Relative Clutch Mass Research Articles

REPRODUCTION IN THE WESTERN COTTONMOUTH, AGKISTRODON PISCIVORUS LEUCOSTOMA, IN A FLOODPLAIN FOREST

Reproductive data on the western cottonmouth, Agkistrodon piscivorus leucostoma, are scarce, generally incomplete, and usually based on pooled years for a given area. Current paradigms suggest that reproductive output in snakes can be influenced by local resource availability so temporal variation is important to document. Pregnant female western cottonmouths were collected for 3 consecutive years (2000–2002) from a lowland hardwood forest in northeastern Texas. This bottomland is exposed to flood pulses during winter that produce variable, but often large, amounts of prey for semi-aquatic snakes. Data recorded from 27 females indicated no difference in their snout-vent lengths (SVL) or masses among years. Of all reproductive traits, only clutch mass was correlated to female SVL and only in 1 year. Clutch mass and relative clutch mass varied temporally, suggesting reproductive output was influenced by prey availability. However, clutch size and mean offspring mass (that together comprise clutch mass) were both consistent among years. There was variation in mean offspring SVL and mass among females, and a negative correlation of both offspring characteristics to clutch size. These results suggest that the reproductive output of individual females might be responding to variation in prey availability in different ways (i.e., some by varying offspring number and others by modifying offspring size). Testing this hypothesis will require monitoring individual females for multiple years.

Pregnancy Decreases Swimming Performance of Female Northern Death Adders (Acanthophis praelongus)

Reduction in locomotor performance during pregnancy is a potential cost of reproduction for female lizards and snakes. Most previous studies have suggested that reduced locomotor performance is a direct result of carrying a physical burden (the clutch). However, recent studies suggest that physiological changes associated with pregnancy can also cause a reduction in locomotor performance, particularly in viviparous species with prolonged gestation. I measured locomotor performance of the Northern Death Adder (Acanthophis praelongus), a viviparous, semiaquatic ambush foraging snake from tropical Australia. Swimming speeds of males and nonreproductive females were very similar, but late-term gravid females swam 30% more slowly than nonreproductive animals. Females with enlarged oviductal follicles carried physical burdens similar in size to those carried by gravid females but did not have impaired locomotor performance. Swimming speed of gravid females was unrelated to two measures of relative clutch mass. These results support the hypothesis that physiological changes during late pregnancy contribute to the decrement in locomotor performance during pregnancy. Because locomotor performance was uncorrelated with the level of reproductive investment, survival costs during pregnancy may be less important than previously thought, particularly if physiological costs during pregnancy render females vulnerable to starvation or predation following parturition. Additional field studies are needed to clarify the nature of survival costs in natural populations and their consequences for the evolution of squamate life histories.

