Wednesday, July 16, 2014

First 2014 die-off observed

First, to start off on a high note before the misery soon to follow, let me show you some new metamorphs! These cute little wood frogs are starting to emerge from the pools, and they can be found around Heiberg in various sizes and states of metamorphosis. Many things can affect the size of newly morphed frogs, including genetics, egg size, population density, competition, food availability, and cannibalism (yes, there are tadpole cannibals!). For a good basic read on the subject (Berven & Chadra 1988), click here

One pre-existing pool was surrounded by some of the tiniest emerging wood frogs I've ever seen! This one, at Gosner stage 45, was only about 7mm long.

This metamorph from a different site is nearly twice the body length (snout-vent) as the one above, but at Gosner stage 43-44 is not as far along in development.


Now for the doom and gloom. The artificial vernal pools in Heiberg Forest were constructed in groups of 1, 3, or 9 pools using a hexagonal grid to separate the groupings. Hexagon 5, the site of die-offs observed in previous years, has experienced yet another wood frog die-off beginning July 10 of this year. At least 3 of the 9 pools were affected. Most wood frog tadpoles had already died and begun decomposing, and those sampled alive were lethargic, swimming erratically, and/or had visible signs of ranavirus including sloughing skin, edema (swelling), and subcutaneous hemorrhaging. Although die-offs can happen very rapidly and are easily missed if diseased individuals die and decompose quickly, this appears to be the first one this year.

This wood frog tadpole clearly shows signs of edema. Poor little thing looked like a balloon compared to its poolmates.
Internal hemorrhaging can be seen in the lower abdomen