Effects of temperature and salinity on body fluid dynamics and metabolism in the estuarine diamondback terrapin (Malaclemys terrapin)

The diamondback terrapin is the only temperate turtle species that exclusively inhabits estuarine environments. Morphological, behavioral and physiological features contribute to the terrapin's ability to regulate body fluid osmotic pressure in a euryhaline environment. Low integument permeability combined with aquatic-terrestrial shuttling behavior limits passive exchange of water and salts with the environment, and terrapins regulate active uptake of salts via alterations in drinking and feeding behavior. The lachrymal salt gland facilitates excretion of excess sodium (Na⁺) and chloride (Cl^-) ions through active transport mechanisms. We investigated body fluid dynamics, oxygen consumption (V̇ _O2 ) and osmotic status of terrapins exposed to an acute increase in salinity (12 to 35 psu) at 10 and 25°C to gain insight into the relative importance of behavioral versus physiological osmoregulatory adjustments over a range of seasonally relevant temperatures. Linear mixed models were used to evaluate the effects of experimental temperature, salinity and mass. Overall, temperature effects were stronger than salinity effects. Terrapins acclimated to 25°C had significantly lower blood osmolality and Na⁺, and higher water turnover rates, daily water flux (DWF) and V̇ _O2  compared with terrapins acclimated to 10°C. Salinity effects were restricted to DWF, which significantly decreased in response to acute exposure to 35 psu. Our results support the notion that behavioral adjustments predominate in the osmoregulatory strategy of terrapins.

Water exchange relationships predict overwintering behavior in hatchling turtles

Neonatal ectotherms face a wide range of environmental hazards because of the diverse habitats that they inhabit and their small body sizes; this is especially true among turtles that live in temperate zones and experience cold winter conditions after hatching. Such hatchlings must balance challenges involving desiccation, freezing, and predation, among other threats. Turtle hatchlings either overwinter in water, terrestrially in relatively shallow nests, terrestrially deep below nests, or terrestrially outside of the nest entirely, and these different microhabitats are associated with different desiccation and freezing risks. We measured desiccation tolerance of individuals of six turtle species, including two (Diamondback Terrapins, Malaclemys terrapin (Schoepff, 1793), and Eastern Box Turtles, Terrapene carolina (Linnaeus, 1758)) that use a strategy that has not previously been explored, along with Wood Turtles (Glyptemys insculpta (Le Conte, 1830)), whose overwintering microhabitat is uncertain. We found additional support for the hypothesis that desiccation resistance is associated with overwintering strategies in hatchling turtles. Further investigation into the overwintering strategies of M. terrapin and T. carolina would be productive.

Standard metabolic rates of early life stages of the diamondback terrapin (Malaclemys terrapin), an estuarine turtle, suggest correlates between life history changes and the metabolic economy of hatchlings

I estimated standard metabolic rates (SMR) using measurements of oxygen consumption rates of embryos and unfed, resting hatchlings of the diamondback terrapin (Malaclemys terrapin) three times during embryonic development and twice during the early post-hatching period. The highest observed SMRs occurred during mid to late embryonic development and the early post-hatching period when hatchlings were still reliant on yolk reserves provided by the mother. Hatchlings that were reliant on yolk displayed per capita SMR 135 % higher than when measured 25 calendar days later after they became reliant on exogenous resources. The magnitude of the difference in hatchling SMR between yolk-reliant and exogenously feeding stages was much greater than that attributed to costs of digestion (specific dynamic action) observed in another emydid turtle, suggesting that processing of the yolk was not solely responsible for the observed difference. The pre-feeding period of yolk reliance of hatchlings corresponds with the period of dispersal from the nesting site, suggesting that elevated SMR during this period could facilitate dispersal activities. Thus, I hypothesize that the reduction in SMR after the development of feeding behaviors may reflect an energy optimization strategy in which a high metabolic expenditure in support of development and growth of the embryo and dispersal of the hatchling is followed by a substantial reduction in metabolic expenditure coincident with the individual becoming reliant on exogenous resources following yolk depletion.

