Affect Hatching Success Research Articles

Shift in Thermal Preferences of Female Oviparous Common Lizards During Egg Retention: Insights into the Evolution of Reptilian Viviparity

Pregnant female Zootoca vivipara select lower body temperatures than males or nonpregnant females, and this shift in the thermal preferendum is believed to be related to optimising the conditions for embryogenesis. Thus, subjecting embryos to the higher temperature selected by males and non-gravid females might have detrimental effects on embryonic development and on hatchling fitness, according to predictions of the “maternal manipulation” hypothesis on the evolution of viviparity. To test the role of gestation environment on embryonic development in oviparous Z. vivipara, we kept a number of gravid females at the temperature selected by non-gravid females in a laboratory thermal gradient, whereas control females were allowed to regulate their body temperature without restrictions. Developmental stage at oviposition was more advanced for embryos of the experimental clutches, which were heavier than those of the control group. Forced gestation temperature also affected hatching success (58.62% in the experimental treatment vs. 97.37% in the control group). In addition, hatchlings from females subjected to high temperatures during pregnancy were smaller, had shorter head length and performed worse in running trials. Our results fulfil the prediction of the “maternal manipulation” hypothesis, and suggest that the shift in female body temperature during pregnancy optimizes embryogenesis and hatchling phenotype by avoiding the negative effects of the high incubation temperatures preferred by non-gravid females.

The influence of thymol+DMSO on survival, growth and reproduction of Bradybaena similaris (Mollusca: Bradybaenidae)

Bradybaena similaris (Ferussac, 1821), commonly known as the Asian trampsnail, is a terrestrial snail native to Asia, introduced in other regions of the world. In Brazil, populations of this land snail are distributed from the state of Amapa in the North to Rio Grande do Sul in the South. This species acts as an intermediate host for parasites and is a difficult-to-control agricultural pest as well, causing great losses to crops and ornamental plant cultivation. This land snail is easily reared in the laboratory and has been successfully used as a biological model in studies that aim at verifying molluscicidal effects of plant extracts. Several studies have demonstrated that B. similaris, like many other species of land and freshwater snails, is physiologically adapted to survival over transitory unfavorable environmental conditions. Moreover, this species seems to have a life history strategy characterized by a short life span and a maximal opportunistic reproductive effort during transient favorable periods. Such biological features may potentially lead to the inefficacy of control attempts and, simultaneously, make this species able to repopulate sites previously treated with biocides. For this reason, studies that aim at verifying the effect of molluscicides on the reproduction, growth and survival of molluscs are greatly required. Molluscicides of plant origin may represent a safe and effective way of controlling these animals. Thymol is a substance of plant origin which has bactericidal, fungicidal and anti-inflammatory properties and has been presented as a promissory biocide of mollusc species. The aim of this work was to assess the molluscicidal property of thymol in combination with DMSO against eggs and adults of B. similaris. During 120 days, we evaluated the effect of thymol+DMSO at different concentrations (2.5 g/L and 5 g/L) on the hatching success, hatchling survival, growth and reproduction of B. similaris under laboratory conditions. We tested thymol+DMSO on 160 eggs, 160 10-day-old and 160 30-day-old juveniles. The results showed that thymol+DMSO (5 g/L and 2.5 g/L) affected hatching success, acting as an ovicide. The tests with 10-day-old juveniles showed that thymol+DMSO at 2.5 g/L and 5 g/L caused 90 and 100% of mortality, respectively. For the 30-day-old juveniles, thymol+DMSO caused 87.5% of mortality at 5 g/L, and 75% at 2.5 g/L. With regard to growth, the results were not significant. The 10-day-old individuals treated with thymol+DMSO showed only one reproductive event during the 120 days of the experiment. Thymol+DMSO showed molluscicidal and residual activity, which makes evident its potential for controlling snails, and consequently, snail-borne diseases.

