Clutches of six female snapping turtles (Chelydra serpentina) each were distributed among six incubators set at one of three constant temperatures (22.0, 25.6, and 28.6 °C) in either a wet (−100 kPa) or a dry (−500 kPa) vermiculite substrate. We tested for influences of egg mass, clutch, and incubation temperature and moisture on survival of embryos and hatchlings, on size at hatching, and on rate of post-hatching growth over 7 months. Intraclutch variation in egg mass had no effect on embryonic mortality. Mass at hatching was correlated with egg mass, but neither variable was related significantly to post-hatching survival or rate of growth. Eggs incubated at the highest temperature produced smaller hatchlings which subsequently grew more slowly than those from eggs incubated at the low and intermediate temperatures. Eggs incubated at the intermediate temperature produced larger turtles at 7 months post-hatching than did eggs incubated at the low or high temperatures. Eggs incubated in wet substrates produced larger hatchlings than those in dry substrates, but post-hatching growth rates were independent of these effects of moisture. Eggs incubated at the two extreme temperatures produced mostly females; those at 25.6 °C produced only males. Interclutch variation was significant for egg mass, mass at hatching, and survival of embryos, and was the most important influence on variation in post-hatching rates of growth. These results indicate that egg size and size at hatching may not be useful indicators of intraspecific variation in egg quality or post-hatching success in turtles, unless differences among clutches and embryonic thermal experience are also considered, particularly in relation to parental investment in the amount, quality, and apportionment of the egg's yolk.

With 5 figures in the text)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.

We incubated snapping turtle eggs at extreme levels of temperature and moisture to test the hypothesis that incubation conditions limit the species' range by affecting hatching success and posthatching survival and growth. We also tested for local adaptations to cold incubation conditions by comparing the responses of embryos and hatchlings from a population near the northern limit of the species' range with those from a population farther south. Eggs of 20 clutches from two Ontario populations were incubated at 21.1 or 25.3 °C at one of three substrate moisture levels (−150, −300, −800 kPa), and hatchling survival and growth were monitored in the laboratory for 23 months. Hatching success, hatchling survival, and posthatching growth were lowest among turtles from eggs incubated at 21.1 °C. They were also uncoordinated and had poor control of their buoyancy. Hatching success was reduced in the drier substrates, but posthatching survival and growth were not affected by substrate moisture. Embryo and hatchling survival were lower in turtles from the southern population (which may be related to contaminants in the eggs) but hatchlings from that population grew the fastest. Hatching success at 21.1 °C or in the driest substrate did not differ between the two populations, but embryos from the northern population did show a greater increase in mortality at 21.1 °C relative to 25.3 °C than embryos from the more southerly population. The effects of lower incubation temperatures may be the most important factor limiting the northern distribution of this species, because lower temperatures during incubation and a shorter growing season probably reduce both the quantity and quality of hatchling turtles produced at northern sites.

Lacertca raddei and Lacerta nairensis have been recognized as two separate species based on morphology and behavior, and each has been implicated as a sexual parent of different parthenogenetic forms. However, recent mitochondrial DNA work failed to distinguish these two as separate species. We examined genetic diversity at 36 allozyme loci from six populations of L. nairensis and four populations of L. raddei. There were no fixed allelic differences between the two. Mean heterozygosity was slightly higher among populations of L. raddei than among populations of L. nairensis. A Distance Wagner phenogram showed that the northernmost population of L. raddei clustered with the L. nairensis populations; the other L. raddei populations clustered together. We suggest that L. raddei and L. nairensis may not be separate species, a finding which has important implications for determining the origins of some parthenogenetic Lacerta.