Document: DEB-3-16-7

Reciprocal hybridization and the threat of invasive hybrid Spartina to salt marshes in California.

AYRES, D.* and D.STRONG

University of California, Davis, CA, 95616 USA ¹

Abstract:
Spartina alterniflora, endemic to the eastern U. S., was introduced into the range of a native congeneric species, S. foliosa, in south San Francisco Bay ca 25 years ago. Using RAPD markers and chloroplast DNA, we determined that extensive hybrid swarms have arisen through reciprocal hybridization; both species have been seed parents to hybrids. The primaeval condition of Pacific estuaries leaves vast expanses of open mud in intertidal habitats upon which animals native to the Pacific rely. Both hybrids and S. alterniflora invade this open mud, modify the hydrology, and threaten the native biota. Spartina foliosa is virtually absent in salt marshes where S. alterniflora was deliberately planted; we found roughly equal numbers of S. alterniflora and hybrid individuals. Hybrids grow vigorously and produce abundant viable seed and pollen. Marshes newly opened to Bay waters were colonized mostly by hybrid seed delivered via tidal currents. There was little temporal overlap in flowering between the 2 species, and we found no F1 hybrids; interspecific crosses are rare. Hybrids bridge the phenological gap. Robust hybrids, producing copious pollen and seed coincident with the flowering of S. foliosa, would predispose hybrids to high fitness in the vast sea of flowers present in a native salt marsh. Thus, hybrids could prove to be an even greater menace to S. foliosa and estuary ecosystems than S. alterniflora.

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This abstract is being presented at: 3:50 PM in session:
Symposium #6: Ecological Consequences of Adaptive Evolution Among Invasive Species in Terrestrial and Marine Systems.