Adverse effects of fipronil on avian reproduction and development: maternal transfer of fipronil to eggs in zebra finch Taeniopygia guttata and in ovo exposure in chickens Gallus domesticus

Two studies were carried out to examine the impact of maternal fipronil exposure on embryonic and offspring development. In the first study, breeding female zebra finches were orally dosed with single sublethal levels of fipronil (1, 5, and 10mg/kg body weight) to determine behavioural and developmental consequences on chicks following maternal pesticide exposure. Significant levels of fipronil and fipronil-sulfone residues were detected in eggs laid by females in all dosed groups, however, these were undetectable in eggs laid 13days after treatment. The level of sulfone detected in eggs was consistently higher than that of the parent fipronil compound. Of the seven eggs laid in the treatment groups, only one (14%) chick hatched and this was from the lowest dose group. This chick was severely underdeveloped at 10days of age in comparison to control chicks and fiproles were detected in brain, liver, and adipose tissues collected following euthanasia of this individual. In contrast, there was 100% hatchability of control group eggs and all chicks fledged nests on schedule. In the second study, domestic chicken eggs were injected with 5.5, 17.5, and 37.5mg/kg egg weight of fipronil directly into the yolk sac on day 12 of incubation. Treatment did not affect hatching success, however, behavioural and developmental abnormalities were observed in hatchlings from the highest dose group. These chicks also demonstrated reduced feeding rates, as indicated by reduced body mass at 48h period post hatch. Both fipronil and fipronil-sulfone residues were detected in brain and liver tissue of hatchlings at all pesticide dose levels tested.

Across and Within-Forest Effects on Breeding Success in Mediterranean Great TitsParus major

Forest type and habitat structure can have profound effects on different aspects of avian life histories. These effects may, however, strongly differ across and within forests that vary in vegetation composition and structure, especially when an ancient forest has been replaced by a new forest. To test for these differences in effect, we studied Great Tit Parus major life-history traits (280 first clutches) in two Mediterranean evergreen forests during 2005–07: an ancient Holm Oak Quercus ilex and a reforested pine forest. A comparison between forests revealed that females breeding in the Holm Oak forest started laying one week later, and produced larger clutches and broods both at hatching and at fledging. Chicks raised in the Holm Oak forest also fledged in better condition. Within forests, however, the reproductive success was not higher for pairs breeding in nestboxes surrounded by oaks within the pine forest, and also reproductive success was not lower in nestboxes surrounded by pines within oak forest. Instead, vegetation maturity around nestboxes, rather than tree species composition, affected hatching success. Surprisingly, hatching success was higher in nestboxes surrounded by immature vegetation. We suggest that this may be due to a lower nest predation rate in nestboxes surrounded by immature vegetation, compared to nestboxes surrounded by mature vegetation. We suggest that different factors appear to affect variation in breeding success in Mediterranean Great Tits comparing across forests (e.g. food availability) vs. within a forest (e.g. nest predation).

Variation in the onset of incubation and its influence on avian hatching success and asynchrony

Variation among species in the onset of incubation has been attributed to differences in life history traits, and variation within species has been related to individual and environmental factors. We quantified within- and among-species variation in the onset of incubation in five cavity-nesting passerines, using a continuous record of diurnal and nocturnal incubation from clutch initiation through completion. We documented 11 potential patterns for the onset of incubation and showed that onset patterns were significantly related to hatching success. The onset of diurnal partial incubation and nocturnal full incubation generally occurred before diurnal full incubation, which started around clutch completion. Increases in precipitation or wind speed significantly delayed most types of incubation onset, supporting predictions of the energy constraints hypothesis. Ancillary predictions of rain and wind disproportionately delaying incubation for aerial foragers, and for species with male feeding during incubation, were not upheld. Larger clutch size accelerated the timing of full incubation onset in diurnal and nocturnal full incubation, supporting predictions of the egg viability hypothesis. Predictions of both hypotheses for the effects of minimum temperature, proportion of time above 24 °C, and seasonality on incubation onset were not supported. We observed egg neglect for up to 4 days or nights; neglect was more common at night, and consecutive nights of neglect occurred during nocturnal full incubation. Egg neglect did not significantly affect hatching success or incubation period. In conclusion, the timing of incubation onset was strongly affected by environmental and individual factors, and patterns of incubation onset affected hatching success.

