PARENT SESSION
Poster Session #32: Plant Ecology I.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
146
Differences in ovule abortion between sprouting and non-sprouting species of California chaparral.
McElwain, Shauna1, McElwain, Kirsti1, Smith, Jana1, Wiens, Delbert2, Davis, Stephen1, 1 2
ABSTRACT- Within the Santa Monica Mountains of southern California, congeneric, co-occurring species of Ceanothus chaparral have two divergent life history characteristics, sprouting and non-sprouting. Species with the sprouting trait have an apparent advantage because they utilize both vegetative regrowth and seed germination to reestablish after wildfire. In contrast, non-sprouters are limited to seed germination alone. However, non-sprouters persist and in some landscapes dominate. We tested the hypothesis that non-sprouters have a genetic advantage, expressed as a greater proportion of ovules maturing into seeds. We compared the seed to ovule (S/O) ratio in fruit of co-occurring, congeneric species of Ceanothus from a total of 14 populations and over three seasons (1997-1999). Non-sprouting species consistently had a significantly higher S/O ratio (range 62%-85%) than adjacent sprouting species (range 13%-45%). When we artificially reduced the number of fruit per plant by ~90% there was a significant increase in fruit volume but no increase in S/O ratio. A comparison of physiological performance during fruit set (photosynthesis, transpiration, water and nitrogen use efficiency) was not significantly different or in the wrong direction to explain differences in S/O ratio based on resource limitation. We conclude that the genetic advantage in S/O ratio for non-sprouters may result from more frequent purging of deleterious mutations in the haploid gametophyte, decreasing the incidence of ovule abortion.
KEY WORDS: Ceanothus, chaparral, ovule abortion