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Environmentally cued plasticity in hatching timing is widespread in animals. As with later life-history switch points, plasticity in hatching timing may have carryover effects that affect subsequent interactions with predators and competitors. Moreover, the strength of such effects of hatching plasticity may be context dependent. We used red-eyed treefrogs, Agalychnis callidryas , to test for lasting effects of hatching timing (four or six days post-oviposition) under factorial combinations of resource levels (high or low) and predation risk (none, caged, or lethal Pantala flavescens dragonfly naiads). Tadpoles were raised in 400-L mesocosms in Gamboa, Panama, from hatching until all animals had metamorphosed or died, allowing assessment of effects across a nearly six-month period of metamorphosis. Hatching early reduced survival to metamorphosis, increased larval growth, and had context-dependent effects on metamorph phenotypes. Early during the period of metamorph emergence, early-hatched animals were larger than late-hatched ones, but this effect attenuated over time. Early-hatched animals also left the water with relatively longer tails. Lethal predators dramatically reduced survival to metamorphosis, with most mortality occurring early in the larval period. Predator effects on the timing of metamorphosis and metamorph size and tail length depended upon resources. For example, lethal predators reduced larval periods, and this effect was stronger with low resources. Predators affected metamorph size early in the period of metamorphosis, whereas resource levels were a stronger determinant of phenotype for animals that metamorphosed later. Effects of hatching timing were detectable on top of strong effects of larval predators and resources, across two subsequent life stages, and some were as strong as or stronger than effects of resources. Plasticity in hatching timing is ecologically important and currently underappreciated. Effects on metamorph numbers and phenotypes may impact subsequent interactions with predators, competitors, and mates, with potentially cascading effects on recruitment and fitness.

Life history theory predicts that organisms with complex life cycles should transition between life stages when the ratio of growth rate (g) to risk of mortality (μ) in the current stage falls below that in the subsequent stage. Empirical support for this idea has been mixed. Implicit in both theory and empirical work is that the risk of mortality in the subsequent stage is unknown. However, some embryos and larvae of both vertebrates and invertebrates assess cues of post‐transition predation risk and alter the timing of hatching or metamorphosis accordingly. Furthermore, although life history switch points of prey have traditionally been treated as discrete shifts in morphology or habitat, for many organisms they are continuous transitional periods within which the timing of specific developmental and behavioral events can be plastic. We studied red‐eyed treefrogs (Agalychnis callidryas), which detect predators of both larvae and metamorphs, to test if plastic changes during the process of metamorphosis could reconcile the mismatch between life history theory and empirical data and if plasticity in an earlier stage transition (hatching) would affect plasticity at a subsequent stage transition (metamorphosis). We reared tadpoles from hatching until metamorphosis in a full‐factorial cross of two hatching ages (early‐ vs. late‐hatched) and the presence or absence of free‐roaming predators of larvae (giant water bugs) and metamorphs (fishing spiders). Hatching age affected the times from oviposition to tail resorption and from hatching to emergence onto land, but did not alter responses to predators or developmental stage at emergence. Tadpoles did not alter their age at emergence or tail resorption in response to larval or metamorph predators, despite the fact that predators reduced tadpole density by ~30%. However, developmental stage at emergence and time needed to complete metamorphosis in the terrestrial environment were plastic and consistent with predictions of the “minimize μ/g” framework. Our results demonstrate that likely adaptive changes in life history transitions occur at previously unappreciated timescales. Consideration of plasticity in the developmental timing of ecologically important events within metamorphosis, rather than treating it as a discrete switch point, may help to reconcile inconsistencies between empirical studies of predator effects and expectations of long‐standing ecological theory.

Flying vertebrates, such as bats, face exceptionally high energy costs during active flapping flight. Once airborne, energy turnover may exceed basal metabolic rate by a factor of up to 15. Here, we asked whether fuel that powers flight originates from exogenous (dietary nutrients), endogenous sources (mostly body lipids or glycogen), or a combination of both. Since most insectivorous bats fly continuously over relatively long time periods during foraging, we assumed that slowly mobilized glycogen, although suitable for supporting brief sallying flights, is inadequate to power aerial insect-hunting of bats. We hypothesized that the insect-feeding Noctilio albiventris rapidly mobilizes and combusts nutrients from insects it has just eaten instead of utilizing endogenous lipids. We used the stable carbon isotope ratio in the bats' exhaled breath (δ 13 C brth ) to assess the origin of metabolized substrates of resting and flying N. albiventris in two nutritional conditions: fasted and recently fed. The breath of fasted resting bats was depleted in 13 C in relation to their insect diet (δ 13 C diet ), indicating the combustion of 13 C depleted body lipids. In contrast to this, δ 13 C brth of bats that had recently fed closely matched δ 13 C diet in both resting and flying bats, suggesting a quick mobilization of ingested nutrients for metabolism. In contrast to most non-volant mammals, bats have evolved the ability to fuel their high energy expenditure rates through the rapid combustion of exogenous nutrients, enabling them to conquer the nocturnal niche of aerial insectivory.