Testing the relationship between clutch size and brood size in the Coot (Fulica atra)

The time between egg laying and chick fledging is of crucial importance for the survival of young birds. I analyzed breeding output at consecutive phases of growth of young Coots (Fulica atra) relative to the clutch size and laying date. Considering the specific breeding biology of the Coot, I tested whether chick survival reveals clutch size-dependent variability. Clutch size did not affect hatching success; it only affected brood size, and that merely temporarily. During the first 20 days after hatching, i.e. during the time of the highest chick mortality, birds with larger clutches lost chicks at a higher rate. As a result, the number of fledged chicks was independent of the initial number of chicks, and pairs with different clutch sizes had a similar number of fledglings. The laying date had no effect. This pattern of age-related chick survival points to the greater role of the type of chick growth (semi-precocial) and behavior in their survival.

Sex-specific developmental plasticity in response to yolk corticosterone in an oviparous lizard

Corticosterone exposure during prenatal development as a result of maternal upregulation of circulating hormone levels has been shown to have effects on offspring development in mammals. Corticosterone has also been documented in egg yolk in oviparous vertebrates, but the extent to which this influences phenotypic development is less studied. We show that maternal corticosterone is transferred to egg yolk in an oviparous lizard (the mallee dragon, Ctenophorus fordi Storr), with significant variation among clutches in hormone levels. Experimental elevation of yolk corticosterone did not affect hatching success, incubation period or offspring sex ratio. However, corticosterone did have a sex-specific effect on skeletal growth during embryonic development. Male embryos exposed to relatively high levels of corticosterone were smaller on average than control males at hatching whereas females from hormone-treated eggs were larger on average than control females. The data thus suggest that males are not just more sensitive to the detrimental effects of corticosterone but rather that the sexes may have opposite responses to corticosterone during development. Positive selection on body size at hatching for both sexes in this species further suggests that increased corticosterone in egg yolk may have sex-specific fitness consequences, with potential implications for sex allocation and the evolution of hormone-mediated maternal effects.

Eggshell Thickness Variation in Red-legged Partridge (Alectoris rufa) from Spain

Eggshell thickness is commonly used as an indicator of habitat quality and effects of environmental pollution on avian reproduction. We present the first data available on eggshell thickness for Red-legged Partridge (Alectoris rufa) in Spain. We compared eggshell thickness between eggs collected in an agricultural area (wild eggs) and eggs from game farms (farm eggs). Wild eggs had shells significantly thicker (x̄ = 0.32 mm, n = 74) than farm eggs (x̄ = 0.28 mm, n = 89), despite game farm partridges being fed a diet rich in calcium and not exposed to agricultural pollutants. Eggshell thickness did not affect hatching success of wild partridges, and population decline observed in this species cannot be linked to reduction in egg viability due to eggshell thickness.

Demographic Responses to Multigeneration Cadmium Exposure in Two Strains of the Freshwater Gastropod, Biomphalaria glabrata

A life table response experiment (LTRE) was used to quantify the population-level effects of continuous, multigeneration cadmium exposure on two strains of the freshwater gastropod, Biomphalaria glabrata: the parasite-resistant BS90 and parasite-susceptible NMRI strains. Snails were exposed to waterborne cadmium for three consecutive generations. Survival, growth, and reproduction were measured empirically and incorporated into a stage-based, deterministic population model. Cadmium significantly affected hatching success, time to maturity, and juvenile and adult survival in both strains. There were significant effects of generation on fecundity, hatching success, time to maturity and juvenile survival in NMRI, and time to maturity and adult survival in BS90. Cadmium significantly affected the population growth rate, lambda, in BS90. Cadmium, generation, and the cadmium x generation interaction had significant effects on lambda in NMRI. At the high cadmium exposure, lambda for NMRI showed a decrease from generation 1 to generation 2, followed by an increase from generation 2 to generation 3. The lambda value in high-cadmium BS90 steadily decreased over the three generations, while NMRI at this same concentration was similar to the controls. The results indicate that strain-specific differences in response to multigeneration cadmium exposure are evident in B. glabrata. Moreover, effects seen in the first generation are not necessarily indicative of effects in subsequent generations. Changes in lambda over the course of the three-generation exposure suggest that acclimation and/or adaptation to cadmium may have occurred, particularly in NMRI at the high cadmium exposure level.

