Ronald Bialozyt

Wind-dispersed pollen mediates postglacial gene flow among refugia

A long-term genetic legacy of refugial isolation has been postulated and was demonstrated for maternal refugial lineages for numerous plant and animal species. The lineages were assumed to have remained separated from each other for several glacial periods. The conifer Abies alba Miller, silver fir, is an excellent model to test whether pollen-mediated gene flow may eliminate the genetic imprints of Pleistocene refugial isolation. Two DNA markers with contrasting modes of inheritance were applied to 100 populations covering the entire range of silver fir in Europe. The markers exhibited each two highly conserved alleles based on an insertion/deletion of 80 bp in the fourth intron of the mitochondrial nad5 gene and on a synonymous substitution in the chloroplast psbC gene. The geographical distribution of the maternally inherited mitochondrial variation supported the existence of at least two refugia with two recolonizing maternal lineages remaining largely separated throughout the range. The cline of the nad5 allele frequencies was much steeper than the one of the two psbC alleles. The psbC cline was as wide as the whole range of the species. Our results provide striking evidence that even a species with very long generation times and heavy pollen grains was able to establish a highly efficient pollen-mediated gene flow between refugia. Therefore we postulate that an exchange of genetic information between refugia by range-wide paternal introgression is possible in wind-pollinated plant species.

Contrasting effects of long distance seed dispersal on genetic diversity during range expansion

Currently many attempts are made to reconstruct the colonization history of plant species after the last ice age. A surprising finding is that during the colonization phase genetic diversity did not decrease as much as expected. In this paper we examine whether long distance seed dispersal events could play a role in the unexpected maintenance of genetic diversity during range expansion. This study is based on simulations carried out with a maternally inherited haploid locus using a cellular automaton. The simulations reveal a close relationship between the frequency of long distance seed dispersal events and the amount of genetic diversity preserved during colonization. In particular, when the colonized region is narrow, a complete loss of genetic diversity results from the occurrence of very rare long distance dispersal (LDD) events. We call this phenomenon the ‘embolism effect’. However, slightly higher rates of LDD events reverse this effect, up to the point that diversity is better preserved than in a pure diffusion model. This phenomenon is linked to the reorganization of the genetic structure during colonization and is called the ‘reshuffling effect’.

DNA fingerprinting validates seed dispersal curves from observational studies in the neotropical legume parkia.

Background Determining the distances over which seeds are dispersed is a crucial component for examining spatial patterns of seed dispersal and their consequences for plant reproductive success and population structure. However, following the fate of individual seeds after removal from the source tree till deposition at a distant place is generally extremely difficult. Here we provide a comparison of observationally and genetically determined seed dispersal distances and dispersal curves in a Neotropical animal-plant system. Methodology/Principal Findings In a field study on the dispersal of seeds of three Parkia (Fabaceae) species by two Neotropical primate species, Saguinus fuscicollis and Saguinus mystax, in Peruvian Amazonia, we observationally determined dispersal distances. These dispersal distances were then validated through DNA fingerprinting, by matching DNA from the maternally derived seed coat to DNA from potential source trees. We found that dispersal distances are strongly right-skewed, and that distributions obtained through observational and genetic methods and fitted distributions do not differ significantly from each other. Conclusions/Significance Our study showed that seed dispersal distances can be reliably estimated through observational methods when a strict criterion for inclusion of seeds is observed. Furthermore, dispersal distances produced by the two primate species indicated that these primates fulfil one of the criteria for efficient seed dispersers. Finally, our study demonstrated that DNA extraction methods so far employed for temperate plant species can be successfully used for hard-seeded tropical plants.

Characterization of nuclear microsatellite loci in the Neotropical tree Parkia panurensis (Fabaceae).

PREMISE OF THE STUDY We present here a set of nine polymorphic nuclear microsatellite loci, identified for the first time within the neotropical legume tree species Parkia panurensis Benth. ex H. C. Hopkins, which is widespread in western and central Amazonia. METHODS AND RESULTS To characterize these loci, 33 Parkia panurensis adult trees were analyzed. The number of alleles ranged from eight to 32, with an average of 14.4 alleles per locus. Mean expected heterozygosity ranged from 0.74 to 0.955. CONCLUSIONS All nine loci could also be verified in six other Parkia species and polymorphic fragments amplified. The new marker set can be used for future studies of genetic diversity and differentiation, as well as estimation of gene flow and parentage analyses in various Parkia species.

Contrasting Molecular Markers Reveal: Gene Flow via Pollen Is Much More Effective Than Gene Flow Via Seeds

Today’s distribution of genetic diversity in plants is to a large extent shaped by historical and recent gene flow mediated by seeds and pollen. It is only recently that in certain plant species DNA markers with contrasting modes of inheritance have been explored. Such markers are desired to differentiate between seed-and pollen-mediated gene flow. The present chapter is a review of our studies in the tree genus fir (Abies sp.). The genus served as a model to study gene flow by contrasting markers, since as a member of Pinaceae its mitochondrial DNA (mtDNA) is uniparentally maternally inherited, whereas its chloroplast DNA (cpDNA) is uniparentally paternally inherited.