Gender-specific heat-shock tolerance of hydrated leaves in the desert moss Syntrichia caninervis

Female plants of the moss Syntrichia caninervis are more common than male plants and are found in more thermally stressful habitats than male plants. We hypothesized that this distribution pattern is due to a more favorable regeneration response of females to thermal stress compared to that of males. Hydrated leaves from four genotypes of both sexes of S. caninervis were exposed for 60 min under lighted conditions to temperatures of 20, 30, 35, 40, and 45°C. Leaves were allowed to regenerate on native sand under recovery conditions (12-h photoperiod, 20°C lighted, and 8°C dark) for 56 days, and over this period, protonemal emergence, growth rate, and shoot production were assessed. Leaves exposed to higher heat shocks produced protonemata significantly later, exhibited significantly reduced growth rates over the course of the experiment, and produced fewer shoots but did not differ in the probability of producing a shoot. Males tended to produce protonemata earlier than females at the highest thermal stress, whereas females tended to produce protonemata earlier under control conditions. Female leaves regenerated at twice the rate of male leaves, producing twice the area of protonemal cover; this gender difference was lessened at the highest thermal stress. Female leaves regenerated significantly more shoots than males, with each sex exhibiting different peaks of shoot production depending on the thermal stress. No interaction effect was detectable between gender and stress treatment. While females had a more favorable regeneration response relative to males, thermal stress diminished this difference, thus suggesting that our hypothesis was not supported.