<i>H. tokyoensis</i> sexual dimorphism?

[jennifer]

I obtained 6 CB juvenile H. tokyoensis about 6 months ago. I believe that all looked similar at the time I received them, but now one of them is much larger and lighter colored. The other 5 still look very similar.

Is it likely that the large one is female, and the others male? Or is it possible that there was a mix-up and the large one is H. dunni (which was part of the same import)? Or is it possible that they will all become lighter colored as they grow up, and this one is simply the "porker" of the bunch?

 

[cameron]

I don't know but I think it has to do with age. Some sals like P. ruber loose their bright color as they get older. Just a guess.

 

[TJ]

Jen, it seems to me that most of your juvenile H. tokyoensis are still showing their typical juvenile pattern and coloration, while the "porker" is either a bit older or has simply developed faster. Were the all the same size when you got them? Juveniles of most if not all hynobiid species of eastern and northern Honshu look pretty much the same to the casual observer, being speckled like that all over the dorsum (including H. tokyoensis, H. lichenatus, H. nigrescens). Then over time the speckles fade away from the top part of the dorsum but speckling of a sort remains on the lower part of the sides.

I'm not aware that coloration is any way of determining sex -- usually one goes by body size and shape, tail shape, and appearance of the cloaca (though I'm no good at this). As you can see by the following picture, there's quite some variation in H. tokyoensis coloration even among those gathered in the same pond during breeding season.

(this is an old photo that I'd posted before)

As for telling male hynobiids apart from females, it's always best to wait for the breeding season when differences are most apparent. Here's something to refer to (though not strictly as the species are different from H. tokyoensis):

http://www5d.biglobe.ne.jp/~hasumi/photo/vent_e.html

http://www5d.biglobe.ne.jp/~hasumi/photo/hh_aquatic_e.html

http://www5d.biglobe.ne.jp/~hasumi/photo/fem_e.html

http://www5d.biglobe.ne.jp/~hasumi/photo/hh_f_cloaca_e.html

(Message edited by TJ on April 21, 2007)

 

[ryan]

Wow they really can vary!

 

[michael]

If I remember correctly the juvenile tokyoensis and dunni look similar but act different. I think the tokyoensis are the jumpy ones. I'm 95% sure you have all tokyoensis.

 

[jennifer]

Thank you for all the good info, Tim!

I remember that photo, but had never given any thought to the color variation among the animals. I think my porker may simply be headed toward being one of the lighter colored ones. At this point, he/she is very different looking from the others, but I think it's just a size difference. I haven't tried to examine cloacas, but I suspect it's too soon to tell a difference; those photo links are excellent.

 

[TJ]

Sure thing

And as Michael suggested, there are behavioral differences. Put a worm in front of its mouth and if it immediately grabs the worm and swallows it down like there's no tomorrow, it's probably an H. dunni. If it's skittish to begin with and reacts cautiously to being hand-fed, it's probably an H. tokoyoensis ... though I suppose H. tokyoensis become "tamer" over time (I've never kept adults, just raised some from egg sacs to the juvenile stage and given them away).

As for those links, yeah, they're nice. I wasn't aware before that the cloacal opening changes from a slit into a hole before egg sacs are laid. I wonder if this applies to all members of Hynobius...