We propose four measures of allocation to sexual reproduction in mosses, and apply these to data obtained from 15 species found fruiting on Signy Island, South Orkney Islands, in the maritime Antarctic. Spore counts and size measurements are reported for each species. Larger spore sizes in most short-lived species suggest that spores may have an important role in local colonisation. Five species with small spore dimensions, high counts and wide Antarctic distributions are identified as potential long-distance colonists. Investment in sexual reproduction is estimated using two measures (the ratio of sporophyte to gametophyte dry weight, and the investment in spores as a proportion of total shoot dry weight). Both measures show that investment by annual and short-lived species is greater than that found in most perennial species. The same short-lived species also show a much stronger relationship between the sporophyte and gametophyte dry weights of individual shoots in regression analyses. The short-lived species examined in this study may be classified as annual or short-lived shuttle species (sensu During). Their reproductive behaviour largely agrees with the predictions of life history models, and they may be described as ruderal (sensu Grime) or r-selected. However, their production of relatively few large spores is at variance with the predictions of these models. The sexual behaviour of longer-lived species agrees less well with theoretical predictions, with some showing surprisingly large levels of investment, although others can be described as a-selected (sensu Greenslade) or stress tolerators (sensu Grime), with much lower investment in sexual reproduction.