by José J. Fumero-Cabán, Elvia J. Meléndez-Ackerman and Julissa Rojas-Sandoval
Flowers, details of
reproductive structures,
and visitors of Guaiacum
sanctum in the Caribbean.
Islands often have plants with reproductive
mechanisms allowing for self-compatibility and low species-rich communities of
pollinators. Islands are also areas more prone to extinction and vulnerable to
invasive species than mainland ones. In this study, we document different
reproductive traits of the tropical tree Guaiacum
sanctum on two insular populations in the Caribbean with contrasting
pollinator assemblages: Guánica on the main island of Puerto Rico where the alien
honeybees (Apis mellifera) were first reported in 1994 and Mona Island
where honeybees do not occur. On these two islands, we performed a series of field
observations and pollination experiments over a period of three years, to
assess pollinator species richness, visitation rates, breeding system, and the
fitness of selfed- vs. crossed-progenies. We found that flowers are pollinated
by insects on both islands, but while the richness of pollinators was higher on
Mona, the visitation rates were considerably higher in Guánica where trees are
almost exclusively visited by the introduced Apis mellifera. Pollinations experiments show that outcrossing treatment
yielded nearly twice the number of fruits and seeds than selfing treatment and
these differences are consistent between populations, which might reflect early
acting inbreeding depression, partial self-incompatibility, or differences in
resource allocation between selfed and outcrossed fruits. Overall, our results
suggest that the substantial reduction in pollinator visitors in areas
dominated by alien honeybees may add an additional level of vulnerability to
these threatened populations.
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