Clonal dynamics and evolution of dormancy in the leafy hepatic Lophozia silvicola

Abstract

Laaka-Lindberg, S. and Heino, M. 2001. Clonal dynamics and evolution of dormancy in the leafy hepatic Lophozia sil6icola. -Oikos 94: 525 -532.Dead shoots of colonies of a leafy hepatic species, Lophozia sil6icola, are replaced by shoots developing from asexual propagules, the gemmae. Observations of two populations of L. sil6icola showed a strong decreasing seasonal trend in germinability of the gemmae. We suggest that the non-germinating gemmae enter dormancy, and that the proportion of gemmae entering dormancy is season-specific. We assume that there are two types of gemmae, dormant and non-dormant and that only the dormant gemmae can survive during winter. Using a stochastic individual-based cellular automaton model, we investigated whether selection on season-specific dormancy fraction would lead to a decreasing proportion of germinating gemmae. Thus the germination schedule is the evolving trait in the model. Parameter estimates for the model were based on data collected from a population of L. sil6icola in southern Finland over a three-year study period. In the simulations, the germination schedule shaped by evolutionary change was similar to the observed pattern. Thus the modelling results give support to the dormancy hypothesis. The qualitative pattern of decreasing germinability towards the end of the growing season is robust. Quantitative predictions are influenced by changes in parameters; for example, if winter mortality of shoots increases relative to mortality during the growing season, production of an increased fraction of dormant gemmae is favoured, especially at the end of the season. S. Laaka-Lindberg

Comparison of gemma production among three Lophozia species during the growing season

“…3). Other liverwort germination studies (Laaka-Lindberg, 1999;Laaka-Lindberg and Heino, 2001) however reported a different germination pattern (highest rates at the beginning of season and lowest at the end of season) and hypothesized that non-germinated gemmae entered dormancy at the end of the season, avoiding risk of mortality induced to non-dormant gemmae by unfavourable environmental conditions in winter. If dormancy is considered a way to escape from the unfavourable environmental conditions (Evans and Cabin, 1995) then the germination pattern observed by us leads to the suggestion that rather mild winters in the Czech Republic (with respect to temperatures and duration of snow cover, cf.…”

“…Norwegian liverworts benefit from the more stable air humidity and thus longer periods favourable for their growth. It may be important, however, to compare counts over several years, as illustrated by the significant interannual variance in the gemma production in the period 1997-1999(Laaka-Lindberg and Heino, 2001, which might be attributed to differences in pattern of the annual precipitation, particularly in the course of the growing season.…”

Reproductive phenology in the leafy hepaticLophozia silvicolaBuch in southern Finland

“…At each sampling, a square of 1 cm 2 was dissected systematically in a different sector of each colony, in order to minimize disturbance caused by the sampling itself. As the shoot density did not change significantly during the study period (Laaka-Lindberg & Heino, 2001), any effect of sampling was regarded as small and has been ignored. The means of the five replicates taken at each sampling time are used in the calculations.…”

Seasonal variation in the bryophyte diaspore bank of open grasslands on dolomite rock

“…Innate dormancy, inhibiting germination at the time propagules are shed from the plant, has been found in spores of several species (Thompson, 1941;Steiner, 1969;Berrie, 1975;Miles & Longton, 1992;Duckett & Renzaglia, 1993;McLetchie, 1999). Induced dormancy has only been demonstrated in two cases so far (McLetchie, 1999;Laaka-Lindberg & Heino, 2001). This is a secondary dormancy that occurs when a propagule is exposed to certain environmental conditions and which continues after the environment changes and prevents germination at the wrong time of year.…”