Limits...
Travelling in time with networks: Revealing present day hybridization versus ancestral polymorphism between two species of brown algae, Fucus vesiculosus and F. spiralis.

Moalic Y, Arnaud-Haond S, Perrin C, Pearson GA, Serrao EA - BMC Evol. Biol. (2011)

Bottom Line: Individual-centered networks were analyzed on the basis of microsatellite genotypes from North Africa to the Pacific American coast, through the North Atlantic.Two genetic distances integrating different time steps were used, the Rozenfeld (RD; based on alleles divergence) and the Shared Allele (SAD; based on alleles identity) distances.Intermediate individuals linking both clusters on the RD network were those sampled at the limits of the sympatric zone in Northwest Iberia.

View Article: PubMed Central - HTML - PubMed

Affiliation: IFREMER, Institut Français de Recherche pour l'Exploitation de la Mer, centre de Brest, BP70, 29280 Plouzané, France.

ABSTRACT

Background: Hybridization or divergence between sympatric sister species provides a natural laboratory to study speciation processes. The shared polymorphism in sister species may either be ancestral or derive from hybridization, and the accuracy of analytic methods used thus far to derive convincing evidence for the occurrence of present day hybridization is largely debated.

Results: Here we propose the application of network analysis to test for the occurrence of present day hybridization between the two species of brown algae Fucus spiralis and F. vesiculosus. Individual-centered networks were analyzed on the basis of microsatellite genotypes from North Africa to the Pacific American coast, through the North Atlantic. Two genetic distances integrating different time steps were used, the Rozenfeld (RD; based on alleles divergence) and the Shared Allele (SAD; based on alleles identity) distances. A diagnostic level of genotype divergence and clustering of individuals from each species was obtained through RD while screening for exchanges through putative hybridization was facilitated using SAD. Intermediate individuals linking both clusters on the RD network were those sampled at the limits of the sympatric zone in Northwest Iberia.

Conclusion: These results suggesting rare hybridization were confirmed by simulation of hybrids and F2 with directed backcrosses. Comparison with the Bayesian method STRUCTURE confirmed the usefulness of both approaches and emphasized the reliability of network analysis to unravel and study hybridization.

Show MeSH
Network topology of F. spiralis and F. vesiculosus individuals + simulated hybrids with the RD. Only links with value smaller than or equal to the percolation thresholds are present. Nodes representing individuals are circles for F. spiralis and square for F. vesiculosus. Nodes representing hybrids are triangles. (A) Hybrids F1 (B) hybrids BC_F_spi, (C) hybrids BC_F_ves, (D) hybrids BC_F_spi_F_ves, blue triangle are F_ves hybrids and purple triangles are F_spi. Colors correspond to geographical regions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3040711&req=5

Figure 4: Network topology of F. spiralis and F. vesiculosus individuals + simulated hybrids with the RD. Only links with value smaller than or equal to the percolation thresholds are present. Nodes representing individuals are circles for F. spiralis and square for F. vesiculosus. Nodes representing hybrids are triangles. (A) Hybrids F1 (B) hybrids BC_F_spi, (C) hybrids BC_F_ves, (D) hybrids BC_F_spi_F_ves, blue triangle are F_ves hybrids and purple triangles are F_spi. Colors correspond to geographical regions.

Mentions: The comparison of network topologies with RD and SAD helped to test for the hybridization scenario best fitting the natural dataset network topology. As revealed by the percolation curves (see Figure A5 in additional file 6), the percolation thresholds shift globally to lower values except for the BC_F_ves dataset (Dp = 7.5 vs. Dp = 7.15 for the natural dataset). As for the natural dataset, at the percolation threshold, hybrids datasets have only one pathway making the connection between each of the two clusters of species (Figure 4). Nevertheless, the network topologies, according to the percolation threshold, reveal an intermediary state between BC_F_ves and BC_F_spi_F_ves datasets where the natural dataset seems to fit in.