Using Nest Temperature to Estimate Nest Attendance of Piping Plovers

Abstract: Recent technological innovations allow remote monitoring of avian nest temperature that minimizes disturbance and expense without altering clutch sizes. However, the efficacy of such techniques has not been determined for ground‐nesting birds. We compared the efficacy of 2 techniques, iButton® data loggers (Maxim/Dallas Semiconductor Corp., Sunnyvale, CA) and custom‐built thermocouples, to measure nest temperature of piping plovers (Charadrius melodus) relative to nest attendance at Cape Cod National Seashore, Massachusetts, USA. Neither technique affected hatching success (U = 389.5, P = 0.874) or rates of predation of nests containing devices (P = 0.894). We estimated nest attendance successfully with thermocouples in nests as long as air and surface temperatures were <29° Cand 43° C, respectively. Although iButtons could not be used to determine duration of on‐bouts and off‐bouts of incubating piping plovers, they were effective at determining when nests were abandoned or predated. We recommend the use of thermocouples for studying nest attendance of ground‐nesting birds, in general, and of threatened and endangered species, in particular, where disturbance should be minimized and altering clutch sizes is not feasible.

The Effects of Nectar–Nicotine on Colony Fitness of Caged Honeybees

Nectar of many bee flowers contains secondary compounds, which are considered toxic for honeybees on repeated exposure. Although many anecdotal reports indicate the toxicity of secondary compounds to bees, only a few studies have tested the extent of toxicity at different honeybee ages, especially at the larval stages. Honeybees encounter nicotine at trace concentrations (between 0.1 and 5 ppm) in floral nectar of a few Nicotiana spp. and in Tilia cordata. Adult honeybee workers tolerate these nicotine concentrations. In controlled nonchoice feeding experiments with caged bees, we investigated the effect of nicotine on hatching success and larval and forager survival. Naturally occurring concentrations of nectar-nicotine did not affect hatching success of larvae or their survival, but the latter was negatively affected by higher concentrations of nicotine (50 ppm). Concentrations of nicotine in fresh honey samples from the hives were 90% lower than the concentrations in the offered experimental sucrose solutions. Our results indicate that honeybees can cope with naturally occurring concentrations of nicotine, without notable mortality, even when consumed in large quantities for more than 3 weeks.

Nest-site selection and characteristics in a mixed-species colony of Avocets Recurvirostra avosetta and Black-winged Stilts Himantopus himantopus

Capsule Causes of breeding failure determined optimal nest location, Black-winged Stilts being better adapted than Avocets to nest close to water. Aims To compare nest size and location between the two species and to test whether there were inter-species differences that might suggest specific nesting adaptations, and to investigate possible correlates between hatching success and nest location. Methods Nest-site selection, characteristics and hatching success were studied during 1989 in a large mixed-species colony located in southern Spain. Results Black-winged Stilt nests differed in composition and size depending on distance to water (nests touching the water were larger and included mud), but Avocet nests did not. Avocets nests were more aggregated and central within the colony than those of Black-winged Stilts. Causes of breeding failure were flooding and rat predation. Successful or unsuccessful Black-winged Stilt nests did not differ significantly in characteristics or location. Successful Avocet nests were further from water than flooded nests and further from dry land than depredated ones. Distance to the centre of the colony did not affect hatching success. Conclusion Black-winged Stilts were better adapted than Avocets to nest near water, due to their greater plasticity in nest-building behaviour. Causes of breeding failure determined optimal nest location.

