Evol Ecol Res 16: 51-62 (2014)     Full PDF if your library subscribes.

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

Facundo Xavier Palacio1,2, Mariela Lacoretz2,3 and Mariano Ordano1,2

1Fundación Miguel Lillo, San Miguel de Tucumán, Tucumán, Argentina,  2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina and  3Laboratorio de Ecología y Comportamiento Animal, Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina

Correspondence: F.X. Palacio, Fundación Miguel Lillo, Miguel Lillo 251, CP T4000JFE, San Miguel de Tucumán, Tucumán, Argentina.
e-mail: facundo_palacio@yahoo.com.ar


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 has been postulated to be uncoupled. However, this key step in the understanding of the co-evolutionary 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 the Biosphere Reserve ‘Parque Costero del Sur’, near the shore of the Río de La Plata, Buenos Aires, Argentina.

Methods: We sampled 24 randomly selected trees. For each focal tree, we recorded bird visits and behaviour, and fruit-related traits. Dispersed seeds were collected at the same location.

Results: At the maternal level, birds exerted positive directional selection on mean sugar concentration. Sub-individual variation in fruit traits was not observed to be a 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.

Keywords: co-evolution, maternal and offspring levels, mutualism, natural selection, phenotypic selection, plant–animal interactions, seed dispersal, selection gradients.

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