First record of hatchling overwintering inside the natal nest of a chelid turtle

Hatchling overwintering inside the natal nest is a strategy used by several Northern Hemisphere species of freshwater turtles. We recorded hatchling overwintering in the nest by Chelodina longicollis (Chelidae) in south-eastern Australia, during three reproductive seasons. Hatchlings spent, on average, 320 days inside the nest from the date eggs were laid until emergence. Some nests were carefully opened adjacent to the nest plug, one during winter and one in spring, to confirm that eggs had hatched and were not in diapause, although we could not precisely confirm hatching dates. Despite our small sample size, we observed a dichotomous overwintering strategy, with hatchlings from one nest emerging in autumn and spending their first winter in the aquatic environment, and hatchlings from three nests overwintering in the nest and emerging in spring. These findings expand the phylogenetic range of turtles exhibiting hatchling overwintering behaviour. Future research should evaluate whether this strategy is widespread among other long-necked turtles in temperate regions and examine physiological mechanisms involved in coping with winter temperatures.

Potential sources of intra-population variation in painted turtle (Chrysemys picta) hatchling overwintering strategy

Many temperate animals spend half their lives in a non-active, overwintering state, and multiple adaptations have evolved to enable winter survival. One notable vertebrate model is Chrysemys picta whose hatchlings display dichotomous overwintering strategies: some hatchlings spend their first winter aquatically after nest emergence in fall, while others overwinter terrestrially within their natal nest with subsequent spring emergence. Occurrence of these strategies varies among populations and temporally within populations; however, factors that determine the strategy employed by a nest in nature are unknown. We examined potential factors that influence intra-population variation in C. picta hatchling overwintering strategy over two winters in Algonquin Park, Ontario. We found that environmental factors may be a trigger for hatchling overwintering strategy: fall-emerging nests were sloped towards the water and were surrounded by a relatively higher percentage of bare ground compared to spring-emerging nests. Fall-emerging hatchlings were also relatively smaller. Overwintering strategy was not associated with clutch oviposition sequence, or mammalian or avian predation attempts. Instead, fall emergence from the nest was associated with the direct mortality threat of predation by Sarcophagid fly larvae. Body condition and righting response, measured as proxies of hatchling fitness, did not differ between overwintering strategies. Costs and benefits of overwintering aquatically versus terrestrially in hatchling C. picta are largely unknown, and have the potential to affect population dynamics. Understanding winter survival has great implications for turtle ecology, thus we emphasize future research areas on dichotomous overwintering strategies in temperate hatchling turtles.

Seasonality and interspecific and intraspecific asynchrony in emergence from the nest by hatchling freshwater turtles

Timing of emergence from the natal nest is a variable trait in the life history of turtles. In theory, hatchling turtles that emerge synchronously, within and among nests, should gain a survival advantage over hatchlings that emerge independently. We examined emergence patterns for seven species of freshwater turtles that use a common nesting area in northern Indiana, USA. Hatchlings of four species emerged from the nest exclusively in late summer or early fall. However, hatchlings of three species usually overwintered in the nest chamber and emerged the following spring. Interspecific and intraspecific emergence from the nest was more synchronous in fall than in spring. Mean date of fall emergence from the nest did not vary among species; however, a species-specific pattern of emergence was observed in spring. Midland Painted Turtles (Chrysemys picta marginata Agassiz, 1857) emerged in late March and early April and, on average, these hatchlings left their nests 2 weeks earlier than Northern Map Turtles (Graptemys geographica (Le Sueur, 1817)) and 4 weeks earlier than Red-eared Sliders (Trachemys scripta elegans (Wied-Neuwied, 1839)). Although hatchlings of C. p. marginata are smaller than those of G. geographica and T. s. elegans, presumably they gain a survival or growth advantage by emerging earlier.