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Accueil du site → Doctorat → Argentine → Ecología de la dispersión de semillas por hormigas en Jatropha excisa Griseb. (Euphorbiaceae)

Universidad de Buenos Aires (2011)

Ecología de la dispersión de semillas por hormigas en Jatropha excisa Griseb. (Euphorbiaceae)

Aranda Rickert, Adriana

Titre : Ecología de la dispersión de semillas por hormigas en Jatropha excisa Griseb. (Euphorbiaceae)

Ecology of seed dispersal by ants in Jatropha excisa Griseb

Auteur : Aranda Rickert, Adriana

Université de soutenance : Universidad de Buenos Aires

Grade : Doctor de la Universidad de Buenos Aires en el área de Ciencias Biológicas 2011

This dissertation describes myrmecochory or seed dispersal by ants in Jatropha excisa Griseb.(Euphorbiaceae), a native plant of Northwest Argentina. The seeds of this plant species have a lipid-rich appendage called elaiosome and a diplochorous dispersal system (explosive autochory followed by myrmecochory). Field studies conducted in the Monte Desert phytogeographical region of the La Rioja Province, showed that the J. excisa elaiosome–bearing seeds are dispersed by ants, and that the presence of the elaiosome enhances their probability of being removed by them. The estimation of the seed dispersal distances achieved by myrmecocohory showed that the distance per se is an important benefit of the plant associated to the ant-mediated transport. Experimental seed offering assays identified 11 ant species attracted to the J. excisa seeds in the study area. Whereas seven of these ant species consumed the elaiosome in situ without transporting the seeds, only three species removed the seeds, being one of them, P. cunicularius pencosensis Forel, responsible of 84% of the observed seed removal events. Seed removal in the study sites was positively correlated with the abundance of this ant species. Once inside the P. cunicularius pencosensis nests, the J. excisa seeds were transported vertically from the deep brood chambers, where the elaiosome was consumed, up to the superficial refuse chambers, where the seeds were discarded. These discarded seeds conserved their viability, and germination assays showed that the experimental removal of the elaiosome enhanced their germination. Finally, some aspects of the biology of P. cunicularius pencosensis are described (diet, nesting ecology, daily and seasonal activity rhythm and behaviour), and are related to the capability of this ant species to act as the most important seed disperser of the J. excisa seeds in the study area. The results here presented support the hypothesis of myrmecochory as an unevenly diffuse mutualism, where a single mutualist ant species dominates the dispersal process, in contraposition to the canonical view of myrmecochory as an evenly diffuse mutualism, where multiple mutualist partners are similar in terms of the frequency and consequences of their interactions.


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