Species introduction shifts a trait's function from mutualism to antagonism: elaiosomes in a myrmecochory cold spot

HIERRO, JOSÉ L.; MUIÑO, WALTER A.; FARJI BRENER, ALEJANDRO; COCK, MARINA C.; PEARSON, DEAN E.

OIKOS

WILEY-BLACKWELL PUBLISHING, INC

Año: 2023 vol. 2023

0030-1299

Placing traits into novel evolutionary contexts may profoundly alter their functionalroles. Here, we investigated whether the elaiosome, a lipid-rich appendage located onseeds, retained its role as a seed dispersal trait promoting mutualisms with insectivorous ants following human-mediated introduction of the elaiosome-bearing Carduusnutans into the Argentinean Caldenal. This system is located within the Neotropicalregion, an alleged myrmecochory cold spot. Specifically, we first tested the assumption that the elaiosome mediates the interaction between C. nutans and the nativeant Pheidole bergi. Then, we explored the hypothesis that, instead of a mutualism, theelaiosome promotes an antagonism between these species because P. bergi predateson both insects and seeds. Finally, we assessed the possibility that the elaiosome israre in our system, as predicted from its location within the Neotropics. By manipulating the presence/absence of C. nutans’ elaiosomes, we demonstrated that P. bergistrongly prefers to collect seeds with versus without C. nutans’ elaiosomes, indicatingthat the elaiosome indeed mediates the interaction between these species. While wedetected no direct signs of predation on nor alteration of viability in seeds recoveredfrom P. bergi’s refuse dumps, 80% of offered C. nutans seeds remained inside P. bergicolonies, where they are likely consumed by ants, buried too deep for emergence ordestroyed by pathogens. Importantly, by quantifying the outcome of the C. nutans–P.bergi interaction, we showed that this relationship is strongly antagonistic. Finally, bysampling taxa most likely to have elaiosomes, we identified eight native species withthat trait, preliminary confirming that elaiosome-bearing species are uncommon in theCaldenal. Taken together, our fndings suggest that the elaiosome promotes an antagonism that deters invasion in a cold spot of myrmecochory diversity. The functions ofphenotypic traits can thus vary according to the ecological and evolutionary contextsin which they operate.