Fig. 1From: Mating behavior and reproductive morphology predict macroevolution of sex allocation in hermaphroditic flatwormsStylized representation of the mating syndromes, details on the general Macrostomum morphology, and the specific in vivo measurements used in the analyses. Most species can be assigned to either the reciprocal mating syndrome (A), with reciprocal mating, a (usually blunt) non-invasive stylet, sperm with lateral bristles and a thickened antrum epithelium, or they show the hypodermic mating syndrome (B), with hypodermic insemination, a needle-like stylet, simple sperm and a thin antrum epithelium. Note that assignments follow the inferred mating syndrome [43], based on morphological data and observations of the location of received sperm. We use colour throughout to represent species assignment to the inferred mating syndromes: hypodermic (yellow, N=40), intermediate (light green, N=2), reciprocal (green, N=69), and unclear (gray, N=9). C In vivo image of M. lignano with visible internal organs and an indicated outline of how the areas of the paired testes (blue) and ovaries (red) were measured (only one testis and ovary are outlined). These area measurements were used to estimate gonad size and gonadal sex allocation (GSA, as testis area/(testis area + ovary area)). Below are drawings of additional reproductive morphology traits, namely a stylet (D), a sperm with sperm bristles (E), and an antrum with received sperm (F), with representations of the measurements taken or the structures scored, which may represent non-gonadal components of male and female allocation and serve as indicators of the intensity of postcopulatory sexual selection (“morphological indicators”). Linear quantitative measurements were taken as indicated in D and E. Such quantitative measures were not possible for the antrum (F), and we thus scored the indicated structures on an ordinal scale and summed these for an overall measure of antrum complexity (high values indicate a more complex antrum). For details see the “Methods” section.Back to article page