Could you elaborate a bit on this (in another thread if you see it fit)? I admit to adhering to the dogma of plant matter being pretty much worthless for caudates and if this is wrong i´d love to learn more.
The latest thing i had heard of that made me doubt the dogma was about plant matter contents in feeder invertebrates and how those represented a valuable nutrition source in the pressence of the invertebrate´s digestive flora.
Sorry for taking up your time.
Here you go
Well we can start with the whole feeder insects must be better when fed on greens etc… There is actually data that disputes this.. There have been several studies, on this exact topic and we can see the first of them discussed in Dierenfeld, Ellen S.; Norkus, Edward B.; Carroll, Kathryn; Ferguson, Gary W.; Carotenoids, vitamin A, and vitamin E concentrations during egg development in panther chameleons (Furcifer pardalis); ZooBiology 21: 295-303. In that article, there is a brief discussion (and further citations) on how “ gut loading with a low levels of preformed vitamin A and high carotenoid (carrots) has resulted in vitamin A deficiency in panther chameleons”. There was also an interesting study done on crickets where they were divided into several groups and then fed different diets. The groups were divided as follows, Group A was only given water ad libitum, Group B was fed only lettuce (Lactuaca sativa), and Group C was fed a commercial cricket chow. (see Hatt, Jean-Michel; Hung, Elisabeth; Wanner, Marcel; 2003; The influence of diet on the body composition of the house cricket (Acheta domesticus) and consequences for their use in zoo animal nutrition; Zool. Garten N.F. 73(4): 238-244.) For vitamin A content, the activity level was what was measured (which means carotenoids that can be converted to vitamin A as well as vitamin A). There were some interesting results to the study.. the crickets fed only water had 73% of the vitamin A that the crickets fed lettuce did.. while the crickets fed lettuce had only 82% of the vitamin A that the crickets fed on the commercial diet (these are not based on the average or there would be a much greater disparity between lettuce and commercial diet but on the final numbers). Outside of plant feeding caterpillars, there is little to indicate that this is different for many other taxa of invertebrates. The only real differences we see are with crustaceans like krill where they contain a vitamin A level of 23.3 µg/g dry matter (compared to crickets (0.03 µg/g dry matter basis).. (see Pennino, Marianne; Dierenfeld, Ellen S.; Behler, John L.; 1991; Retinol, α-tocopherol and proximate nutrient composition of invertebrates used as feed; Int. Zoo Yb. 30: 143-149).
We can move onto the next section… Vitamin A deficiency hasn’t been documented in amphibians found in the wild at this time, yet we know that many feeder invertebrates are a poor source for not only preformed vitamin A, but carotenoids with previtamin A activity (with the exception of plant feeding caterpillars and a few other exceptions). This seems to create a conflict of what we know. So we now need to look at other potential sources of vitamin A particularly since the majority of amphibians are not consuming sufficient levels of vertebrates to meet their vitamin A needs. One potential source occurs when the amphibians capture their prey. In general when the strike to capture prey occurs, we see that routinely that other items are ingested along with the prey items. If we look at the older literature we can find reports of percent plant matter in the digestive tract while more modern studies on gut contents lump plant matter together with other matter like soil particles as one category giving little data on the prevalence in the diet. However as time goes on, we see more and more exceptions to the idea that with the exception of many tadpoles, amphibians are obligate carnivores. For example seasonally adult Rana hexadactyla can have as much as 80% of their diet consist of plant matter (see Das, I.; 1996; Folivory and seasonal changes in the diet in Rana hexadactyla (Anura: Ranidae); J. Zool., Lond. 238:785-794). Plant consumption has been reported as well for greater sirens, marine toads, and most famously Hyla truncata. So with the possible exception of greater sirens which appear to be hind gut fermenters, how do these animals with short digestive tracts get sufficient nutrition from plants? One potential method is that as with some other taxa commensual bacteria or protozoa, this is seen in some surprising taxa (such as rats and pigs). An alternative possibility is as with other taxa, pinworns (oxyurids) are enabling the animal to digest the plant matter. It is well known that in a number of taxa (such as chelonians,and bullfrog tadpoles (see http://accstr.ufl.edu/publications/Pryor&Bjorndal_JEZ2005.pdf)), pinworms breakdown the walls of the plant matter allowing better digestion and uptake. Various genera of pinworms are found in virtually all species and while the taxa that aids in digestion in bullfrog tadpoles isn’t commonly found in caudates, other genera of oxyurids are.