Ontogenetic Effects of Hatching Plasticity in the Spotted Salamander (Ambystoma maculatum) due to Egg and Larval Predators

The ability to respond plastically to the environment has allowed amphibians to evolve a response to spatial and temporal variation in predation threat (Benard 2004). Embroys exposed to egg predation are expected to hatch out earlier than their conspecifics. Larval predation can induce a suite of phenotypic changes including growing a larger tail area. When presented with cues from both egg and larval predators, embryos are expected to respond to the egg predator by hatching out earlier because the egg predator presents an immediate threat. However, hatching early may be costly in the larval environment in terms of development, morphology, and/or behavior. We created a laboratory experiment in which we exposed clutches of spotted salamander (Ambystoma maculatum) eggs to both egg (caddisfly larvae) and larval (A. opacum) predators to test this hypothesis. We recorded hatching time and stage and took developmental and morphological data of the animals a week after hatching. Larvae were entered into lethal predation trials with a larval predatory sunfish (Lepomis sp.) in order to study behavior. We found that animals exposed to the egg predator cues hatched out earlier and at earlier developmental stages than conspecifics regardless of whether there was a larval predator present. Animals exposed to larval predator cues grew relatively larger tails and survived longer in the lethal predation trials. However the group exposed to both predators showed a cost of early hatching in terms of lower tail area and shorter survival time in predation trials. The morphological and developmental effects measured of hatching plasticity were transient as there were no developmental or morphological differences between the treatment groups at metamorphosis. Hatching plasticity may be transient but it is important to the development and survival of many amphibians.

Predator-Induced Plasticity in Spotted Salamanders (Ambystoma maculatum)

The ability to respond plastically to the environment has allowed amphibians to evolve adaptive responses to spatial and temporal variation in predation threat. However, animals exposed to predators may also show costs of plasticity or tradeoffs. This study examines predator-induced plasticity in larval development, behavior, and metamorphosis in the spotted salamander, Ambystoma maculatum. Salamanders were raised in two treatments: with predator cues (a fish predator, genus Lepomis, on the other side of a divided tank), or without predator cues. During the larval stage the predator treatment group experienced higher mortality rates than the no-predator treatment group. Behavioral trials revealed that predator treatment animals ate less than those not exposed, and that this feeding response was immediately inducible and had lasting effects. Animals in the predator treatment group had smaller tail areas during the mid-larval period. Feeding and body size effects may have contributed to increased mortality in the predator-treatment animals. The timing of metamorphic onset was not affected by the presence of predators, but predator-treatment salamanders had shorter snout/vent lengths at metamorphosis. The duration of metamorphosis showed a potentially adaptive plastic response to the presence of predator cues: metamorphosis was longest in the no-predator treatment group, reduced in the predator treatment group, and even further reduced for animals exposed to predator cues only during metamorphosis. Overall, we found a mix of potentially adaptive and costly plastic responses in spotted salamanders.

The Devil’s Calculus: Mathematical Models of Civil War

In spite of the movement to turn political science into a real science, various mathematical methods that are now the staples of physics, biology, and even economics are thoroughly uncommon in political science, especially the study of civil war. This study seeks to apply such methods - specifically, ordinary differential equations (ODEs) - to model civil war based on what one might dub the capabilities school of thought, which roughly states that civil wars end only when one side’s ability to make war falls far enough to make peace truly attractive. I construct several different ODE-based models and then test them all to see which best predicts the instantaneous capabilities of both sides of the Sri Lankan civil war in the period from 1990 to 1994 given parameters and initial conditions. The model that the tests declare most accurate gives very accurate predictions of state military capabilities and reasonable short term predictions of cumulative deaths. Analysis of the model reveals the scale of the importance of rebel finances to the sustainability of insurgency, most notably that the number of troops required to put down the Tamil Tigers is reduced by nearly a full order of magnitude when Tiger foreign funding is stopped. The study thus demonstrates that accurate foresight may come of relatively simple dynamical models, and implies the great potential of advanced and currently unconventional non-statistical mathematical methods in political science.