A novel approach to an old problem: tracking dispersed seeds

Abstract

Animals are the principal vectors of dispersal for a large number of plant species. Unfortunately it is not easy to discern their movement patterns or the fate of their dispersed seeds. Many animals transport seeds by consuming them and then, some time later, defecating them. Others gather seeds and then store them for later consumption. Both circumstances lead to a set of seeds that have been dispersed in a clumped pattern, which offers a unique opportunity to assess seed movements. We introduce a novel approach that uses maternally inherited seed tissue to quantify the genetic structure of dispersed seed pools. This direct approach measures the genetic variability within and among seed pools, and estimates the scale of seed movement, without requiring a highly polymorphic battery of markers or the location and genotypes of all possible seed parents. We demonstrate this approach with the specific case of seed transport of valley oak (Quercus lobata) acorns by acorn woodpeckers (Melanerpes formicivorus). These territorial birds store acorns in drilled holes in the bark of trees, called granaries. We sampled stored acorns from different granaries, extracted DNA from the maternally inherited pericarp, and then assessed individuals for three microsatellite markers. We found extremely high genetic structure among granaries, a low number of effective seed donors per granary, and restricted seed movement. A maternity analysis performed on the same sample with seven microsatellites confirms acorn transport is limited to approximately 100-m radius. Our findings provide insight into the foraging and seed-dispersal behaviour of acorn woodpeckers, with an approach that can be widely extended to other systems.

Frugivores, seeds and genes: analysing the key elements of seed shadows.

“…This enables us to identify uniquely the source tree for a dispersed seed and to infer the contribution of different species of frugivore to the seed rain in different microhabitats (Godoy and Jordano, 2001;Jordano and Godoy, 2002). Other applications of this approach can be found in recent work by Ziegenhagen et al (2003), Grivet et al (2005) and Jones et al (2005).…”

“…However, by taking advantage of tissue of maternal origin still attached to the dispersed seed in some way (e.g. endocarp tissue, ancillary structures of winged seeds like pappus, wings, acorn pericarp, etc), assignment of the most likely source tree can be inferred directly and robustly (Godoy and Jordano, 2001;Jordano and Godoy, 2002;Ziegenhagen et al, 2003;Grivet et al, 2005;Jones et al, 2005;García et al, 2007a). In contrast to direct observation methods, parentage and maternity analysis of dispersed seeds works from the dispersed seed backwards to infer the origin.…”

“…We still lack detailed data on the frequency of immigrant seeds dispersed from other populations into a given population or fragment and on how different frugivore species contribute to this. We especially need a tighter integration of ecological and molecular DNAbased methods to be able to assess dispersal patterns in high-density situations (Grivet et al, 2005;Jones et al, 2005;Hardesty et al, 2006) and in complex systems where the total dispersal kernel (see Nathan,Chapter 11,this volume) can have very distinct components. However, it is becoming more and more evident that frugivores potentially have a dramatic influence on LDD events and patterns of gene flow via seed dispersal (Godoy and Jordano, 2001;Oddou-Muratorio et al, 2001;Webb and Peart, 2001;García et al, 2005;Bacles et al, 2006;Hardesty et al, 2006;Jordano et al, 2007) compared with pollinators; a view not traditionally supported in the literature (Ennos, 2001).…”

Influence des pentes fortes sur la dispersion et la structure génétique des populations de Quercus crispula

“…The major oak species in this region are Q. crispula and Q. serrata, the latter predominantly in warmer areas than Q. crispula. The endocarps of hypogeal cotyledons attached to the seedlings were also sampled, where possible, since the endocarp is a tissue of maternal origin, allowing the mother trees of the respective seedlings to be identified [9,10,31]. However, too many seedlings germinated in 2005 in plot C to analyze them all, so we collected at random one fifth of these seedlings, together with their endocarps.…”

“…However, recent advances, such as the development of stable isotope ratio and molecular genetic marker techniques, are helping to overcome this difficulty [12,35]. For example, Grivet et al [10] successfully tracked seeds dispersal by acorn woodpeckers (Melanerpes formicivorus) in granaries using microsatellite markers.…”