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Summary1. The evolution of island syndromes has long served as a model to understand the mechanisms accounting for phenotypic differentiation. Combining literature data with actual observations, we determine whether typical syndromes such as the loss of dispersal power and the bias towards selfcompatibility (Baker's law) apply to vagile organisms, using bryophytes as a model. 2. The life-history traits (LHTs) observed in oceanic island floras were statistically different from those observed on continents, evidencing the evolution of island syndromes. In contrast, LHTs of continental and continental island floras were similar, pointing to differences in migration intensity between continents, continental islands and oceanic islands. 3. The proportion of bisexual species was significantly higher on oceanic islands than on continents. A significant proportion of species that are unisexual or bisexual on continents shifted towards exclusive bisexuality on oceanic islands, suggesting that Baker's law applies to bryophytes. The underlying mechanisms, however, probably differ from in situ selection for selfing. 4. The proportion of species producing specialized asexual diaspores, which are assumed to play a role in short-distance dispersal (SDD), was higher on oceanic islands than on continents. The proportion of species producing spores, which are involved in long-distance dispersal (LDD), exhibited the reverse trend, suggesting a shift in the prevalent reproductive strategy to favour SDD on oceanic islands. Approximately 50% of the species, however, maintained the ability to produce sporophytes on oceanic islands, and the relative frequency of fertile shoots within collections of four model species was even higher on islands than on continents. 5. Synthesis. Bryophytes exhibit typical island syndromes, indicating that migration rates between oceanic islands and continents are not sufficient to prevent the effects of genetic drift and contradicting the view that the sea does not impede migration in the group. Significant shifts in life-history traits (LHTs) towards increased production of specialized asexual diaspores and decreased sporophyte production on oceanic islands indeed point to a global loss of long-distance dispersal (LDD) ability. The maintenance of traits characteristic for LDD in a large number of species has, however, substantial consequences for our understanding of island plant evolution, and in particular, for our vision of islands as evolutionary dead ends.

L. 2004. Mate limited reproductie success in two dioicous mosses. Á/ Oikos 104: 291 Á/298.We tested whether mate availability in the pleurocarpous dioicous mosses Rhytidiadelphus triquetrus and Abietinella abietina affects fertilization success by transplanting individual male shoots into non-sporophytic female colonies. Fertilization success in both species was limited by the availability of mates and distance-dependent, and the number of sporophytes produced was higher in R. triquetrus than in A. abietina . Our estimate of a maximum fertilization distance of 34 cm in R. triquetrus is an order of magnitude larger than previous estimates that have been based on non-manipulative approaches. In R. triquetrus the number of female reproductive branches and plot inclination (horizontal vs sloping) had significant effects on the number of sporophytes produced. In A. abietina , the number of female reproductive branches per plot did not affect sporophyte production. Within sloping experimental plots, sporophyte number was significantly higher, and the distance of sporophytes from the spermatozoid source was larger below the male transplants than above. We conclude that mate availability may be important for reproductive success in sessile dioecious organisms, and that the spatial structure at various scales is essential to understand their dynamics.

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Most dioecious plants do not exhibit discernible sexual dimorphism before sexual maturity. Therefore, it is impossible to address any sex-related questions during the prereproductive phase unless a genetic sex marker is available for gender determination. The aim of the present study was to develop a genetic sex marker for the moss Pseudocalliergon trifarium to allow gender and sex ratio determination at any stage in the life cycle. A high proportion of P. trifarium populations do not express sex. The screening of genomic DNA with inter simple sequence repeat (ISSR) primers was used to discover sex-specific polymerase chain reaction (PCR) amplification products. A presumably female-specific band was found, excised from the gel, cloned, and sequenced. A sequence-walking method was used to characterize the same region in males. A primer pair was designed to allow the amplification of a 159-bp portion of the female-specific DNA region. All tested material, up to 16-year-old herbarium specimens, provided unambiguous amplification products. This study successfully provides, for the first time in a moss, a sex-specific DNA marker. It allows reliable determination of gender and sex ratios. The short length of the amplification product is an advantage as satisfactory PCR products are more likely when the targeted sequence is short. The amount of variation in the DNA region shared by both sexes was relatively high. If the male sequence can be better characterized, the sex-specific regions could possibly be used to evaluate sex-specific phylogeographic patterns.

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A fundamental assumption in life-history theory is that reproduction is costly. Higher reproductive investment for fruits than for flowers may result in larger costs of reproduction in females than in males, which is often used to explain male-skewed sex ratios in unisexual seed plants. In contrast, bryophytes have predominantly female-biased sex ratios, suggested to be a product of a higher average cost of sexual reproduction in males. Empirical evidence to support this notion is largely lacking. We investigated sex-specific reproductive effort and costs in the unisexual moss Pseudocalliergon trifarium that has a female-dominated expressed sex ratio and rarely produces sporophytes. Annual vegetative segment mass did not differ among male, female, and non-expressing individuals, indicating that there was no threshold-size for sex expression. Mean and annual mass of sexual branches were higher in females than in males, but branch number per segment did not differ between sexes. Prefertilization reproductive effort for females was significantly greater (11.2%) than for males (8.6%). No cost for sexual branch production in terms of reduced relative vegetative growth or decreased investment in reproductive structures in consecutive years was detected. A higher realized reproductive cost in males cannot explain the unbalanced sex ratio in the study species.

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