Bird-mediated selection on fruit display traits in Celtis ehrenbergiana (Cannabaceae)

FACUNDO XAVIER PALACIO; MARIELA LACORETZ; MARIANO ORDANO

EVOLUTIONARY ECOLOGY RESEARCH

EVOLUTIONARY ECOLOGY LTD

Lugar: Tucson; Año: 2014 vol. 16 p. 51 - 62

1522-0613

Background: In mutualistic interactions of fleshy-fruited plants and seed-dispersing birds, dispersers act as natural selection agents on fruit display traits. Bird-mediated phenotypic selection on maternal and seed level plant traits have been proposed to be uncoupled. However, this key step in the understanding of the coevolutionary processes has seldom been explored. Goals: To study the pattern and strength of phenotypic selection exerted by birds on two different plant life stages: maternal (mean and within-plant variation of fruit traits) and offspring (individual seed size) levels. Organism: The one-seeded fleshy-fruited tree, Celtis ehrenbergiana (Klotzsch) Liebm. Field site: Natural forests of t he Biosphere Reserve ?Parque Costero del Sur?, near the Río de La Plata shore, Buenos Aires, Argentina. Methods: We sampled 24 randomly selected trees. For each focal tree, we recorded bird visits and behavior, and fruit-related traits. Dispersed seeds were collected in the same place. Results: At the maternal level, birds exerted positive directional selection on mean sugar concentration. Subindividual variation in fruit traits was not detected as target of bird-mediated selection. At the individual seed level, birds exerted positive directional selection on seed size. Conclusions: While birds exert selection pressures on reward related traits, plants obtain an advantage through a larger seed size.