Travelling in time with networks: Revealing present day hybridization versus ancestral polymorphism between two species of brown algae, Fucus vesiculosus and F. spiralis.

Moalic Y, Arnaud-Haond S, Perrin C, Pearson GA, Serrao EA - BMC Evol. Biol. (2011)

Network topology of F. spiralis and F. vesiculosus individuals + simulated hybrids with the RD. Only links with value smaller than or equal to the percolation thresholds are present. Nodes representing individuals are circles for F. spiralis and square for F. vesiculosus. Nodes representing hybrids are triangles. (A) Hybrids F1 (B) hybrids BC_F_spi, (C) hybrids BC_F_ves, (D) hybrids BC_F_spi_F_ves, blue triangle are F_ves hybrids and purple triangles are F_spi. Colors correspond to geographical regions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3040711&req=5

Figure 4: Network topology of F. spiralis and F. vesiculosus individuals + simulated hybrids with the RD. Only links with value smaller than or equal to the percolation thresholds are present. Nodes representing individuals are circles for F. spiralis and square for F. vesiculosus. Nodes representing hybrids are triangles. (A) Hybrids F1 (B) hybrids BC_F_spi, (C) hybrids BC_F_ves, (D) hybrids BC_F_spi_F_ves, blue triangle are F_ves hybrids and purple triangles are F_spi. Colors correspond to geographical regions.
Mentions: The comparison of network topologies with RD and SAD helped to test for the hybridization scenario best fitting the natural dataset network topology. As revealed by the percolation curves (see Figure A5 in additional file 6), the percolation thresholds shift globally to lower values except for the BC_F_ves dataset (Dp = 7.5 vs. Dp = 7.15 for the natural dataset). As for the natural dataset, at the percolation threshold, hybrids datasets have only one pathway making the connection between each of the two clusters of species (Figure 4). Nevertheless, the network topologies, according to the percolation threshold, reveal an intermediary state between BC_F_ves and BC_F_spi_F_ves datasets where the natural dataset seems to fit in.

Bottom Line: Individual-centered networks were analyzed on the basis of microsatellite genotypes from North Africa to the Pacific American coast, through the North Atlantic.Two genetic distances integrating different time steps were used, the Rozenfeld (RD; based on alleles divergence) and the Shared Allele (SAD; based on alleles identity) distances.Intermediate individuals linking both clusters on the RD network were those sampled at the limits of the sympatric zone in Northwest Iberia.

View Article: PubMed Central - HTML - PubMed

Affiliation: IFREMER, Institut Français de Recherche pour l'Exploitation de la Mer, centre de Brest, BP70, 29280 Plouzané, France.

ABSTRACT

Background: Hybridization or divergence between sympatric sister species provides a natural laboratory to study speciation processes. The shared polymorphism in sister species may either be ancestral or derive from hybridization, and the accuracy of analytic methods used thus far to derive convincing evidence for the occurrence of present day hybridization is largely debated.

Results: Here we propose the application of network analysis to test for the occurrence of present day hybridization between the two species of brown algae Fucus spiralis and F. vesiculosus. Individual-centered networks were analyzed on the basis of microsatellite genotypes from North Africa to the Pacific American coast, through the North Atlantic. Two genetic distances integrating different time steps were used, the Rozenfeld (RD; based on alleles divergence) and the Shared Allele (SAD; based on alleles identity) distances. A diagnostic level of genotype divergence and clustering of individuals from each species was obtained through RD while screening for exchanges through putative hybridization was facilitated using SAD. Intermediate individuals linking both clusters on the RD network were those sampled at the limits of the sympatric zone in Northwest Iberia.

Conclusion: These results suggesting rare hybridization were confirmed by simulation of hybrids and F2 with directed backcrosses. Comparison with the Bayesian method STRUCTURE confirmed the usefulness of both approaches and emphasized the reliability of network analysis to unravel and study hybridization.

Show MeSH