Excess females from M. alpestris apuanus?

[jennifer]

Has anyone else noticed odd M/F ratios in M. alpestris apuanus? In the batch I raised last year, I got a lot more females than males. I've heard other rumors of excess females, but I'm interested in any firsthand experiences.

 

[alan]

This has been my experience too, over several seasons. I couldn't cite you exact numbers, but it's at least 2:1, probably more.

 

[joan]

Do you think it may have something to do with the genetic defect that causes half the larvae to die? Maybe it's more effective on males?

 

[joseph]

Thats pretty odd. Can sex ratios of caudates be affected by external factors?

One thing this does is that it means the species will be able to spread around alot faster.

 

[mike]

My M. a. apuanus also produce an excess of females, I would guess 3:1.

Some of my stock are from Alan, perhaps there is a genetic trait in favour of female offspring!

Joan the defect that causes half the eggs to die only effects the crested newt complex... Genus Triturus.

Joseph that's a thought, but seeing alpines in the wild I estimate that adults in breeding condition have a 50/50 ratio.

 

[joseph]

Mike: But in the case of a breeding pond wouldn't their normally be more males than females due to females staying for a brief time to mate and lay eggs and the males staying around in case they get a chance at another girl? Also, males are probably more noticeable with their breeding garb and being out in the open opposed to any females who might be hidden in the plants laying eggs. At least thats what it supposedly is like with Taricha.

(Message edited by fishkeeper on August 09, 2006)

 

[alex]

I would think the surplus of females is not detrimental. As they are polygamous one male can easily fertilise several females. In my opinion more females than males has a positive effect on the amount of offspring and so increases the chances of survival of the species in general and the genes of the male in particular.
There also may be a possibility that females have a slighter chance for surviving. Although in general they may stay for a shorter period in the water during egg-laying they are frequently and for longer periods exposed to predators. Often close to the surface. So on average there may be a larger portion of the females, than of the males, that meets an untimely end.

 

[mike]

Joseph: The ponds that I mentioned were in northern Italy, often above the tree line. They are shallow and saucer shaped, and normally teeming with Bufo bufo tadpoles when the alpine newts make an appearance. These newts can be seen easily on the bare mud of the ponds, and I surmise that both sexes stay aquatic for the whole breeding season, feeding on the tadpoles, and then probably their own young. I have never seen such fat individuals as I have seen in these often seasonal ponds.

 

[joseph]

Interesting. Would their be any safe way to feed anuran tadpoles to our newts?

 

[ian]

Just a thought but could temperature be anything to do with it. With some reptiles i.e crocodiles the incubation temp alters the ratio of male/female offspring.

 

[joseph]

Ian: Thats sort of what I was thinking. Fishkeepers often claim PH, water temperature, or hardness affect sex ratio...in most claims, the most easily attainable water conditions tend to result in more of the undesirable sex of fish .

 

[mike]

Alex: The predators that I have seen in these ponds have been a single grass snake (Natrix natrix), also many larvae of the Great Diving Beetle (Dytiscus marginalis). Many of the surviving adult newts have large healed chunks out of their bodies and tails.

Ian: I doubt that temperature-dependent sex determination (TSD), as found in some egg-laying reptiles is relevant to newt eggs, surely heritable sex chromosomes determine the sex of their offspring.

Joseph: safe way to feed anuran tads to newts ?

 

[joseph]

Mike: Its generally not reccomended due to possible parasites...if their was a species cheaply and easily bred maybe you could treat them to some special and doubtlessly nutritious food. Before I knew the risks I put a Cynops orientalis into a tank that had hatched a few hundred bullfrog tadpoles and she ate em up readily.

I'd wonder if males would be more vulnerable due to being out and about courting females plus their coloration(don't think the two predators Mike mentioned are sight predators though).

(Message edited by fishkeeper on August 10, 2006)

 

[jennifer]

Wow, has anyone NOT found more females than males? Perhaps with other subspecies of alpestris?

The surplus of females is surely not detrimental (assuming one has enough newts to have both sexes). But it's hard to explain.

 

[terry]

Hello Jenn and the rest,
I do not know about alpestris but my batch of T. pygmaeus and T. dobrogicus resulted in more females than males. My T. dobrogicus juveniles alone resulted in 4 females and two paedomorphic males.

 

[mark]

Mike, I thought temperature-dependent sex determination was documented in the eggs of Pleurodeles waltl. At high temperatures female eggs undergo sex reversal, or so I've read in numerous places.

I'm not suggesting that is what's happening here but maybe other members of Salamandridae
have TSD to some extent.

 

[mike]

I didn't know that Mark, way to go TSD

Joseph, when I had a much smaller collection I used to breed Painted Frogs (Discoglossus) to feed to my newts. They would spawn "to order" with a rise of water temperature.

But that doesn't solve Jenn's original question.

 

[frank]

Well, interesting discussion. For Pleurodeles, it has been described that, when eggs are exposed to high temperatures (> 30°C), females become males. This means that TSD does exist. Similar processes can be suspected in two cases I know of:
1) a captive breeding of Neurergus crocatus, with only a handful (2 if I recall well) of males and > 80 females.
2) a captive breeding of Eurycea lucifuga some years ago (in Germany, anyone of this forum?), also resulting in a high number of females. One might hypothesize that average incubation temperatures in the aquarium are significantly higher than in nature, possibly resulting in a disturbance of the normal sex ratio...

 

[jennifer]

I had heard of Pleurodeles having temperature effects in sex determination. They have a comparitively primitive genetic sex-determination mechanism, called Z/W. We have this reference in the Pleurodeles caresheet, in fact:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=2393628&query_hl=6&itool=pubmed_docsum

Triturus (and former-Triturus) have an X/Y chromosome method of sex determination (like mammals). I would have guessed that this mechanism would not be subject to temperature effects. But I was wrong. See:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=11128575&query_hl=1&itool=pubmed_docsum

However, I'm still mystified. In the Triturus study, high temperature produced an excess of males. Most of us are raising animals at temperatures that are on the "warm" end of the animals' natural tolerance, so why are we getting females? Also, I suspect that the temperatures we have are not "extreme" enough to get much of any effect. I'm not convinced that temperature is the explanation here.

 

[joseph]

What is the mortality rate of the alpestris larvae/morphs? If it is decent then maybe most of the ones dying are males for one reason or another.

I've been raising a group of Triturus karelinii(currently 7) and the largest 2 turned out to be females. Maybe males grow slower or feed/act in a way that gives them a disadvantage in captive settings that results in more of them not thriving?

I know in some fish the males grow faster and may give an impression of a male skewed sex ratio.

Doubt that is the deal, but just a thought.

(Message edited by fishkeeper on August 11, 2006)