Intraespecific diversification in floral traits mediated by divergent selection imposed by pollinators: patterns of contemporary phenotypic selection and flower integration in the hummingbird-pollinated Nicotiana glauca.

NATTERO J.; SÉRSIC, A.; COCUCCI A. A.

J. Evolutionary Biology

Año: 2007

ABSTRACT To asses if differences in floral phenotype that exhibit three populations of the hummingbird-pollinated Nicotiana glauca were related to adaptation to local pollinators, patterns of contemporary phenotypic selection and flower integration were studied. Results show that corolla length was consistently under directional selection: weakly for longer corollas in the two naturally established populations with low flower-pollinator mismatch, and strongly for shorter corollas in the recent population with flowers considerably longer than the pollinating hummingbird’s beak. Integration indexes were better explained by functional hypotheses in all populations suggesting that flower phenotype has responded co-ordinately to selection while patterns of integration differed between populations. These results support the view that flower phenotype is moulded by pollinator-mediated selection and conform with the idea that the recent population is still in process of readjustment to a new adaptive peak and naturally established populations are still slowly drifting to long established adaptive peaks.  Key words: floral evolution, floral integration, phenotypic selection, hummingbird pollination, pollinators, floral traits.