Plants stand still, but their genes move- rephrasing the title of a BES symposium held in Aug 2000. And for many plant species this movement is the result of mutualistic interactions with pollinators and frugivores. A long-standing challenge in studies of seed dispersal by animal frugivores has been the characterization of the spatial relationships between dispersed seeds and the maternal plants, i.e., the seed shadow. The difficulties to track unambiguously the origin of frugivore-dispersed seeds in natural communities has been considered an unavoidable limitation of the research field and precluded a robust analysis of the direct consequences of zoochory.

Together with José A. Godoy and Cristina García, we are using the multilocus genotype at SSR (microsatellite) loci of the woody endocarp, a seed tissue of maternal origin, to provide an unequivocal genetic fingerprint of the source tree. We have the help of JuanMi Arroyo and Cristina Rigueiro, technicians at the lab. By comparing the endocarp genotype against the complete set of genotypes of reproductive trees in a population, we were able to unambiguously identify the source tree for 79.7 % of the seeds collected in seed traps and hypothesized that the remaining 20.3 % of sampled seeds come from other populations.

Identification of the source tree for Prunus mahaleb seeds dispersed by frugivores revealed a marked heterogeneity in the genetic composition of the seed rain in different microhabitats, with a range of 1-5 distinct maternal trees contributing seeds to a particular landscape patch. Within-population dispersal distances ranged between 0-1112 m, with up to 62 % of the seeds delivered within 15 m of the source trees. We are interested in the ecological and evolutioary implications of our results, indicating strong distance limitation of seed delivery combined with infrequent long-distance dispersal events, extreme heterogeneity in the landscape pattern of genetic makeup, and a marked mosaic of multiple parentage for the seeds delivered to a particular patch. A detailed description of our field methods and lab protocols is available here.

Together with Arndt Hampe and Rémy Petit I’m investigating how seed dispersal by animals influences plant population genetic structure and its geographic patterns. We have a bilateral agreement between MEC and the INRA that funds this collaboration, including an exchange program between our labs.