Mating and Fitness Consequences of Sexual System in the Moss Atrichum undulatum s.l. (Polytrichaceae)

Populations of the moss Atrichum undulatum contain females, males, and hermaphrodites, and hermaphrodites can have sex organs in close proximity or spatially separated across branches. Here we ask whether differences in gender influence selfing rates or progeny fitness. We used allozyme electrophoresis to measure selfing rates of female and hermaphrodite gametophytes. We measured size and spore number of sporophytes from females and hermaphrodites and germination, survival, and photosynthetic capacity of their gametophytes grown on medium with supplemental nutrients or only with tap water to simulate a harsher environment. Females showed no significant selling between sibling gametophytes. Significant within-gametophyte selling was found in hermaphrodites with minimal spatial separation of male and female sex organs. Parental gender did not influence sporophyte size, but sporophytes from females contained slightly more spores. After 6 mo, only progeny from females survived on tap water media. When progeny were transplanted onto tap water media, progeny of females had greater photosynthetic capacity but also higher nonphotochemical quenching than that of hermaphrodites, resulting in realized photosynthetic rates similar to those of hermaphrodites. While the observed fitness differences are small, they suggest that there may be selection on sexual systems in A. undulatum, perhaps through either increased provisioning of resources to progeny by females or gametophytic inbreeding depression following selling in hermaphrodites.