 ? 1.4) d between first and second clutches, and 18.6-32.1 (mean = 25.2 + 1.2) d between second and third clutches. Clutch size was 3-11 (mean = 5.0 ? 0.2) for first clutch and 2-6 for second (mean = 3.9 + 0.2) and third (mean = 4.0 + 0.3) clutches, and was positively correlated with female SVL. Although there was a trade-off between egg mass and the total number of eggs produced per season, eggs from first clutches were larger than eggs from subsequent clutches. In all three clutches, an increase in egg mass was accommodated by a decrease in egg length. There were both among clutch and among individual variation in clutch size and among clutch variation in egg mass, but no individual de- pendence of egg mass was found.

Reproductive Cycle and Brood Size of Eumeces lynxe from Pinal de Amoles, Queretero, Mexico

Females of Eumeces lynxe in the temperate environment of the Transvolcanic belt of central Mexico mated in August-October, ovulated in the December, and produced live young in April during 1988. Brood size averaged 4.7 neonates, and there was no relationship between brood size and female SVL. Young were produced at the beginning of the summer. Most of the annual rainfall occurs during summer, and we suggest that, similar to other species in this environment, offspring production is timed to the best season to promote juvenile growth and survivorship Testes increased in size from May-October and de- clined rapidly in November. Because ovulation in females occurred considerably later than mating, females likely store sperm as reported in other Eumeces. The reproductive cycle of E. lynxe is very similar to other montane species of Eumeces in the Transvolcanic belt of central Mexico as well as lizards in the families Phrynosomatidae and Anguidae occurring in the same environment Taken together, these studies suggest that the montane environment (relatively cool temperatures, short growing season, and rainfall during the summer) in which E. lynxe lives has played a role in the evolution of the set of reproductive characteristics shared by evolutionarily-distant montane lizards.

Influence of Clutch Date on Egg and Hatchling Sizes in the Annual Clutch of Lacerta schreiberi (Sauria, Lacertidae)

with egg mass and shows no variation among years. However, egg size and hatchling SVL show among-year and interindividual variation and are not related to female SVL or relative clutch mass. Egg mass is positively correlated only with the laying date. We suggest that clutch size depends only on stored lipids remaining after wintering and environmental factors could be responsible for egg size variation during vitellogenesis.

Sexual Dimorphism in Lacertid Lizards: Male Head Increase vs Female Abdomen Increase?

Lacertid lizards exhibit sexual dimorphism in size corrected values for abdomen (always larger in females) and head (larger in males) lengths. Relative abdomen length increased with SVL in females but did not in males. The mean abdomen/head ratio for juvenile lizards (sexes pooled) was lower than that of females but did not differ from that of males in any of the studied species. Therefore, the ontogenetic development of the main body segments (abdomen and head) was isometric in male lizards, whereas female abdomen exhibited positive allometric growth. Standardized independent contrasts (Felsenstein's method) of female abdomen to head ratio and of the slope of the regression of clutch size on SVL explained a significant amount of variation in sexual size dimorphism in a stepwise multiple regression model. The fact that sexual size dimorphism was best explained by variables related to female reproductive investment, together with the ontogenetic trajectories of body segments suggest that sexual size dimorphism results mainly from variation in female size. Despite the suggested prominent role of selection on female body size in determining the outcome of size dimorphism, there was also evidence of selection for increased body size in males, which were the largest sex in species with low selective pressure towards increased female size (constant clutch size or low fecundity slope over size). Evidence for intersexual food (prey size) partitioning was weaker than expected from the widespread dimorphism in body size or relative head size found among lacertid lizards. Furthermore, the development of body segments was in some instances inconsistent with the competitive hypothesis, the largest sex having relatively smaller trophic structures.

Reproductive Ecology of the Spectacled Caiman (Caiman crocodilus) in the Venezuelan Llanos

In the Venezuelan llanos, the reproductive cycle of the spectacled caiman (Caiman crocodilus) was constrained temporally by seasonal variation in water availability. Gonadal recrudescence in males and females began during the late dry season (April-May). Testicle mass peaks in May and June (early wet season), just prior to courtship. Peak spermatozoa levels were from June through Aug. Among vitellogenic females, ovarian mass and follicle size increased throughout the early wet season and peaked at the beginning of the nesting season (ulyAug.). Caiman were sexually size dimorphic with adult males (i = 96.0 cm SVL, maximum 145.5 cm SVL) approximately 30-40% larger than females (i = 72.0 cm SVL, maximum 99.0 cm SVL). Males were physiologically mature at 75 cm SVL (approximately 7 yr), but small mature males may not reproduce because of social factors. Females matured at minimum size of 60 cm SVL, but the mean size at first reproduction was 64 cm SVL (approximately 7 yr). Mean clutch size was 22.2 (? 5.8), and mean clutch mass was 1392 g (? 426 g). Clutch size and clutch mass, but not egg mass, were positively correlated with female SVL. An average of 54.3% of females > 60 cm SVL nested annually, but the reproductive frequency was size dependent. Female reproductive output increased both in absolute and relative terms as females grew. No evidence of a trade-off between egg size and clutch size was found.

Comparative Ecology and Life History of the Racer (Coluber constrictor) in Michigan

The racer, Coluber constrictorfoxii, was studied over a six-year period in southeastern Michigan. The minimum age at maturity was 11 months in males and two years in females. Both sexes grew rapidly, exceeded 600 mm SVL at the end of the first full season of growth, and individuals of both sexes attained SVL >1300 mm. There was no sexual size dimorphism. Autumn body mass was correlated strongly with SVL (r = 0.994). There was a single clutch per year averaging 15.0 eggs, and clutch size was positively correlated with female SVL (r = 0.937). All hatchlings and some yearlings overwintered at dispersed locations, while some yearlings and all large adults overwintered at communal dens. Adults dispersed up to at least 2.2 km from major hibernacula. During the warm season, mean distance between recaptures was 424 m for large adults, 188 m for yearlings, and 62 m for small juveniles. These traits indicate high rates of energy acquisition and use. In contrast, adult survivorship appears to have been low, at an estimated 0.54 per annum. Adult and subadult survivorship appear to be uncertain because of winter frost penetration, consistent with a bet-hedging hypothesis explaining life-history differences among this population and those previously studied in Kansas and Utah. Published data on variation of body size throughout the geographic range of the racer were examined to test this hypothesis; small body sizes found in subspecies inhabiting relatively stable climatic regions were not consistent with the hypothesis. Instead, racer size and diet, and the presence of snake species with similar habits and diets, were correlated across the geographic range of the racer.

The breeding migration and mating system of a Swiss population of the common frog Rana temporaria

AbstractA population of the explosive breeder Rana temporaria was studied from 1983 to 1985. The breeding periods lasted less than 10 days each year. Males were distributed non-randomly in the pond: large males tended to gather at the spawning site and small ones tended to search elsewhere in the pond and on land. Dislodgement of amplexed males was never observed, but in 7 out of 50 recaptured pairs males were found to be replaced. Males caught in amplexus did not differ significantly in SVL from single males. No correlation existed between SVL of males and females in amplexus. In both sexes a positive correlation existed between the date of individual arrival in consecutive years. The same was true for the date of individual departure. The direction of arrival and use of the pond as an overwintering site was non-random.