Latitudinal Variation in Seasonal Activity and Mortality in Ratsnakes (Elaphe obsoleta)

The ecology of ectotherms should be particularly affected by latitude because so much of their biology is temperature dependent. Current latitudinal patterns should also be informative about how ectotherms will have to modify their behavior in response to climate change. We used data from a total of 175 adult black ratsnakes (Elaphe obsoleta) radio tracked in Ontario, Illinois, and Texas, a latitudinal distance of \u3e 1500 km, to test predictions about how seasonal patterns of activity and mortality should vary with latitude. Despite pronounced differences in temperatures among study locations, and despite ratsnakes in Texas not hibernating and switching from diurnal to nocturnal activity in the summer, seasonal patterns of snake activity were remarkably similar during the months that snakes in all populations were active. Rather than being a function of temperature, activity may be driven by the timing of reproduction, which appears similar among populations. Contrary to the prediction that mortality should be highest in the most active population, overall mortality did not follow a clinal pattern. Winter mortality did increase with latitude, however, consistent with temperature limiting the northern distribution of ratsnakes. This result was opposite that found in the only previous study of latitudinal variation in winter mortality in reptiles, which may be a consequence of whether or not the animals exhibit true hibernation. Collectively, these results suggest that, at least in the northern part of their range, ratsnakes should be able to adjust easily to, and may benefit from, a warmer climate, although climate-based changes to the snakes\u27 prey or habitat, for example, could alter that prediction

Ratsnake response to bottomland flooding: implications for avian nest predation

Lower predation has been documented for birds’ nests located over water and a recent study found lower predation on wood duck (Aix sponsa) nests in bottomland forest during flooding. In a three-year study we used radio telemetry to determine whether flooding affected use of bottomlands by ratsnakes (Elaphe obsoleta) and thus might explain reduced nest predation. Of the 22 ratsnakes we tracked, only five used bottomlands and three of them did so exclusively, suggesting a surprising degree of habitat specialization by individual snakes. Those individuals regularly moved into flooded forest and their frequency of movement and distance moved appeared unaffected by flooding. Although it seems unlikely that ratsnakes leave bottomlands during floods, they may prey more extensively on small mammals that are restricted to trees when the forest is flooded, thereby reducing predation pressure on nesting birds

Linking Snake Behavior to Nest Predation in a Midwestern Bird Community

Nest predators can adversely affect the viability of songbird populations, and their impact is exacerbated in fragmented habitats. Despite substantial research on this predator-prey interaction, however, almost all of the focus has been on the birds rather than their nest predators, thereby limiting our understanding of the factors that bring predators and nests into contact. We used radiotelemetry to document the activity of two snake species (rat snakes, Elaphe obsoleta; racers, Coluber constrictor) known to prey on nests in Midwestern bird communities and simultaneously monitored 300 songbird nests and tested the hypothesis that predation risk should increase for nests when snakes were more active and in edge habitat preferred by both snake species. Predation risk increased when rat snakes were more active, for all nests combined and for two of the six bird species for which we had sufficient nests to allow separate analyses. This result is consistent with rat snakes being more important nest predators than racers. We found no evidence, however, that nests closer to forest edges were at greater risk. These results are generally consistent with the one previous study that investigated rat snakes and nest predation simultaneously. The seemingly paradoxical failure to find higher predation risk in the snakes\u27 preferred habitat (i.e., edge) might be explained by the snakes using edges at least in part for non-foraging activities. We propose that higher nest predation in fragmented habitats (at least that attributable to snakes) results indirectly from edges promoting larger snake populations, rather than from edges directly increasing the risk of nest predation by snakes. If so, the notion of edges per se functioning as ecological traps merits further study

Differential Uptake of Gold Nanoparticles by 2 Species of Tadpole, the Wood Frog (Lithobates Sylvaticus) and the Bullfrog (Lithobates Catesbeianus)

