Sperm production is a key male reproductive trait and an important parameter in sperm competition theory. Under sperm competition, paternity success is predicted to depend strongly on male allocation to sperm production. Furthermore, because sperm production is inherently costly, individuals should economize in sperm expenditure, and conditional adjustment of the copulation frequency according ...

Previous studies on sex allocation in simultaneous hermaphrodites have typically focused either on evolutionary or one-time, ontogenetic optimization of sex allocation, ignoring variation within an individual's lifetime. Here, we study whether hermaphrodites also possess facultative sex allocation, that is, a phenotypic flexibility, allowing them to distribute resources to either sex in an oppo...

PIWI proteins and piRNA pathways are essential for transposon silencing and some aspects of gene regulation during animal germline development. In contrast to most animal species, some flatworms also express PIWIs and piRNAs in somatic stem cells, where they are required for tissue renewal and regeneration. Here, we have identified and characterized piRNAs and PIWI proteins in the emerging mode...

The analysis of the three-dimensional arrangement of cells and tissues is fundamental for the understanding of their individual contribution to the whole organism. High-resolution microscopy outputs seriated two-dimensional images in which, due to the experimental limitations in the labeling, the objects of interest are hardly segmentable by automated means. On the other hand, the outcome of ma...

Sex allocation theory for simultaneous hermaphrodites predicts an influence of the mating group size on sex allocation. Mating group size may depend on the size of the group in which an individual lives, or on the density, but studies to date have not distinguished between the two factors. We performed an experiment in which we raised a transparent simultaneous hermaphrodite, the flatworm Macro...

 The scanning electron microscope was used to investigate the ultrastructures of the egg membrane surface (unfertilized egg) of an endemic cyprinid fish, Cyprinion tenuiradius Heckel, 1849. The eggs of this species were almost circular in shape, had a smooth surface and one type II micropyle consisting of the flat pit and a long canal in the animal polar region. The micropyle region was not fla...

Members of the DAZ (Deleted in AZoospermia) gene family are important players in the process of gametogenesis and their dysregulation accounts for 10% of human male infertility. Boule, the ancestor of the family, is mainly involved in male meiosis in most organisms. With the exception of Drosophila and C. elegans, nothing is known on the function of boule in non-vertebrate animals. In the prese...