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Thanks Jeroen, and Alexander again. You both certainly have a point. The conditions Alexander describes are very close to these at our spot except that the breeding pool/puddle (I won't even call it a pond) is tiny and is basically at the base of a spout from which the spring water flows creating a constant (but not strong) current. For some reason I always thought this is the preferred breeding habitat (clean oxygen rich flowing water) for Salamandra at least here because I've never seen lavae in still water and even some of the other (maybe dirtier) streams are never used. Maybe it's to do with wider habitat and bigger choice of spots. Anyway, there's very little variety of food at our local spot, actually besides a good number of Gammarus and maybe the occasional drowned worm I don't think there's much else for the larvae to eat. There are also pretty much no predators. I'm sure there are no aquatic ones and for over 20 years I've never seen a snake there. There's also no chance of the larvae drifting downstream. Nevertheless, a (very) small number of the larvae survive to metamorphosis which makes me think that there's a good amount of cannibalism going on (although I've never seen it). This leads me to metabolism which should be directly connected to grow rate. So, my question is - are some (the bigger) larvae adopting better to the winter conditions hence metabolising faster (and growing faster) or are they simply better hunters catching more food? In other words is it possible that there's different metabolic rates between individual larvae (like in humans)? The other thing in this race to grow which I notice is that some larvae are just born larger than others. Do they ever manage to make up for this or are they destined to be food for the larger ones?

Ilian, sometimes inside S. salamandra females her baby larvas eat each other.

Michal, that's very interesting! Do you have a source? I thought salamandra larvae are enclosed in egg capsules while inside the female.

Ilian, Salamandra salamandra ssp. bernardezi is viviparous...

Ilian Velikov wrote:Michal, that's very interesting! Do you have a source? I thought salamandra larvae are enclosed in egg capsules while inside the female.

They can leave egg capsules. Piotr Sura wrote in his book published in 2005 that adelophagy is known in Salamandra atra, Salamandra lanzai, 2 subspecies of S. salamandra, Lyciasalamandra spp. and Typhlonectes compressicaudus. Włodzimierz Juszczyk wrote in the eighties that this phenomenon can be present in axolotls and in oviducts of S.salamandra and it happens when female is far from water and does not give birth to larvas.

Jose Luis Perez wrote:Ilian, Salamandra salamandra ssp. bernardezi is viviparous...

Yes, Jose and not only this ssp. The Salamandra here are viviparous too but they are still in egg capsules and leave them shortly before birth. Look further back in this thread and you'll see one of Jeroen's photos with a larva born still in the capsule.

Michal, thanks! I didn't know that. I'll try to find the publications. However, this doesn't answer my question about cannibalism after birth.

Then they are ovoviviparous...

Much appreciated, Alexander!

Alexander Pieh wrote:I would speculate that cold (oxygen rich) water allows the larvae to feed for a longer time on water organism and to grow larger until they metamorphose. This might be an advantage if they change into the land habitats. So, it might be an advantage to release the larvae in winter.

Maybe they stay in the water longer because cold water means unsuitable season? However, we have these permanent groundwater-fed spots in Belgium too, and I can't wrap my head around the logic behind the presence of larger larvae overthere. Also, why can't they feed equally long (and grow equally large) in somewhat warmer water? Oxygen levels surely remain suitable throughout the year in small brooks in forest environment (provided there's no nutrient pollution messing things up). In short, I don't know if oxygen really is the driver...

Alexander Pieh wrote:Is a larger size better than a faster metamorphosis? – depends on predators in the water / terrestrial habitat etc…

Well, long-term survival fortunately is promoted by plasticity - dropping water levels leading to earlier metamorphosis etc.

Michal Szkudlarek wrote:

Ilian Velikov wrote:Michal, that's very interesting! Do you have a source? I thought salamandra larvae are enclosed in egg capsules while inside the female.

They can leave egg capsules. Piotr Sura wrote in his book published in 2005 that adelophagy is known in Salamandra atra, Salamandra lanzai, 2 subspecies of S. salamandra, Lyciasalamandra spp. and Typhlonectes compressicaudus. Włodzimierz Juszczyk wrote in the eighties that this phenomenon can be present in axolotls and in oviducts of S.salamandra and it happens when female is far from water and does not give birth to larvas.

Hmmm... I'm not sure if S.s.t. and S.s.s. do this very often, or at all. While infertile eggs most often are part of the clutch, most S.s.t. larvae I have seen being born only pierce through the membrane that surrounds them after leaving the female's body. My experience is limited, but come to think of it, I do remember that this was not the case with fastuosa's that I saw hatching - big larvae within membrane as soon as they leave the female's body. Bernardezi is know to display adelphophagy (Dopazo & Alberch call it siblicide), presumably promoting intrauterine larval competition and finally viviparity. It seems quite obvious that adelphophagy would occur if/when larvae remain longer in the uterus (which can be due to several reasons e.g. due to seasonal lack of water). Once they have spent all their yolk, they can leave the membrane and feed on infertile eggs or smaller siblings inside the uterus. If you look at it like this, the difference between ovoviviparity and viviparity becomes much more (at least evolutionary) fluid than we might want to think when we want to say that taxon A does and taxon B doesn't have it.

Ilian Velikov wrote:Thanks Jeroen, and Alexander again. You both certainly have a point. The conditions Alexander describes are very close to these at our spot except that the breeding pool/puddle (I won't even call it a pond) is tiny and is basically at the base of a spout from which the spring water flows creating a constant (but not strong) current. For some reason I always thought this is the preferred breeding habitat (clean oxygen rich flowing water) for Salamandra at least here because I've never seen lavae in still water and even some of the other (maybe dirtier) streams are never used. Maybe it's to do with wider habitat and bigger choice of spots. Anyway, there's very little variety of food at our local spot, actually besides a good number of Gammarus and maybe the occasional drowned worm I don't think there's much else for the larvae to eat. There are also pretty much no predators. I'm sure there are no aquatic ones and for over 20 years I've never seen a snake there. There's also no chance of the larvae drifting downstream. Nevertheless, a (very) small number of the larvae survive to metamorphosis which makes me think that there's a good amount of cannibalism going on (although I've never seen it). This leads me to metabolism which should be directly connected to grow rate. So, my question is - are some (the bigger) larvae adopting better to the winter conditions hence metabolising faster (and growing faster) or are they simply better hunters catching more food? In other words is it possible that there's different metabolic rates between individual larvae (like in humans)? The other thing in this race to grow which I notice is that some larvae are just born larger than others. Do they ever manage to make up for this or are they destined to be food for the larger ones?

In part due to what I wrote about intrauterine stuff, clutches largely consists of many small larvae or fewer larger ones. Yes, the larger ones can eat the smaller ones. As deposition period is quite long, smaller larvae can also become prey just because they were deposited later on. Cannibalism is particularly common in small waterbodies (of course...). Partial cannibalism can leave signs into adulthood - tail tips, feet, toes, ... are often bitten off and may regenerate only partially. The spot I mentioned that has yearround ground water here in Belgium has a clearly much higher percentage of (post-metamorphically observed) mutilated animals, often leading to weird, stubby toes, but sometimes leading to regeneration errors, such as 6 toes or even a smaller fifth leg.