THE NESTING ECOLOGY OF THE ALLEN CAYS ROCK IGUANA, CYCLURA CYCHLURA INORNATA IN THE BAHAMAS

The nesting ecology of the Allen Cays rock iguana was studied on Leaf Cay and Southwest Allen's Cay (= U Cay) in the northern Exuma Islands, Bahamas, during 2001 and 2002. Mating occured in mid-May, and females migrated 30–173 m to potential nest sites in mid to late June. Females often abandoned initial attempts at digging nest burrows, and average time from initiation of the final burrow to completion of a covered nest was six days. At least some females completely buried themselves within the burrow during the final stages of burrow construction and oviposition. Females defended the burrow site during the entire time of construction, and most continued that defense for at least three to four weeks after nest completion. Nests were completed between mid-June and mid-July, but for unknown reasons timing was seven days earlier on U Cay than on Leaf Cay. Nest burrows averaged 149 cm in length and terminal nest chambers usually angled off the main burrow. Depth to the bottom of the egg chamber averaged 28 cm, and was inversely correlated with shadiness of the site, suggesting that females may select depths with preferred temperatures (mean, 31.4 C in this study). Overall, only about one in three females nested each year, although nesting frequency increased with female size such that the largest females usually nest annually. Nest fidelity was common, despite the potential for observer effects; seven of 13 two-year nesters placed nests within 0.7 m of that constructed the previous year.Nesting females averaged 32 cm snout–vent length (SVL) and 1336 g body mass, and larger, older females nested earlier than smaller, younger ones. Sexual maturity is reached at 26–27 cm SVL, about 750 g body mass, and twelve years of age (nearly twice as old as any previously studied lizard). Longevity of females apparently exceeds 40 years. Clutch size ranged from 1–10 eggs (mean 4.6) and was correlated with female body size and age. Eggs averaged 66 mm in length, 35 mm in width, and 49 g in mass. Egg mass was not correlated with female body size, although egg length was negatively correlated, and egg width was positively correlated with female size. The production of elongate eggs in the smaller females allowed them to invest the same total mass in each egg as a larger female, while being constrained by the limits of the pelvic opening. No trade-off existed between standardized clutch size versus egg size. Relative clutch mass (clutch mass/gravid female body mass × 100) averaged 16.5 and did not vary with female size or age. Hatching apparently occurs in late September and early October after about 80–85 days incubation, with emergence within just a few days. Hatchlings averaged 9.5 cm SVL and 33 g body mass. Survivorship to emergence was 78.9%, and was inversely correlated with soil moisture.The reproductive ecology of other iguanids (sensu strictu) is reviewed for comparison with that of the Allen Cays rock iguana. Comparisons of these data with those available for other rock iguanas of the genus Cyclura suggest that colonization of smaller islands has produced reductions in adult female body size, clutch size, clutch mass, and relative clutch mass, but no change in egg or hatchling mass. Because this pattern is also demonstrated by a population of Cuban iguanas introduced to a small island only 40 years ago, it may primarily be a proximal response to decreased resource availability and/or physiological processability on small islands rather than an evolved response to reduced predation rates or other factors affecting survivorship.

Measures of reproductive allometry are sensitive to sampling bias

SummaryIn both interspecific and intraspecific comparisons, maternal body size is the strongest predictor of fecundity for many kinds of animals. However, it has not been widely appreciated that the usual empirical descriptors of this relationship (correlation coefficient, slope andP‐value of the linear regression between maternal body size and offspring number) are sensitive to a factor that is very labile and subject to methodological bias: the degree of maternal investment, specifically the ratio of litter mass to maternal body mass (relative clutch mass, RCM).Samples of females used to assess reproductive allometry may often be biased with respect to RCM. For example, RCMs may vary through time within a single population as a consequence of prey availability, or may vary geographically among populations. Also, females with low RCMs may be more difficult to capture, or may be discarded by researchers who do not realize that they are reproductive.Our analyses on 173 litters of aspic vipers (Vipera aspisLinné) from central western France show that estimates of reproductive allometry are very sensitive to RCM: samples composed of high‐RCM females show a positive and highly significant reproductive allometry, whereas samples composed of low RCM females do not. Conclusions also depend on the method of regression analysis used. This result has strong implications for methodology (i.e. selection of samples, choice of analytical methods and timescales of study) in this field of research.

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.

MULTIENNIAL REPRODUCTION IN FEMALES OF A VIVIPAROUS, TEMPERATE-ZONE SKINK, TILIQUA NIGROLUTEA

We examined the reproductive frequency in wild-caught and captive females of Tiliqua nigrolutea over five consecutive reproductive seasons. Reproductive frequency (0.38 ± SE 0.035) was clearly different from an annual pattern (1.0) in which all females reproduce every year. Individual females did not reproduce every year, but “skipped” seasons were staggered such that a proportion of the population produced a clutch each season. We attribute skipped reproductive opportunities to a combination of a long gestation, high relative clutch mass (0.43 ± SE 0.034), parturition late in the active season, a cessation of feeding in the latter stages of gestation, and low autumn temperatures that limited post-partum feeding opportunities.

