I must disagree on the lack of necessity for evidence, and i think rightfully so precisely because of your claim of irrefutability. I disagree that you only need your eyes to see it. As species they are generally fairly easily recognizable, but it´s definitely not possible to infer hybridization simply from superfitial appearance. Both species are highly variable, with plenty of populations showing intermediate characteristic. Assuming that appearance infers an event of genetic introgression is not entirely safe. Even field experts have to resort to genetics to safely identify certain individuals, specially in sympatric populations.
I certainly don´t see why my objection, just as Joost´s should be interpreted as an attack. I´m also definitely not contesting everything that is said, or that you say. I do, however, think it´s very reasonable and not at all comfrontational to contest your claim of irrefutability.
I, by no means, pretend to question the knowledge and expertise of the german hobbyists. But i have my reservations as to how a local observation, however true it may be, warrants irrefutability in a global scheme of the hobby. I´m sure those germans with which you talk have very good reasons to make their claims. Mind you, i can only assume that their observations are at least largely limited to the german hobby. In order to apply to the entire hobby, and to be irrefutable, it must certainly be based on a lot more than just words. Certainly the only way to allow for a claim of irrefutability would be to provide evidence. Without it, and in this case that means, without a genetic study, you can only claim probability. I think this is particularly so in a community such as this which for obvious reasons is tinted with a scientific view.
Please note that i´m not doubting or contesting the validity of its possibility, and in fact i´m entirely prepared to believe it if evidence is shown to me. Precisely because of the particular characteristics of the german system and it´s laws, i can picture how their captive populations of T.marmoratus would be susceptible to genetic damage throughout the decades. I fail to see how that can be safely applied to any other country, for the reasons i already mentioned.
I agree that the fact that pygmaeus and marmoratus were recognizible and separate populations even before they were segregated into different species, doesn´t mean it prevents people from mixing them, but it makes my point that just because at one time they weren´t separated, it didn´t mean that people were incapable of distinguising them and so countless events of hybridization were impossible to avoid. They were and are very much avoidable, which of course doesn´t eliminate the possibility of genetic introgression. That can´t be adressed without genetic studies. So once again in order for the claim of irrefutability (which is a VERY strong one) to be valid, you need evidence. That evidence needs to be genetic. If the germans have made such studies, he fact that nobody else seems to know about them can only mean that those studies are limited to german captive populations in which case their suitability as representation for other captive populations is highly contestable.
I´m sorry to ramble so much and make my point so inconcise, but i´m merely trying to make it clear that there is absolutely no attack in my post, there´s only justified skepticism towards what represents a very strong claim of irrefutability. It´s most definitely not about you. No matter who had made that claim, i would have had a problem validating it without any proof.
As far as deviating from the original topic, i find it´s unfair for you to blame me with it being as it was you who originally deviated from it, making it possible for others to elaborate on it. Anyway, i agree that i should probably say something about the original topic.
Pms17, T.marmoratus as a whole certainly has a strict terrestrial phase. There is variation in this, and there are exceptions. Some specific, although very rare, populations have juveniles which remain aquatic after metamorphosis at least for a certain amount of time. The same kind of exceptions can be seen in even more strictly terrestrial species like S.slamandra. However, they are not representative of the whole species. You should certainly expect any unidentified individuald or population to have a very marked semi-aquatic life. In other words, the vast majority of marms will leave the water, both in captivity and in the wild.
As i said, however, there is variation in the wild. Some populations (in particular i know of populations in my area) have very extended aquatic phases, to the extent of representing the majority of the year. These individuals have a short terrestrial phase exclussively during the summer months, but inmediately return to the water at the very beginnings of autumn. This is particularly so in males, for obvious reasons.
Also, in captivity you can observe variation from the norm. You´ll find a minority of keepers that have suceeded in keeping T.marmroatus aquatic year-round, and you can also see that juveniles are much more likely to become aquatic in captivity than they are in the wild. It is possible to keep even relatively young juveniles of this species aquatic (even though it may not be possible to do so continously throughout the year).
So, basically the answer to your question is that most marms do indeed leave the water, and only a very small minority don´t. The difficulty of observing them in their terrestrial phase lies in the fossorial, secretive and opportunistic habits of the species, not in the assumption that they are simply not there which is obviously not true xDDD
