Meet the cast

Week 11, Day One

Pictures and videos of the lead cast:

A 100 milligram Arabian tadpole:

Several dozen, actually. Plus, a 100 milligram dragonfly larva:

The tadpoles are stored in small tanks with small rocks as refuges and anchorage points for both algae and tadpoles:

After several casualties- upstream swimmers that got caught in the multiple sponge and cloth layers in the filter- wire mesh was used to cover the inlet and outlet pipes. Sometimes though, the odd mini tadpole finds its way into an alternate tank in the array of tanks.

Some unfortunate tadpoles will wind up as dinner, like this one:

...others just get the aftertaste.

I basically watch what they do once they've got a whiff (literally) of the dinner I fed their predators. Amphibian young are famous for their ability to detect the presence of predators through little chemical cues dispersed in the water. These cues have been found to be quite specific, and reveal both qualitative and quantitative information. It tells them which predator is nearby, how near it is, if it's been killing their kin or is just an opportunistic feeder, and varies with time as well. Sound and smell have always been the best developed senses in all aquatic creatures.

So, I keep tabs on any behavioural or morphological changes in large set-ups like these:

I'm also trying to figure out if their respiration rate rises, which is the hard part. After much reading, hunting, improvising, tweaking and testing, I concocted this set-up:

Water is pumped out of two tanks- one without any predators, and another with a predator in its cage fed at regular intervals- into identical glass chambers with five tadpoles and the controls without them. Based on previous studies, the larvae predators release chemical substances as do the dead tadpoles. These diffuse through the water and alert the tadpoles of the impending danger. Once the tadpoles in the glass chambers sense this in the water that's flowing in, their respiration rate should rise. The tubes coming out of these chambers are periodically attached to the meter at the end that records oxygen concentration. Should the decline in oxygen be significantly different between the predator tank and control tank, it would constitute a viable experiment.

The whole idea behind setting this up is to get small doses of pesticides and metals into the tanks as well. If respiration increases, toxin uptake will increase as well, resulting in mortality. Given the (still) widespread use of pesticides, such studies are strong scientific evidence that specify appropriate (if that's what they are!) concentrations of such potent chemicals in natural water sources. And for the fast declining amphibians water contamination can be a death sentence because of the synergistic effects of predation and toxin intake.