Herps in the news: links to athleticism in poison dart frogs

Two articles came out in the last month measuring the athletic fitness of South and Central American frogs and correlating this fitness to other variables.  Both of these studies were lead by Juan Santos from the National Evolutionary Synthesis Center.  To measure athletic fitness the frogs were made to run in a rotating tube similar to a hamster wheel for four minutes, and their metabolic rates and aerobic capacity were measured before and after exercise.  The authors compared the results of poison dart frogs to non-toxic frogs from the same regions and found two interesting connections, publishing each in separate articles. 

The first is that the poison dart frogs are more athletically fit than non-toxic frogs from the same regions.  It is explained that this is necessary because poison dart frogs are dietary specialists, relying on certain foods (ex. ants, mites) which contain the alkaloids that provide their toxicity.  As specialists seeking patchily distributed resources, these frogs must move greater distances to satisfy their picky diet than most frogs with generalist diets.

I find the attempt to determine the cause and effect relationship for this fitness the most interesting part of the study.  One possible explanation given by the authors is that the frogs' aposematic coloration evolved while the frogs had a generalist diet (some of which contained alkaloids), deterring predators and allowing greater resource acquisition abilities which led to greater athletic fitness and diet specialization.  The second explanation is that diet specialization occurred first, leading to aposematic coloration which reinforced the foraging for alkaloid containing prey.  Specialization and the patchy distribution of the prey led to the need for a greater foraging area, which was facilitated by aposematic protection.  This caused the development of greater athletic fitness.  I think the second explanation generally sounds the most reasonable, though the authors think that different circumstances governed these developments for different groups of poison dart frogs.  

The second correlation found by Santos is that greater fitness is linked to faster changing genomes.  He discovered this by sequencing 15 genes and estimating the number of mutations for lineages of the resulting evolutionary tree.  Links to mutation rates were investigated for other factors such as body and clutch size, but athletic fitness drew the only significant correlation.  It is hypothesized that this is due to greater accumulation in the body of free radicals generated through excercise, which could damage DNA of gametes and be passed on in this manner.  I would be interested to see a molecular study done testing the degree that free radical production is manifested by mutations in frogs.  The concept seems feasible but I'm a little skeptical of the concept of exercise substantially damaging DNA.



http://www.sciencedaily.com/releases/2012/04/120412182332.htm
http://www.sciencedaily.com/releases/2011/03/110329134250.htm
http://www.pnas.org/content/108/15/6175.full