How many losses when raising larvae?

I'm curious, having raised two sets of larvae this spring:

what is a normal percentage of larvae loss from egg to morph?I realize real-life scenarios vary from 0 to 100%, but:

By "normal" I mean a sort-of long-term average for those of you who have done it a lot: assuming you start out with 100 hatchlings, how many of those can you reasonably expect to bring to a healthy morphed juvenile size? If it varies by species, please elaborate: which ones have more or less losses? What are the typical causes of death?

And are mortalities of juveniles after morphing generally lower than those of larvae?

btw, you can choose more than one poll option if you've had different results for different species

There is a genetic issue with T. mormoratus causing a minimum of 50% loss.... isn't it?

FRANCOIS said:

There is a genetic issue with T. mormoratus causing a minimum of 50% loss.... isn't it?

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true - but that's before they hatch, in the egg stage. Those who hatch out don't have that genetic defect.

I've gone for 70-90. In my experience, that's normal UNLESS I make a stupid mistake that kills a lot of larvae (e.g. my thread on alpestris apuanus losses, which was due to some tanks being overloaded with larvae before they had cycled properly). Even in that case, I still have about 50-60% of hatchlings as nice large larvae, some of which are beginning to morph.

In species with more delicate larvae that i have worked with (Paramesotriton spp come to mind here), losses tend to either be no different to other species, with only weaklings/deformed larvae/those that were unlucky enough to encounter a larger larva from which they had not been separated dying, or be catastrophic, if a parameter goes out of their narrow comfort zone.

In my experinece, almost all deaths happen in relatively small larvae, maybe up to the point when they have spindly back legs, after which point deaths in larvae are about as low as deaths in new morphs. However, I've never reared very large numbers of juveniles, having given away animals soon after metamorphosis (once they have stabilised and started feedinge etc).

Chris

PS I had to edit the poll as I accidentally selected two options, so removed my accidental vote.

according to several studies cited in Griffith's book on the newts and salamanders of Europe, egg survival in the wild may only be 2-5% or so, and hatchling-to metamorphosis survival only about 10% or so. Survival of adults is better.

If that's true, then out of 200 eggs of a given newt mama only one or two might make it to metamorphosis in any given year...

Wel, that gives an idea about how relaxed natural selection is in captivity!

C

Yeah, no predators!

And a living carpet of food!

froggy said:

And a living carpet of food!

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It's not necessarily the case that captive animals have an advantage here. Some studies (with adult newts) in the UK have found that food in ponds is pretty much in excess all the time. If our larvae can ever manage to eat all the food we give them, they may be less well-fed than wild ones...

Molch said:

according to several studies cited in Griffith's book on the newts and salamanders of Europe, egg survival in the wild may only be 2-5% or so, and hatchling-to metamorphosis survival only about 10% or so..

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I think Beebee & Griffiths' book on the UK herps referred to one study that found even lower hatch rates- I'll see if I can find this.

Even if food is in excess, do the newts not need to put more foraging effort in to finding it? We often feed non-aquatic animals (e.g. whiteworms), which are often immobilised even more by chopping them up. With smaller numbers of larvae, we often hand-feed, too.

C

I agree with Caleb and have been looking for a populations of newts nearby. Food exist in tremendous numbers and all the larvae look extremely plump and well feed. Despite being hundreds of larvae none or nearly none has bitten tails. They are so dense i found 15 mature larvae in 30x30cm area. I think one had a huge net really wide one could harvest kg an kg of them. Hundreds Climb on land each summer.
That study is a authentic fail when this pond enters the game. Nearly all the hatched might survive in there. There is food in huge amounts, shelter, a few predators that's right. But the huge number of mature larval individuals I see weeks before morphing gives me no doubts.

Both in the wild and in captivity, the original poll question is impossible to answer (except by selecting all of the options). I've given it some thought and still feel unable to choose. In captivity, I've had the whole spectrum of outcomes from 0 to 99%. It depends on many many many factors.

Regarding species, I would usually expect nearly 100% survival for hatchlings from A. mexicanum, for example. This assumes some things, like having plenty of food, low-density housing, etc. I tend to have consistently poor survival for I. alpestris apuanus, but it could be the particular strain or set of parents that I had. For a number of groups, I've had higher/lower survival depending on circumstances, but in many cases it's "all or nothing". If I lose some, I lose the whole bunch, or nearly so.

I agree entirely with Jen. Actually I had made a huge reply to this but I lacked the courage to release it since I thought It would be a bit, if not to harsh. Basically I gave emphasis to what Jen says. Thats a way too Random question to be asked. I had myself lucky times and truly dark times loosing nearly all or saving almost all of the hatch-lings. Like she said its a question based in way too many factors. Thus I still cant select a answer myself. Its nearly impossible to answer just one. There are thousand factors to have in mind.
Cheers,

caleb said:

I think Beebee & Griffiths' book on the UK herps referred to one study that found even lower hatch rates- I'll see if I can find this.

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It was the other way round, as it turned out- they cite two studies in smooth newts; one (as mentioned by Molch) found a hatching rate of 2% hatching, 10% metamorphosis; the other found egg to metamorphosis survival of 2% (so ten times better).

Jehle et al's book on crested newts gives data from a study on T. cristatus in Germany that found an estimated egg to metamorphosis survival of about 3.5%. The worst year of this study found 0.1 metamorphs for each breeding female in the pond.

froggy said:

Even if food is in excess, do the newts not need to put more foraging effort in to finding it? [...] With smaller numbers of larvae, we often hand-feed, too.

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I'm not sure much effort goes into foraging- the larvae of the species I'm familiar with seem to do very little active hunting, they just sit and wait. I guess this works very well when food is in massive excess, not so well when there's a shortage.

Hand-feeding is a good point, though- that could easily exceed anything that they'll manage in the wild.

Thanks all The responses are all over the poll, which confirms that the original question was too fuzzy I guess

I've seen phenomenal food densities in wild settings, so it dowsn't surprise me that they are not necessarily food-limited in the wild. Of course that can change in late summer, when invertebrate populations crash and ponds dry out and larvae densities are high....

For me it depends on species.

With some I get low hatch rates, others, I lose some around metamorphosis time.

I have had clutches of eggs where 90% make it to adulthood, and others where none make it.

As Jen stated, there are far too many variables, even in captivity to give a truly accurate response.

So far i have attempted to raise larval alpine newts from eggs twice and both time they all just slowly die! I don't know what I'm doing wrong but i cant seem to raise any larvae!