PARENT SESSION
Oral Session # 46: Evolutionary Ecology I: Plants.
Presiding: P Minchin
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.
Evolution of self-compatibility in an invasive plant is not suppressed by inbreeding depression.
Davis, Heather*,1, 1 University of California, Davis, hgdavis@ucdavis.edu
ABSTRACT- This study compared patterns of self-compatibility and rates of inbreeding depression between the self-incompatible, perennial Spartina alterniflora from the Atlantic coast of North America with an invading, inbred, population on the Pacific coast. Invasive plants were more self-compatible with twice the self-pollinated seedset (50%) than plants from the native range. Outcrossing with pollen from either the Atlantic natives or Pacific invaders produced a more than 60% increase in seedset over selfing rates for the native plants but no differences in the invasive plants. Native selfed seed germinated at only 75% the rate of those from the Pacific in preliminary data analysis. Invasive plant seeds outcrossed with invasive pollen had twice the germination rate (70%) as the outcrossed seeds of all other combinations. This caused a higher measure of inbreeding depression for invasive plants (0.4) compared to native (0.07) despite the selfed invasives' higher germination rate. To investigate the mechanism of change in the invader's self-compatibility, I contrasted plants from multiple invasive subpopulations representing the time since colonization (old > 60 yrs; intermediate 10-60 yrs; young < 10 yrs), equivalent to plant age, with the younger the plant the more generations there were since initial colonization. Young plants had twice the seedset when selfed, at 40%, than old plants. Inbreeding depression of the young plants (0.2) was nearly half that of the old plants. These results suggest the exotic Pacific population, that at the low densities at the leading edge of the invasion suffers from greatly reduced fecundity, has evolved from the predominantly self-incompatible state of the dense, competitive marshes on the Atlantic coast. Extreme inbreeding has not hindered this invader's developing self-compatibility since the inbreeding depression is not large and is decreasing over generations.
Key words: invasive species, inbreeding depression, self-incompatibility, evolution