We are interested in a number of aspects of postcopulatory sexual selection in Macrostomum. Firstly, sex allocation theory predicts that one of the main factors responsible for variation in male allocation is sperm competition. We therefore aim at understanding 1) how male allocation translates into sperm production, 2) which processes influence sperm competition, and 3) if there is any cryptic female choice.
We address the first aspect in three published papers, where we have shown that bigger testes indeed have a higher gonadal activity (Schärer et al. 2004b), that they have a higher sperm production rate (Schärer & Vizoso 2007), and that this plasticity in testis size does not lead to plasticity in sperm size (Janicke & Schärer 2010). We are currently trying to understand if the testis can also modulate the speed of spermatogenesis.
To estimate sperm competition we have developed a number of tools to follow the success of male gametes in the recipient and to look at the resulting paternity patterns. One tool is the so-called sperm-tracking technique (Schärer et al. 2007a), which allows to estimate sperm-transfer success (Janicke & Schärer 2009). Another is classical microsatellite paternity analysis, which allows to estimate sireing success (Sandner et al. submitted). And we are currently evaluating a new tool, which will allow to measure both sperm-transfer and sireing success simultaneously in a non-invasive way, by taking advantage of recently established lines that express green-fluorescent protein (GFP) in the sperm.
As the third aspect, cryptic female choice, was poorly understood theoretically, we have developed some theoretical models to explore the effect of different types of cryptic female choice on sex allocation (Van Velzen et al. 2009). The results clearly suggest that this can be an important factor in the evolution of male allocation (and thus sex allocation). We are currently aiming to test for cryptic female choice by taking advantage of established inbred lines.