Ecological Divergence in a Tropical Tree: Protium subserratum (Burseraceae)

Previous international research experience includes a research assistantship in Sabah, Malaysia studying the evolution of social monogamy in the large tree shrew.  I obtained my Master’s degree at Northwestern University and the Chicago Botanic Garden during which I conducted field research in the field of pollination biology in Cameroon.  During my time at Berkeley I have worked as a field research assistant for my advisor in Iquitos, Peru.  The purpose of my trip was to follow up previous population genetics research by carrying out a set of exploratory experiments aimed at determining the strength and importance of reproductive isolating barriers between to subspecies of the tropical tree Protium subserratum occuring on adjacent white sand and clay soils.  In order to test that environmental barriers have not developed between the subspecies of P. subserratum, and generalist pollinators would visit both the clay and white sand subspecies Pollinator visitation was monitored on flowering trees in both soil types. I will be able to use these recordings to quantify the diversity and abundance of potential pollinators and compare visitation between the two subspecies. In order to test that environmental barriers occurring after fertilization are responsible for isolating white sand and clay soil subspecies I conducted parental and ‘hybrid’ crosses between trees growing on both soil types. 16.4% of hybrid crosses were successful while 39% of parental crosses were successful. This result demonstrates that fertilization between subspecies is possible however whether the observed lower seed set between hybrid crosses is due to genetic mechanisms resulting in low fertilization rates or the result of high mortality or fruit abortion post fertilization is equivocal.  Due to overall high seed mortality I could not conduct the reciprocal transplant experiment. These results suggest that genetic barriers to reproduction are important in the isolation of these two subspecies and will direct my future experiments aimed at determining whether barriers to reproduction are most important before or after fertilization.