Effects of Phos-Chek G75-F and Silv-Ex on developing northern bobwhite quail (Colinus virginianus).

Eggs of nesting birds situated in peripheral areas serving as fire breaks are at risk of being sprayed with fire control chemicals. Acute toxicity tests were conducted by immersing northern bobwhite quail eggs for 10 s in different water-based concentrations of Silv-Ex(R) (SE), a foam-suppressant chemical, and Phos-Chek(R) G75-F (PC), a fire retardant chemical, on day 4 or day 11 of incubation. An attempt was made to relate the treatment concentrations to the actual field application levels. Mortality appeared higher in most groups exposed on day 11 than on day 4, suggesting that on day 11 the extensive chorioallantoic vascular network permitted greater uptake of chemical. Only 24-60% of the embryos survived to hatch at exposure concentrations of 202, 269, and 454 g/L PC when treated on incubation day 11. At higher concentrations including 681956, and 1211 g/L PC, the compound did not completely dissolve in water and clumped on eggshells, resulting in greater hatching success. Exposures to SE at 100 g/L on incubation day 11 did not significantly affect hatching success of embryos but did significantly reduce the percent hematocrit in blood compared with controls. Incubation day 11 exposure to 202 and 1211 g/L PC led to a significant increase in plasma aspartate aminotransferase, and day 4 exposure to 1211 g/L PC resulted in a significant increase in alanine aminotransferase. In addition to elevated liver enzymes, these treatments resulted in a decrease in the number of hepatocyte profiles (1211 g/L PC at day 4 and day 11) and an increase in hepatocyte size (202 and 1211 g/L PC at day 11) in hatchlings. A combination of SE and PC was synergistic (202 g/L PC and 50 g/L SE) at day 11 of incubation with respect to decreased hatching success and reduced bone lengths. However, lower concentrations of SE (10 g/L or 30 g/L) combined with 202 g/L of PC appeared antagonistic. This may be due to SE, as a surfactant, altering the ability of PC to penetrate the egg. Our results show fewer adverse effects following exposure to SE than to PC; therefore application of SE may be less harmful to breeding bird populations.

The effects of thermal and hydric environments on hatching success, embryonic use of energy and hatchling traits in a colubrid snake, Elaphe carinata

We examined the effects of thermal and hydric environments on hatching success, the embryonic use of energy and hatchling traits in a colubrid snake, Elaphe carinata. The eggs were incubated at four temperatures ranging from 24 to 32°C on substrates with water potentials of 0 and −220 kPa using a 4×2 factorial design. Both thermal and hydric environments affected the water exchange between eggs and their surroundings. Eggs incubated in wetter substrates gained mass throughout the course of incubation, whereas eggs in drier substrates gained mass during the first half of incubation and lost mass thereafter. Hatching success was noticeably higher at 26 and 30°C than at 24 and 32°C, but among treatments, differences in hatching success were not significant. Temperature significantly affected the duration of incubation and most hatchling traits examined. Deformed hatchlings were found in all temperature treatments, with more deformities observed at 32°C. Hatchlings from eggs incubated at different temperatures differed in wet body mass, but the differences stemmed mainly from variation in water contents. Embryos at different temperatures completed development at nearly the same expenditure of energy and catabolized nearly the same amount of lipids, but hatchlings from different temperatures differed in the development condition of carcass at hatching. Hatchlings from eggs incubated at 26°C were larger in SVL than those from other higher or lower incubation temperatures, characteristically having larger carcasses; hatchlings from 32°C eggs were smaller in SVL and had smaller carcasses but larger residual yolks than those from lower incubation temperatures. Hatchlings from eggs incubated at 24°C were shorter in tail length but greater in size (SVL)-specific body wet mass than those from higher incubation temperatures. Within the range from −220 to 0 kPa, the substrate water potential did not affect hatching success, the embryonic use of energy and all hatchling traits examined, and the effects of temperature were independent of the effects of substrate water potential. Therefore, our data add evidence showing that embryonic development in reptiles with pliable-shelled eggs is relatively insensitive to variation in hydric environments during incubation.

