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Schärer Group
Evolutionary Biology
Zoological Institute
University of Basel
Vesalgasse 1
CH-4051 Basel

Macrostomum lignano: mating behaviour
We have described, and quantified different elements of the copulatory behaviour of Macrostomum lignano. The copulation is reciprocal, and often followed by an intriguing postcopulatory suck behaviour. Below you find short movie sequences of copulating worms. The worms are enclosed in a small drops of water between two glass slides. This setup allows detailed observation of several groups of worms under both dissecting and compound microscopes (for details see Schärer et al. 2004a).
Movie 1: precopulatory behviour and copulation
In this movie you can see two worms that start to interact with a behaviour that we call reeling, which appears to be a precopulatory behaviour, where the worms may be assessing each other. The following copulation then consists of worms forming a tight disc, and when watched at a higher resolution one can clearly see that they each worm introduces its copulatory organ into the female genital opening of the partner.

time-lapse movie of a pair of Macrostomum lignano showing reeling and a copulation
(double-click to see the movie)

Movie 2: circling and reeling
This movie shows details of a worm pair that starts with circling and goes into reeling. Note the translucent cones on the tail-plate that we consider "erections", which indicate that the worms are motivated to copulate.

a reeling pair of Macrostomum lignano with "erections"
(double-click to see the movie)

Movie 3: copulation and suck
In this movie you can see another example of a copulation. Interestingly it ends with both worms showing a suck behaviour (a co-called double-suck). We are not sure yet what this behaviour involves, but we currently favour the interpretation that the worms attempt to suck out the sperm or ejaculate that they have just received from their partner (see Vizoso et al. 2010 and Schärer et al. 2011 for more details). Many hermaphrodites have been suggested to digest sperm, but it usually is via a direct duct between the sperm receiving organ, and the gut. Here it seems that the worms may have developed a behavioural solution to the problem, leading to interesting evolutionary consequences on the evolution of the sperm design in this group (Schärer et al. 2011).

time-lapse movie of a pair of Macrostomum lignano showing a copulation followed by a double-suck
(double-click to see the movie)

Movie 4: copulation, details
This movie shows details of a copulation after which one one worm performs the suck behaviour. Note the bundle of sperm that stick out of the female genital opening after the suck, actually suggesting that at least some sperm are not removed during this behaviour.

a copulating pair of Macrostomum lignano with one worm performing the post-copulatory suck behaviour
(double-click to see the movie)

Movie 5: egg laying
This movie shows that other behaviours can also easily be observed. Here one worm is laying an egg, while the other is racing around in the drop.

time-lapse movie of a Marostomum lignano laying an egg
(double-click to see the movie)

Movie 6: scaled up
This observation technique can be scaled up to simultaneously record time-lapse video of up to 20 pairs of worms. This allows us to collect massive amounts of behavioural data in a very short time.

time-lapse movie 18 pairs of Macrostomum lignano
(double-click to see the movie)

this page was last updated on Tuesday, December 22, 2015