Abstracts (first author)
Quantifying pre- and post-copulatory episodes of sexual selection in a simultaneous hermaphrodite
Classical sex roles are often assumed to apply to all sexually reproducing organisms with males being typically more eager to mate whereas females being more choosy. For simultaneous hermaphrodites this implies that mating should be more beneficial for the male than for the female sex function, but empirical tests are scarce. Specifically, a high mating activity (mating success) is expected to lead to the successful transfer of numerous sperm cells (insemination success) and thus to the fertilization of numerous eggs (fertilization success), jointly leading to a high male reproductive success. These consecutive episodes of sexual selection are often challenging to quantify separately, especially given the generally cryptic nature of post-copulatory processes, usually occurring inside the sperm recipient. A recently established transgenic line in the transparent flatworm Macrostomum lignano expresses green fluorescent protein (GFP) in all cell types, including the spermatozoa, which enables us to observe the mating interactions, the number of sperm received from a GFP-expressing mating partner and the resulting offspring produced (as the GFP locus is a dominant marker). We created 72 groups of 5 individuals, including one focal GFP-expressing individual, and assessed the mating success, the insemination success and the male and female reproductive success of these focals, of which we also measured a suite of morphological traits (including testis and ovary size, as well as the morphology of the male copulatory organ and the sperm cells). We aim to quantify (1) how mating success affects male and female reproductive success, (2) how mating success, insemination success and fertilization success contribute to male reproductive success, and (3) how these episodes of selection are affected by specific morphological traits. To our knowledge, this is the first study that quantifies all of the above mentioned episodes of sexual selection in a same individual.