PARENT SESSION
Poster Session #50: Evolutionary Ecology.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

A wild annual sunflower of hybrid origin and its ancestral parents differ in their relative fitness, biomass allocation and integrated water use efficiency in response to resource availability.

ROSENTHAL, DAVID¹, DONOVAN, LISA¹, ¹

ABSTRACT- Helianthus deserticola, a narrowly distributed desert species of hybrid origin, is reported to occur in lower resource habitats than its widely distributed parents, H. annuus and H. petiolaris. A comparison of these species under relevant environmental conditions may help us to understand the apparent local adaptation of the hybrid species and ecological factors underlying hybrid speciation. We exposed seedlings of all three of these annual species to high resource (water + nutrients) and low resource conditions in a greenhouse study and followed them through seed set. We predicted that H. deserticola would do relatively poorly in the high resource treatment but would outperform the other species under limiting resources. As expected in the high resource treatment H. deserticola had the lowest fitness based on lower biomass and lower seed output. In the low resource treatment, all species exhibited decreased biomass and seed output but H. deserticola did not outperform the other species. H. annuus was more plastic, shifting biomass allocation from stem to resource gathering (leaf and root) structures, but this did not translate to fitness gains in the low resource treatment. H. deserticola traits values tended to be intermediate except for having the lowest water use efficiency and lowest relative fitness. Overall, the responses the hybrid species H. deserticola are not consistent with the expectation that it is more tolerant of low resource conditions than its ancestral parents.

KEY WORDS: Hybrid speciation, adaptation, relative fitness