Temperature stress and the sex bias: The influence of heat-shock events on bryophyte population dynamics

Background/Question/Methods

In bryophytes, the majority of species have separate sexes and sex ratio bias is the norm. Female’s ability to better cope with stress events than males has been proposed as a mechanism contributing to sex bias in bryophytes. The cosmopolitan moss Bryum argenteum inhabits a variety of geographic regions and exhibits an extreme female bias in sex ratio. Campylopus introflexus is known throughout Europe and along the west coast of North America as an invasive moss that can inhabit harsh environments from sand dunes to geothermal areas. Here, we used manipulative experiments with B. argenteum and C. introflexus to determine whether females recover more quickly than males after a heat shock event. We used two life history stages (the asexual propagule stage and the adult gametophyte life stage) for B. argenteum and only the adult gametophyte stage for C. introflexus. We used three geographically separated populations for each species for comparison. Rather than conducting a typical dry-heat experiment, we sought to examine the effects of temperature while in a hydrated state to separate temperature stress from dehydrate stress. We quantified the recovery rate of the plants after heat shock by measuring Fv/Fm (using chlorophyll fluorometer) and the time to first growth, over a series of days.

Results/Conclusions

Males and females differed significantly in their response to temperature stress and they did so at both the asexual propagule stage and the gametophyte stage for B. argenteum. In C. introflexus, females had significantly higher Fv/Fm readings on day one after the stress event but otherwise did not differ significantly from males. Populations in both species were not significantly different in tolerance to heat stress. These results suggest that males and females have significantly different responses to stress which may help explain sex ratio bias in some species. Our results counter what is typical of dioecious angiosperms; females are often found to inhabit areas that are less stressful then where males are typically found. This study supports the notion that there are sex-specific stress-tolerance in bryophytes and that these differences are influencing the population structure of bryophytes.