Goings-on inside a worm: Functional hypotheses derived from sexual conflict thinking
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Dita B. Vizoso


Institute of Zoology
Evolutionary Biology
University of Basel
Vesalgassesse 1
4051 Basel

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Vizoso, D. B., Rieger, G. & Schärer, L. 2010. Goings-on inside a worm: Functional hypotheses derived from sexual conflict thinking. Biological Journal of the Linnean Society. 99: 370-383 [pdf]

Different interests between mating partners regarding the fate of their gametes can lead to sexual conflicts in many species. Although these conflicts can sometimes be dealt with pre-copulatorily (e.g. by choosing with which partners to mate), they often extend beyond copulation. Post-copulatory sexual conflicts are expected to be particularly strong in simultaneous hermaphrodites because an individual may have to accept sperm in order to obtain an opportunity to donate sperm, reducing the effectiveness of pre-copulatory conflict resolution. The present study investigates the post-copulatory interactions between male and female sexual traits of a highly promiscuous simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano. Using light and electron microscopy, we show the different levels of complexity of the sperm and the genitalia, and derive hypotheses about how the different traits may represent evolutionary responses to such sexual conflicts.

Movie S1. A free-swimming sperm of Macrostomum lignano. Note the undulating movements of the feeler and the shaft. The nucleus can be seen in the posterior half of the shaft, forming a chain-like structure.

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Movie S2. 'Probing' behaviour of the feeler of Macrostomum lignano sperm in the female antrum. Most sperm are polarized and only their brushes can be seen (right-bottom quadrant). Some sperm are unanchored and move in the antral lumen. Note the sperm in the middle, which actively touches the antral epithelium with its feeler, the so-called 'probing' behaviour.

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Movie S3. Sperm of Macrostomum lignano anchored in the cellular valve of the female antrum. Note the feelers radiating towards the sides of the cellular valve.

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