Reproductive ecology of a tropical natricine snake, Tropidonophis mairii (Colubridae)

AbstractAlthough most snake species are tropical, very little is known about their biology. We monitored reproductive histories of individually marked natricine colubrid snakes (keelbacks, Tropidonophis mairii) for 18‐months in a tropical Australian floodplain. Our data provide the first unambiguous records (for any snake species) of individual females in a natural population producing multiple clutches of eggs during a single breeding season. The snakes bred throughout drier months of the year. The mean size of reproducing females decreased over the season, whereas relative clutch mass increased significantly over the same time period. Larger females produced eggs that were not only larger, but also shorter and wider, than those of smaller females. Despite producing two clutches in short succession, female keelbacks grew over the intervening period. Thus, they switch from ‘capital breeding’ (building up stores of energy during the wet season to use for reproduction in the dry season) to ‘income breeding’ (relying on recently ingested energy to support both growth and reproduction during the dry season). Two females marked at hatching were recaptured as breeding adults <12 months later, confirming that maturation is attained more rapidly in this species than in temperate‐zone natricines.

Male-Male Combat and Head Morphology in a Fanged Frog (Rana kuhlii) from Taiwan

Annual Review of Ecology and Systematics 2:369404. . 1989. Should hindgut contents be included in lizard dietary compilations? Journal of Herpetology 23:455-458. SCHOLTZ, C. H., AND E. HOLM. 1986. Insects of southern Africa. Butterworths, Durban, South Africa. SKAIFE, S. H. 1979. African insect life. Rev. ed. Struik, Cape Town, South Africa. SOKAL, R. R., AND E J. ROHLF. 1981. Statistical tables. 2nd ed. Freeman and Co., San Francisco, CA. VITT, L. J., AND H. J. PRICE. 1982. Ecological and evolutionary determinants of relative clutch mass in lizards. Herpetologica 38:237-255. ZAR, J. H. 1984. Biostatistical analysis. 2nd ed. Prentice Hall, Inc., Engelwood Cliffs, NJ.

Reproductive Cycle and Characteristics of the Widely-Foraging Lizard, Cnemidophorus communis, from Jalisco, Mexico

A 1993-1994 study of the reproductive biology of Cnemidophorus communis in the Chamela region, Jalisco, Mexico, revealed that males reached sexual maturity at a snout-vent length (SVL) of 59 mm, and females reached sexual maturity at a SVL of 68 mm. Males exhibited maximum testicular activity from May through October, decreasing in November, and females were reproductive, having vitellogenic follicles or oviductal eggs, from July through October. The mean number of vitellogenic follicles was 6.69 ′ 0.59 (2-10, n = 13) and mean clutch size of oviductal eggs was 4.8 ′ 0.44 (3-9, n = 17). Clutch size and egg mass were positively correlated with SVL but relative clutch mass remained constant among females and years. Proximal climatic factors influenced timing and intensity of reproduction in C. communis, but the historical effect of foraging mode on teiid lizard morphology constrains relative clutch mass.

COMPARACIÓN DEL ESFUERZO REPRODUCTOR EN DOS ESPECIES HERMANAS DEL GÉNERO SCELOPORUS (SAURIA: PHRYNOSOMATIDAE) CON DIFERENTE MODO REPRODUCTOR

Se estudió el tamaño y la masa relativa de la camada o la nidada en dos especies de lacertilios emparentados (Sceloporus aeneus y S. bicanthalis) que presentan diferente modo reproductor (ovíparo y vivíparo, respectivamente). En ambas especies, el tamaño de la camada o la nidada se incrementó con el peso de las hembras y no hubo diferencias significativas entre ambas especies. S. bicanthalis presentó una masa relativa significativamente mayor que su especie hermana S. aeneus. Los índices del esfuerzo reproductor obtenidos en el estudio, son los más altos registrados para el género Sceloporus. No se presentaron diferencias significativas en el peso de las crías después de la eclosión o del parto, lo que sugiere que la diferencia en los valores de la masa relativa entre especies es debida a los estadios embrionarios en que se encuentra la progenie al ser analizada.

Phenotypic plasticity for life history traits in a stream population of the threespine stickleback,Gasterosteus aculeatusL.

