Sexual dimorphism in bryophytes: Patterns and consequences
Stark, Lloyd R. .
A gender based approach to desiccation tolerance in a desert moss.
Syntrichia caninervis (Tortula) exhibits a sex ratio of ~20 females: 1 male at low to middle elevations in the Mojave Desert. Given that males are absent from the lowest, driest habitats, and also that males are very rare on exposed desert soils at all elevations, the hypothesis was put forward that sex-differential desiccation tolerance (DT) was operating in this system. Responses to DT were carried out using detached leaves and a protonemal growth assay. Leaves of Syntrichia were isolated from each of 10 mixed-sex patches, allowed to deharden for 3 days, and subsequently subjected to the following number of wet/rapid dry/wet cycles: 0, 2, 4, and 6 (representing control, low, middle, and high DT treatments). During each cycle, drying occurred in <30 min at ~15% relative humidity, and the intervening hydrated period was 2 hr @20C. After the stress treatment, leaves were allowed to regenerate in a growth chamber for 56 days at low light intensities under a 12 hr photoperiod with day/night temperatures of 20/8C. Desiccation stress was strongly correlated to regenerational vigor of the detached leaves, with the high stress treatments (4, 6 cycles) exhibiting significantly higher leaf mortality, higher levels of microbial infection, longer protonemal emergence times, slower growth rates, and lower shoot production than the lower stress treatments (0, 2 cycles). Female leaves outperformed male leaves under all treatments, growing up to twice as fast as males using protonemal extension rates and protonemal biomass accumulation rates. However, a significant interaction between gender and stress was not detected. We conclude (i) that the protonemal growth assay works well as a response variable for DT studies, because desiccation stresses had marked effects on leaf regeneration; and (ii) that gender based DT, at least with respect to responses to rapid drying cycles, is not present in Syntrichia.
1 - University of Nevada, Department of Biological Sciences, 4505 Maryland Parkway, Las Vegas, Nevada, 89154-4004
Presentation Type: Symposium
Location: Ballroom 3 (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 8:30 AM