Effects of Thermal and Hydric Environments on Incubating Eggs and Hatchling Traits in the Cobra, Naja naja atra

We examined in the laboratory the effects of thermal and hydric environments on incubating eggs and hatchling traits of Naja naja atra collected from a population near the northern distributional limit of the species in Zhejiang, eastern China. Eggs were incubated at temperatures of 24, 26, 30, and 32 ?C on substrates with water potentials of 0 and -220 kPa using a 4 x 2 factorial design. Temperature strongly affected hatching success, incubation length, water uptake by eggs during the course of incubation, and most morphological hatchling traits examined; it even affected embryonic mobilization of inorganic material from the shell. Hatching success was higher at 26 and 30?C but lower at 24 and 32?C. Eggs incubated at 26 and 30?C produced larger and heavier hatchlings that also contained more inorganic material and energy than did eggs incubated at lower and higher temperatures. Hatchlings from eggs incubated at 24 and 32?C were similar in size and mass, but hatchlings from eggs incubated at 32?C had larger residual yolks. De- formed hatchlings were found at 24, 30, and 32?C, the frequency being independent of incubation temper- ature. At the time of hatching, shells from eggs incubated at 24?C had greater dry mass and contained more ash, suggesting that less inorganic material was withdrawn from the shell by embryos developing at 24?C. Compared with temperature, water potential was not an important source of variation for the hatchling traits we examined, although it did influence water uptake by eggs during incubation and hatching success at 24?C. The effects of temperature were independent of the effects of water potential. Variation in size and mass induced by incubation temperature may be important to posthatching survival and fitness of hatch- lings.

Costs of Parasitism Incurred by Two Songbird Species and Their Quality as Cowbird Hosts

Abstract We measured the costs of Brown-headed Cowbird (Molothrus ater) parasitism incurred by Field Sparrows (Spizella pusilla) and Indigo Buntings (Passerina cyanea). We predicted that the frequent occurrence of nest desertion as a response to cowbird parasitism in Field Sparrows would be reflected by a higher cost of parasitism for that species. We also compared growth and survival of cowbird nestlings between hosts, predicting that they would do poorly at Field Sparrow nests because the latter appear to be avoided by cowbirds. Both species experienced reduced body mass gain in parasitized broods, but only Indigo Bunting suffered reduced tarsus growth. Both species experienced reductions in clutch size, hatching success, and nestling survival due to parasitism, but these losses did not differ among the two hosts. Multiple parasitism did not affect hatching success or nestling survival more than single parasitism for Indigo Buntings. Once accepted, cowbird offspring fared equally well in nests of both species, but almost half of all cowbird eggs laid in Field Sparrow nests were lost through nest abandonment. As parasitism costs to both species appear to be substantial, the rarity of nest desertion in Indigo Buntings may be due to other factors. Infrequent parasitism of Field Sparrows is consistent with host avoidance by cowbirds but other explanations should be explored.

COSTS OF PARASITISM INCURRED BY TWO SONGBIRD SPECIES AND THEIR QUALITY AS COWBIRD HOSTS

Abstract We measured the costs of Brown-headed Cowbird (Molothrus ater) parasitism incurred by Field Sparrows (Spizella pusilla) and Indigo Buntings (Passerina cyanea). We predicted that the frequent occurrence of nest desertion as a response to cowbird parasitism in Field Sparrows would be reflected by a higher cost of parasitism for that species. We also compared growth and survival of cowbird nestlings between hosts, predicting that they would do poorly at Field Sparrow nests because the latter appear to be avoided by cowbirds. Both species experienced reduced body mass gain in parasitized broods, but only Indigo Bunting suffered reduced tarsus growth. Both species experienced reductions in clutch size, hatching success, and nestling survival due to parasitism, but these losses did not differ among the two hosts. Multiple parasitism did not affect hatching success or nestling survival more than single parasitism for Indigo Buntings. Once accepted, cowbird offspring fared equally well in nests of both s...

