CONICET | Buscador de Institutos y Recursos Humanos

p { margin-bottom: 0.25cm; line-height: 120%; }Oil-flower speciesare highly specialized attracting a narrow group of oil-collectingbees in contrast to nectar-flower species visited by a wide diversityof pollinators. The vast majority of the oil species lack nectar as apollinator reward; this suggests that the ancestors of plants withoil flowers had either nectar-less flowers or faced strong selectionagainst the production of nectar once oil secretion evolved. Montteaaphylla is one of the few species that simultaneously offers oil andnectar in the same flower to pollinators. In particular, we studiedphenotypic selection in 16 populations in the Monte desert ofArgentina that spanned the entire geographical range of the species.In each population, we determined the relationship between plantpollination success and floral rewards. Positive directionalselection dif- ferentials were detected in three of the populations.One northern population favoured selection on oil production, twocentral or southern populations favoured selection on nectarproduction. Directional selection gradients were consistent with theabove results and correlational selection was significant for onenorthern population where pollination success was favoured by anincreased selection on oil and a decreased selection on nectar.Geographic variation in phenotypic selection models showedlatitudinal increase in directional selection on nectar. Geographicvariation in visitation frequencies of the specialist oil-collectingbee and relative abundance of other floral sources were related to anincrease in directional selection on nectar. Thus, evolution ofrewards appears to respond to a geographic mosaic where either oil ornectar are favoured in different contexts of ecologically specialisedoil collecting bees. Although phenotypic selection was detectable infew and was absent in most populations, the general pattern wasconsistent with current geographic differentiation in reward amounts.

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