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.
Abstract Phenotype-environment associations in neonatal animals may arise in wild environments by virtue of ecological dynamics within the nest. Such dynamics may be of special importance to the evolution of temperature-dependent sex determination (TSD), an enigmatic trait which can be adaptive when the incubation temperatures that affect sexual differentiation also have differential effects on fitness of the sexes. To infer causal effects of the nest environment on fitness-relevant phenotypes, we apply structural equation modeling (SEM) to a 14-year dataset of 3085 individual embryos whose position in 179 wild snapping turtle nests could be estimated. We find that temperature has a positive effect on hatchling size, and that the same temperatures that predict hatchling size also predict sex of hatchlings. Further, the probability that embryos develop as males is correlated with hatchling size in the wild, where across all environments, males are slightly and significantly larger than females at hatching. Our SEM reveals that the covariance between size and sex arises because of temperature effects on size, and because of a predictable covariance between egg placement within the nest coupled with maternal effects on egg size. Finally, embryos deep in the nest have a high probability of becoming male even in the hottest years. Our study suggests ecological dynamics occurring within the nest are an interesting and underappreciated source of phenotypic variation. Our study also supports the view that TSD is an adaptive trait, rather than a neutral trait, by showing consistent associations between phenotype and temperature in wild nests of a TSD reptile.
Scats of mink (Mustela vison) and otter (Lutra canadensis) in northeastern Alberta contained different food items in different habitat types according to type of water body. Brook stickleback (Culaea inconstans) was the most frequently encountered food item in scats of both species from a drainage system dominated by lakes and for otter from a second drainage system dominated by streams. However, mink had varying hare (Lepus americanus) as their primary food item by frequency of occurrence in this latter situation and mammalian items were significantly (P < 0.01) more frequent. Otter scats contained more fish and invertebrates (P < 0.01) and fewer mammals (P < 0.01) and birds (P < 0.05) than mink scats. Both otters and mink appeared to exploit avian species to a greater degree (P < 0.01) in the lake-dominated drainage. The frequency of avain remains in otter scats was very high and probably reflected high utilization of breeding and moulting waterfowl.
AbstractSpecies with environmental sex determination (ESD) have persisted through deep time, despite massive environmental perturbation in the geological record. Understanding how species with temperature-dependent sex determination (TSD), a type of ESD, persist through climate change is particularly timely given the current climate crisis, as highly biased sex ratios and extinction are predicted. Since 1982, we have studied primary sex ratios of a reptile with TSD (Chelydra serpentina). Primary sex ratios remained unchanged over time, despite warming in the environment. Resilience of the primary sex ratio occurred via a portfolio effect, realized through remarkable intra-annual variation in nest-level sex ratios, leading to a relatively consistent mean annual sex ratio. Intra-annual variation in nest-level sex ratios was related to variation in egg burial depth coupled with large clutch sizes, creating thermal gradients in the nest and promoting mixed-sex clutches. Furthermore, both locally and globally, sustained increases in nighttime air temperature contribute more to warming than increases in daily maximum temperature, but development rate was affected more strongly by maximum daily air temperature, conferring additional resilience to overall warming. Our study suggests that some TSD species may be resilient to warming and provides an example of how ESD may persist under environmental change.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)