Capacity of discontinuous egg development and its importance for the geographic distribution of the warm water stenotherm,Dinocras cephalotes(Insecta: Plecoptera: Perlidae)

Aspects of the egg biology of the perlid stonefly, Dinocras cephalotes (Curtis), were studied experimentally. Development under constant laboratory conditions did not differ from development under variable field conditions. Exposure to 4°C, the lower threshold temperature for egg development, caused abrupt interruptions of embryonic development. Development was resumed after return to favourable temperatures, with an approximate two-week-delay. Up to six interruptions of egg development did not negatively affect hatching success, regardless of developmental stage at which disturbances occurred. However, the older embryos grew, the more rapidly development was resumed after a cold disturbance; embryos from fully developed eggs hatched even at 4°C, although this is too cold to support larval growth. While eggs at 4°C remain dormant and vital for long periods of time, eggs exposed to suboptimal temperatures (10°C) remain only temporarily dormant and eventually develop and hatch. D. cephalotes is assumed to satisfy its high thermal demand for egg development under harsh conditions, for example in arctic Scandinavia, by opportunistically using summer warmth and spreading embryogenesis over more than one year. I suggest that high cue temperatures required to initiate egg development in Scandinavian populations are adaptive and ensure that larvae in the Arctic hatch under favourable seasonal conditions.

Adaptive Significance of Egg Size in the European Starling: Experimental Tests

Reproductive success in relation to egg size was studied in European Starlings (Sturnus vulgaris) by swapping whole clutches between nests at the stare of the incubation period. Egg size did not reflect parental quality as no measure of reproductive success was correlated with the foster mothers' mean egg size. There was a significant positive relationship between the mean size of the cross—fostered egg and the subsequent mean size of hatchlings. The mean size of cross—fostered eggs did not affect hatching success or nestling growth rates, and initial nestling size differences between broods with large and small eggs persisted for <1 wk. No effect of mean egg size on mean nestling survival could be detected. Furthermore, a partial cross—fostering experiment, where nestlings were swapped between nests the day after hatching, failed to demonstrate any lasting effect of egg size on nestling size. It is suggested that mean egg size may only influence reproductive success during particularly inferior environmental conditions.

Interclutch and interpopulation variation in the effects of incubation conditions on sex, survival and growth of hatchling turtles (Chelydra serpentina)

We tested the hypothesis that larger egg and hatchling sizes in the snapping turtle confer posthatching advantages, by comparing the growth rates and survival of hatchlings from different thermal and hydric environments during embryonic development. We also tested for sex‐specific differences in survival and growth, two indices of hatchling fitness, as predicted by the Charnov & Bull (1977) model of environmental sex determination (ESD). In addition, we examined interclutch and interpopulation variability in the responses of embryos and hatchlings to incubation conditions. Eggs of 21 clutches from four Ontario populations were incubated at 22·0, 25·5 or 29·3°C in a dry (–350 kPa) or wet (–150 kPa) vermiculite substrate, and hatchling survival and growth in the laboratory were monitored for 11 months. Initial egg mass and substrate moisture were positively correlated with mass at hatching, but did not affect hatching success, posthatching growth or posthatching survival. Initially heavier hatchlings were more likely to survive, but did not grow more quickly. The effects of incubation environment and hatchling mass were not consistent among clutches or populations. Intermediate incubation temperatures produced mostly males, with higher embryo and hatchling survival, as well as posthatching growth, than the mostly females from the extreme temperatures. These results support the Charnov—Bull model. Embryo and hatchling mortality and deformities were higher in clutches from two populations which are contaminated with organochlorine toxins. Interclutch differences were significant for all variables, even when initial egg or hatchling sizes were considered. Hatchlings from the population near the northern limit of the species' range grew the slowest. These results indicate that hatchling size cannot be used as an index of hatchling quality or posthatching success, unless interclutch and interpopulation variation are taken into account.