Sex ratio, sex-specific pattern in vegetative growth and gemma production in an aquatic liverwort, Scapania undulata (Marchantiophyta: Scapaniaceae)

Abstract

Scapania undulata is an aquatic dioicous liverwort growing in shallowstreams in boreal to subtropical zones. We studied the expressed sexratio, sex-specific differences in shoot architecture and possibletrade-off between sexual and asexual reproduction in ten populations ofS.undulata by surveying 100 plots in ten streams in southern Finland.The expressed sex ratio was male biased, in contrast with the sex ratioin most dioicous bryophytes. It was also highly variable between thestreams, but individual plots frequently comprised shoots from only onesex. The overproduction of males might be a strategy to overcome spermdilution and ensure fertilization over longer distances in water. Nosize differences between females and males were detected, but theydiffered in branching patterns. Evidence for a higher cost of sexualreproduction in females than males can be seen from the following: themale-biased sex ratio; low number of sex-expressing female shoots infemale-only plots; no co-occurrence of gemmae and female sex organs on asingle branch, and no more than one sexual branch per female shoot. Incontrast, high gemma production of male and female sex-expressing shootsindicates a minimal trade-off between sexual and asexualreproduction.(c) 2014 The Linnean Society of London, Botanical Journalof the Linnean Society, 2014, 175, 229-241.