Engineered nanoparticles are aquatic contaminants of emerging concern that exert ecotoxicological effects on a wide variety of organisms. We exposed cetyltrimethylammonium bromide–capped spherical gold nanoparticles to wood frog and bullfrog tadpoles with conspecifics and in combination with the other species continuously for 21 d, then measured uptake and localization of gold. Wood frog tadpoles alone and in combination with bullfrog tadpoles took up significantly more gold than bullfrogs. Bullfrog tadpoles in combination with wood frogs took up significantly more gold than controls. The rank order of weight-normalized gold uptake was wood frogs in combination \u3e wood frogs alone \u3e bullfrogs in combination \u3e bullfrogs alone \u3e controls. In all gold-exposed groups of tadpoles, gold was concentrated in the anterior region compared with the posterior region of the body. The concentration of gold nanoparticles in the anterior region of wood frogs both alone and in combination with bullfrogs was significantly higher than the corresponding posterior regions. We also measured depuration time of gold in wood frogs. After 21 d in a solution of gold nanoparticles, tadpoles lost \u3e83% of internalized gold when placed in gold-free water for 5 d. After 10 d in gold-free water, tadpoles lost 94% of their gold. After 15 d, gold concentrations were below the level of detection. Our finding of differential uptake between closely related species living in similar habitats with overlapping geographical distributions argues against generalizing toxicological effects of nanoparticles for a large group of organisms based on measurements in only one species

Growth Inhibition of Tadpoles Exposed to Sertraline in the Presence of Conspecifics

Sertraline (“Zoloft”) is a selective serotonin reuptake inhibitor (SSRI) suspected of causing developmental abnormalities in some aquatic organisms at environmentally relevant concentrations. SSRIs have been detected downstream from wastewater treatment plants, but the risks associated with environmental exposure have not been well documented. We tested the effects of sertraline on development of Wood Frog (Lithobates sylvaticus) larvae. Tadpoles hatched from wild-collected egg masses were exposed to concentrations of 0, 0.1, 1.0, or 10.0 μg/L of sertraline through metamorphosis. We tracked tadpole development using image analysis (452 digital images) to estimate mass periodically during the tadpole stage, and also, we recorded mass at metamorphosis. Time to metamorphosis did not differ between treatments, but sertraline-exposed tadpoles grew less when raised among conspecifics. However, this effect was not detected when the study was repeated with tadpoles raised individually. This indicates that the effects of sertraline and other SSRIs may be enhanced when tadpoles are raised under more stressful conditions

Latitudinal Variation in Thermal Ecology of North American Ratsnakes and its Implications for the Effect of Climate Warming on Snakes

The authors show that despite numerous differences among populations of ratsnakes across a latitudinal gradient of \u3e1500 km, overall behavioral thermoregulation was surprisingly similar. These results suggest that the snakes’ ability to respond to climate warming will be determined largely by their capacity to adjust timing of activity

Long-term Exposure to Gold Nanoparticles Accelerates Larval Metamorphosis Without Affecting Mass in Wood Frogs (Lithobates sylvaticus) at Environmentally Relevant Concentrations

Nanoparticles are environmental contaminants of emerging concern. Exposure to engineered nanoparticles has been shown to have detrimental effects on aquatic organisms. We synthesized gold nanoparticles (18.1 ± 3.5 nm) and tested their effects on time to and weight at metamorphosis in wood frog (Lithobates sylvaticus) tadpoles, a species known to be sensitive to environmental stressors. Continuous exposure to all concentrations of gold nanoparticles (0.05, 0.5, and 5 pM in particles) for up to 55 days significantly reduced time to metamorphosis by as much as an average of three days (p \u3c 0.05). However, exposure to gold nanoparticles had no effect on tadpole mass at metamorphosis. The ∼18 nm gold nanoparticles used in this study were metastable in dechlorinated tap water resulting in a change in surface charge and aggregation over time leading to negatively charged aggregates that are on the order of 60–110 nm. Nanoparticle aggregation could exacerbate the effect on time to metamorphosis. To our knowledge, this is the first report on the effect of engineered nanoparticles of any kind on life history variables in an amphibian, a taxonomic group that has been declining globally for at least 25 years