Abstract – The life history traits of breeding size, clutch size, egg size and relative clutch mass were examined for evidence of plasticity within a set of six annual samples of threespine stickleback,Gasterosteus aculeatusL., females from south‐central Alaska, USA. Three samples (from 1992, 1996 and 1999) were of stickleback native to, and living within, a stream environment, while three (from 1995, 1996 and 1999) represented fish living within a pond environment recently colonized by the stream stickleback. Significant differences between stream and pond fish were found for all four traits. For most traits, pond‐living females showed greater variation both across and within years than did stream‐living females. Although extremely rapid evolution within the pond, or genetic drift caused by low founding population size, could not be completely ruled out, trait changes across years in both environments were interpreted as representing adaptive plasticity.

Variation and trade-off in reproductive output of the Andean frog Hyla labialis.

I analysed variation in number and size of eggs in association with variation in body size of Hyla labialis females from three altitudinally widely separated populations in the Colombian Andes. Females at 3,500m were significantly larger and heavier than those at 2,700m, which in turn were larger and heavier than those at 2,000m. After accounting for interpopulational differences in body size, clutch size (i.e. number of eggs) and egg size differed significantly between populations, but clutch mass did not. At 3,500m, large relative clutch mass tended to be associated with larger eggs, whereas at lower altitudes it was associated with relatively larger clutch size. Within each population, females showed a significant trade-off between clutch size and egg size, even though relative clutch mass varied substantially and a clutch rarely used up the carrying capacity of their body cavity. At 3,500m, comparisons between the early and late breeding season within a year suggested that climate fluctuations may play a role in reproductive-output variation within a population. Laboratory-kept females in a high somatic condition after spawning laid larger clutches in the next breeding event, but the trade-off persisted despite ad libitum food supply. Comparisons between field and laboratory suggest that limits to reproductive output were due to physiological, but not morphological restrictions. Therefore, the trade-off is better explained by energy limitation for egg growth depending on clutch size, than by the body cavity limitation hypothesis.

CHICK GROWTH AND BREEDING SUCCESS OF THE BURROWING PARROT

Abstract We present the first data on the breeding biology of wild Burrowing Parrots (Cyanoliseus patagonus). We studied chick growth and breeding success at the largest colony of the species in the province of Rio Negro, Patagonia, Argentina, during the 1999–2000 breeding season. A very high fledging success was observed and related to the absence of nest predation and the colonial breeding system. Safe nest sites were also thought to favor large mass recession of the nestlings before fledging. Mortality during the nestling period tended to be higher for fourth and fifth nestlings of a brood, indicating that brood reduction occurred. Burrowing Parrots in the study colony showed large variability in growth parameters between nestlings, possibly related to the hatching asynchrony observed. Allometric relationships for egg mass, clutch size, relative clutch mass, and nestling period of 29 wild psittaciform species are described and compared with the data from the Burrowing Parrots. Desarrollo de los Pichone...

Allometry of reproduction in broad-snouted caiman (Caiman latirostris).

In the present study regression equations are established between broad-snouted caiman (Caiman latirostris) captive reproductive females snout-vent length (SVL) and body mass (BM) and the following clutch characteristics: egg mass, egg "length" (maximal diameter), egg "width" (minimal diameter), hatchling BM, hatchling SVL, clutch size (number of eggs), clutch mass and relative clutch mass (clutch mass/female BM). Female body-length presented a positive correlation with egg mass, egg length, egg width, hatchling BM and hatchling SVL. No clear correlation was found between female SVL and clutch size. Female BM showed a significantly positive correlation with egg mass, egg-length, egg-width, hatchling BM, hatchling SVL and clutch mass. A highly significant negative correlation was found between female BM and the relative clutch mass. No clear correlation was found between female BM and clutch size.

