14 February 2008

Limax maximus mating - part 2

In the 1st part of this series, using some of the main literature references, I gave a brief description of how the slug Limax maximus mates.

One steamy August nite last summer, while checking out the evening creatures in my backyard, I saw 2 L. maximus going single file up a pine tree. I had never seen L. maximus mate before, but because I had read about it, I realized immediately that this was how it was supposed to start. Someone once said that chance favors the prepared mind; that was indeed true my case (having a camera at hand was also quite helpful).


Luckily the slugs didn't climb high, but stayed at a height that was very comfortable for picture taking.

After their climb ended, they started circling around each other.


Such circles always rotate in a clockwise direction, because the genital openings of dextral slugs are on the right sides of their heads. If they were rotating in a counterclockwise direction, their genital openings would not face each other.

This was followed by a sudden embrace and the twisting of their bodies around each other.


While they were rolling down the trunk, one slug had already everted its penis and the tip of the other slug's penis was visible.


Soon, their penises were fully everted and intertwined. Here is a close-up of their tips.


Finally, the penises expanded into a bell-shaped structure with a cool blue color. I suspect this is when they actually exchange spermatophores (cases of sperm).


The bell was present for only about 3 minutes and was followed by the withdrawal of the penises. You can see the tips of the disappearing penises of the still intertwined slugs in the next picture.


It was all over when one of the slugs quickly left the scene of their affair. But the other one remained behind and ate up the copious slime that they had secreted. The entire process, from the moment I took the 1st picture until the picture below, took 43 minutes.


The mating of L. maximus and several other species in the genus Limax, appears to be a very resource intensive way of exchanging sperm by a couple of hermaphrodites. Why not just do it on the ground like most other slugs? In fact, Limax flavus indeed mates on the ground.

Without elaborating, Leonard (2006) suggested that the mating behavior of L. maximus may have evolved under sexual selection. A talk by Gerhard Falkner & Barbara Klee at the World Congress of Malacology in Antwerp last July also discussed the possibility of sexual selection as the driving force behind the evolution of long penises in some members of the genus Limax. There is so much more to learn about these slugs. I can hardly wait until the next mating season!

Here is another set of pictures of mating L. maximus over at A Snail's Eye View.

The next part of this series will take a look at the genitalia of a dissected L. maximus.

Janet L. Leonard. 2006. Sexual selection: lessons from hermaphrodite mating systems.
Integrative and Comparative Biology 46:349-367.


Melissa said...

This is the best V-Day posting I've seen all day. :D

jem said...

Is this, perhaps, the Férussac and Deshayes plate you referred to in your previous Limax maximus post? It's from a Japanese site: http://www.planetology.jp/gm-library/pict16_5.html

Megan said...

Great pics, as always!

I also read somewhere (Rollo and Wellington papers) that L. maximus pairs may climb up and suspend themselves in order to avoid being harassed by others in their aggressive species. (They find a little private place by themselves up in the trees...)

Sexual selection and avoidance of fellow slug aggressors may both lead to some fancy mating.


Melissa: It wasn't intentional. I had totally forgotten that today is Valentine's Day when I was writing this post.

Jem: Yes, that's it. Thanks for the link. That'll save me a trip to the library.

Megan: That's an interesting idea that suspension may be a way of avoiding intruders. But they don't always suspend themselves; my slugs were not suspended, for example.

Tomodactylus said...

I'm confused about how sperm transfer takes place. Are sperm packets deposited in the bell? When the two slugs separate do each then fertilize themselves with sperm from the other individual?
Great photos!


I don't know how exactly the spermatophores are transferred from one penis to the other.

But yes, the slugs are hermaphrodites. So, each individual fertilizes its eggs with the sperm it received from its partner.

Snail said...

This is one of the things that's really cool about molluscs. No, not the exhibitionist mating - but that there's still so much to find out about even the most common species!

Robert Nordsieck said...
This comment has been removed by the author.
Robert Nordsieck said...

Dear Aydin, thank you very much for those fabulous pictures and for the information included. I gladly put a reference on my page on Limax, but sadly have not been able to see and to photograph Limax mating in nature. Still hoping :) Kind regards from Vienna. Robert Nordsieck.
Mating of the Leopard Slug (Limax maximus).

Blackbird said...

Thank you for your beautiful post. I just came across it as I think I saw Limax maximum mating on my kitchen floor!

Mafu said...

Could I use your photos for an art and science exhibition on animal reproduction? They are fantastic!


Mafu: send me an e-mail (snailstalesATearthlink.net) & tell me more about your intended use.

Petra said...

This is a fascinating spectacle indeed. I just witnessed it last night as my pet leopard slugs mated. Although the mating was not entirely successful (they had attempted twice in the previous nights but the enclosure was not high enough). The other slug was still nibbling its mate when said mate was everting its penis, and well, ended up wasting the spermatophore on the slugarium wall. I was not actually aware this could happen to gastropods, so it's good I videoed the whole thing to have "evidence"!

I'm hoping for some sluglets from this pair, but could it be that slugs mate for social reasons as well as reproduction? This pair of slugs seems to locate each other and rest side by side despite me moving things around their enclosure or even moving the slugs to a new box.