Document: AND-3-39-4

Effects of habitat fragmentation on salinity and moisture tolerances and the genetic structure of a rare salt marsh plant.

THORPE, A.*

San Diego State University, San Diego, CA, USA ¹

Abstract:
Reduced gene flow from habitat fragmentation increases the potential that inbreeding depression, genetic divergence, and erosion of genetic variability will occur. In salt marsh plants, these processes may affect tolerance to different combinations of soil salinity and moisture. I tested the germination rates of seeds from five populations (located in three lagoons) of Lasthenia glabrata ssp. coulteri (Coulter's goldfields, Asteraceae), a rare species, endemic to the southern California salt marsh, to four salinity levels by three moisture levels (12 treatments total). Rate of germination (# seeds germinated/day) and proportion of germinated seeds were measured for each population. Tissue was also collected from the five populations for genetic diversity testing using allozymes. The populations differed in both the proportion of seeds that germinated and the rate of germination; however, the three populations located within the same lagoon responded most similarly and had the highest proportion of germination (at highest germination rates, 15%-25% higher final germination compared to the other 2 populations). Of particular interest, a population that has been exposed to elevated freshwater inputs due to irrigation has a reduced tolerance (14%-19% lower final germination) to salinity under water stress when compared to the other populations. Germination rates varied over all populations and all treatments. The varying population responses give evidence for population divergence. Furthermore, the low germination rates in the two most isolated populations may be an indicator of inbreeding depression. These results, combined with the genetic structure between the populations, suggest that habitat fragmentation has restricted gene flow between populations, including populations that are located within the same lagoon.

Keywords: salt marsh, habitat fragmentation, population divergence, gene flow

This abstract is being presented at: 10:30 AM in session:
SALT MARSHES