Abstracts (first author)
Sex allocation plasticity on a transcriptome scale
Predicting an organism’s optimal sex allocation has long been a central concern of evolutionary biology research. In simultaneous hermaphrodites, the question concerns the balance of investment into the male versus the female sex function. Theory predicts that individuals should bias investment more towards the male function as the number of available mates increases, and this is indeed a well-documented phenotypically plastic response in the free-living flatworm Macrostomum lignano. However, the details of how sex allocation plasticity is achieved at a molecular level are currently unknown. To address this, we performed an RNA-Seq experiment on worms raised in different social environments (i.e. in isolation, in pairs or in octets), known to lead to different optimal sex allocations, and investigate how these worms respond on a transcriptome scale. We demonstrate that up to 10% of all known transcripts are differentially expressed between different social environments, with this figure rising to >30% for gonad-specific genes that are presumably directly involved in the switch away from oogenesis towards spermatogenesis under increased mating group size. As predicted, most differentially expressed testis-specific genes are upregulated in larger groups, and most differentially expressed ovary-specific genes are downregulated in larger groups (although there are some notable exceptions to this general pattern). Moreover, we identify many tail-specific genes that are upregulated in larger groups, many of which are prostate-specific genes involved in seminal fluid production, a previously unquantified aspect of male allocation. Our data provide a rich repertoire of candidate genes for functional characterization in the context of the control of gametogenesis and sex allocation (which we can now investigate using RNAi and other tools available in this system), and offer broad insights into the molecular underpinnings of phenotypic plasticity.