Field update

The 2013 field season is underway, with most of this year's wood frog clutches hatched! Congrats to all the little wood frogs that managed to escape last year's green frog tadpoles. For those who don't know, green frog tadpoles overwinter in the ponds that don't dry out during any given year, and by the time next year's wood frog egg masses are deposited, the green frogs have grown into some massively large tadpoles with equally large appetites! Wood frog eggs are a perfectly bite-sized nutritionally rich meal for these predators.

However, last week during a routine water level check, Jim found a bunch of dead, decomposing green frog tadpoles and two adult green frogs in one of the forest pools. This pool was extremely healthy and productive last year, and located far away from any of the ranavirus (RV) infected pools.  Furthermore, it is very early in the season to be seeing anything like this yet! The carcasses were too decomposed for RV sampling and testing, so this week I went out and collected 5 live green frog tadpoles to test for RV.  If it's there, that means these guys survived the outbreak and could provide evidence for green frogs as vectors.

Here's a video of the pool, Pond 8A. This is one of the isolated pools - the video starts at the trail turnoff, about 100 meters from the service road leading to the forest pools. This is just to illustrate how isolated this pool is, and to give a sense of our day-to-day field treks (this is one of the short ones). I am no videographer and the beginning is very Blair Witch-y, so if you get motion sick I might suggest skipping to 1:15. At about 1:28-1:34 you can get a good sense of the canopy cover for this time of year. This is one of the pools that is in at least partial sun all season. at 1:36 keep an eye out at the bottom of the screen for a darting green frog tadpole. It stops toward the middle of the screen, so you should still be able to see it and get a sense of how big it is. At this stage they are about 6-8 cm (~2.5-3 in) long - WAY bigger than the 1-1.5 cm wood frog tadpoles in this pond.

Speaking of wood frogs, I found some of those alive too! This means if there was a RV outbreak, they either survived with a sub-clinical infection or are still at such an early development stage that they are not yet susceptible due to a changing immune system. I captured five of them via dip-netting, and am raising them in the lab until they are big enough to test for RV. This way I can track their development stages as they grow and answer a couple questions: 1) Are they already infected, but not yet susceptible? If so, then they may die of RV once they reach a certain stage. 2) Did they manage to avoid becoming infected? They are too far along to have still been embryos when the outbreak occurred, so maybe the pool sustained a low enough viral load that they weren't infected. 3) Did they become infected, but for some reason these individuals are more resistant? If so, they may survive until metamorphosis but still test positive for RV.  Stay tuned for the start of sampling next week, including a demonstration of the pipe sampling technique.