Egg-Laying Activities and Reproductive Traits in Females of Oplurus cuvieri cuvieri

Egg-Laying Activities and Reproductive Traits in Females of Oplurus cuvieri cuvieri

The reproductive biology and diet of sea snake bycatch of prawn trawling in northern Australia: characteristics important for assessing the impacts on populations

Trawlers catch up to 17 species of sea snake as bycatch in the Northern Prawn Fishery (NPF) in northern Australia. We examined the biological characteristics of 660 sea snakes caught by research, scientific observer and commercial vessels between 1986 and 1998 as part of a project to assess their vulnerability. Three species accounted for more than 75% of the total sea snakes caught. Hydrophis species were more common in unstructured habitats close to prawn trawling grounds, while Aipysurus species were the dominant species in areas having reef structure. Sea snakes were caught more frequently at night on commercial trawlers and even more were caught during the day by research trawling. Female sea snakes were caught more often than males for 10 out of 13 species examined. The proportion of mature sea snakes in trawl catches was high (67% males, 89% females). Juvenile sea snakes of most species are not caught suggesting there is little impact of trawling on recruits. We found all species breed annually, producing a few large young after a gestation period of 6-7 months. Litter size varied between 1 to 20 and young of most species were born during the NPF closed season (Nov-Mar). Except for Aipysurus duboisii, Disteira major and Hydrophis ornatus, pregnant females of most species were not more catchable by prawn trawls than non-pregnant females. The relative clutch mass had little effect on the catchability of pregnant females. Most sea snake species had a specialized diet, feeding on one to four benthic fish species and did not appear to be attracted into trawl grounds by the increased availability of discarded bycatch. Their reproductive characteristics mean that populations of many species caught by trawlers in northern Australia are potentially vulnerable.

Reproductive Ecology of the Whiptail LizardCnemidophorus lineatissimus(Squamata: Teiidae) in a Tropical Dry Forest

We studied the reproductive ecology of the teiid lizard Cnemidophorus lineatissimus during 1993 and 1994 near Chamela, Jalisco, México. We estimate that males reached sexual maturity at a snout–vent length (SVL) of 51 mm and an age of five months, and females reached sexual maturity at a SVL of 62 mm and an age of seven months. Testicular mass increased from April to July, reaching maximal size between August and December, and decreased in January of the next year. Gonads of females began to increase in mass during June when vitellogenesis occurred. They reached maximum mass from July to November when most egg production occurred. Some egg production occurred in January as well. The reproductive season for males and females is extended, similar to many other tropical lizards. Mean clutch size was 4.1 ± 0.2 eggs. Clutch size was correlated with female size, but egg size and relative clutch mass remained constant among females and between years. Mean clutch size and female body condition were lower in 1993 compared to 1994, presumably reflecting the effects of annual variation in resource availability on females. Proximal climatic factors influence the timing and intensity of reproduction in C. lineatissimus, but the historical effect of foraging mode on teiid lizard morphology constrains relative clutch mass. Sexual dimorphism is evident with males reaching larger size than females, and seasonal variation in mean SVL in both sexes suggests that much of the population is replaced annually.Estudiamos la ecología reproductiva de la lagartija teíida, Cnemidophorus lineatissimus, durante 1993 y 1994 cerca de Chamela, Jalisco, México. Estimamos que los machos alcanzaron la madurez sexual a la longitud hocico-cloaca (LHC) de 51 mm y a una edad de 5 meses, y las hembras alcanzaron la madurez sexual a una LHC de 62 mm y a una edad de 7 meses. La masa testicular aumentó de abril a julio, llegando a su tamaño máximo entre agosto y diciembre, y disminuyó en enero del año siguiente. Las gónadas de las hembras empezaron a aumentar en masa durante junio cuando la vitelogénesis sucedió. Alcanzararon su masa máxima de julio a noviembre cuando ocurrio la mayo producción de los huevos. Una parte de la producción de los huevos también ocurrió en enero. La época reproductiva para los machos y las hembras es prolongada, parecida a muchas otras lagartijas tropicales. El promedio de la puesta fue de 4.1 ± 0.2 huevos. El tamaño de la puesta estuvo correlacionado con el tamaño de la hembra, pero el tamaño del huevo y la masa relativa de la puesta se mantuvieron constantes entre hembras y entre años. El promedio de la puesta y la condición corporal de las hembras fueron más bajos en 1993 que en 1994, presumiblemente reflejando los efectos de la variación de la disponibilidad anual de recursos para las hembras. Factores climáticos inmediatos influyen el patrón temporal y la intensidad de reproducción en C. lineatissimus, pero en el efecto histórico del modo de alimentar en la morfología de las lagartijas teíidas restringe la masa relativa de la puesta. Se nota el dimorfismo sexual, en que los machos alcanzan un tamaño mayor que las hembras, y la variación estacional en el promedio LHC de ambos sexos sugiere que mucho de la población cambia anualmente.

