Tuesday, August 5, 2008

PS 20-44: Bet-hedging strategies in annual and perennial species of Eriogonum from the high desert of the Intermountain West

Jeremie Fant, Northwestern University & Chicago Botanic Garden, Andrea T. Kramer, University of Illinois-Chicago, and Kay Havens, Chicago Botanic Garden.


Temporal variation in germination, referred to as a bet-hedging, is measured as the fraction of seeds that don't germinate under ideal conditions in their first year but do under the same conditions in subsequent years. This strategy allows for germination to be spread over several years to cope with year-to-year variation in environmental conditions and promotes the maintenance of a soil seed bank. Populations from sites that experience erratic weather patterns may have multiple germination strategies within the same population, including bet-hedging mechanisms, seed dormancy and variability in seed size. Bet-hedging strategies have been studied in desert annuals, but few studies have included perennial populations. Annual and perennial species in the genus Eriogonum make up an important component of many plant communities in the western United States, including the high deserts of the Intermountain West; an area which experiences some of the most varied and extreme climate conditions in North America.

In a multiple-year study, we have investigated seed germination strategies of three species of Eriogonum with different life histories; E. cernuum a summer annual, which flowers from mid-late summer, E. ovalifolium a spring flowering perennial and E. microthecum a late summer flowering perennial. Seed was collected from multiple sites which differ in local weather conditions. We asked: 1) In desert environments is bet hedging strategies restricted to annual species or is it also found in perennial species; 2) How does germination fraction vary with life history and 3) with variability in environmental conditions?


Seed was split into different germination treatments that replicated winter, summer and mild spring/fall conditions; this was repeated over multiple seasons. As expected the germination response varied by species, population and treatment. Evidence of bet-hedging was seen in all populations of the desert annual, the proportion of seed to remain dormant was correlated to treatment and local environmental conditions; Populations from Hot deserts showed had more ungerminated seed in hot treatments, while seed from desert with harsh winters had more ungerminated seed in cold treatment. Perennial species did have a portion of ungerminated seed, however this was restricted to some treatments, and not others, suggesting an induced dormancy rather than bet-hedging. This induced dormancy was correlated to treatment and local environmental conditions. In both perennial species, seed from areas with harsher winters showed delayed germination in cool and warm conditions in the first year but not the second. This was also true for the spring flowering perennial