N. strauchii eggs: 1st year versus 4th year

[Jennewt]

I have two groups of N. strauchii laying eggs this year. For the older animals, this is their 4th egg laying year (6-year-old animals). For the younger animals, this is their 1st egg laying year (3-year-old animals). Interestingly, the eggs from the two tanks are very different!

• The eggs from the older animals are noticeably larger. (It's even more obvious by eye than it is in these photos.)
• Most of the eggs from the older animals are developing normally.
• Few (perhaps none) of the eggs from the younger animals are developing (mostly duds).

The first photo shows 5 eggs from each tank, for comparison of sizes. The other two photos are closer-up photos of each set of eggs. All of these eggs were pulled from the tanks yesterday, so they are all 0-2 days post-laying. You can see that some of the eggs from the older animals are in the early stages of cell division. None of the eggs from the younger animals are obviously developing.

[Louise Selfridge]

Great news Jen!

[Mark]

Very interesting, Jen. There's certainly a trend for young animals to produce infertile eggs. My young marms laid literally hundreds of duds this year. My guess is that sexual maturity is reached somewhat quicker in captivity due to a bountiful supply of food leading to fast growth. Clearly size isn't everything and age is an important factor in reproductive success.

[Pete]

That's a very interesting observation. It makes me wonder what the mechanism is that underlies this difference, and if it has a biological significance. Have you mated a young one with a old one (male vs. female and vice versa)?

[Jacob Bidinger]

Originally Posted by Jennewt

• The eggs from the older animals are noticeably larger. (It's even more obvious by eye than it is in these photos.)
• Most of the eggs from the older animals are developing normally.
• Few (perhaps none) of the eggs from the younger animals are developing (mostly duds).

Jen, I've noticed the same with axolotls. 2 year+ females lay healthy large eggs, but females under a year old normally lay much smaller eggs that result in smaller, weaker larvae that sometimes don't make it. Also, the clutch size for the older females are much larger while females laying their first time don't lay nearly as many.

Keep it up!

[Jennewt]

Interestingly, the NUMBER of eggs per female is (so far) almost exactly the same for the older and younger groups. I'll post some tabulation after I get some more data.

I do wonder if it would help to put the young females with the older male and see if he could do a better job with the fertilization. But I don't want to disturb things for the older group. The older group is 1:2 and the younger group is 2:3.