Maternal Effects Associated with Gestation Conditions in a Viviparous Lizard, Niveoscincus metallicus

Viviparous squamates offer opportunities for exploring the importance of past maternal resources (yolk) and current resources (placentotrophy) to support embryonic growth during gestation, and to optimize offspring fitness. Both thermal and nutritional environment of the mother during gestation may be expected to be important in determining offspring fitness. Using a two-way factorial design, we have investigated possible interactions between food intake and thermal environment during gestation in the viviparous skink Niveoscincus metallicus . Among the females given restricted basking opportunities, fewer females gave birth, there was a significant increase in gestation length, and relative clutch mass was reduced due to smaller neonatal size; none of these parameters were influenced by nutritional status. Neonates from mothers given restricted basking opportunities were lighter, had shorter snout-vent lengths (SVL), and smaller fat bodies than neonates from mothers given optimal basking opportunities; their postnatal growth rate (over eight weeks) was also significantly lower and they showed a reduced incidence of basking behavior. There were interaction effects between thermal regime and food supply for neonate SVL and neonatal fat body weight. Sprint speed within 24 hours of birth was significantly increased in neonates from mothers given restricted thermal opportunities; however, for weeks 1-8 postnatally, there were no differences in sprint speed in offspring from any of the treatments. These results suggest that, contrary to our initial hypothesis, females maintained in nutritionally favorable conditions are unable to compensate for the gestational effects of a thermally poor environment. We now suggest that in Niveoscincus metallicus facultative placentotrophy may allow mothers to improve offspring fitness by increasing neonatal fat body size.

Reproductive Ecology of the Concho Water Snake, Nerodia harteri paucimaculata

The reproductive biology of the Concho water snake (Nerodia harteri paucimaculata) was studied from 1988 to 1992 in central Texas. Minimum snout-vent lengths (SVL) at maturity were 380 mm in males and 460 mm in females. Mating occurred primarily in late April and early May, although we observed some evidence of fall mating. Gestation was approximately three months. Parturition occurred predominantly in mid-August, ranging from 29 July to 22 September. Approximately 85% (range 79.5-88.8) of adult females were gravid each year with the proportion of reproductive females varying as a function of body size. Litter size averaged 11.1 (range 4-29) and varied both among and within study sites. Maternal SVL was correlated with litter size and mass but not offspring SVL or mass with litter size held constant. Litter size had no effect on offspring SVL or mass when female SVL was held constant. Relative clutch mass averaged 0.46 and was independent of female size. Mean offspring length and mass were 175 mm SVL and 3.8 g, respectively, showing no overall sexual differences. However, mean SVL was typically greater for females within litters.

On the reproductive biology of the herbivorous spiny-tailed agamid Uromastyx philbyi in western Saudi Arabia

The reproductive biology of the Spiny-tailed Agamid Uromastyx philbyi, a herbivorous desert lizard, was studied in western Saudi Arabia. Reproduction is seasonal, with mating in early spring (March), oviposition in late spring (May–June), and hatching in summer (July). The mean clutch size was 6.67 eggs. Eggs are large (mean mass = 7.48 g) and relative clutch mass (RCM) averaged 0.49. Clutch mass and RCM increased with increasing egg mass. Clutch size, egg size, clutch mass, and RCM were significantly correlated with maternal body size.