Metamorph Stream Plethodontids

[kristen]

In surveying some of the posts on this website, I've noticed that many people seem to have fed metamorphs successfully. In a study I conducted last summer, I non-lethally stomach flushed over 30 pseudotriton ruber metamorphs and found no stomach contents at the same time that nearly 50% of larvae and adults stomach flushed had stomach contents. Furthermore, I have kept 2 P. ruber and 1 P. montanus metamorphs that would not eat for a few months after they morphed. Has anyone else noticed this either in wild-captured metamorphs or captive individuals raised from their larval stage through metamorphosis?

 

[jennifer]

Interesting work, kudos to you. Just out of curiosity, what had the larvae and adults been eating? Will your work be published in some form?

Most newts/sals will refuse food for several days, up to a couple of weeks, right during/after metamorphosis. After that point, there are some individuals (of some species) that do seem to eat very little (if at all). I had always assumed that this was a captive-care problem; that we don't have the best foods available to feed them. For some, it does seem that "hiding" is much higher on their agenda than "eating".

However, it seems to me that if a metamorph ever wants to reach adulthood it HAS to eat. In captivity, the morphs that begin eating more/sooner are the most successful (though this might not be the case in the wild). The morphs that you kept captive... did they eventually start eating?

I should add... my observations are not based on Plethodontids, but on other newts/sals.

(Message edited by jennewt on February 01, 2007)

 

[kristen]

Larvae and adults were primarily eating a variety of stream invertebrates including crayfish, but I also found beetles and an occasional salamander in their diet. This paper is currently in review with J. Herp. It seems like maybe the process of metamorphosis is too stressful for the individuals, so they hide for a long period of time. I would assume they need to eat at some point to grow, but I wonder if after metamorphosis they rarely move because of stress, reducing energetic needs and utilize stored fats in the tail for some reason. I'm completely baffled by the behavior. In the lab, all of the metamorphs began eating approximately 6-8 weeks or so after metamorphosis.

Does anyone else have any theories or thoughts on why the delay in feeding?

 

[mark]

If you haven’t already done so I would recommend reading the “Metamorphosis” chapter in “The Biology of Amphibians”, Duellman & Trueb. There’s lots of detailed information about the hormonal, structural and biochemical changes that take place during metamorphosis in amphibians.

There’s nothing in there that suggests feeding stops when caudates morph but in comparison to anurans who’s entire mouth structure changes during metamorphosis caudates have quite an easy time of it. During metamorphosis, with regards to the digestive system the intestinal tract decreases in size, the pancreas is re-structured and the urea-cycle starts. That’s just the tip of the iceberg –there are so many changes taking place and any one of them could be enough to put you off your food.

Metamorphosis is controlled by hormones produced by the thyroid – maybe someone has studied thyroid activity in these sals post metamorphosis. Maybe there are changes taking place that are not apparent to the eye.

Not much help but food for thought.